Wikipedia:WikiProject Astronomy/Image Review

Welcome to the WikiProject Astronomy Image Review Page To request a new astronomical image: Add a new sub-section to the top section of this page. Indicate which article it would illustrate, and please specify, as specifically as possible, the constraints required of the image. Example: === [[Gliese 581 c]] === Image needed of a rocky planet, ~1.5x earth radii, dense atmosphere, orbiting a red dwarf star, with other planets in the system.~~~~ To claim an image task as an artist: Add a note in the request sub-section, including your intention to produce the image, and your signature. Example: : I got this one, I can make it easily with Celestia. ~~~~ To post an image for review: Once the artist has generated a candidate image for review, move the request sub-section from the top section of this page, to the bottom of the lower (review) section. Add the image as a thumbnail. Once the image, or subsequent revisions of it attain a consensus approval, place it into articles.

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Images under review

Gliese 581

version 1

version 2

Diagram needed of star system, showing the orbits of Gliese 581 b, Gliese 581 c and Gliese 581 d. I'm not looking for something artistic, just a simple diagram of the orbits. Thanks.Pharos 19:32, 12 May 2007 (UTC)

I created this using Celestia. Rubble pile 14:32, 13 May 2007 (UTC)

Everything looks good but the way the star rendered makes it look as if "b" is right at the surface of the star (at least in the small version, the full size looks much better). I think the star itself looks to be about the right size in relation to the orbits but the effect around it makes it looks much bigger at first glance. --AndrewBuck 15:31, 13 May 2007 (UTC)

While this is more of a cosmetic issue, perhaps you should enlarge the dots representing the planets. It isn't nessciary, but it would make it more appealing without sacrificing scientific accuracy. Fusion7 16:11, 13 May 2007 (UTC)

Shouldn't the letters be close to the planets? Sagittarian Milky Way 00:06, 14 May 2007 (UTC)

Here is version 2. I actually got rid of the dots representing the planets, since they are distracting, and the orbit is all that matters. Unfortunately I can't get rid of the 'planet B being burnt by the sun effect' which seems to be a limitation of Celestia. Maybe someone more artistic can find a solution. Rubble pile 01:16, 15 May 2007 (UTC)

Here's one without planet burned into the sun effect. Sagittarian Milky Way 06:50, 15 May 2007 (UTC)

version 3

Looks very good. The only final suggestion I have would be to crop the sides a bit to reduce the file size for bandwidth reasons, but I'm not sure if this would even make the file smaller due to compression. --AndrewBuck 17:36, 15 May 2007 (UTC)

No offense meant, but I think version 2 (by me) is better than version 3. Version 3 is too big and yet its labels are too small to see. But I agree that the 'burnt by the sun' effect has gone in version 3. It would be nice to produce a happy medium. Rubble pile 21:22, 17 May 2007 (UTC)

Yah, I knew that but I'm busy now and don't have time to change it. Sagittarian Milky Way 22:47, 17 May 2007 (UTC)

Version 4 Sagittarian Milky Way 23:25, 21 May 2007 (UTC)

version 4

Awesome! I did a bit of processing to brighten it up a bit. Here is version 5. I like this. Rubble pile 14:45, 22 May 2007 (UTC)

version 5

This one is without the green letter artifacts and the sun is reantialiased to be round again. (only visible at high resolution)

It was rounder before but compression took away two valuable anti-aliasing pixels! Sagittarian Milky Way 09:00, 25 May 2007 (UTC)

version 6

Nice. I think this is ready to go. Rubble pile 16:56, 25 May 2007 (UTC)

Yes, it's good to go. Sagittarian Milky Way 18:18, 25 May 2007 (UTC)

It's up. Fusion7 17:38, 27 May 2007 (UTC)

Gliese 876 b and 51 Pegasi B

While it was not one of our original intentions to review existing artist's impressions, I would like to bring these images to our attention:

Something tells me that these two images might be too speculative, but I'm not sure. So, Perhaps we shoul spend a little time with these two images after we are done with the previous request. Fusion7 16:30, 13 May 2007 (UTC)

According to the copyright tags they are both NASA creations so they do at least come from a reliable source. I'll split off a separate sub section for each to make the discussion more clear. --AndrewBuck 17:49, 13 May 2007 (UTC)

Gliese 876 b

File:GJ876b.jpg

Artist's impression of the outer planet Gliese 876 b.

