Wikipedia:Reference desk/Archives/Science/2013 April 25

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April 25

Proper motion of stars

According to the article on Proper motion, these motions are measured as coordinate changes on the celestial sphere, and celestial coordinates are in turn, as far as I can gather, defined based on projections of the Earth's Equator and point(s) where the sun crosses the plane of the Equator. It seems to me that this entire coordinate system will shift as the Earth's orientation wobbles and precesses in various ways over time. Given that stars' proper motions are usually tiny anyway, why are their measurements not distorted or even swamped by such effects? 86.160.222.208 (talk) 02:39, 25 April 2013 (UTC)

Minor historical note, as I don't know the answer to your question (I have a suspicion I know what the reason is, but I have nothing to cite for now) -- the celestial coordinate system actually came first; the latitude and longitude lines on the earth's surface are, IIRC, a projection of those onto our planet. Evanh2008 ^{(talk|contribs)} 03:04, 25 April 2013 (UTC)

Quoting from the equatorial coordinate system article "...these motions necessitate the specification of the equinox of a particular date, known as an epoch, when giving a position." The current International Celestial Reference Frame standard specifies the equinox of J2000.0. I'm not an astronomer though, so if there is any more to this to followup on, I'm sure others will chime in. -Modocc (talk) 04:07, 25 April 2013 (UTC)

See epoch (astronomy). As Modocc said, celestial coordinates are always specified with respect to an epoch, and the standard epoch is redefined every 50 years. The most recent one is J2000.0 (the beginning of Julian year 2000). You can convert between epochs by accounting for the effect of precession, which is by far the most important cause of axial drift. When a new epoch is about to begin--in the 1990's, for example--some people decide to be ahead of the game and specify coordinates using the new epoch. This is highly annoying because it forces other astronomers to convert back and forth. --140.180.249.226 (talk) 04:47, 25 April 2013 (UTC)

Thank you. 86.160.85.235 (talk) 17:49, 25 April 2013 (UTC)

About electrification

I'd like to hear others' opinions regarding these:

a. why we don't get electrified when just touching an exposed conducting wire, despite the fact that current does flow thru us ? (while the touching body is kept isolated and unearthed). b. when an exposed wire is being touched by a bare hand (in principle), can the hand lit a bulb while unearthed ?

c. the danger in touching a wire while earthed is due the immense current due to the voltage falling on the body, according to Ohm's law (since the voltage can reach hundreds to thousands of Volts). Does this explanation describe the situation, correctly & fully ?

Thank you, BentzyCo (talk) 04:42, 25 April 2013 (UTC)

a) You do get a bit of a jolt from the spark, but it's only a fraction of a second, until the charge in your body equals the charge in the wire. That's not nearly as bad as the continuous flow of electrons through you which would occur if you were grounded ("earthed" to you).

b) Not an incandescent bulb, as that would require a continuous flow of electrons. Fluorescent bulbs can be lit by just being near a live electrical wire though, due to the way they react to the fields around the wire.

c) I prefer my continuous flow of electrons explanation.

BTW, if you've ever seen one of those science demonstrations where a (well-insulated) kid puts his hand on the metal ball, then his hair stands on end from the electrical charge, you will note that the ball doesn't have any charge when he first touches it, or he would get a wicked spark. They slowly turn up the charge after he has steady contact with it. StuRat (talk) 05:35, 25 April 2013 (UTC)

a. "until the charge in your body equals the charge in the wire" ???

c. Your declaration regarding "continuous flow" needs clarification & substantiation. BentzyCo (talk) 06:58, 25 April 2013 (UTC)

Regarding a, what Stu means is that current only flows until the voltage of your body equals the voltage of the wire, not charge. Someguy1221 (talk) 07:05, 25 April 2013 (UTC)

a) I meant the "relative charge". So, if there was 1 free electron for every trillion atoms in the wire (totally made up number), then the flow of electrons continues until you have one free electron per trillion atoms in your body, more or less.

c) If you hold a live wire in one hand and the other hand is grounded, and the voltage/current are sufficient, then electrons will continue to flow through your body, heating it and causing damage, until you let go (or your charred body becomes an effective insulator). StuRat (talk) 07:16, 25 April 2013 (UTC)

If the wire is carrying an AC current, then you do get a continuous flow of AC current through you even if you aren't touching anything but the wire, due to your body's self-capacitance. However, human body capacitance is only about 100pF, which at 60Hz produces a capacitive reactance of about 25MΩ, which at 120V results in a current of about 5µA, which is about 200 times smaller than the 1mA minimum that can be felt. Red Act (talk) 06:58, 25 April 2013 (UTC)

... though a current as small as that can be "felt" by Electrovibration. (For forty years, I wondered why I could detect electricity in my fingertips at currents much too small to be "felt" according to conventional theory.) Dbfirs 12:03, 25 April 2013 (UTC)

Finding planets around smaller sized star

I wonder if brown dwarf have their own planetary system. I am not sure exactly how big average brown dwarf will be. They say average brown dwarf is around 10-60 Jupiter mass, I thought Y typed brown dwarf is smaller than the size of Saturn and average brown dwarf star is about the comparable size of Jupiter. If brown dwarfs have planets around it are they able to measure correctly the distance the planets are from their brown dwarf star? I hear red dwarfs have found alot of earthliked planets, and I have seen alot of comparable earth planets around red dwarfs on science magazines. Based on what I thought scientists are still able to measure correctly to far the planets are away from their red dwarfs systems. I thought average red dwarfs are four times the size of Jupiter. Is M7 or higher brown dwarfs, or red dwarfs? I thought M0-M9V are all red dwarfs. But according to what I hear when scientist try to study planets around white dwarf to predict what will happen to our solar system in the future, we just get more confused and everything just goes more anomaly. Could it because white dwarfs are too small to measure planets from star with an accurate distances? If star is too small will it be harder to measure distances the planet is to their parent star? Is it even hard to tell if white dwarf is white dwarf, or some scientist often confuse white dwarf with subBdwarf or subOdwarf.--69.233.255.83 (talk) 05:26, 25 April 2013 (UTC)

You are confusing the spectral classification (i.e. M, L, T, Y) with the classification by mass. For instance a young brown dwarf ~ 15 Jupiter masses will have M spectral class. As it cools down it will eventually became Y-type. The average size of all brown dwarfs is about the Jupiter size irrespective of mass. Ruslik_Zero 09:37, 25 April 2013 (UTC)

(ec) There seems to be some confusion of size and mass.

If you could add mass to Jupiter, it wouldn't grow in size; Jupiter is about as big as planets get. Its mass and therefore its gravity would increase, and compress the mass. Depending on how much you add, Jupiter would even shrink, because compression would more than offset the volume of the additional mass. If unclear fusion didn't ensue at one point or the other, you could add the mass of the Sun and end up with something the size of planet Earth (ballpark estimate).

And that's what happens when stars like the Sun run out of fusion fuel. After some burping and farting, their dead body gets all pale and wrinkly - and a Brown dwarf is a stillborn star in comparison; it never gains the mass required to "rise and shine."

Also keep in mind that you need radiation to analyze if you want to find exoplanets. Brown dwarf radiation is just too faint to analyze (yet?), and while Red dwarfs aren't exactly bright either, they are far more common than any other type. - ¡Ouch! (^{hurt me} / _{more pain}) 10:44, 25 April 2013 (UTC)

White dwarfs have radiations although fainter. If scientists try to capture the planets around white dwarfs can they mis-estimate the distance? Will star being too small make finding planets hard? They can still see the planets though.--69.226.44.190 (talk) 00:14, 26 April 2013 (UTC)

The misspelling of the word "nuclear" as "unclear" makes the answer above a bit unclear. Dauto (talk) 17:42, 25 April 2013 (UTC)

Yes, my mother's brother's husband Kenny once tried to have me engage in "uncle-ar fusion" with him, but I told him he wasn't my type. A little too av-nucular for my taste. -- Jack of Oz ^[Talk] 04:46, 26 April 2013 (UTC)

Oops, epic typo, on the scale of "marital arts" on IRC. Thanks for pointing that one out. (You say "unclear", you lose, right? :S )

<still smaller> That one was hard to catch but sometimes I wonder why some non-words pass just as easily...</still smaller> - ¡Ouch! (^{hurt me} / _{more pain}) 11:38, 26 April 2013 (UTC)

p.s. WHAT? Those bastards killed Kenny AGAIN? ;)

Yes if the star is smaller there is less chance of an eclipse happening, with a planet in line with the earth and the star. However a planet will be a similar size to the star and so dimmming of light will be much more dramatic. Detection by gravitational microlensing should not make a difference with the size. But for the very dim stars yuou will struggle to get enough light to measure the radial velocity very accurately. Reflected light detection will be extra hard. Graeme Bartlett (talk) 07:47, 29 April 2013 (UTC)

Does energy have mass?

