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Thomas comments on Open Thread, September 30 - October 6, 2013 - Less Wrong Discussion

4 Post author: Coscott 30 September 2013 05:18AM

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Comment author: Thomas 30 September 2013 04:29:45PM 2 points [-]

If you didn't know it already

Comment author: shminux 30 September 2013 04:42:08PM 6 points [-]

Not quite true:

An earthrise that might be witnessed from the surface of the Moon would be quite unlike moonrises on Earth. Because the Moon is tidally locked with the Earth, one side of the Moon always faces toward Earth. Interpretation of this fact would lead one to believe that the Earth's position is fixed on the lunar sky and no earthrises can occur, however, the Moon librates slightly, which causes the Earth to draw a Lissajous figure on the sky. This figure fits inside a rectangle 15°48' wide and 13°20' high (in angular dimensions), while the angular diameter of the Earth as seen from Moon is only about 2°. This means that earthrises are visible near the edge of the Earth-observable surface of the Moon (about 20% of the surface). Since a full libration cycle takes about 27 days, earthrises are very slow, and it takes about 48 hours for Earth to clear its diameter.

Comment author: Thomas 30 September 2013 05:31:21PM 2 points [-]

Thanks, a correction has been made.

Comment author: ZankerH 02 October 2013 06:54:56PM 0 points [-]

The Earthrise videos from Apollo were shot while orbiting around the Moon.

Comment author: ZankerH 02 October 2013 06:55:34PM 0 points [-]

The Earthrise videos were shot while orbiting around the Moon in an (approximately) equatorial circular orbit, not from the surface. That's why the effect is similar.

Comment author: Thomas 02 October 2013 07:06:59PM 1 point [-]

Agree. My intention was and still is, that people would understand how peculiar sky is above the Moon. For one, there is Earth just hanging (oscillating a little, that's true) in the sky. Here we have Polaris, doing the same, but on the northern, not equatorial sky. It's worth to mention, that from the Moon south pole, you always see the Sun and Earth. Sun orbiting around, Earth not.

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