Using the stars radius and b's orbital radius Gliese 876 should have an angular radius of .461 degrees compared to .266 degrees for the sun seen from Earth. However Gliese 876 has only a .0124 solar luminosity. So the star should be big, possibly bigger than it is now, but fairly dim. Brightness falls with the square of the distance so the planet being 4.8 times closer gains a factor of ~23 increase in apparent brightness relative to the Earth's orbit. Multiplying the luminosity by this factor of 23 yeilds about 28 percent as bright as the sun seen from Earth (note: this is a very crude calculation done by myself, and I'm not 100% sure it accounts for all that it needs to). As for the moons in the picture they coincide with the discussion above as being rather featureless, so on the whole I don't think it's too bad of a picture. I think they would have to be pretty close to the planet to make the planet look so big but they could just be small moons too. --AndrewBuck 17:49, 13 May 2007 (UTC)

The absolute luminosity of the star will affect the star's behavior, and the planets' climates, and all that, but it's not all that relevant to pictures of its planets. What matters in a picture is the brightness and reflectivity of the different objects in it, relative to each other.

Imagine photographing a basketball in a black room illuminated by a single table lamp with no shade. You can overexpose the lightbulb in the image and take a good photo of the basketball, or show detail on the bulb but the basketball will be too dim. Doesn't matter how bright the bulb is. Glycerinester 13:39, 15 May 2007 (UTC)

I agree with what you're saying I hadn't thought about the relative nature between the planet lighting and the star. However, I wasn't trying to compute the absolute luminosity of the star, rather the apparent luminosity, observed at the distance of the planet. It should be noted I am neither studying astronomy nor am I artistically trained at all, I was just trying to provide comparative estimates for others to use. I'm not sure how to take what you have said about the relative brightness of the two into account so I guess my previous comment about the image itself is possibly incorrect but I think the calculation on the solar flux received at the planet is on the right track. This number (the 28%) should presumably then set the factor by which the star is overexposed (at least as much as the sun is overexposed relative to the earth) but I'm not sure. Also this is as you mentioned neglecting the planet's albedo, however this is just another term to be multiplied into the above calculation. What to use for the albedo of these planets is another matter entirely, and as for that I have no idea. --AndrewBuck 17:57, 15 May 2007 (UTC)

If a star is 28% as bright as the Sun at a given planet's orbit, then it also illuminates the planet 28% as brightly as the Sun would. The whole scene is dimmer, by a uniform amount. The photographer changes f-stops or film speeds or whatever and the picture comes out looking exactly the same.

(Of course, the whole scene is uniformly affected by the star's color too.)

Try focusing on the apparent size of the star. When the scene illumination is coming from a larger area of the sky, it's less concentrated and should look less overexposed. A star that looks bigger than the Sun should look less bright, compared to the rest of the scene. It still won't "look dim," because it'll always be the brightest thing in the picture.

In this case the star in the picture should look 73% wider and thus (.266/.461)² = one-third as bright as the Sun does from Earth, compared to the illuminated features of the planets. I don't know how big the star would have to be in the sky for a camera to take a good picture of the surface of the star and the surface of the planet at the same time. Maybe really big. Glycerinester 00:00, 17 May 2007 (UTC)

What do you mean? Do you mean illumination, like with 47 Ursae Majoris b, where the side of the planet you can see would be almost completely dark unless the light source was tens of degrees wide; or do you mean relative size, for the planet to show any detail the star would have to be huge since it's physically much smaller than the star? The second one wouldn't be a problem since you can just be close to the planet and far from the star. Sagittarian Milky Way 08:20, 23 May 2007 (UTC)

Um, what do I mean by what, specifically? Glycerinester 12:47, 23 May 2007 (UTC)

"I don't know how big the star would have to be in the sky for a camera to take a good picture of the surface of the star and the surface of the planet at the same time. Maybe really big." Sagittarian Milky Way 17:18, 23 May 2007 (UTC)

OK, by "good picture" I meant technically correct exposure vs. overexposure. We assume our imaginary photographer will do whatever's necessary to get the exposure he wants of the planet he's trying to photograph. The question is, how does that affect the exposure of the star. I'm not saying overexposing the star is "bad," just when does it happen and when does it not.