In the article Conservation of mass, it is stated that energy has mass. But I thought only matter has mass. If energy has mass, what is the difference between energy and matter? — Preceding unsigned comment added by G.Kiruthikan (talk • --G.Kiruthikan (talk) 06:19, 25 April 2013 (UTC)contribs) 06:18, 25 April 2013 (UTC)

You are mostly right. In classical mechanics, only matter has mass. In the more advanced mechanics discovered by Albert Einstein, mass and energy are found to be equivalent rather than totally different entities. The principle of the equivalence of mass and energy shows that mass can be converted to energy in accordance with the famous equation E=mc²; and energy also has mass. See Mass-energy equivalence and Mass in special relativity. Dolphin (t) 06:48, 25 April 2013 (UTC)

Indeed. Mass-energy equivalence means that mass is energy and energy is mass - you can't have one without the other, because they are just different ways of measuring the same property. Matter is a less well defined concept in modern physics - as you will see from our article, there are various working definitions depending on context. One definition is that matter is anything that both has mass/energy and occupies volume. An alternative definition in terms of elementary particles is that matter is composed of fermions (rather than bosons). Gandalf61 (talk) 07:43, 25 April 2013 (UTC)

In some contexts the Higgs boson is considered matter even though is not a fermion. Dauto (talk) 18:18, 25 April 2013 (UTC)

Often confusion arises because force-carrying bosons photons and gluons are massless. In this context, these massless particles have mass-energy (as explained above by Dolphin51 and Gandalf61), but they do not have invariant mass (an invariant mass with respect to different reference frames). See the section on massless particles though, in which a system of two massless particles have an invariant mass iff their momenta forms a nonzero angle. -Modocc (talk) 14:25, 25 April 2013 (UTC)

Not all force-carrying bosons are massless. See W and Z bosons. Dauto (talk) 17:24, 25 April 2013 (UTC)

Thanks. I meant only that the gluons and photons are massless particles so I corrected that. --Modocc (talk) 20:12, 25 April 2013 (UTC)

There is also a definition based on whether a particle's energy is larger than its rest mass (AKA invariant mass) in which case it is considered radiation, or whether its energy is smaller than the rest mass in which case it is considered matter. Those are the definitions used when contrasting a matter dominated universe (Currently the case) with a radiation dominated universe (early universe). The cold hard truth is that the word matter doesn't really mean anything.Dauto (talk) 17:34, 25 April 2013 (UTC)

So then matter doesn't matter? What's the matter with that? --Jayron32 00:07, 26 April 2013 (UTC)

"You must lie upon the daisies and discourse in novel phrases of your complicated state of mind, The meaning doesn't matter if it's only idle chatter of a transcendental kind". -- Jack of Oz ^[Talk] 04:39, 26 April 2013 (UTC)

"This particularly rapid unintelligible patter / Isn't generally heard, and if it is, it doesn't matter."AlexTiefling (talk) 10:41, 26 April 2013 (UTC)

What we call matter fairly well aligns with what you might consider "tangible". Or at least that distinction fit for a long time. A brick is matter - you can hold it in your hands. A brick's thermal or kinetic energy are not. You can't isolate and hold "a gram of kinetic energy". Same goes for a gram of gravitational potential energy, or a gram of heat. Some forms of energy are not so abstract, but are intangible nonetheless, such as the electromagnetic energy carried by photons. But as has been mentioned above, the definition of "matter" doesn't matter. It's just a choice of how to classify things. Someguy1221 (talk) 04:45, 26 April 2013 (UTC)

Momentum operator in energy basis

What is the momentum operator in the energy basis?

150.203.115.98 (talk) 11:33, 25 April 2013 (UTC)

If H commutes with p (e.g. if H is just the kinetic energy p^/(2m)), then p is already diagonal in the energy basis. Otherwise, it's just given by the matrix elements of p. You can write the identity operator as:

$I=\sum _{m}\left|m\right\rangle \left\langle m\right|$

where the sum is over any complete set of states. You can thus take these states to be the energy eigenstates. You can then write:

$p=pI=\sum _{m}p\left|m\right\rangle \left\langle m\right|$

If you then multiply by the identity on the left, you get:

$p=\sum _{n,m}\left\langle n\right|p\left|m\right\rangle \left|n\right\rangle \left\langle m\right|$

Count Iblis (talk) 13:08, 25 April 2013 (UTC)

And if you are dealing with a continuum of states instead of quantized states, you simply replace the sums with integrals

$p=\int dxdy\left\langle y\right|p\left|x\right\rangle \left|y\right\rangle \left\langle x\right|$

Dauto (talk) 17:19, 25 April 2013 (UTC)

All right. So, for example, what would it be for a particle in a box?, the discrete energy levels being ${n^{2}h^{2}\pi ^{2}} \over {2mL^{2}}$, I think. So I guess the (n,m)th entry of this matrix is $\left\langle n\right|p\left|m\right\rangle$, how do you calculate that?

I'm not really sure if this is the right way of doing it, but can you define $p$ as $-ih{\frac {\partial }{\partial x}}$ in the position basis then $\left\langle n\right|p\left|m\right\rangle ={\frac {2}{L}}\int _{0}^{L}\sin {\frac {n\pi x}{L}}\left(-ih{\frac {\partial }{\partial x}}\right)\sin {\frac {m\pi x}{L}}dx$? I get a complex value though, so this can't be right.

150.203.115.98 (talk) 21:54, 25 April 2013 (UTC)

There are some subtle issues here, this has to do with the fact that the infinite potential barrier means that you are necessarily going to look at only the interior of the box. There H = p^2/(2m), however, p actually does not commute with H due to the boundary conditions which break translational invariance. What you can do here is consider some arbitrary plane wave exp(i k x), this can always be expanded in the region within the box in terms of the energy eigenstates, clearly this amounts to a Fourier expansion. The physical interpretation would be that if you start out with a momentum eigenstate which is upon a measurement found to be inside a box (without there bing an infinite potential well), and we then lock the particle up there by switching on the potential well, you can then consider expanding the state in terms of the energy eigenfunctions. Count Iblis (talk) 12:43, 26 April 2013 (UTC)

Simple Amplifier

Can I build a simple sound amplifier using a simple micrphone, transistor (what type) and battery etc, in what order shall I place them ? 124.253.255.39 (talk) 13:58, 25 April 2013 (UTC)

The design of such an amplifier depends on what you want it to do. What type of microphone? What do you want it to drive - headphones? loudspeaker? With normal dymamic (electromagnetic) microphones, a single transistor will not give enough amplification even for headphones. However the output of carbon and electret microphones is much greater, and a single transistor will be sufficient to drive sensitive headphones. Driving a loudspeaker will reqire a more complex circuit - an audio amplifier integrated circuit will be a better choice. You can google "simple amplifier" and look for circuits. However, the wording of your question indicates a knowlege of electronics at a level where you may require a lot of help. I suggest you subscribe to one or more electronics magazines. Keit 120.145.168.40 (talk) 14:08, 25 April 2013 (UTC)

This page (linked from our common emitter article) has an example circuit (with component values) that the OP might find useful. Tevildo (talk) 19:14, 25 April 2013 (UTC)

Length of minor and major axis of the earth's elliptical orbit

Earth revolves around the sun in an elliptical orbit and we know every ellipse has two axis (one minor and the other major). I have read at many places that the distance of earth from the sun is 150 million kilometers, but I am confused whether this distance is of major axis or of minor axis. So, I want to know both the distances of major and minor axis of the Earth's orbit. Scientist456 (talk) 14:14, 25 April 2013 (UTC)

That number is an approximation to an average. The article Earth's orbit has more details and more precise values. RJFJR (talk) 14:54, 25 April 2013 (UTC)

Also, you should be aware that the sun is at one focus of the ellipse, not at its geometric centre. Dbfirs 16:12, 25 April 2013 (UTC)

