Talk:Meteoroid

How are meteoroids stopped from hitting hard on the earths surface?

How are meteoroids stopped from hitting hard on the earths surface —Preceding unsigned comment added by 59.183.246.63 (talk) 06:45, 17 October 2010 (UTC)

Please reread the introduction to this article. You'll see that Meteoroids that survive the plunge through the Earth's atmosphere and land on the Earth are called meteorites (click on the link to see that article). Best: HarryZilber (talk) 17:15, 17 October 2010 (UTC)

I think the questions was not what but how.

Meteoroids arrive in the upper atmosphere at a given cosmic velocity: typically 25,000-78,000kph(??? approximate from memory needs to be verified???) This cosmic velocity x mass of the meteoroid = momentum/ kinetic energy which is greatly converted to heat and light energy. Much of the mass is carried off as a molten mist further reducing the speed.

• Previous paragraph unnecessarily wordy. Simpler: "Force of friction slows the incoming meteors." — Preceding unsigned comment added by 77Mike77 (talk • contribs) 14:12, 2 November 2012 (UTC)

The result is both the speed and the mass of the meteoroid is decreasing at an increasing rate. IF the meteoroid is small it will not survive the ablation of entry. Once the speed falls below approximately 4200mph the meteorite stops ablation and incandescence( glowing) . It enters "dark flight" and decelerates to "free fall" velocity. Incandescence cannot continue below approximately 5 miles above sea level. As 95%(???) of the atmosphere lies below 5 miles, the 5 mile mark represents a relatively dense fluid compared to the 120-140 miles of atmosphere the meteoroid has traversed. For most meteoroids under 1 meter at entry, all the cosmic velocity has been depleted at or above by this altitude and the body free falls under normal gravitational acceleration. Depending on initial velocity and mass, can enter dark flight between 100 and 5 miles about sea level. Thus a meteoroid arrives at the ground constrained between 120-400 miles per hour(sorry about the cross use of metric and American measurements) So they do hit the ground hard enough to excavate an "impact pit" which may be none to a few inches to a few feet deep. — Preceding unsigned comment added by Mstreman (talk • contribs) 17:56, 18 September 2011 (UTC)

link rot

This reference can't be called up any more. ^ a b meteorshowersonline.com The Leonids and the Birth of Meteor Astronomy 4.249.63.30 (talk) 17:30, 1 March 2011 (UTC)

People/Objects hit by meteors

I think there is a need for info on people getting hit by it or a link directing to articles that talk about it. Thanks. — Preceding unsigned comment added by 160.109.98.44 (talk) 18:50, 2 August 2011 (UTC)

There are some references to people being struck by meteorites in the article Meteorite. You need to consider that a meteor is simply the visible expression of the passage of a meteoroid through the atmosphere, i.e. the illuminated trail of ionised plasma it leaves behind. In the vast majority of cases, the meteoroid either ablates totally or slows down sufficiently so that it is no longer leaving a plasma trail long before it reaches the surface of the earth. Somewhere I remember reading that even for meteorites reaching the earth's surface intact, the visible meteor (i.e. the plasma trail) always ceases at altitudes greater than 8km (5 miles) - this might be worth including in the article with suitable references. Therefore you cannot possibly be struck by a meteor. Peter b (talk) 21:54, 23 March 2012 (UTC)

The direction the Earth travels in its orbit

I am not sure that I improved the article. The explanation that I wrote is true, but the clause preceding the word as in not logically connected to the second clause. Meteors hit the leading hemisphere of the Earth more frequently than they hit the trailing hemisphere, but they hit both hemispheres night and day. Perhaps the reference to the direction the Earth travels in its orbit should just be dropped. Fartherred (talk) 21:08, 12 September 2011 (UTC)

