Comments on: The Dance of the Galilean Satellites

The Dance of the Galilean Satellites

dkg — Mon, 06 Aug 2007 21:43:11 -0800

Time lapse animations of planets and satellites. See what an amateur digital astrophotographer could do a decade ago. This is what the animated gif was designed to do.

By: delmoi

delmoi — Mon, 06 Aug 2007 21:57:16 -0800

Oldschool

By: event

event — Mon, 06 Aug 2007 21:58:20 -0800

Nice!

By: weapons-grade pandemonium

weapons-grade pandemonium — Mon, 06 Aug 2007 22:08:08 -0800

Cool. More on libration.

By: Poolio

Poolio — Mon, 06 Aug 2007 22:11:48 -0800

ANNOY ↑ This is what the blink tag was designed to do.

By: Poolio

Poolio — Mon, 06 Aug 2007 22:12:45 -0800

BTW... cool.

By: otherthings_

otherthings_ — Mon, 06 Aug 2007 22:16:55 -0800

This is awesome. My favorite is the one of the out-of-focus star... next time someone asks me why stars twinkle, I'm just gonna show them that!

By: daninnj

daninnj — Mon, 06 Aug 2007 22:58:13 -0800

The Comet Hale Bopp animation is inaccurate. There's no UFO following it. Nice site.

By: eye of newt

eye of newt — Mon, 06 Aug 2007 23:01:25 -0800

I didn't realize the moon appeared to bobble so much from day to day. I wonder what causes this effect.

By: YoBananaBoy

YoBananaBoy — Mon, 06 Aug 2007 23:03:35 -0800

This is what the animated gif was designed to do. Where exactly are the hamsters?

By: interrobang

interrobang — Mon, 06 Aug 2007 23:10:55 -0800

Cool find, thanks.

By: samw

samw — Mon, 06 Aug 2007 23:42:30 -0800

eye of newt: the orbit of the Moon around the Earth takes it above and below the plane of the Earth's orbit about the Sun. When the Moon is above the Earth's orbital plane, you see more of the "bottom" of the Moon. When the Moon is below the plane, you see more of the "top". (Above/below, top/bottom relative to the hemisphere you are in.) This is also why we don't get eclipses every month. If the Moon orbited the Earth in the same plane as the Earth orbited the Sun, then the Moon, Earth and Sun would line up every month (twice a month, even!) causing frequent eclipses.

By: Lynsey

Lynsey — Mon, 06 Aug 2007 23:54:56 -0800

Nice post, dkg, and good answer from samw!

By: DU

DU — Tue, 07 Aug 2007 04:20:54 -0800

The inclination of the moon's orbital plane is what causes the up and down bobble, but there's also a left/right bobble. That's because the orbit is not perfectly round, so sometimes it gets ahead or behind relative to the rate at which it is revolving on its axis.

By: bwg

bwg — Tue, 07 Aug 2007 05:15:18 -0800

DUN DUN DUNNNNNNNNNN!

By: TechnoLustLuddite

TechnoLustLuddite — Tue, 07 Aug 2007 07:01:08 -0800

this moon, it vibrates?

By: lathrop

lathrop — Tue, 07 Aug 2007 08:32:10 -0800

Cidadao's idea of collecting photographs to show galactic rotation over millions of years is gloriously nutty. Our galaxy rotates once every 200 million years or so -- speed varies by distance from center. Seeing the movie would be grand.

By: steef

steef — Tue, 07 Aug 2007 08:43:33 -0800

Excellent and appropriate use of animated .gifs! Let me tell you, there's nothing like seeing the Jovian moons with your own eyes for the first time. Even with a cheap pair of binoculars, you can get the same rush that Galileo must have felt: other worlds in orbit around another world.

By: kendroberts

kendroberts — Tue, 07 Aug 2007 11:34:41 -0800

dkg, samw and DU: thank you. This answers questions and poses more for me: So when we see more of the bottom edge of the moon (because it is above the Earth's orbital plane) that bottom edge should appear darker than the rest? Is it true that the same side of the moon faces us because it is eggish shaped and over time our gravity has has pulled its "butt" to face us? And if so: Is the moons rotational speed measurably not quite in sync yet? Do other moons do this? Will the Sun do this to the earth? Thanks

By: phliar

phliar — Tue, 07 Aug 2007 15:03:10 -0800

Once you get to a certain size, rock isn't hard enough to resist gravity, so the moon is not egg-shaped. Like all spinning bodies it is spherical with an equatorial bulge from centrifugal force. The moon faces us because its period of rotation on its axis is the same as its period of revolution in its orbit around the earth. This happens because of tides. On the earth, the moon's gravitation causes there to be two bulges, one where the moon is directly overhead and another at the antipodal point. (This is of course easier to see where the surface is liquid, that is, on the ocean.) As the earth spins, this bulge moves around the earth, and friction converts some of the spinning energy to heat. The earth's rotation is constantly slowing down. The moon, being much smaller, faces much stronger tides from the earth, and over the years the friction has slowed its spin down until the tidal bulge is stationary -- another way to put it is that it always shows the same face to the earth.

By: pax digita

pax digita — Tue, 07 Aug 2007 20:48:27 -0800

Looked at 'em in Firefox, and for some reason not a single one animated for me. Odd.