Using the numbers from that article, we find that the semimajor axis is 149,598,261 km with eccentricity 0.01671123. The semiminor axis is therefore 149,577,371 km. As you can see, these numbers are extremely close to each other, and both can be rounded up to give 150 million km. --140.180.249.226 (talk) 16:29, 25 April 2013 (UTC)

Note, though, that the variability in Earth's distance from the Sun is much larger -- 147.1 Mkm for the point of closest approach (perihelion), 152.1 Mkm for the point of greatest distance (aphelion). Looie496 (talk) 16:51, 25 April 2013 (UTC)

That's still only about a 3% difference. --Jayron32 00:39, 26 April 2013 (UTC)

But the radiation received goes down as the square so it is a 6% difference that way. And temperature is relative space which is near to absolute zero so it should mean about 16°C difference I'd have thought which is enormous. I wonder why it makes so little difference. Dmcq (talk) 03:47, 26 April 2013 (UTC)

The Greenhouse effect. 202.155.85.18 (talk) 06:55, 26 April 2013 (UTC)

That should just be a constant factor as far as this is concerned, the only sort of thing I can see affecting it much is the heat capacity of the earth, especially the oceans. Dmcq (talk) 11:25, 26 April 2013 (UTC)

I've read somewhere that this has to do with the fact that most of the land area is in the Northern hemisphere, while the Earth if farthest from the Sun during the Summer there. Count Iblis (talk) 12:21, 26 April 2013 (UTC)

Thanks, that gave me a search term that got this [1]. Incredibly the earth as a whole is on average 2.3°C warmer when it is farther from the sun because of the effect you said! It also says northern summers are about 3 days longer than southern ones because the earth moves faster when it is closer to the sun. Dmcq (talk) 12:40, 26 April 2013 (UTC)

Look, we don't need to be speculating on this, especially because the OP's question has already been answered. The effective temperature of a planet can be calculated by determining how much radiation it absorbs from the Sun, and balancing that with the blackbody radiation the planet emits. The result is show here--temperature changes as the inverse square root of the Sun-planet distance. This is because the power emitted from a blackbody goes as the fourth power of temperature, so if Earth moves 1% farther from the Sun, it receives 2% less radiation, but only needs to decrease its temperature by a tiny amount to decrease its emitted radiation by 2%.

So since Earth's distance to the Sun changes by 3%, its temperature is expected to change by 1.5%, or 4 degrees. But this calculation assumes that Earth has no thermal inertia. In reality, the oceans and landmasses will take a long time to respond to changes in solar irradiation, so the actual temperature change is smoothed over a few months and is expected to be less than 4 degrees. --140.180.240.146 (talk) 19:54, 26 April 2013 (UTC)

that should be te other way round, 6% not 1.5%. Dmcq (talk) 22:51, 26 April 2013 (UTC)

Did you read the article I linked to? Temperature is proportional to the square root of the distance. If the distance changes by 3%, temperature changes by 1.5%. --140.180.240.146 (talk) 00:37, 27 April 2013 (UTC)

Sorry didn't spot that. So the square root is due to the power being radiated at a rate proportional to the fourth power of the temperature. Thanks that explains everything. Dmcq (talk) 06:26, 27 April 2013 (UTC)

Li-ion batteries in new electronics

I heard that Li-ion batteries only last 2-3 years even if unused. Does that mean if a brand new, unopened electronic item, working on a Li-ion battery, just sat there for 2-3 years, it would become useless, assuming the item doesn't allow you to change the battery? Clover345 (talk) 14:51, 25 April 2013 (UTC)

That's not a simple question. There are many variations of battery technology that are swept together as "Li-ion" - and their shelf-life varies immensely. Also much depends on how much charge is in the battery as it is stored. SteveBaker (talk) 15:23, 25 April 2013 (UTC)

Li-on batteries usually have a controller with a safety cut-out that disconnects the battery if it falls below a certain minimum charge. This might possibly make the battery unchargeable if it has been allowed to discharge below this minimum. One doesn't hear of this happening very often, either because dealers open the packaging and re-charge after three years on the shelf, or because the batteries hold their charge for longer than 2-3 years. As Steve says above, there is a wide variation in battery specifications. If you are going to store Li-on powered equipment unused for many months, it is usually advised that you leave it at least partially charged. Dbfirs 16:10, 25 April 2013 (UTC)

Properly stored batteries (in a low temperature and low humidity environment) would have a longer shelf-life, whatever this is. A new battery will also be charged with the right amount to last longer. Add to this that a good supply chain management and shop management won't let any electronic sit on a shelf there for 2-3 years. The life circle of most products is probably much shorter than that nowadays. OsmanRF34 (talk) 17:09, 25 April 2013 (UTC)

See Lithium-ion_battery#Disadvantages. Just sitting there isn't as bad as using it, but even if you use it what typically happens is the battery only lasts half the time on charge after three years. However my experience is that quite a number also do fail totally in that time. Dmcq (talk) 11:36, 26 April 2013 (UTC)

Kangaroos hit by cars

I understand this is quite a problem in Australia. Why is this ? Their eyes are high enough to see cars coming with plenty of warning, and they seem fast enough to get off the road in time. Also, most of Australia is flat and treeless, allowing them to see for miles. (Do collisions occur mainly where there are trees and buildings, blocking their view ?) StuRat (talk) 16:51, 25 April 2013 (UTC)

Maybe they freeze and stare at headlights like deers. So, the question is probably why some animals do it. OsmanRF34 (talk) 17:13, 25 April 2013 (UTC)

In the case of deer, coming out from the woods without looking where they are going seems to be the problem, along with the freezing behavior you describe. They also seem to have a problem that they often travel in a group (say mom and a fawn), and the followers assume the path is safe if the leader crossed the street, while the leader barely makes sure the path is clear for herself, much less others. Then there are creatures like badgers, with both eyes low to the ground and a slow speed, meaning that once they see the car, they can't get out of it's way. StuRat (talk) 17:15, 25 April 2013 (UTC)

I doubt you are right about deers being hit by cars because they don't look when crossing roads. Where did you got that from? Walt Disney? It's actually instinct and it controls the deer's behavior. Until the deer's brain has a chance to understand what a car's headlights means to the deer, and what the deer should do about it. Often, the deer doesn't get that time. The environment in which deer evolved did not have cars with headlights. So unless a deer has had a chance to learn about cars with headlights, it goes into the deer brain as "unknown possible danger" (UPD). Before cars, the safest thing any animal could do when faced with a UPD was to freeze. The is because the UPD is likely to be a predator, and predators have trouble seeing still objects while the most dangerous ones (wolves, big cats, bears) react to retreating animals by chasing them. If the UPD turns out to be a non-predator danger (fire, earthquake, falling tree) what's the point of running away until the deer can figure out which way to run? On the other hand, if the UPD turns out not to be dangerous, or another deer that wants to horn in on whatever the deer is eating, why waste energy running and giving up on whatever objective the deer was following. The UPD might even be something the deer wants to scare away--which they deer can do by stamping their front feet at or by charging at a smaller animal. OsmanRF34 (talk) 17:24, 25 April 2013 (UTC)

(Pssst... the plural of "deer" is still "deer".) Deer often run into the sides of cars on roads, and it's hard to explain that unless they didn't see the car at all. StuRat (talk) 04:17, 26 April 2013 (UTC)

Kangaroo behaviour does seem to have some parallels with that of deer. There's probably also the fact that, unlike deer, kangaroos haven't historically had much in the way of predators, so watching for threats the size of a car hasn't been part of their evolution. And, most of Australia is not flat and treeless, or at least the parts where most of the cars are isn't. Even where there are not large trees, there's usually plenty of scrub. It's also just possible that movie and photographic imagery of Australia doesn't not give a true picture of the country to the rest of the world. HiLo48 (talk) 17:27, 25 April 2013 (UTC)

Australia is not flat and treeless? Everybody knows it's a big desert. Have you ever been there? OsmanRF34 (talk) 17:35, 25 April 2013 (UTC)

Where I live in the UK I regularly have to avoid deer suddenly crossing the road. When I drove in Australia (I spent around seven months there), I'd often have a 'roo jump out from the trees/bushes on the side of the road and "near miss" me. A lot of this has to do with the fact that deer (in the UK) and 'roos (in Oz) are prevalent so the odds of seeing them try to cross the road right in front of you in certain places (e.g. the "countryside") is high. The Rambling Man (talk) 17:45, 25 April 2013 (UTC)