The direction of travel of earth in orbit and the approach azimuth of the meteoroid has implications for meteoroid survival: at 12 noon the speed of the earth along its orbit (15k/sec?) is added to the speed of the meteor-while at 12 midnight the speed is subtracted. Therefore statistically speaking a meteoroid arriving at night undergoes less ablation and is therefore has a better chance of reaching the ground. I am not sure that the argument is true that meteoroids hit the leading edge more often than the trailing edge. Once a meteoroid comes under the gravitational pull of the earth they are drawn in regardless. Some approaching from the rear can be deflected forward and vice versa. Unless we have a specific citation to the contrary I too think this "fact" should be left out.Mstreman (talk) 17:27, 18 September 2011 (UTC)

Near the equator, it is generally the location with local time of 6 a.m. that is "at the front" and 6 p.m. that is "at the back". However, near the time of the equinoxes it is not so straightforward for locations near the poles; the poles point slightly "forwards" and "backwards" with respect to the direction of travel of the Earth around the Sun. - 86.139.167.126 (talk) 17:23, 25 February 2013 (UTC)

Colors of meteors

The color section is misleading and the caveat of "possible colors" should be revisited. The current spectra listing is for a chem lab and not for meteoroid composition. Meteor color is derived from both the atmosphere and the makeup of the meteoroid. For example copper is not found in meteorites above the rare microscopic occurrence. Nickel emits a green spectra but the Green color from meteors is a combination of magnesium( minor), atmospheric oxygen(Major).

For fodder, here is a draft blurb from a paper I am authoring: ... on to specific spectral emissions, the common emissions for metallic elements in meteors and for atmospheric elements can be seen at. <http://leonid.arc.nasa.gov/meteor.html>

Combinations of the two sources of emissions produce the colors one sees in the fireball. “Colors of meteors: The color of many meteors is caused (sic)by light emitted from excited atoms of various elements in the meteoroid (blue, green, and yellow) plus light emitted by excited atoms and molecules of the air (red). The metal atoms emit light much like in our sodium discharge lamps: sodium (Na) atoms give an orange-yellow light, iron (Fe) atoms a yellow light, magnesium (Mg) a blue-green light, ionized calcium (Ca+) atoms may add a violet hue. Actual spectral captures were rare until recently while. The intensity and therefore detectability with the naked eye is almost nill at distance. At longer distances the light from excited atmospheric gases is the most dominant. Light emitted from excited molecules of atmospheric nitrogen (N2) and oxygen atoms (O2) give a green light initially but change to red/orange as the meteoroid goes deeper into the atmosphere. The meteor color depends on whether the metal atom emissions or the air plasma emissions dominate the eye and that is inversely proportional to the difference“...NASA <http://leonid.arc.nasa.gov/meteor.html>... Mstreman (talk) 13:24, 29 January 2013 (UTC)

Unmerge with meteor

I don't understand why the articles on meteor and meteoroid got merged. These are not the same topic. Meteors can result when large objects pass through the atmosphere, not just small ones. So meteors should not be a subtopic under meteoroids. I suggest unmerging. JeffG (talk) 19:58, 26 December 2011 (UTC)

Thank you for for your suggestion JeffG, however, I must strongly disagree with you. In the lead section it is clearly stated that a meteor is the visible expression of the passage of a meteoroid through the atmosphere. Being inherently related phenomena, I believe they quite appropriately described within the same article. Your argument regarding the size of a meteoroid does not really warrant separating the sections of this article either, because, since there is no general agreed definition in either the astroscience community, nor among amateur astronomers as to precisely what size range constitutes a meteoroid (as discussed in Meteoroid#Meteoroid), it is less confusing for non-experts to find all they need to know about the basics of this topic in the one place. If a particular sub-topic warrants a longer explanation than can be reasonably accommodated within the scope of the parent article, it is common practice to summarise that particular sub-topic within the main article along with a link to the separate more detailed stand-alone main article in its own right e.g. Meteoroid#Meteorite. I'm not sure that the subject Meteoroid#Meteor is sufficiently broad to warrant a separate article. Peter b (talk) 21:28, 23 March 2012 (UTC)

