Starship Asterisk*

APOD Robot wrote: ↑Mon Nov 19, 2018 5:08 am Gibbous Moon beyond Swedish Mountain

Explanation: The featured image was taken in Jämtland, Sweden near the end of last month. That gibbous moon turned, in a few days, into a crescent moon, and then a new moon, then back to a crescent, and a few days ago back to gibbous. And this same gibbous moon is visible again tonight, leading up to the Full Beaver Moon that occurs Friday night. Setting up to capture a picturesque gibbous moonscape, the photographer was quite surprised to find an airplane, surely well in the foreground, appearing to fly past it.

seattlemonster@gmail.com wrote: ↑Wed Nov 28, 2018 1:24 am
Doesn't the moon phase move from right to left in the northern hemisphere?
Wouldn't that make this a waning gibbous, not a waxing?

Chris Peterson wrote: ↑Tue Nov 20, 2018 8:35 pm
Well, he specifically said he used the polarizer to increase the contrast between the Moon and sky. And the polarizer will have the greatest effect at the quarter moons, and that's pretty close to what we have here (117° separation between the Sun and Moon). So unless you have some good reason to believe this is a composite of images taken at significantly different times, I think I'll go with what the imager claims: Just as I had set the camera for the correct exposure of the Moon and the mountain, I saw this plane emerging in the viewfinder. I quickly snapped a couple of shots and this is one of them.

neufer wrote: ↑Tue Nov 20, 2018 8:15 pm

Chris Peterson wrote: ↑Tue Nov 20, 2018 7:54 pm

neufer wrote: ↑Tue Nov 20, 2018 7:39 pm
AFAIK, this is amalgam of two separate (though gorgeous) pictures
...the moon is bright simply because it was taken well before sunrise.

That doesn't make sense (but I don't think you meant it quite that way).
Rather, I assume what you're suggesting is that it's a composite of two images made with different exposure times.

(But the photographer's explanation of technique does not suggest the Moon was taken while the sky was dark, since he used a polarizing filter to increase its contrast... which requires a sunlit sky.)

I don't doubt that the photographer' used a polarizing filter to increase the contrast for the plane/mountain photo.

But, he then inserted a nighttime photo of the Gibbous Moon (with a different exposure time), IMO.

(A polarizing filter of a daytime non-Quarter Moon wouldn't do all that much anyway.)

Chris Peterson wrote: ↑Tue Nov 20, 2018 7:54 pm

neufer wrote: ↑Tue Nov 20, 2018 7:39 pm
AFAIK, this is amalgam of two separate (though gorgeous) pictures
...the moon is bright simply because it was taken well before sunrise.

That doesn't make sense (but I don't think you meant it quite that way).
Rather, I assume what you're suggesting is that it's a composite of two images made with different exposure times.

(But the photographer's explanation of technique does not suggest the Moon was taken while the sky was dark, since he used a polarizing filter to increase its contrast... which requires a sunlit sky.)

neufer wrote: ↑Tue Nov 20, 2018 7:39 pm

Chris Peterson wrote: ↑Tue Nov 20, 2018 7:25 pm

neufer wrote: ↑Tue Nov 20, 2018 5:51 pm
Let's just agree that the best professional astrophotography always involves the cutting of some corners
such that half of us can just enjoy it as a pretty picture and the other half can point out the obvious flaws.

The question is, is it a "flaw" if processing distorts the linearity of intensity
but produces an image that more closely represents what the eye would see?

AFAIK, this is amalgam of two separate (though gorgeous) pictures
...the moon is bright simply because it was taken well before sunrise.

Chris Peterson wrote: ↑Tue Nov 20, 2018 7:25 pm

neufer wrote: ↑Tue Nov 20, 2018 5:51 pm
Let's just agree that the best professional astrophotography always involves the cutting of some corners
such that half of us can just enjoy it as a pretty picture and the other half can point out the obvious flaws.

The question is, is it a "flaw" if processing distorts the linearity of intensity
but produces an image that more closely represents what the eye would see?

neufer wrote: ↑Tue Nov 20, 2018 5:51 pm Let's just agree that the best professional astrophotography always involves the cutting of some corners
such that half of us can just enjoy it as a pretty picture and the other half can point out the obvious flaws.

Chris Peterson wrote: ↑Mon Nov 19, 2018 4:18 pm ...
The actual analysis is quite complex. Snow is a reasonably Lambertian reflector (although less so if this is more ice than powder). The Moon is distinctly non-Lambertian, with reflectance dropping much faster with viewing angle than we get with snow. So on the whole, I'd expect this to actually make the Moon less bright in comparison with snow, not more.

https://www.etymonline.com/word/gibbous#etymonline_v_6070 wrote:
gibbous (adj.): c. 1400, "bulging, convex," from Late Latin gibbus "hunchbacked," from Latin gibbus "a hump, a hunch," as an adjective, "bulging," from Proto-Italic *gifri- "hump," *gifro- "hump-backed," of uncertain origin. De Vaan suggests a PIE *geibh-, with possible cognates in Lithuanian geibus "gawky, plump," geibstu, geibti "become weak;" Norwegian dialect keiv "slanted, wrong," keiva "left hand," perhaps united by a general sense of "bodily defect." Of the moon from early 15c.; also used from 15c. of hunchbacks. Related: Gibbosity.