I live and drive in Australia and I concur with HiLo48, The parts where most of the cars are isn't flat and comletely empty of fauna. Deserts_of_Australia has a decent map which shows that the majority of the eastern half of Australia does not have any desert in it. I live in victoria where plenty of Kangaroos get hit on the roads and we have no deserts, similarly with New South Wales and Queensland which only have small parts of their western most borders in desert. Well over half the population of Australia live in Victoria and the eastern parts of the other two states. Vespine (talk) 23:40, 25 April 2013 (UTC)

(Oi. Victoria has the Little Desert and the Big Desert, but I'm not after a fight over it.) HiLo48 (talk) 06:57, 26 April 2013 (UTC)

Deserts of Australia has a few maps that contradict each other on exactly where there is desert and where there isn't, but this map shows that most of the eastern half of Australia is either desert or grassland, and if you have a look at some of the grassland areas using google maps (such as here, here and here), you'll see that while there is grass, a layman could be forgiven for calling it a desert. 202.155.85.18 (talk) 07:39, 26 April 2013 (UTC)

I don't know anything about deer, but if you want to know about kangaroos, ask an Australian, such as me. They are indeed a significant problem - several have done serious damage to my car. If you hit a big red at highway speeds, your car can be a write-off.

While I don't know anything about deer, I imagine that as ruminants that run in herds, their behaviour would be something like goats, which my parents farmed. Goats are not very intelligent, but they have a range of instincts. One of which is that if one senses possible danger, it lift it's head and points in the direction of the suspected danger, while watching to see what other goats in the herd do (they can do this because the position of their eyes gives about a 320 degree all round view. If another goat does the same, both goats run AWAY from the danger. All this happens in less than a second. When the two goats run, the rest of the herd run with them - they do not bother with assessing the danger. If for some reason a second goat does not react, nothing further will happen. If a goat gets out on a road and is blinded by headlights, it literally has no idea what to do and just stands there looking into the lights. As a child I occaisonally amused myself by getting a school friend to come with me into the goat paddock, and suddenly break into a run with me. The result will invariably be the entire herd running in the same direction in panic.

Kangaroos are completely different.

While kangaroos like to gather with other roos, they spend a lot of time on their own. And while they are biologically VERY sophisticated (their calorific requirements are very low, and their hormone and reproduction system is amazing), they are truely the stupidest of anything that has fur. So their intincts/pre programmed reaction to danger have adapted to suit. When a kangaroo senses danger, it imediately hops away at top speed IN A COMPLETELY RANDOM DIRECTION. I have often been walking in the State forrest and, snapping a twig on the ground, startled a roo. More than once the stupid thing has ran directly toward me - I've had to get out of the way.

This is what happens if you are driving at night and there is a roo on the road, or just happens to want to cross the road as you approach: He's blinded by your lights, and at first doesn't know what lights mean, so he just stands there looking at them. As you get closer, he sees the lights getting bigger and brighter and he hears the sound of the tires and motor. He then decides "Danger" and hops at maximum speed IN A RANDOM DIRECTION. If he turns and goes directly away, fine. You can brake heavily and wait for him to get well clear. If he hops away at right angles to the road, fine. But sometimes they hop directly toward you, and then there is going to be a crash.

I had a big one that ran directly toward me, and ran at full speed directly into my car, after I had braked to a complete stop! The damm thing casued $2000 worth of damage.

Sometimes they will hop off the road at right angles and become unblinded and then concerned presumably with hitting a tree, and turn and run on the road. They certainly are stupid.

Incidentally, Osman clearly has not been to Australia. Its a bit like the USA. About the same land area, it certainly does have a lot of desert in the centre, but within 200 to 400 km of the coast it is pretty lush. In my State, we have the Jarrah forrest, which is dense forrest with very large trees about the area of one average US State. The wood from Jarrah trees has been extensively used for building construction and furniture both here and in the UK, and has been exported to the USA and other countries. However, its' use is now restricted to high quality furniture only.

Wickwack 121.221.220.87 (talk) 00:03, 26 April 2013 (UTC)

As someone who doesn't "know anything about deer", you perhaps should have avoided speculating so much about them. Unlike caribou or bison or some Indian deer, North American deer are not generally herd animals. Males are usually solitary, except at mating times, and a female is usually accompanied only by a few children less than a year of age. So the assumptions based on herd instincts don't really apply. Dragons flight (talk) 01:00, 26 April 2013 (UTC)

Whatever. What I said about goats is valid. Deer are farmed here - kept together in large paddocks. Whatever sort of deer they are, they clearly like to be together. Wickwack 124.178.174.155 (talk) 01:21, 26 April 2013 (UTC)

• "Deers"? (Rggggh....venison) Both times I almost hit a deer it was because they were crossing the road as a group at the darkest spot in otherwise well-lit roads. Don't know diddly about kangaroo behavior. μηδείς (talk) 00:51, 26 April 2013 (UTC)

One time when I was driving from Mataranka to Katherine(where Australia is a big, flat dessert) shortly after sunrise, I saw two kangeroos (actually more like wallabies I guess) on the road over a kilometer up ahead. I was doing about 130km/h in a 4x4 Toyota Hilux, and the kangeroos saw me straight away. One hopped promptly off into the bush to the left side of the road, but the other hopped along the road towards me, then darted away again, never actually moving off the road. Then it stopped and by this stage I was getting rather close. I was just about to ease off the accelerator to give a bit more time when it darted off into the bush on the right side of the road. I continued along without slowing until the kangeroo that originally ran straight off the left side of the road came back straight towards the driver's side tyre. Given the car's bull bar and high suspension, the roo went straight under the wheel. To us in the cab, it felt like a small bump in the road. In summary, roos get hit by cars because they're extremely stupid animals. You also see this when shooting at them (I wouldn't call it hunting, because there's pretty much no skill involved); they often hop towards where the shots are coming from and I've even seen them not react at all as their mob falls around them. 202.155.85.18 (talk) 01:10, 26 April 2013 (UTC)

Yes, all that is typical roo behavior. For those who don't know, a wallaby is a kangarro that is a small variant. Variants of wallabies/roos vary for 600 mm high to over 2 m (2 to 6 foot). They are all equally stupid. Hit a 2 m big red at highway sppeds and you've just had a serious accident. Wickwack 124.178.174.155 (talk) 01:24, 26 April 2013 (UTC)

We all know what a wallaby is. Did IP 202 not beep his horn? μηδείς (talk) 01:25, 26 April 2013 (UTC)

Don't know if he did. But it would make no real difference. What roos do when startled is completely random. If you see a roo on or near the road, the only thing to do, is stop until it goes away. Wickwack 124.178.174.155 (talk) —Preceding undated comment added 01:29, 26 April 2013 (UTC)

My point is that beeping while the roo's on the road at a distance and continuing to beep if it stays on the road might work. It works somewhat for geese which are the daytime hazard in the US N.E. Or are they as stupid as opossums? Oh, god, the idea of leaping opposums is indeed a scary one. μηδείς (talk) 01:38, 26 April 2013 (UTC)

I don't know how stupid opossums are. But, no, beeping as you suggest doesn't work. Roos don't understand what it means - it can only scare them, which provokes hopping at speed in a random direction. The best approach is as I said, stop until they go away. The idea is to try and avoid scaring them - if they are not startled and don't feel threatened, they MIGHT do something sensible like standing still or hopping away. This is not always possible, as when you are travelling at speed and a roo hops out from the bush at roadside, you may not have enough time. Emergency brake if there is any possibility of hitting one assuming it comes straight at you, and minimise the risk. Wickwack 124.182.174.187 (talk) 02:39, 26 April 2013 (UTC)

I didn't use my horn and never have with roos. It has never occurred to me before that it might work, and based on my experience with them I think Wickwack is probably right about it having no helpful effect. Also, a car travelling at 130km/h makes a fair bit of noise without honking the horn, especially compared to the cicardas and bird calls in the bush, so if noise would work, I think the car should do it on its own. Because of the size of the wallabies in the NT and the size of the car I owned at the time, I wasn't too concerned that they might damage the vehicle. The most dangerous thing I could have done would be to try and turn to evade the things since that risks running off the road. Emus are also a bit of a hazard because they can try to "race" the car and cut in front of it. Often you see them slowing down as they approach the road ahead, then dart quickly across when you get close. In the NT, road trains can be up to 4 trailers long (>40 wheels, >50 metres long and up to 120 ton) and many drive through the night. With their huge size and heavy bull bars, they just mow down the wildlife that they frequently encounter on the highways including kangaroos, dingos, emus and various feral animals. When you drive along the highway during the day you see the results littered all down the road. The smell is so bad it makes rest stops very unpleasant. 202.155.85.18 (talk) 03:45, 26 April 2013 (UTC)

I'd agree with "stop until they go away". I should have taken my own advice for the only time I hit a roo, back in 2007. I saw it quite clearly up ahead, munching on some grass on the side of the road. So I slowed right down as I approached it, hoping it would hop out of my way. It stayed put as I continued to approach very slowly. I actually came to a dead stop for about 10 seconds. It seemed like it was going nowhere fast, so I gingerly started up again. Just as I was almost past it, it suddenly jumped towards the other side of the road, right in front of my car. I had no time to stop or swerve, and we made contact. I lost a headlight and had some damage to the body and paint work. The roo was injured, but still able to limp away. It would have been far worse for the car, the roo and me, if I'd been moving faster.