I agree with JeffG. The article, as written, is all about meteors and hardly about meteoroids, apart from some basics. I would advocate for a smaller article after looking over some foreign versions. Meteoroids are a much broader topic than what happens as and after they enter the earth's atmosphere. Also, meteoroids have effects all over the solar system, not just on earth. User:HopsonRoad 03:24, 21 January 2013 (UTC)

FWIW, not wishing to be negative, and having just come to this article to check a fact, I think that the meteor-related articles are among the most disorganised that I have yet encountered on Wikipedia for someone who just wants to know about meteors. This is probably inevitable given that there is a spectrum of phenomena from a faint meteor to a brilliant fireball, but anyone trying to get information about meteors as such will have difficulty in finding it among the several articles on the subject. I can't see what's wrong with having a separate topic on meteors, which is an observable phenomenon that people will want to know more about. There is a separate article on meteor showers, which actually gives more useful information, and there are separate articles on individual showers. In general usage, the term meteor refers to the trail left by cometary dust entering the atmosphere, either as a shower or an individual sporadic particle. The average reader would surely expect to find such an article on Wikipedia, not to have to jump around several related topics. I believe that the larger meteoroids, those of maybe 10 mm and larger but I'm guessing, give rise to fireballs and not to meteors. Having said all that, I am not volunteering to do any work on it!Robin Scagell (talk) 12:54, 23 January 2013 (UTC)

Meteors are caused by (small) meteoroids. Larger Asteroids are more likely to cause a Tunguska event. Meteors come from comet debris and small asteroids. Meteoroids are so small they can only be studied when they are near Earth since they are too faint to detect at other times. -- Kheider (talk) 14:47, 23 January 2013 (UTC)

No Meteors in ISS video

After several viewings, I could not identify any evidence of meteors in the ISS video (Aurora_Australis_2.ogv). There appear to be some instances of other satellites visible early in the clip (i.e. well above the atmosphere in the field of view, and travelling far too slowly to be meteoroids), but no meteors that I can readily determine. Neither does the original source (apparently http://eol.jsc.nasa.gov/Videos/CrewEarthObservationsVideos/) make any mention of meteor trails. If anyone knows at what time during the clip there are unmistakable meteors visible, please mention it in the caption. Otherwise, as interesting as the video clip is, I suggest it be removed in favour of something which unequivocally supports the article topic. Peter b (talk) 04:15, 23 March 2012 (UTC) with subsequent revision Peter b (talk) 20:52, 23 March 2012 (UTC)

I noticed the same thing independently. I went over and over it and the moving dots can be nothing other than satellites. They even appear right when they cross the shadow line just like they do when viewing from the ground. They are also about the same height or above the ISS which is at about 220 miles high, meteors light up at around 40 miles high. The claim that the video has meteors in it is unsupported, uncited, dubious. It's a shame because it's a really really really great video! I LOVED IT! And, it introduced me to that particular series of videos and I am grateful. But unfortunately the video is out of place here. Peter b would have been justified in removing it directly. Now that that there have been no objections in four months since it was brought up, it is even more justified to remove. Sadly, I will do that. ("Sadly" because it is otherwise such a great video.) -- 108.7.241.56 (talk) 16:00, 18 July 2012 (UTC)

A few shooting stars can be seen in this ISS video.