The point is, the difference between pictures with blown-out stars in them like Image:GJ876b.jpg, and pictures with stars showing surface detail like Image:51pegasi-b.jpg, should not be the luminosities or apparent magnitudes of the stars but rather the geometries of the scenes and the albedos of the planets. This is all in response to AndrewBuck saying "the star should be ... fairly dim." Glycerinester 05:26, 24 May 2007 (UTC)

51 Pegasi B

File:51pegasi-b.jpg

Artist's impression of 51 pegasi b.

This doesn't appear to be as bad as I thought at first glance either. The star looks like it is very sun-like only a bit older. As for the planet the Wikipedia article says although its mass is less than Jupiter due to its high tempurature it should be quite large. This does almost look like a side by side comparison though and even given the immense size of the planet the star should probably be a lot bigger, or qualified with "not to scale". --AndrewBuck 17:49, 13 May 2007 (UTC)

From an artistic perspective, it looks like roughly half the planet is lit up, which gives the impression it is orthogonal to the viewing angle - but if that were true, it would be resting on the star. Debivort 17:56, 13 May 2007 (UTC)

Maybe it's just hot? 51 Pegasi B is 1800 degrees (F) Then only the red sunward lip would be interpreted as sunlit. The star should be much brighter and whiter sure (51 Peg is a solar twin), but artistically it's an expressive painting. Sagittarian Milky Way 07:11, 15 May 2007 (UTC)

Surely there are lots of stars out there to illustrate that are actually red. (Aren't there? Is it a myth, and they're all really yellow or peach-colored?) This one would need a disclaimer, like "artist's impression of 51Pegb through a red filter." Glycerinester 00:29, 17 May 2007 (UTC)

Yes, for example incandescent light bulbs aren't even as hot as red dwarf stars yet they still look yellow. Stars generally are so bright that the color doesn't matter much. It's the surface brightness. You'd have to get far enough from the star that it becomes a point and the number of photons decreases enough so it doesn't cause 'clipping' in any of the three types of retinal cones. Then you'd be able to see the 'true' colors [1] As you get farther, at about magnitude +2 the stars become too dim to see color in and once again look white. The painting is art not science. Sagittarian Milky Way 21:10, 17 May 2007 (UTC)

I find that many artist's impressions of red stars fail to capture the fact that these things are still incredibly bright and hot even though they're less bright than our sun. I would like a more vivid impression of the way this planet is being blasted to a crisp, rather than just warmly toasted.Rubble pile 21:26, 17 May 2007 (UTC)

PSR B1257+12 and its 3 planets

File:Ssc2006-10c.jpg

Artist's impression of PSR B1257+12 (by NASA)

I love this picture artistically, but I wonder how accurate it is. Do pulsars really look like that? Rubble pile 21:30, 17 May 2007 (UTC)

I Am Not A Real Astrophysicist, But:

• The prominent loops in the picture might be sideways.
• If the light source is high-temperature blue, of course, then those sides of the planets should be lit the same color, not the generic white that artists seem to prefer. If we're imagining the color is being corrected, it should correct the pulsar color at the same time.
• The planets are Venus-and-Mercury-type distances apart. From the numbers on the pulsar's page, Planet A is too large in the picture, or B is too small. Depending on which it is, the "camera" could be either, uh, about .004 AU or .03 AU further out from the pulsar than Planet C. That would make the whole picture either maybe two degrees of arc across, or a quarter of a degree across. ... I think.
  (These are rough approximations based on the proportions in the picture and math done partially in my head.)
• The pulsar itself should look about .004%, that's 4×10^-5 as wide as the Sun does from Earth. The pulsar's page says its luminosity and temperature are unknown. With such a tiny point source, any luminosity might be believable. It could drown out the background stars in the picture, or not.
• On the other hand, this is a millisecond pulsar, which would need high-speed photography to catch detail like this. Can you get dim objects at high speed? To a human being, the pulsar would be a blurred propeller in the sky, or a pair of cones. My monitor flickers more slowly. Actually, given the speed of light, the pulsar would be a pair of conic spirals with hundreds of loops across the width of the picture.
  ... Unless all that blue junk is just supposed to be some kind of lens flare.

So, uh, probably this particular pulsar doesn't look like this. For an example of a real-world picture of a similar scale, I found a crescent Moon and a crescent Venus together in the same photo. Glycerinester 04:47, 18 May 2007 (UTC)