I'd still take issue with Stu's premise, in that it very much depends where you are in Australia. We have this image of the "real" country people and the golden sunsets over unending plains of wheat and sheep and cattle etc, but the truth is that we're one of the most urbanised countries on Earth. Most people live in the state capitals, and would never see a kangaroo from cradle to grave except in zoos, or while touring in the countryside. Canberra is a little different, as it was designed to have elements of the bush intermingled with a cityscape, so there are definitely places there where roos can be an issue (the back road to the airport, for example, is notorious; and they occasionally gambol over the top of Parliament House, while the politicians gamble with our lives below). I lived there for 27 years and luckily never had a collision (with a roo, that is). But it took only a few months after moving to Gippsland for the inevitable to happen. -- Jack of Oz ^[Talk] 03:55, 26 April 2013 (UTC)

Well, looking at the climate maps of Australia, most of it is desert and grassland. However, it's also true that most of the people, and presumably roos, live in parts that actually have trees. So, most Australians might well think of Australia as a lush green land (except for a few opal miners in Coober Pedy). StuRat (talk) 04:15, 26 April 2013 (UTC)

Roos are essentially very shy creatures. Ones bred in captivity or tamed for touristic purposes are fine, but wild ones will shun humans. Ergo, a conurbation is not generally the place to expect to find a roo. -- Jack of Oz ^[Talk] 04:35, 26 April 2013 (UTC)

I used to live on the green patch you can see here. As you can see, there's plenty of other places for the roos to go, but they chose to stay in the camp and eat our nice green grass. They wouldn't stir if you walked passed within a metre of them, but they did if you stopped walking near them. They're not really that shy, but since the major cities are always in areas with high rainfall, I guess keeping away from people is more of a viable prospect. 202.155.85.18 (talk) 04:49, 26 April 2013 (UTC)

Follow-up: What's the evolutionary reason roos sometimes run towards danger ? I can see it possibly being helpful for the pack, as a predator would be afraid to attack a pack that might slam into them at top speed and cause an injury. It also might be harder to attack a roo that's charging right at them. And while full-sized adult roos might not have many predators, a pack of dingos must be a potential threat to wallabies or to roo joeys. StuRat (talk) 04:23, 26 April 2013 (UTC)

I'm not 100% sure, but I think a large kangaroo charging at a dingo would probably succeed in getting away most of the time. Dingos hunt roos in pairs or larger groups and try to catch them alone or single them out. They try to herd the roos toward fences (so before white fellas showed up maybe rivers or whatever else is impassible. Forget cliff faces, the roos would just jump), so simply refusing to be herded probably mucks up the dingos plan. 202.155.85.18 (talk) 04:33, 26 April 2013 (UTC)

An adult red kangaroo can jump fair over a dingo; apparently they jump 1.8m [2] high, which I suspect is too high for the dingo to even jump and take hold. 202.155.85.18 (talk) 04:41, 26 April 2013 (UTC)

Now we've beaten kangaroos to death, does anyone, particularly eastern Victorians, want to talk about wombats and cars? HiLo48 (talk) 06:57, 26 April 2013 (UTC)

Squirrels have an interesting brain defect that results in many dying on roads. They seem to be indecisive. I will be driving up to one in the street, it will start to run to one side, change it's mind, turn and run for the other side, then turn around again. StuRat (talk) 07:21, 26 April 2013 (UTC)

Wow, so kangaroos are stupid and squirrels have a brain defect that makes them indecisive - what a complete load of unscientific crap! Both these species have developed escape strategies that have served them well for hundreds of thousands of years but unfortunately humans have used their intelligence to break free of evolution and have developed ways of killing, and even wiping out, other species faster than they can evolve into something with more suitable strategies for escape. Clearly the seemingly random escape patterns described above worked well for the situation they found themselves in before cars and guns were developed but aren't suited to the world we have created over the last couple of hundred years as evolution doesn't work that fast. There are examples of species evolving because of our effect on the environment such as the peppered moth becoming darker during the industrial revolution and lighter again as pollution gets less (see: Peppered moth evolution). Given enough time I would think that squirrels and kangaroos would evolve, by natural selection, into animals with different escape strategies but it won't happen for a long time yet. Richerman (talk) 09:34, 26 April 2013 (UTC)

In both cases they seem to be strictly going on instinct, rather than assessing the situation and coming up with a strategy to fit the situation. This is not a good indication of intelligence. StuRat (talk) 09:38, 26 April 2013 (UTC)

I would suggest you read Anthropomorphism#In science. "Stupid" is a term we use for humans who lack intelligence or common sense - applying it to other species is meaningless - and squirrels do not all have a brain defect. Richerman (talk) 09:51, 26 April 2013 (UTC)

What point are you trying to make? -- Jack of Oz ^[Talk] 09:49, 26 April 2013 (UTC)

(ec) That answers on this page are supposed to be scientific. Richerman (talk) 09:55, 26 April 2013 (UTC)

He's suggesting that he is smarter than a roo. We won't know for certain until we throw a car at stu and see how he reacts. Someguy1221 (talk) 10:02, 26 April 2013 (UTC)My comment makes the assumption that Jack is replying to stu. With all the edit conflicts, i'm not certain who is talking to whom. Someguy1221 (talk) 10:03, 26 April 2013 (UTC)

Yes, I was asking Stu. But Richerman then added an extra colon to Stu’s post, which put the cat among the pigeons, sense-wise. -- Jack of Oz ^[Talk] 10:54, 26 April 2013 (UTC)

Oops! - now that was me being stupid...or clumsy...or both :-) Richerman (talk) 11:40, 26 April 2013 (UTC)

Stu asked what's the evolutionary reason why roos sometimes head toward danger. The key to it is that the direction they take is random as I said. I thought I had covered it, but here it is again:

While roos like to gather together, as they do if there is a spot with nice food, they spend a lot of time on their own. So instincts that serve well in a herd are not so good. Compare with goats, which are herd animals that use a crude but very rapid way of voting on what to do (see my 1st post above). By immediately running at top speed in a RANDOM direction, most of the time it works, because almost any direction not directly at a natural predator is a good direction. And no time is wasted trying to make a decision. And, sometimes heading toward danger is not a bad idea also. I can tell you that, from personal experience, having a kangaroo going full tilt directly at you reliably provokes an immediate emergency reaction from a human: GET OUT OF THE WAY!

Having said that, if a group of roos are startled, they don't act like goats, sheep, and other herbivores and all run in the same direction. Roos don't waste time deciding direction. Roos in groups on sensing danger scatter and head off on all points of the compass. That's not a bad strategy. With natural predators, only one roo might be killed - the rest will get away. And, when food is plentiful, nothing as large as a roo can reproduce as fast and as effectively. That's why farmers pay people to shoot them and why they are shot for food - they reproduce so well (with their hormone and reproductive process that is way more sophisticated than than standard mammals) there's not the slightest risk of them becoming extinct.

A comment on whether or not roos are stupid: StuRat is right - an animal that relies on pre-programmed instincts is not an intelligent animal that can tailor a response to suit any new situation. If, like me, you have encountered quite a few roos on the road while driving, and encountered quite a few while bushwalking or rogaining, you can only come to one inescapable conclusion: roos ARE stupid. Very effectively evolved, but definitely stupid.