If anyone wants to review the video to see for themselves, here is the video with the original caption. You can also watch it just because it is a great video! The "shooting stars" are actually other satellites. I made the thumbnail smaller, but you can click on it to see larger sizes. 108.7.241.56 (talk) 16:22, 18 July 2012 (UTC)

The streak on the upper right-hand edge of the screen at 1.5 seconds in might be a meteor, but it seems too high and possibly too fast. I don't know what it is. In any case, to say that it absolutely is a meteor is still dubious and also isn't justified by a reliable source like it would be if the original source's description said so. -- 108.7.241.56 (talk) 16:34, 18 July 2012 (UTC)

Boulder-sized

Only just registered with Wiki, so not confident enough to edit articles yet! However, I think the basic description of meteoroid is too vague. How big is a boulder? The International Astronomical Union defines a meteoroid as: "a solid object moving in interplanetary space, of a size considerably smaller than an asteroid and considerably larger than an atom." The Hubble site defines a meteoroid as "a piece of interplanetary matter that is smaller than a kilometer and frequently only millimeters in size." Also, the description of meteor shower needs clarifying. Meteors appearing seconds or minutes apart could be pure coincidence, but frequent meteors appearing from a common point in the sky are obviously linked, and are referred to as a meteor shower. Billrush (talk) 22:51, 23 December 2012 (UTC)

Bill, welcome to Wikipedia and thank you for registering. I do not think there is clear upper limit for the size of a meteoroid. It is much like the grey area of asking when a hill becomes a mountain or a creek becomes a river. The Sutter's Mill meteorite source meteoroid/asteroid was around 3 meters in diameter, the Tunguska event impactor was around 40 meters, and the Arizona meteor crater was caused by a dense-iron impactor about 50 meters in diameter. We are always looking for a better way to word things without losing the casual reader. -- Kheider (talk) 00:27, 24 December 2012 (UTC)

I've briefly expanded the description of meteor shower in the opening paragraph, as it didn't make clear the fact that the meteors in a shower all appear to originate from a single point in the sky, due to them sharing a common origin, usually (or always?) the dust stream from a comet. Billrush (talk) 21:27, 26 December 2012 (UTC)

DELETED MstermanMstreman (talk) 14:33, 28 January 2013 (UTC)

Peter Jenniskens misidentified the Novato meteorite when he first looked at it, he did not misidentify the Sutter's Mill meteorite. What this article needs is more "verifiable" reliable sources, not unreferenced statements/claims. Best estimates for the Tunguska event are now around 40 meters (with an asteroid being somewhat more likely than a comet as the source). The best estimate for Meteor Crater is a 50 meter iron-nickel asteroid. This article also needs a section on dark flight. No cometary meteorites have ever been confirmed because they simply weather very quickly (and will look a lot like terrestrial rocks) if not immediately recovered. -- Kheider (talk) 17:09, 28 January 2013 (UTC)

UPDATE: I have read the revision and other than checking citations and the color chart find noting to add for clarity. I'll leave my comments for a time for reference. Excellent rewrite!

Moving up then back down the learning curve, I have removed/relocated most parts of my earlier brainstorm since it is mostly covered in the proposed revision. What was left over was appended below. The previous post/revision was just a laundry list of topics just from memory which would have been underpinned with citations. I will hence forth stick to specific paragraphs in the revision. I am recovering from a brain injury and can see on some things I am not back to par.

I've seen estimates for Tunguska in the 30 megaton/1200 meter range so to avoid confusion-- avoid specifics/values in this article all together and let their individual articles speak. Both Meteor Crater's and Tunguska's impactors were in the size range of "asteroid". They would have been given an asteroid designation had we discovered them today headed on a non collision course. So it begs if they should be in the meteor or meteoroid wiki articles at all, other than links.

Kevin's statement that the "only reason cometary(shower derived) meteorites have not been found is because of their fast weathering" isn't supported by meteoritical knowledge. Objects moving at cometary speeds simply do not survive stresses/ablation, and their actual occurrence is improbable given they would have to be very large sheds/chunks from the stable long period comets associated with a given shower. That said, we may have in fact have cometary-like meteorites as large chunks of space matter suggesting a comet connection are being recovered almost monthly-- but we don't have any from meteor showers and no radiant fireballs of sufficient size/ magnitude year in and year out.(TMK).(Note: Jennskins has a recent publication on sporadic major disintegration giving rise to comet debris discs but doesn't apply to all comet debris streams)

I raise the meteor shower /non-meteorite connection because every major shower brings forward a slew of meteor-wrongs for identification. It also brings uninformed comments from any psuedo-expert (e.g planetarium gift-shop clerk) the local news crew can ambush. I presume many on that audience would read this article and foreclose this misconception. Perhaps we will see a meteor/meteorite myths section.

