APOD: A Total Lunar Eclipse Over Tajikistan (2018 Jan 28)

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APOD: A Total Lunar Eclipse Over Tajikistan (2018 Jan 28)

Postby APOD Robot » Sun Jan 28, 2018 5:06 am

Image A Total Lunar Eclipse Over Tajikistan

Explanation: If the full Moon suddenly faded, what would you see? The answer during the total lunar eclipse in 2011 was recorded in a dramatic time lapse video from Tajikistan. During a total lunar eclipse, the Earth moves between the Moon and the Sun, causing the moon to fade dramatically. The Moon never gets completely dark, though, since the Earth's atmosphere refracts some light. As the featured video begins, the scene may appear to be daytime and sunlit, but actually it is a nighttime and lit by the glow of the full Moon. As the Moon becomes eclipsed and fades, the wind dies down and background stars can be seen reflected in foreground lake. Most spectacularly, the sky surrounding the eclipsed moon suddenly appears to be full of stars and highlighted by the busy plane of our Milky Way Galaxy. The sequence repeats with a closer view, and the final image shows the placement of the eclipsed Moon near the Eagle, Swan, Trifid, and Lagoon nebulas. Nearly two hours after the eclipse started, the moon emerges from the Earth's shadow and its bright full glare again dominates the sky. This Wednesday another total lunar eclipse will take place -- but this one will be during a rare Super Blue Blood Moon.

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Re: APOD: A Total Lunar Eclipse Over Tajikistan (2018 Jan 28)

Postby ta152h0 » Sun Jan 28, 2018 5:08 pm

if a sattelite was placed on the midnight side of the Earth, at what distance would it have to pace the Earth and suffer a total solar eclipse ? That would make the sky dark where it is always too bright to observe the stars on that hemisphere, woul it not ?
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Re: APOD: A Total Lunar Eclipse Over Tajikistan (2018 Jan 28)

Postby neufer » Sun Jan 28, 2018 7:47 pm

ta152h0 wrote:
if a sattelite was placed on the midnight side of the Earth, at what distance would it have to pace the Earth and suffer a total solar eclipse ? That would make the sky dark where it is always too bright to observe the stars on that hemisphere, woul it not ?

Can't quite follow that ...please restate question.
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Re: APOD: A Total Lunar Eclipse Over Tajikistan (2018 Jan 28)

Postby BobStein-VisiBone » Sun Jan 28, 2018 8:46 pm

At 0:38 in the video it is neat to watch the Moon move slightly leftward against the starry background, but the Earth's shadow remains fixed.

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Re: APOD: A Total Lunar Eclipse Over Tajikistan (2018 Jan 28)

Postby Chris Peterson » Sun Jan 28, 2018 11:35 pm

ta152h0 wrote:if a sattelite was placed on the midnight side of the Earth, at what distance would it have to pace the Earth and suffer a total solar eclipse ? That would make the sky dark where it is always too bright to observe the stars on that hemisphere, woul it not ?

You mean you want the satellite to always be in the Earth's shadow? That's not an Earth orbit at all, it's a solar orbit (unstable) a bit beyond the Earth that takes one year to complete. It's at the Sun-Earth Lagrangian point #2. However, it's too far from the Earth to totally block the Sun, so you actually have an annular eclipse. With active station keeping (burning a lot of fuel) you could get closer to the Earth and maintain a non-Keplerian orbit around the Sun with a period of a year, in order to be in permanent darkness.
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Re: APOD: A Total Lunar Eclipse Over Tajikistan (2018 Jan 28)

Postby ta152h0 » Tue Jan 30, 2018 6:08 pm

Muito obrigado
W
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Re: APOD: A Total Lunar Eclipse Over Tajikistan (2018 Jan 28)

Postby neufer » Tue Jan 30, 2018 7:34 pm

Chris Peterson wrote:
ta152h0 wrote:
if a sattelite was placed on the midnight side of the Earth, at what distance would it have to pace the Earth and suffer a total solar eclipse ? That would make the sky dark where it is always too bright to observe the stars on that hemisphere, woul it not ?

You mean you want the satellite to always be in the Earth's shadow? That's not an Earth orbit at all, it's a solar orbit (unstable) a bit beyond the Earth that takes one year to complete. It's at the Sun-Earth Lagrangian point #2. However, it's too far from the Earth to totally block the Sun, so you actually have an annular eclipse. With active station keeping (burning a lot of fuel) you could get closer to the Earth and maintain a non-Keplerian orbit around the Sun with a period of a year, in order to be in permanent darkness.

Alternatively, the Sun-Earth Lagrangian point #2 space station could drop a 100,000 km long tether in the direction
of Earth with an eclipse probe at the end. (Or a much much shorter tether with an occulting disk at the end.)
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Re: APOD: A Total Lunar Eclipse Over Tajikistan (2018 Jan 28)

Postby Chris Peterson » Tue Jan 30, 2018 7:57 pm

neufer wrote:
Chris Peterson wrote:
ta152h0 wrote:
if a sattelite was placed on the midnight side of the Earth, at what distance would it have to pace the Earth and suffer a total solar eclipse ? That would make the sky dark where it is always too bright to observe the stars on that hemisphere, woul it not ?

You mean you want the satellite to always be in the Earth's shadow? That's not an Earth orbit at all, it's a solar orbit (unstable) a bit beyond the Earth that takes one year to complete. It's at the Sun-Earth Lagrangian point #2. However, it's too far from the Earth to totally block the Sun, so you actually have an annular eclipse. With active station keeping (burning a lot of fuel) you could get closer to the Earth and maintain a non-Keplerian orbit around the Sun with a period of a year, in order to be in permanent darkness.

Alternatively, the Sun-Earth Lagrangian point #2 space station could drop a 100,000 km long tether in the direction
of Earth with an eclipse probe at the end. (Or a much much shorter tether with an occulting disk at the end.)

Occulting shields are already used by probes that are placed at L2 (or more technically, in orbits around L2).
Chris

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