Atmospheric distortion -- a feature request

[Size_Mick]

Well, I did a forum-wide topic search all the way back to whenever it started and only found one topic mentioning the term "atmospheric distortion" and it appeared to be a discussion about earth textures and, presumably, the effects of atmospheric distortion upon the satellite imagery, though I confess I didn't read the thread. Nonetheless, I feel confident that this subject is worth taking a stab at. To wit:

I use Celestia to get an idea of where everything in the night sky is located if I step outside to my back yard. That is, I have the camera positioned a few hundred meters above my town, and I set set the time to current time. It's very educational, by the way. At any rate, when I see the moon in Celestia, it appears so very tiny compared to what it appears to be in the real sky. I messed around with the FOV a bit but I'm not satisfied that this is the problem. So I was wondering about the atmospheric distortion that everyone tells me is responsible for the moon appearing so close. Is it possible to cause some sort of "atmospheric distortion effect" when atmospheres are enabled, which actually has the same apparent size change thing going on in the real atmosphere?

Eh, if it's a stupid idea, just delete it so I don't get ridiculed out of the forum. TIA.

[HankR]

I suggest you try a forum search for "moon illusion"...

- Hank

[granthutchison]

It has nothing to do with atmospheric distortion - though that particular story has been known to be false for hundreds of years, it seems to be very difficult to kill . Read the FAQs at http://shatters.net/forum/viewtopic.php?t=2291&postdays=0&postorder=asc&start=0, number 7.

Grant

[Size_Mick]

It has nothing to do with atmospheric distortion - though that particular story has been known to be false for hundreds of years, it seems to be very difficult to kill :cry: . Read the FAQs at http://shatters.net/forum/viewtopic.php?t=2291&postdays=0&postorder=asc&start=0, number 7.

Grant

I completely disagree with that notion. I believe it *must* either be a flaw in Celestia, or atmospheric distortion. Even with a very narrow FOV I can't make out *any* details of the surface of the moon in Celestia, which are extremely apparent to the naked eye in real life. (Correction -- it starts to look like it does outside to my naked eye at an FOV of about 5 00' 30", whatever that means). If someone would care to take a stab at this apparent discrepancy, by all means please do so. Does this mean that in order to see it properly, I'd have to have a 240" wide wrap-around concave hemispherical monitor?

Please note that I'm not trying to be a smartaleck, but what you say and what I see are at odds with each other as far as I can tell.

Update: I don't know, maybe it's me. I held my hands in a framing sort of way about 17" apart and about 2 and a half feet from my face, as a sort of reference to see how much sky I can expect Celestia to show me if I'm at the same FOV as in "real life" and it didn't encompass much. So maybe it's an FOV thing after all. Sorry to have wasted everyone's time.

Update to the Update: Nah, sorry, not convinced. I used a couple of stars as a point of reference and the moon still looks too tiny in Celestia. (Close to the edges of my "screen" while looking at it in the above manner outside were, I believe, the stars HD 1522 on the left edge, and HD 219615 on the right edge, with the moon in the center and Mars off to the lower right of it. At any rate, I live in a city so I don't get to see much. It was the 2 brightest objects to the left and right of the moon, not counting Mars of course. Station yourself over the Miami area of FL., set the time to this post's time -- which in my browser shows up as GMT 04:46, don't know if that's a preference thing or what -- and crank the magnitude limit down, set FOV to around 26 18' 38"and what you got left after everything else disappears are the two stars I refer to.)

[revent]

The average distance to the moon is 384400 kilometers. A circle of that radius has a circumference of 2415256 kilometers. The diameter of the moon is 3475 kilometers, or 0.001439 of the circumference of the orbit. Thus, the moon should span approximately that proportion of a full circle in the sky, or 0.517957 degrees. That is 0 degrees, 31 minutes, 46 seconds, on average.

In Celestia, the moon fills the window on my display with a FOV of 30 minutes, 41 seconds as of right now from the sublunar point. Reasonably close.

If I use the current distance Celestia gives to the moon, 387290 km, I get an even closer calculation of 30 minutes, 50 seconds.

What's this about a bug?