REVISED: METEOROID vs ASTEROID: The Hubble Site is likely wrong if it says a kilometer is the largest size meteoroid--There are named asteroids much smaller. I side with Rubin and Grossman on definition(1 meter) but can see that there is no unified agreement as to meteoroid size limits. Frankly, we rarely discuss/use the term "meteoroid" at all --and only because of the former narrow definition of "meteor". "Meteoroids" have never been observed in orbit and are ambiguous prior to their becoming meteorites. I've always thought the definitions/distinctions pedantic and impractical for the average user. If "meteor" becomes all inclusive then "meteoroid" almost goes away except in scientific texts.

POSSIBLE NEW DEFINITION FOR "METEOR" I believe I read that as of the Fall,2012, the International Astronomical Union( IAU) revised the definition of meteor to include the whole phenomena--not just the visible flash of light. If so it would now is now "proper" to talk about a meteor and it meaning the light, sound, meteoroid, etc. It also permits discussion about a meteor's separate features (e.g. trail or train).(I saw a news release but I cannot find verification yet on the IAU web site)

METEOR RELATED TERMS: It goes that we should list/link all meteor descriptive phenomena: train,trail, shock wave/sonic booms, bow wave, point meteor, fireball, bolide, radio meteors, dark flight, incandescent flight, magnitude, electrophonic sounds and etc.

FRICTION VS RAM COMPRESSION: I read in the meteoroid article something about "friction causing a meteor to glow". This is a common misconception. It isn't air friction proper which causes ablation or incandescence. It is the heat liberated by ram compression of the air ahead of the meteoroid.( Citation needed)

METEOR SOCIETIES: This article should include a link to the main world bodies who focus on meteors and meteor observing 1) The American Meteor Society and 2) International Meteor Society. Plus, a paragraph on the history and practice of meteor observing with a link to the fireball reporting form/site of the AMS (American Meteor Society) or the AMS wiki article

METEOR COLOR. The whole topic of meteor color and spectra is complicated As written now it says something about "layering of minerals" but that misconception of my own doing. I think generic verbiage about interaction with the meteor and atmospheric gases may suffice. There is evidence that a fireball color change indicates a deeper penetration in the atmosphere owing to a spectral shift in nitrogen above and below certain elevations.(specifics to follow)

COMETARY VS ASTEROIDAL Meteors: The key information to convey is that one class of meteoroid/meteor can be specifically associated with comets and Annual Meteor Showers.

Meteors of cometary origin which give rise to meteor showers, are very small, grain-sized, meteoroids moving very high speeds. No(cometary) meteorite from a "meteor shower"proper has ever been confirmed. There is some vignette evidence that some of the non-shower related carbonaceous chondrite clans have closely matching spectra. Not to further muddle things, but two of the major annual meteor showers (e.g. one body, inbound and outbound passes = 2 showers) do have a spectra matching an asteroid class and are NOT thought to strictly be of a cometary origin.

Asteroidal Meteors/Sporatics which do have a chance of producing meteorites and are the random intercepts of orbiting asteroidal debris. Technically, we have planetary meteors/meteorites but make no distinction.

REMOVE: Discussion re "fireballs can come from any direction" but tend to survive when approaching 6 o'clock. I would not include this in the article.

RE: Notable/documented fireballs: ADD link Wiki article Meteor Procession aka The Great Meteor Procession.

DOPPLER RADAR: There is a new field of meteor/meteorite study developed by Marc Fries of NASA using US Weather Service radar to compute the trajectory of fireballs. It has facilitated recovery of upwards of 10 meteorites.