Chris Peterson wrote: ↑Mon Nov 19, 2018 4:18 pm

Cousin Ricky wrote: ↑Mon Nov 19, 2018 4:02 pm

Chris Peterson wrote: ↑Mon Nov 19, 2018 2:41 pm
Using a polarizing filter certainly explains the dark sky and increased contrast of the Moon, but not the apparent brightness of the Moon. As noted, it is almost exactly the same intensity of white as the snow, while it is, in fact, almost an order of magnitude less reflective. I'm thinking you used a fairly typical "S" curve transfer function to flatten out both the bright and dark end of the intensity profile.

In addition, the Sun is at a very shallow angle, so that can explain the relative darkness of the snow overall. Some ridges in the snow that face the Sun are much brighter than the rest of the snow, although they get close to the dynamic range of the image, so it’s impossible to tell how much brighter.

The actual analysis is quite complex. Snow is a reasonably Lambertian reflector (although less so if this is more ice than powder). The Moon is distinctly non-Lambertian, with reflectance dropping much faster with viewing angle than we get with snow. So on the whole, I'd expect this to actually make the Moon less bright in comparison with snow, not more.

Cousin Ricky wrote: ↑Mon Nov 19, 2018 4:02 pm

Chris Peterson wrote: ↑Mon Nov 19, 2018 2:41 pm Using a polarizing filter certainly explains the dark sky and increased contrast of the Moon, but not the apparent brightness of the Moon. As noted, it is almost exactly the same intensity of white as the snow, while it is, in fact, almost an order of magnitude less reflective. I'm thinking you used a fairly typical "S" curve transfer function to flatten out both the bright and dark end of the intensity profile.

In addition, the Sun is at a very shallow angle, so that can explain the relative darkness of the snow overall. Some ridges in the snow that face the Sun are much brighter than the rest of the snow, although they get close to the dynamic range of the image, so it’s impossible to tell how much brighter.

Chris Peterson wrote: ↑Mon Nov 19, 2018 2:41 pm Using a polarizing filter certainly explains the dark sky and increased contrast of the Moon, but not the apparent brightness of the Moon. As noted, it is almost exactly the same intensity of white as the snow, while it is, in fact, almost an order of magnitude less reflective. I'm thinking you used a fairly typical "S" curve transfer function to flatten out both the bright and dark end of the intensity profile.

astrofotografen.se wrote: ↑Mon Nov 19, 2018 9:16 am Hi and thanks for your comments.

To explain the Moon's brightness I used a polarizing filter when taking the photo. This darkens the sky quite a bit so the Moon stands out. The polarizing effect is most effective 90° from the Sun so in this case I got a lot of that polarizing effect. The mountains are lit by the Sun.

astrofotografen.se wrote: ↑Mon Nov 19, 2018 9:16 am Hi and thanks for your comments.

To explain the Moon's brightness I used a polarizing filter when taking the photo. This darkens the sky quite a bit so the Moon stands out. The polarizing effect is most effective 90° from the Sun so in this case I got a lot of that polarizing effect. The mountains are lit by the Sun.

/Göran

Ann wrote: ↑Mon Nov 19, 2018 8:42 am

jojo.dodo wrote: ↑Mon Nov 19, 2018 6:31 am Very nice photo... but...
Something shocked me with this picture and thinking about what it can be, if fact I realized that it's impossible to take such king of photo without post-processing... the albedo of moon is less than 0.1 and in this photo the moon seems as bright as snow... Can the author explain what he really did ?

Click to view full size image

A gibbous Moon over snowy mountains.
Photo: Göran Strand.

Click to view full size image

Snowy mountains and a faint Moon.
Credit: dzamikhoff

I guess you think that the Moon is too bright in today's APOD compared with the snowy mountains, in view of the fact that the Moon is really so intrinsically dark (like asphalt, in fact) while the snow is white?

How can the dark moon and the white snow seem to be equally bright in today's APOD?

The short answer is that most of the Moon is brightly lit by the Sun in the APOD, while the mountains are in darkness. The Sun had set at the time and place where this picture was taken, and the landscape was dark. I guess that the mountains must be lit up by something, but not by anything even remotely as bright as the Sun.

In the other picture that I posted, the snow-clad mountains are indeed lit up by the Sun. The snowy mountains are brightly lit and the Sun-facing parts of them look mostly brilliantly white. A pale Moon can be seen in the sky, and I think that at least part of it is sunlit. Why does it look so dark compared with the snow-clad mountains?

Why, because because both are sunlit, but the Moon is intrinsically so much darker than the snow, of course. But a sunlit Moon will look brighter than snow-clad mountains in the night.

Ann

jojo.dodo wrote: ↑Mon Nov 19, 2018 6:31 am Very nice photo... but...
Something shocked me with this picture and thinking about what it can be, if fact I realized that it's impossible to take such king of photo without post-processing... the albedo of moon is less than 0.1 and in this photo the moon seems as bright as snow... Can the author explain what he really did ?