APOD: Total Lunar Eclipse at Moonset (2019 Jan 19)

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APOD: Total Lunar Eclipse at Moonset (2019 Jan 19)

Post by APOD Robot » Sat Jan 19, 2019 5:06 am

Image Total Lunar Eclipse at Moonset

Explanation: The Moon slid through Earth's shadow on January 31, 2018 in a total lunar eclipse. In this time-lapse sequence of that eclipse from Portal, Arizona, USA, the partial eclipse starts with the Moon high in the western sky. The eclipse total phase lasted about 76 minutes, but totality ended after the dark, reddened Moon set below the horizon. The upcoming total lunar eclipse, on the night of January 20/21, will be better placed for skygazers across the Americas, though. There, all 62 minutes of the total phase, when the Moon is completely immersed in Earth's dark umbral shadow, will take place with the Moon above the horizon. Watch it if you can. The next total lunar eclipse visible from anywhere on planet Earth won't take place until May 26, 2021, and then the total eclipse will last a mere 15 minutes.

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MarkBour
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Re: APOD: Total Lunar Eclipse at Moonset (2019 Jan 19)

Post by MarkBour » 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.
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Re: APOD: Total Lunar Eclipse at Moonset (2019 Jan 19)

Post by Kippiis » Sat Jan 19, 2019 9:21 am

What a wonderful event! Oh, nature, such a gift!

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Re: APOD: Total Lunar Eclipse at Moonset (2019 Jan 19)

Post by De58te » 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.

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Re: APOD: Total Lunar Eclipse at Moonset (2019 Jan 19)

Post by Chris Peterson » 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.
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MarkBour
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Re: APOD: Total Lunar Eclipse at Moonset (2019 Jan 19)

Post 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.
Mark Goldfain