by MarkBour » Sun Jan 20, 2019 4:42 am
De58te wrote: ↑Sat Jan 19, 2019 10:50 am
MarkBour wrote: ↑Sat Jan 19, 2019 6:44 am
Lovely sequence. What causes the background sky to appear to have the variations it has? I would describe it as a set of concentric disks of ever lightening color as one proceeds to the western horizon.
This is just a guess but I guess that as the moonlight brightness diminishes, the automatic light sensor in the camera compensates becoming more sensitive thereby allowing more background light of the Milky Way in. Also as the Moon nears the setting horizon, the dawn of the rising Sun in the opposite sky reflects across the sky. But my question is why do the stars or planets to the left and the right of the Moon disappear when the Moon begins to turn red. You'd think that with the decrease of moonlight that the stars would become brighter as they seem to do in the last position before they disappeared.
Thanks, those sound like helpful guesses as to why it progressively gets lighter. Particularly the idea about the light sensor raising the sensitivity. The Sun rising on the opposite horizon seems less likely, since it would light the other side of the sky more than the western horizon.
I'm still not clear how the increasing sensitivity would result in a gradient in the composited sky, but there's a lot about how such an image works and gets stacked into a time-lapse that I don't understand.
In return, I have a conjecture about the stars. I'm guessing they were
not on the left and right of the Moon, but were instead trailing well behind it, so their sequence of images would start out of view in the first frames and end when the last moon image was at the horizon. In keeping with your idea about the light sensor, the last images of those stars do appear brighter than the first ones.
Chris Peterson wrote: ↑Sat Jan 19, 2019 2:23 pm
MarkBour wrote: ↑Sat Jan 19, 2019 6:44 am
Lovely sequence. What causes the background sky to appear to have the variations it has? I would describe it as a set of concentric disks of ever lightening color as one proceeds to the western horizon.
Looks like JPEG artifacts to me. The image is not a very high quality JPEG (it is highly compressed), and that almost always turns gradients into banded zones.
Thanks, I think that makes sense, as to why it is banded. In this case, it does not need to be the result of all of the processing, it could just be that the western horizon was lighter, and the gradient was thus crudely rendered in the JPEG. I suppose there are always sources of light pollution and they're almost always near the horizon.
[quote=De58te post_id=289089 time=1547895057 user_id=141631]
[quote=MarkBour post_id=289085 time=1547880241 user_id=141361]
Lovely sequence. What causes the background sky to appear to have the variations it has? I would describe it as a set of concentric disks of ever lightening color as one proceeds to the western horizon.
[/quote]
This is just a guess but I guess that as the moonlight brightness diminishes, the automatic light sensor in the camera compensates becoming more sensitive thereby allowing more background light of the Milky Way in. Also as the Moon nears the setting horizon, the dawn of the rising Sun in the opposite sky reflects across the sky. But my question is why do the stars or planets to the left and the right of the Moon disappear when the Moon begins to turn red. You'd think that with the decrease of moonlight that the stars would become brighter as they seem to do in the last position before they disappeared.
[/quote]
Thanks, those sound like helpful guesses as to why it progressively gets lighter. Particularly the idea about the light sensor raising the sensitivity. The Sun rising on the opposite horizon seems less likely, since it would light the other side of the sky more than the western horizon.
I'm still not clear how the increasing sensitivity would result in a gradient in the composited sky, but there's a lot about how such an image works and gets stacked into a time-lapse that I don't understand.
In return, I have a conjecture about the stars. I'm guessing they were [i]not[/i] on the left and right of the Moon, but were instead trailing well behind it, so their sequence of images would start out of view in the first frames and end when the last moon image was at the horizon. In keeping with your idea about the light sensor, the last images of those stars do appear brighter than the first ones.
[quote="Chris Peterson" post_id=289092 time=1547907793 user_id=117706]
[quote=MarkBour post_id=289085 time=1547880241 user_id=141361]
Lovely sequence. What causes the background sky to appear to have the variations it has? I would describe it as a set of concentric disks of ever lightening color as one proceeds to the western horizon.
[/quote]
Looks like JPEG artifacts to me. The image is not a very high quality JPEG (it is highly compressed), and that almost always turns gradients into banded zones.
[/quote]
Thanks, I think that makes sense, as to why it is banded. In this case, it does not need to be the result of all of the processing, it could just be that the western horizon was lighter, and the gradient was thus crudely rendered in the JPEG. I suppose there are always sources of light pollution and they're almost always near the horizon.