Wickwack 124.178.131.148 (talk) 12:20, 26 April 2013 (UTC)

Why do humans keep damaging their vehicles by banging into deer and kangaroos? They have good eyesight and are aided by lights at night, and they supposedly have high intelligence. One would have thought they would avoid such collisions instead of blithely driving along assuming everything will be okay. You can only come to one conclusion: humans ARE stupid. Dmcq (talk) 13:04, 26 April 2013 (UTC)

It's a matter of risk assessment. If you want to be 100% certain of never hitting a deer, you'd probably have to drive everywhere at 20 miles per hour. However, the personal cost to drive (as I recently did) 1,000 miles from Austin Texas to Phoenix Arizona - then doing so at 20 miles per hour in complete deer-proof safety would requires 50 very tedious hours - if you drive at the speed limit, then you can do it in 14 hours...but the price for doing that is a statistical chance of hitting a deer.

Let's crunch some numbers:

• 1.5 million deer are killed on US roads every year.
• Americans drive around 3 trillion miles per year.
• That's one deer impact for every 2 million miles driven (presumably most of those miles were driven at or near the speed limit).
• If I drive slowly enough (let's say, 20mph) to be sure that I won't ever hit a deer - then I need to spend 100,000 hours driving those 2 million miles rather than 50,000 hours if I drive at 40mph or 25,000 hours if I push it up to 80mph.
• Let's say that by driving faster (at 40mph) and risking deer impact, then on average I'll spend an extra 50,000 hours in order to avoid hitting a single deer. Even if I drive 2 hours a day on average right now - then by driving twice as slowly (for 4 hours per day, at 20mph), I'd avoid one deer impact every 68 years of my life. I doubt I'll drive for that many years! Since there are an average of 1,400 human deaths each year from deer impacts (and 1.5 million such impacts), you're asking me to spend an extra 50,000 lifetime-hours behind the wheel in order to improve my chances of avoiding a deer impact by one in 1,000! It's simply not worth it. Doubling the amount of time I'm on the road doubles the chances of being killed by a drunk driver...that VASTLY outweighs the risks of deer impact.

Conclusion is that only an idiot drives slowly enough to reliably avoid hitting deer.

SteveBaker (talk) 14:48, 26 April 2013 (UTC)

Well put. And, as has been stated above, kangaroos will even collide with cars and put dents in them after the car has been brought to a stop. In nearly 50 years of driving I've hit about 5 to 6 roos. Do you want me to never go anywhere? Wickwack 124.178.131.148 (talk) 15:49, 26 April 2013 (UTC)

Guys, the notion of intelligent adaptation is simpler than that. See deer/roo/posum/turtle. Slow down and avoid impact. Help the poor critter out if you must. But then go on your merry way full throttle. The risk is minimized. Road engineers and maintenance crews help out too by improving road conditions. But road conditions are marginal at times and there are too many distracted and inattentive drivers that simply don't care what or who they hit. But perhaps in a few decades we will be smart enough to develop ways to do without paved roads and improve our lot. -Modocc (talk) 16:10, 26 April 2013 (UTC)

Exactly. Hopefully stupid inattentive drivers will be replaced by robots and this sort of thing will be a thing of the past. Dmcq (talk) 16:43, 26 April 2013 (UTC)

I don't know where Steve Baker got that 1.5 million deer collisions figure. 2000, there were 247,000 deer-vehicle collisions in the US. Could the number have increased by a 6x factor within one decade? To avoid hitting one you also don't have to drive at 20 miles. There are deer whistles that make noise when attached to your vehicle and would drive deer away. Anyway, I'm sorry to have triggered a discussion about deer vs. car collisions when the question was clearly about kangaroos. OsmanRF34 (talk) 17:26, 26 April 2013 (UTC)

Well...

1. This says that "According to the Insurance Institute for Highway Safety, a driver hits a deer an estimated 1.5 million times each year in the U.S.[1], up from 200,000 just 25 years ago"...so yeah - the number has gone *way* up.
2. I'm intrigued that you referenced our deer whistles article in the same sentence where you suggest using them! I guess you didn't look where you linked! That article clearly states: "Scientific studies of these devices have indicated that they do not in fact reduce collisions."...so *NO*, do not under any circumstances get deer whistles! Our article points out: "Deer are highly unpredictable, skittish animals whose normal reaction to an unfamiliar sound is to stop, look and listen to determine if they are being threatened."...so far from scaring them off - these devices would more likely cause them to stop in their tracks in order to figure out where this weird noise is coming from!
3. That same article mentions the "Roo Shoo" device that does the same thing to scare off kangaroo - but there is no indication of whether they work for that species. My bet would be "no"...but there doesn't seem to be much information about that.

Anyway, I'm sure the answer I gave earlier is equally relevant to kangaroo collisions - the underlying message is the same, though the numbers are clearly going to come out differently. SteveBaker (talk) 19:56, 26 April 2013 (UTC)

OK, on a second glance, the thing with the deer whistle seems as effective as the ultrasound against cockroaches or cholesterol-lowering food or anti-barking product or whatever other poorly thought product. On the other hand, your 1.5 million figure could be wrong. It comes from the Insurance Institute for Highway Safety, and it's from the year 2004. The Centers for Disease Control and Prevention, a federal agency, cites a figure of 247,000 accidents that " involved incidents in which the motor vehicle directly hit an animal on the roadway." Mostly, these animal were deer. The figure is from 2002, so I doubt they went up by that much in such a short time. OsmanRF34 (talk) 00:34, 27 April 2013 (UTC)

While I agree it's unlikely the figure changed so much from 2000 (or 2002) to 2004, I wouldn't conclude it's wrong. Ultimately, whether a federal agency or not, it's difficult to conclude their figure is inherently more reliable without a careful consideration of the methodology in comparison to the other methodology. From what I understand from the source [3], they are relying on police reports of accidents. I don't know much about the US, but are police reports required for every single accident even if they only involve one vehicle and without injury to any person in all states? Or for all insurance claims? If no to both, then one obvious possibility is that some of these minor accidents are going unreported. BTW while a minor point, I don't know where 2002 is coming from. The source and our article clearly says the estimate is for 2000. They provide some estimates of hospitalisations and fatalities for 2001-2002 as well as percentage of accidents which involved a deer in one state for 2002, but I didn't see any estimate of the number of accidents in 2002. Nil Einne (talk) 17:06, 27 April 2013 (UTC)

There's a couple of other points that haven't been mentioned yet that Sturat might be interested in. One is that there are a lot of areas where the only fresh grass shoots (known as "green pick") are, is on the road verges. I was told that this was caused by dew forming at night in the air above the roadway. This means that the Kangaroos are more often feeding right beside the road than randomly distributed through the bush. Also I am a strong believer in the theory that if they are not dazzled by the oncoming headlights, they will often jump into the only area where they can see the ground clearly, ie the roadway in front of your car because it's lit up by your headlights. Certainly my observations from many years as a Wildlife Ranger are that when they are hopping along in front of you at night, they are much more likely to leave the road if you turn off your headlights.122.108.189.192 (talk) 07:13, 27 April 2013 (UTC)

I agree that the only green grass, or the most abundant dry grass, is often found alongside a paved road, cycle path or footpath. This is unlikely to be related to dew forming in the air above the roadway. It is largely because whatever rain falls on a paved surface mostly runs off the surface on to the adjacent soil. Consequently, when rain falls in the vicinity, the soil alongside a paved surface receives many times the amount of water received elsewhere. Dolphin (t) 07:38, 27 April 2013 (UTC)

And now for a little light entertainment. For reasons that have nothing to do with this thread but which would take too long to explain, this afternoon I had cause to listen to a recording of the classic version of The Carnival of the Animals with verses by Ogden Nash spoken by Noël Coward. The section called "Kangaroos" is at 8:55 here, but the whole piece is well worth a listen for those who don't know it. To hear Noël Coward pronounce "kangaroo meringues" to rhyme with "boomerangs" is an experience like no other, really. (The video has a bet each way with the spelling; it's 'kangaroo' intially, then it deteriorates to 'kangeroo'). -- Jack of Oz ^[Talk] 07:46, 27 April 2013 (UTC)

• How about car horns that make dingo calls, would that scare roos away? μηδείς (talk) 16:01, 28 April 2013 (UTC)

Probably no good, but might work. Dingos make three kinds of noise: Short barks, which they make only once as a warning. The nature of this noise is such that to a Kangaroo it's probably just another noise. They make howls to call other dingos - a sound that travells long distance in the bush/forrest. Kangaroos hear howls routinely and take no notice unless it is very close. A howling dingo is a dingo on its own. At highway speeds a car making a howl noise will sound distant but might work. The third noise is a quiet "ahhhgggghhhhh" noise, useless for the purpose. There may be a serious technical problem in reproducing a howl such that a roo will think "dingo". It is a mistake to think animals hear sounds as we do. What is an obvious difference to a human may be very subtle to an animal and vice versa, and other unknown factors may apply. I had a dog that would come when I called his name with total reliability. I tried an experiment a few times with a good quality microphone, an amplifier, and a very good hifi loudspeaker. I called his name over the speaker positioned some distance away. I expected the dog to come to me, or maybe look at the speaker. He did absolutely nothing - totally ignored it. Wickwack 121.221.28.17 (talk) 00:57, 29 April 2013 (UTC)

Why can't LCDs be made capable of displaying interlaced video?