[granthutchison]

As to the matter of surface detail, you can't really expect your computer monitor, with a resolution of a thousand or so pixels, to provide the level of detail visible in the real world.

Grant

[Size_Mick]

As to the matter of surface detail, you can't really expect your computer monitor, with a resolution of a thousand or so pixels, to provide the level of detail visible in the real world.

Grant

I most certainly agree with you there. However, it still doesn't account for this apparent diameter discrepancy. I wish I had a digital camera that was good enough to take a picture. The moon is most definitely much smaller looking in celestia than it is in real life, even when looking only at the same section of sky. I suppose it might be an unanswerable question, since apparently it's not a hot topic of debate, this apparent diameter thing.

I suppose what I should do instead is just look around on the internet for earth-based photos of the moon that have a wide enough FOV to show some background stars near it, and compare those to what I can get out of Celestia. Of course, zoom and FOV are two different things in the world of cameras, so it'd be helpful to find pics that have data of the magnification settings used. If anyone knows of the existence of such photos on the internet, by all means please post links in a reply.

P.S. This isn't anything to do with the argument about the moon looking larger on the horizon than it does high in the sky. This has only to do with the Moon looking larger in the night sky than it does in Celestia.

[granthutchison]

Why not take a look here, where there's a direct comparison of Celestia and the real world during the recent Mars occultation. The match is precise, with no sign that the Celestia Moon is smaller than it should be.
No-one here is denying that the Moon looks smaller in Celestia - all we're saying is that it is the correct size relative to the FOV and the background stars, as I hope the link above demonstrates to you. The difference you're seeing just is a very powerful psychosensory illusion, generated from the fact that your computer screen is only a foot or so from your face (so you're brain knows the image of the Moon is a small thing), whereas the real Moon is at visual infinity and so is perceived as huge.

Grant

[Rassilon]

The average distance to the moon is 384400 kilometers. A circle of that radius has a circumference of 2415256 kilometers. The diameter of the moon is 3475 kilometers, or 0.001439 of the circumference of the orbit. Thus, the moon should span approximately that proportion of a full circle in the sky, or 0.517957 degrees. That is 0 degrees, 31 minutes, 46 seconds, on average.

In Celestia, the moon fills the window on my display with a FOV of 30 minutes, 41 seconds as of right now from the sublunar point. Reasonably close.

If I use the current distance Celestia gives to the moon, 387290 km, I get an even closer calculation of 30 minutes, 50 seconds.

What's this about a bug?

That pretty much sums it up...Thanks for that bit...I was wondering what the correct visual FOV would be for quite a while...I had it at 33 min...fairly close...

[HarrieS]

Size_mick, have you ever taken a photo of the moon. You'll be disappointed in what you actually see, even with a moderate 105 mm tele. Just a tiny dot with no detail to speak of.

Here is something you might try: a finger at arm's length is about two degrees wide for most people. That means that you can fit four moons side by side. Go outside and check it. Now have a direct look at your finger indoors. Can you still believe that four moons will fit on it?

Harrie

[revent]

The average distance to the moon is 384400 kilometers. A circle of that radius has a circumference of 2415256 kilometers. The diameter of the moon is 3475 kilometers, or 0.001439 of the circumference of the orbit. Thus, the moon should span approximately that proportion of a full circle in the sky, or 0.517957 degrees. That is 0 degrees, 31 minutes, 46 seconds, on average.

In Celestia, the moon fills the window on my display with a FOV of 30 minutes, 41 seconds as of right now from the sublunar point. Reasonably close.

If I use the current distance Celestia gives to the moon, 387290 km, I get an even closer calculation of 30 minutes, 50 seconds.

What's this about a bug?

That pretty much sums it up...Thanks for that bit...I was wondering what the correct visual FOV would be for quite a while...I had it at 33 min...fairly close...

In order to be really accurate, you'd have to model the orbit as an n-gon, with n somewhere on the order of 695 sides. (IOW, double the atan of distance/radius) The way I calculated it above treats the diameter of the moon as an arc instead of a straight line.

Not that I expect anyone to be that picky, but the windows calculator doesn't do trig.