APOD: Gibbous Moon beyond Swedish Mountain (2018 Nov 19)

[APOD Robot]

Gibbous Moon beyond Swedish Mountain

Explanation: This is a gibbous Moon. More Earthlings are familiar with a full moon, when the entire face of Luna is lit by the Sun, and a crescent moon, when only a sliver of the Moon's face is lit. When more than half of the Moon is illuminated, though, but still short of full illumination, the phase is called gibbous. Rarely seen in television and movies, gibbous moons are quite common in the actual night sky. 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.

<< Previous APOD

This Day in APOD

Next APOD >>

[Ann]

This is usually not my kind of picture, but I like the dreamy quality of the image, with the Moon apparently magically suspended like a rocky balloon over the snowy mountain slopes of Jämtland. The airplane seemingly flying above this "Moon-balloon" makes the scene even more dreamingly surreal. The mist-like clouds seemingly streaming out of the mountains, as if to provide "anti-gravity" to keep the Moon suspended, adds to the otherworldly feeling.

Click to view full size image

Seeing this scene makes me think how much Newton must have wondered what kept the Moon suspended in the sky, so that it did not fall down on our heads. Ah, Isaac, as you figured out, the Moon is trying to fly off in the tangential direction, but the Earth keeps snaring it with its own gravity. Or rather, the mass of the Earth is deforming the fabric of spacetime so much that the Moon can't make it out of the Earth's gravitational well.

Ann

[jojo.dodo]

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 ?

[Ann]

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

[Boomer12k]

pretty pic for this time of year....

:---[===] *

[Boomer12k]

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

Ahhh....the cold and the snow on the Stortorget, Stockholm in Winter....

:---[===] *

[astrofotografen.se]

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]

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

Thanks, Göran!

So jojo.dodo was right and I was wrong.

It's a magical photo.

Ann

[neufer]

Jämtland torn between Norway and Sweden.

---

---

[chubso]

The gibbous moon in the picture is a morning gibbous moon. The left side features are illuminated. The moon tonight is lit on the right side meaning that it is in the evening sky.

There are two distinct gibbous moons.

Great picture!

[Cousin Ricky]

The Moon looks oddly polished in this photo. When I looked more closely, I realized that, at this phase, Kepler is at about the right position for a specular highlight, and Copernicus is at a position for an interior reflection, as if the Moon had a glass mantle!

[Chris Peterson]

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.

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. That makes perfect sense, since a truly linear image as captured by most digital sensors doesn't actually look as natural as one modified in that way. When we see a scene like this with our eyes, that's exactly what our own visual system does, which is why we typically would see the Moon and the snow as fairly close in brightness. So that kind of processing makes the image truer to the visual experience than one which leaves the relative intensities accurately scaled.

[Cousin Ricky]

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]

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.

[neufer]

---

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.

[Fred the Cat]

The moon is such an inviting target but getting the focus correct between foreground and background has proven difficult for me.

Göran seems to have pulled it off perfectly in today’s APOD along with the other aspects of a great photograph. The setting is magnificent making me curious from which vantage point it was taken and the planning involved?

[neufer]

---

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.

[alter-ego]

...
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.

Complex in detail it is, but I think all is consistently explained by geometry. The scattering angle for the snow is different than for the moon. The moon's phase angle is about 60° or so. Conservatively, the magnitude drop is around 2 mag. For a Lambertian surface, the same magnitude drop is reached at ~80° wrt the incident light. Given the view angle is about 90° from the sun, and the general slope direction is favorable for higher scattering angles, it's not surprising that the reflectances are close. (Lambertian reflectance ideally = 0 at 90°)
The surface plot presents the relative seen brightness in this image. It's clear the snow regions more directly facing the sun are locally the brightest. I think the image is a natural consequence of the moon phase and snow illumination angles. Although some processing, as you say, may contribute to a more pleasing view to the eye, I don't believe it's required for the brightnesses to be close.
 

[Tragic Astronomy]

And as the moon groomed the airplane
In a benevolent way
And as the moon groomed the airplane
With its benevolent rays

[neufer]

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]

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]

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]

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.

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]

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]

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.)

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.