APOD: Central Lunar Eclipse (2018 Aug 03)

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APOD: Central Lunar Eclipse (2018 Aug 03)

Post by APOD Robot » Fri Aug 03, 2018 4:08 am

Image Central Lunar Eclipse

Explanation: Reddened by scattered sunlight, the Moon in the center is passing through the center of Earth's dark umbral shadow in this July 27 lunar eclipse sequence. Left to right the three images are from the start, maximum, and end to 103 minutes of totality from the longest lunar eclipse of the 21st century. The longest path the Moon can follow through Earth's shadow does cross the shadow's center, that's what makes such central lunar eclipses long ones. But July 27 was also the date of lunar apogee, and at the most distant part of its elliptical orbit the Moon moves slowest. For the previous lunar eclipse, last January 31, the Moon was near its orbital perigee. Passing just south of the Earth shadow central axis, totality lasted only 76 minutes. Coming up on January 21, 2019, a third consecutive total lunar eclipse will also be off center and find the Moon near perigee. Then totality will be a mere 62 minutes long.

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aneedham

Re: APOD: Central Lunar Eclipse (2018 Aug 03)

Post by aneedham » Fri Aug 03, 2018 7:50 am

Should the start and end images not be juxtaposed? I'm having difficulty seeing these images as a chronological sequence.

De58te
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Re: APOD: Central Lunar Eclipse (2018 Aug 03)

Post by De58te » Fri Aug 03, 2018 10:17 am

aneedham wrote:
Fri Aug 03, 2018 7:50 am
Should the start and end images not be juxtaposed? I'm having difficulty seeing these images as a chronological sequence.
Well you could say that. the motion of the Moon is complicated. Because the Moon orbits the Earth counterclockwise, as seen in the northern hemisphere, the Moon would enter the Earth's shadow starting on its western limb and exit on its east, as seen from Earth. But however the Earth rotates counterclockwise too but a heck of a lot faster. So we would see the Moon move east to west. Like in the photo. The left image is a shot at the beginning of the eclipse and the right an hour later as the Earth has turned that much.

ChrisKotsiopoulos
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Re: APOD: Central Lunar Eclipse (2018 Aug 03)

Post by ChrisKotsiopoulos » Fri Aug 03, 2018 10:58 am

Nice, sharp and informative. Well done Anthony!

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Re: APOD: Central Lunar Eclipse (2018 Aug 03)

Post by Ayiomamitis » Fri Aug 03, 2018 11:42 am

aneedham wrote:
Fri Aug 03, 2018 7:50 am
Should the start and end images not be juxtaposed? I'm having difficulty seeing these images as a chronological sequence.
The sequence is presented from the perspective of a ground-based observer who was fortunate enough to enjoy the eclipse. The moon gained altitude during totality (from 18 to 29 degrees above the horizon) while moving from the southeast to south. In other words, the sequence presented in the APOD simply shows the movement of the eclipsed moon as seen by a ground-based observer.
Anthony Ayiomamitis
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Ayiomamitis
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Re: APOD: Central Lunar Eclipse (2018 Aug 03)

Post by Ayiomamitis » Fri Aug 03, 2018 11:44 am

ChrisKotsiopoulos wrote:
Fri Aug 03, 2018 10:58 am
Nice, sharp and informative. Well done Anthony!
Thanks, Chris!

The moon during totality was relatively low in the sky starting at 18 degrees during the onset of totality and reaching 29 degrees at the end of totality. However, it has been a very wet summer this year and the atmospheric turbulence last Friday was quite favourable (ie very good seeing) and which led to very sharp images of the moon at 1200mm focal length.
Anthony Ayiomamitis
http://www.perseus.gr