Comments on: An eclipse from space with a two-way Moon

By: Oh, good – It’s just the Moon being all ‘parallax’-y. « Anguished Repose

Tue, 08 Mar 2011 08:06:30 +0000

[...] As Phil Plait over at Bad Astronomy explains, the Moon’s back-and-forth movement is all about parallax. The Solar Dynamics Observatory orbits the Earth in what, for our purposes, can be called a counterclockwise rotation. When the SDO is in the “bottom” half of its orbit (in clock terms, when it’s moving from 9:00 to 6:00 to 3:00), it is moving rightwards, while in the “top” half of the orbit (3:00 to 12:00 to 9:00) it is moving left. [...]

By: Joseph G

Joseph G — Tue, 08 Mar 2011 00:59:36 +0000

Actually, I’m a doofus – I think there would be two zones on opposite sides of the lunar disc (seen from the earth). Folks close to the lunar poles would see the earth move back and forth laterally.

By: Joseph G

Joseph G — Mon, 07 Mar 2011 20:16:51 +0000

@MTU: You might want to mention, too, that the eccentricity is Mercury’s orbit is the deciding factor, there. I believe it’s the same mechanism that causes the libration of the moon.

Heh, come to think of it, I’m remembering this old show that I used to watch – the end credits showed the earth rising over the lunar horizon. I always used to think that was a ridiculous bit of hokey graphical puffery, but come to think of it, I suppose that if you’re in a certain ring-shaped zone on the moon, the Earth would appear to bob up and down over the horizon, once per (lunar) day…

By: Joseph G

Joseph G — Mon, 07 Mar 2011 19:55:19 +0000

That prominence on the left-side limb of the sun early on in the video looks an awful lot like the video that was posted earlier last week. Is that by any chance the same flare?

By: Alex

Alex — Mon, 07 Mar 2011 12:51:35 +0000

Any idea on the time exposure for that video? If that’s in real time then it really drives home how fast that satellite was moving.

By: Messier Tidy Upper

Messier Tidy Upper — Mon, 07 Mar 2011 10:33:20 +0000

@ me at #1 : The same or a very similiar phenomenon here – with SDO and the Moon motion reversal – also explains why certain places on Mercury experience two sun-rises – ie. the Sun rising, setting and rising again, correct? Or am I too tired and not thinking clearly thus confused on that?

I *was* just too tired as it turns out.

Mercury’s rotation rate relative to it’s orbital speed is the cause.

This Youtube clip :

http://www.youtube.com/watch?v=nPprOO2u1gk

has more on that Mercurian phenomon.

By: Don

Don — Mon, 07 Mar 2011 07:14:16 +0000

I think the even cooler part of the video is seeing the sun’s rotation.

By: Brian Schlosser

Brian Schlosser — Mon, 07 Mar 2011 04:22:58 +0000

Beautiful! Just one question:

Are there satellites that NASA has that AREN’T in space? I mean, I guess there are plenty in clean rooms and warehouses and whatnot, but usually they don’t take such clear pictures…

By: Neal

Neal — Mon, 07 Mar 2011 03:34:15 +0000

Oh, right, the satellite is in a circumpolar orbit. The moon’s motion nearly perpendicular to the sun’s rotational plane caught me by surprise.

Also:

With a video keeping the background stars in fixed positions it’s different again.
Which is correct? It’s all relative…

It’s all an equivalence class of transformations!

I think a video with fixed background stars would be so similar to the video in the post that it wouldn’t warrant disagreement. The video taken couldn’t have been over more than a couple of days, so the sun’s motion w.r.t. the background stars would have been only a couple of degrees at most.

By: Wissydig

Wissydig — Mon, 07 Mar 2011 00:23:58 +0000

Oh yeah i love it – more pls