SKYCAM NETWORKS:The past decade has seen the rise of formal and informal backyard video installations for the purpose of digitally capturing fireballs for triangulation of the trajectory. There is no wiki article yet on these video cams and network coverage. NASA sponsors and operates one out of Redstone Arsenal, Alabama. The Canadian government has a collaborative union of Gov't, Academic, and private skycam operators.

NASA METEOROID ENVIRONMENTS OFFICE: NASA now has a meteoroid office. One of its charters is/was to disseminate data from Dept of Defense Nuclear Treaty compliance assets ( satellite and infrasonic sensors) in non-classified form. The director is Bill Cooke.

TAXONOMY: The origin and history of the use of the word "meteor" needs inclusion. Mstreman (talk) 12:28, 29 January 2013 (UTC)

• NASA defines a "meteoroid" as a small particle from a comet or asteroid.
• The free dictionary: meteoroids
• Science dictionary: meteoroid
• Infographic: What’s the Difference Between a Comet, Asteroid and Meteor? (Universe Today. February 20, 2013)
• "Meteorite and meteoroid: New comprehensive definitions" (2010)
• "...asteroids are smaller than planets but larger than meteoroids". (Universe Today)

184.158.96.147 (talk) 16:20, 21 February 2013 (UTC)

Re-organization needed

This article is mostly about what happens as meteoroids enter the earth's atmosphere (meteors) and their ultimate state as meteorites and micrometeorites. It is barely about meteoroids, their makeup and composition, their origin, etc. To address the latter, would require citations about samples obtained in space as well as inferences drawn on the origins of meteoroids from the study of meteorites and micrometeorites. I propose the following:

• Promoting subsection "Meteoroid" to a section, which would segue to the successive phenomena of atmospheric entry and post impact.
• Creating a new section on "Meteors", whose subordinate sections would describe the frequency, appearance, sound, history, etc. of observed meteors.
• Creating a new section on "Meteorites and micrometeorites" with links to the main articles and descriptions of what they can tell about meteoroids.

I would expect such a structure to reduce the confusion in the minds of average readers among meteoroid, meteor, and meteorite, which the current article only increases! Sincerely, User:HopsonRoad 15:13, 20 January 2013 (UTC)

I believe that I have made contact with all the correspondents to date on this Talk page to alert them of the proposal. User:HopsonRoad 14:02, 21 January 2013 (UTC)

I have also contacted recent substantive contributors. User:HopsonRoad 21:21, 21 January 2013 (UTC)

Responses

• Why do you want a re-organization when a meteoroid is just a small asteroid? -- Kheider (talk) 15:21, 20 January 2013 (UTC)

Because it's not currently principally about meteoroids--it's about meteors and meteorites, the manifestations of meteoroids intersecting with the earth and its atmosphere. Not all meteoric material is from asteroids. User:HopsonRoad 16:40, 20 January 2013 (UTC)

Hmmm. Just noticed that meteor does re-direct here. -- Kheider (talk) 17:05, 20 January 2013 (UTC)

Yes, the articles were combined, a while back. There is active discussion, above, on that topic. Perhaps if the Meteoroid section is strengthened sufficiently to stand on its own, Meteor could be come an article. I have structured my proposal to allow that. User:HopsonRoad 14:15, 21 January 2013 (UTC)

• A reorganization does make sense. The information about e.g. meteors is very spread out, but should probably be in one section. --Tobias1984 (talk) 08:25, 21 January 2013 (UTC)
• It seems to me that anything written about meteors or meteorites intrinsically also concerns meteoroids. The language refers to these things by different words but that does not make the concepts separate from one another. Having more written about meteors than meteoroids is the result of people seeing meteors and mostly only inferring meteoroids. If the title or lead section could make it more clear that the article is about both of these words that might help. - Fartherred (talk) 23:18, 21 January 2013 (UTC)