As the title says - why can't LCDs be made capable of displaying interlaced video, when the progressive scan used on modern LCDs produces far inferior video quality to that of interlaced video? Whoop whoop pull up ^{Bitching Betty | Averted crashes} 23:29, 25 April 2013 (UTC)

The design of LCD's does not lend itself to interlaced scanning, but you wouldn't want it anyway.

Interlaced scanning was done with CRT displays becasue the response of the screen to the scanning electron beam is very fast, but the energy required to force enough current through the scanning coils for a high scanning speed, and the cost of achieving the high video bandwidth required for non interlaced display was too great. LCD's have a slow response, so they can be scanned at a lower speed without flicker.

Interlaced scanning is not superior in quality to non-interlaced - it is a compromise that was acceptable for low definistion television. You were mis-informed. In systems where there is not much movement, and the user sits close, as in computer displays, interlaced scanning causes an annoying line crawing effect. While analog television always used interlaced scan, only the earliest CRT computer displays used it, as it was not really acceptable. For computer displays, the cost of high energy wideband non-interlaced scanning had to be accepted.

Keit 120.145.177.181 (talk) 00:45, 26 April 2013 (UTC)

That answer is incorrect in almost every regard!

• LCD's can (and are) easily used to display interlaced images.
• You might (and indeed do) want it when bandwidth is limited.
• Interlaced scanning was done on CRT's to save bandwidth and for no other reason. The BBC broadcasted non-interlaced television using the Baird system in 1936 - and the few people who watched it evidently used non-interlaced CRT's. Non-interlaced CRT's were made in the billions as computer monitors - they work just fine.
• LCD's can be made with all sorts of response rates - managing 60Hz is relatively easy - so can CRT's. Indeed "Storage tube" CRT's could hold an image on the phosphor more or less indefinitely without re-scanning.
• Interlaced scanning DOES produce superior video quality when compared to non-interlaced in an environment such as analog broadcast TV or limited capacity videotapes and such where bandwidth is at a premium.

SteveBaker (talk) 15:34, 26 April 2013 (UTC)

When video editing in the digital age, little is more of a pain in the butt than interlaced video. — Preceding unsigned comment added by 217.158.236.14 (talk) 09:57, 26 April 2013 (UTC)

It's a slightly more nuanced argument than that. Using non-interlaced rendering at 60 frames per second produces much better video than interlaced frames at the same display resolution. HOWEVER: If you have limited amounts of bandwidth, it is much better to use that bandwidth to deliver interlaced images than to halve the resolution to send a non-interlaced video stream.

It's a bit less clear-cut than that...for very dense information (text, graphics), the flicker you get with thin horizontal lines in interlaced systems can be very annoying...and for fast-action motion, the interlacing can be objectionable...but for most image content, interlacing at higher resolution produces a far superior picture than lower resolution non-interlaced video.

So for bandwidth-limited systems, interlacing is a good thing for picture quality...which shouldn't be a surprise - the guys who invented broadcast television weren't idiots. They thought very carefully about things like that.

What changes the game isn't LCD versus CRT. It's fancier video compression systems made possible with computers doing the work of decoding the video stream. With compression standards like MPEG, there is nothing much to be gained in terms of bandwidth or resolution in using interlaced images. With video being transmitted over the Internet, via Satellite or Cable TV, and via Digital broadcast TV, we have pre-compressed images that use even less bandwidth than interlacing saves us.

This really has nothing to do with LCD versus LED versus Plasma versus Cathode-ray tubes. You can display non-interlaced images on a cathode-ray tube - or interlaced pictures on LCD/LED/Plasma screens. Computer displays were non-interlaced even when we were still using CRT displays - and analog broadcast TV is still interlaced even on fancy flat-panel LCD/LED/Plasma displays.

So it's all about compression and bandwidth - it has nothing whatever to do with the display technology.

SteveBaker (talk) 14:22, 26 April 2013 (UTC)

MPEG isn't a compression standard, it's a group of experts. — Preceding unsigned comment added by 217.158.236.14 (talk) 14:47, 26 April 2013 (UTC)

That's the most overly pedantic statement I've heard on the ref desks in many weeks! Sure, MPEG is a committee which produces compression standards, numbered MPEG-1, MPEG-2, and so forth. These standards are collectively known as "The MPEG video compression standards"...which (being a bit of a mouthful) is universally reduced to "MPEG" by all practitioners of the video transmission arts. Pointing out this completely trivial distinction may be a great ego-inflating thing for you - but it doesn't help in answering this question in the slightest degree. Please learn when a clarification is needed - and when it's a muddification - as it clearly is here. (Since he who lives by the pedantry should also die by it: "MPEG" is only the informal name for the group - it is properly called "ISO/IEC JTC1/SC29 WG11" or "Coding of moving pictures and audio, ISO/IEC Joint Technical Committee 1, Subcommittee 29, Working Group 11.") SteveBaker (talk) 15:13, 26 April 2013 (UTC)

It has almost EVERYTHING to do with display technology, and a fair bit to do with viewing distance. Sorry SteveBaker, but you do not know what you are talking about.

Firstly, as I said before, CRT phospors repond to the scanning electron beam very fast - much faster than the eye responds to light. LCD's repond very slowly. For a field rate (the rate at which the picture is updated) fast enough for motion picture display, you'll see more flicker with a CRT than you will with and LCD. So for a CRT system, the bandwidth, which is directly proportional to field rate, must be high enough to minimise flicker. Interlacing is a method of tricking the eye by replacing the flicker with a linecrawling effect, which is acceptable if you sit far enough away so you can't make out the lines - which is what you normally do when watching TV. People sit close enough to computer screens to see the line crawling effect. The flickering with a low field rate does not occur with LCD's, as the pixels are slow to respond, slower than the human eye.

Secondly, when TV was developed in the late 1930's, the cost of receivers had to be minimised. Tube technology was expensive - a typical TV set in 1939 was a very different proposition compared to today's solid state sets. It was like purchasing a car - husbands discussed it with wives, saved up for a deposit, and bought the thing on hire-purchase, to be paid off over several years. Even in the 1970's, a (colour) TV set cost me over $800, compared to my annual salary then as a professional engineer of only ~$4,000. What affected the cost was the scanning rate, as scanning a CRT consumes considerable energy directly proportional to the scanning rate, due to use of magnetic scanning coils. Also, with tube (valves to the Brits, not to be confused with the picture tube) circuitry, one single tube/valve could easily provide the ~5 MHz bandwidth required for an interlaced picture, but to provide the 10 MHz bandwidth for a non-interlaced picture would have required several tubes or a very large tube, either way a lot more power. All this means that a non-interlaced tube and CRT TV set would have cost a lot more.

With computers, the interlaced display was not acceptable, due to users sitting close, so, except for the very first computer CRT displays, non-interlaced displays have always been used. When the first PC's and displays with a resolution good enough for serious grpahics and CAD work became widely available in about 1984, they were EXPENSIVE. In 1984 I bought a 17 inch colour CRT display of 640 x 480 resolution, about the same resolution as a good TV set, for about $900. 21 inch colour TV's were by then only half that. The cost penalty of complexity and energy requirements does not apply with today's solid state electronics and LCD displays because they do not have magnetic scanning, and because it costs much the same to make a video chip with 1,000 transistors as it does to make one with 10. The cost is instead determined weakly by the resolution, and is so low it really doesn't matter. A few months ago I bought an LCD TV, 20 inch, full HD, for $149.99. The salary for a professional engineer of the same level as I was in the 1970's is now around $140,000 a year.