Thanks for your comments, Fatherred. I believe that I have done that in my proposed reorganization at User:HopsonRoad/sandbox. I have also incorporated your recent contributions to the article here. Please let me know what you think of the proposed rewrite. Sincerely, User:HopsonRoad 23:49, 21 January 2013 (UTC)

I am not very good at organization. I can hardly tell what changes you make, much less evaluate them. I think I will let others comment on the worth of the changes. - Fartherred (talk) 01:01, 22 January 2013 (UTC)

Mockup of proposed reorganized article

Those who would like to visualize the proposed restructuring may view it in my sandbox, until I do something else there. User:HopsonRoad 23:16, 20 January 2013 (UTC)

Reorganized version implemented

Absent any objections in the discussion, above, I have:

• Brought across the reorganized article. I included two changes that were made to the original version during this discussion period.
• Redirected Meteor, Meteors, Bolide and Superbolide to Meteoroid#Meteor.

User:HopsonRoad 13:05, 22 January 2013 (UTC)

Bolide should point to Meteoroid#Fireball. -- Kheider (talk) 14:10, 22 January 2013 (UTC)

I now see how to do that. I'll take care of it. User:HopsonRoad 14:46, 22 January 2013 (UTC)

I see that you did, already. Thanks! User:HopsonRoad 14:51, 22 January 2013 (UTC)

Meteor that hit Russia today

A Meteor hit Russia today and injured 500 people so far. Lots of INCREDIBLE footage was captured: http://www.youtube.com/watch?v=BcUhQThTiMM

The Chelyabinsk object doesn't fit the cited definitions of a meteoroid because it was too large (latest estimate is 17m diameter). So why is it referred to as a meteoroid?--88.73.133.140 (talk) 13:11, 18 February 2013 (UTC)

It is just the historical usage of the term from an era when the smallest known asteroid was large compared to the Tunguska event impactor. -- Kheider (talk) 13:43, 18 February 2013 (UTC)

Add entry times?

This article can add "entry times",

 http://brams.aeronomie.be/img/meteor.gif

to readers undertand the sky observations and the tragetory after explosion.

metre/meter

In countries that actually use the metric (SI) system, the unit is spelled "metre", so I don't see why someone changed this to the US spelling, "meter", given that the US doesn't even use the metric system. Is there a wikipedia guideline about this? (PS I didn't write the article, am just wondering.)77Mike77 (talk) 20:25, 21 February 2013 (UTC)

See Wikipedia:Style#Retaining the existing variety: When no English variety has been established and discussion cannot resolve the issue, the variety used in the first non-stub revision is considered the default. -- Kheider (talk) 20:51, 21 February 2013 (UTC)

Thanks for the clarification.77Mike77 (talk) 00:14, 22 February 2013 (UTC)

In the Netherlands, Belgium (Flanders) and Germany for example, the unit is also spelled as "meter". You ar not going to tell me that these counties do not actually use the metric system. Wikiklaas (talk) 02:50, 22 February 2013 (UTC)

In Canada's public school system we use the international (SI) metric system and use the spelling "meter". Although "metre" is accepted as it the French spelling. BatteryIncluded (talk) 15:30, 22 February 2013 (UTC)

Edit request - Sounds

Article claims "how these sounds could be generated remains...mystery" I think it should be "how these sounds are generated remains..." There are only a couple of ways they could be generated, and unless you are talking about the details, we know what they are. Also, the pressure wave (sonic boom) should not be characterized, imho, as being "delayed" - it propagates as it should through a gradient of compressible fluid, there is no "delay". Finally, the last part confuses the known causes of sound generation, with the unknown. I have no idea if the plasma it speaks about causes a delayed signal, relative to physical propagation of a pressure front, or happens in seconds, milliseconds or microseconds after the visual flare. EMR, once generate, propagates at c, of course. Could you specify what exactly the NASA guys are attempting to explain?173.189.75.50 (talk) 00:51, 14 August 2013 (UTC)