So, in the 1970's, a (CRT) TV set cost ~2.5 month's wages, but today's TV sets of about the same screen size (LCD), but far better picture, cost a bit less than half a day's wages. That's why it was important, when CRTs were used, to mimimise the cost, and interlacing was the way to do it.

Keit 124.178.131.148 (talk) 15:22, 26 April 2013 (UTC)

I strongly disagree - and before you impune my qualifications, I worked as a researcher in this field at Philips Research labs in the displays and television group between 1977 and the mid 1980's. I even hold a patent for a novel TV scanning system...and I've been a researcher in the field of computer graphics ever since then.

So: You can choose fast or slow phosphors for a CRT to get almost any reasonable response rate you want. In NTSC, each pixel gets lit up 30 times a second in interlaced rendering and 60 times in non-interlaced - so you actually need a somewhat longer phosphor/LED response times to do good interlacing with less flicker...which is the opposite of what you're asserting! There are PERFECTLY GOOD non-interlaced CRT's - and PERFECTLY GOOD analog TV's that use LCD, LED and Plasma technologies. I own at least two of each of those things!

The flicker due to interlacing is most objectionable in computer displays because the data is produced digitally with abrupt brightness changes between consecutive lines. Analog TV camera and film scanners produce soft transitions from one scanline to the next - so when viewing natural scenes, you don't have terrible line-crawl or interlace flicker.

Computer screens were always more expensive than TV's but that's down to economy of scale - this was a big bone of contention in the Philips research group where we were concerned with promoting home computers (my team invented the CD-ROM) and we didn't want to get stuck with connecting them to interlaced TV's. Back then, TV's sold in the billions - and computer screens in hundreds of thousands...certainly not in the millions. It was only with the arrival of the cheap PC and home computers that the market for non-interlaced screens got big enough to drop the prices. LCD and LED prices have been almost the same between TV's and computer screens because these days they sell in comparable quantities. SteveBaker (talk) 16:00, 26 April 2013 (UTC)

Well, if you were an expert display technology researcher at Philips, then I am Bernard Tellegen come back from the grave (look him up in Wikipedia!). Increased production volume reduces unit cost - but there is definite law of diminishing effect. The 640 x 480 NEC monitor I bought was made in volumes exceeding that of many TV models. The TV prices I quoted for comparison are for TV's that were made for use in Australia only, but the NEC monitor was World market. Both TV's and monitors came in a multitude of brands, but under the hood, there has always been a limitted number of component manufacturers, so the production volume is effectively higher.

The less frequent line refresh rate with interlacing, which causes line crawl, is only important if you sit close enough to (just) make out the individual lines, which you do with computer monitors, but not when watching TV - how many times must I say this obvious fact? I haven't got it wrong way round - you have. Yes, a manufacturer can select a phosphor with a range of persistance times. They do just that with radar displays and oscilloscopes. However the low cost but good colour and brightness phosphors used have a fast response. The decay in light output is gradual and somewhat inverse exponential, so a phosphor than is slow enough to eliminate flicker tends to cause "comet trailing" on moving objects depicted. LCD decay once it starts is more abrupt, although comet trailing was a problem until the technology was mastered.

If you worked at Philips you should be aware for example that the Philips 19AX, 20AX, and later variants of colour TV display component systems were used by dozens of set makers. I also have CRT and LCD TV's and monitors of good quality - but what does that prove? Nothing. Both will do the job if enough money is spent. If you think that minimising cost was not the object when TV standards were developed, go research the then quantity cost of a 6CM5 (a power vacuum tube/valve most commonly used for TV line output until solid state took over, considered a marvel of modern tech in its day, and only just capable of handling the power required to scan a 625 line picture on a 21 inch 110 degree TV set) - you'll find it was more, in real terms, than an entire LCD set costs retail today) Then get a good 1950's engineering textbook on TV technology from the Library - you'll find it's all about compromises to keep the darn cost down. You certainly, back then, not want to almost double the power dissipation and cost by using non-interlaced scan when TV's were the third biggest cost to the average family (after purchase of a home, and purchase of a car). What was your patent title? Keit 121.215.9.85 (talk) 16:33, 26 April 2013 (UTC)

I agree with Keit. I worked for a TV repair company while going thru college. It was pretty obvious that interlaced scan was selected when TV's were tube and CRT-based, as the cost of selecting non-interlaced scan would have made TV sets so expensive that they would not have been viable as a mass consumer product back then. In isn't just the the line output tube (6CM5 or 6DQ6B and european equiv) would need to handle double the power, the video circuits would also be double power and the set power supply would need to be almost double in size. Steve Baker claims that sharp edges do not occur in natural scenes in television. What utter poppycock! If edges going from full black to full white or vice versa in from one line to the next (or from one pixel equivalent to the next), such as the edge of a dark suit against a light coloured background, did not oocur frequently in television, then the number of lines required, and the video bandwidth, could have been considerable reduced. When TV started in the USA, 525 lines was chosen as a compromise between an acceptably sharp picture and not too much cost. When TV started in European countries and Australia, 625 lines was chosen, as technology had advanced at bit, American experience could be drawn upon, and thus a slightly better cost vs picture quality was viable. The UK, which started broadcast TV ealier than everyone else, chose 405 lines in order to get the cost realy down so folk in a poor economy could stretch themselves to buy sets. The 405 line picture was never really acceptable though, especially in colour, and the UK scraped it and went to 625 lines in the early 1960's rendering millions of sets obsolete at considerable cost. One suspects that if Steve was actually a researcher in Philips Display and Television Group, then from the misinformed nonsense he wrote, he was probably in cabinet design or something. Ratbone 121.215.33.216 (talk) —Preceding undated comment added 02:15, 27 April 2013 (UTC)

In the UK at least, 405 lines never existed in colour. Transmission on UHF/625 lines started around 1964, with the launch of the third channel BBC2, and BBC1 and ITV were transmitted in both UHF/625 and VHF/405 for quite some years, all in black and white. Colour was introduced a few years later only on UHF/625. "Dual standard" sets were sold during the 60s so those didn't become obsolete unless you wanted to switch to colour. Not really relevant to the question but to the detail above. Sussexonian (talk) 10:16, 27 April 2013 (UTC)

405 line colour was actually seriously proposed though, in order to allow existing sets to remain in use. The BBC spent vast sums of money adapting the NTSC method to 405 lines, and built a complete line of colour cameras, studio processing equipment, studio monitors, and 405 line colour recievers. When they got it all going end to end, and could test viewer reaction to pilot shows, it was very evident that, while 405 line gave an almost acceptable black and white picture, it was never going to be acceptable in colour. It was this large scale expensive experiment by the BBC that was a major factor in the British decison to scrap 405 line and go to 625 line. Other factors were the economics of making set components for the World market and a (mistaken) belief that with 625 lines British firms could help the economy by exporting complete sets, and the severe restrictions on artistic camera shot direction due to the low resolution of 405 lines, which reduced the export value of British TV shows (back then a lot of shows were shot on 35 mm film facilitating showing in 625 line in other countries, and because shooting on film was more tolerant of lighting, but artistic direction still had to allow for showing in 405 line at home). The BBC work on 405 line NTSC colour was extensively documented in contemporary professional engineering journals and in the electronics magazine Wireless World. The published information on the BBC experiment makes fascinating reading.

You are misinformed about UHF broadcasting in the UK. Because VHF channels were taken up by 405 line transmission, 625 line had to be started on UHF, an unfortunate circumstance as more transmitters are required for coverage in hilly areas and in cities, and UHF tuners are more expensive to make. The major reason to change to 625 line was to enable a good colour picture as I said. 625 line PAL BBC broadcasts, using colour studio equipment, links, and colour transmitters right from the word go started on 1 July 1967. However not all shows were available immediately in colour, even though some that were exported had been shot on colour film for years. Also, colour sets were for a few years very very expensive, & prone to poor picture and trouble due to lack of experience in the trade. So for several years many consumers continued to buy black and white sets, albiet 625 line UHF capable. Many folk in the USA continued to buy b&w sets for years after their earlier colour introduction for similar reasons.

Ratbone 58.169.243.248 (talk) 10:50, 27 April 2013 (UTC)