Ask MetaFilter questions tagged with planets

Is there a perfect orbit?

doublehappy — Fri, 16 Oct 2009 16:56:05 -0800

Is there a distance at which a satellite will orbit a body indefinitely? Is this distance a universal constant? As I understand it, satellite bodies are generally getting closer or further away from the body they orbit. Our moon, for example, is getting further away.

This morning I was reading a great essay by Amy Leachin the Best American Essays 2009.

In the second paragraph, it is noted that unless you [a satellite] happen to roll onto a track precisely 18,254 miles above your planet, the law ejects you or dashes you down. One moon in our solar system has achieved synchronous orbit, being pledged forever to its planet--Pluto's moon Charon. The other 168 moons have not.

According to google, 18,154 miles = 29,216 kilometers.

The wikipedia article about Charon cites a distance of 17,536 ± 4 km to system barycenter, 19,571 ± 4 km to the center of Pluto
. The radius of Pluto is, apparently, 1,153 ± 10 km. 19,571-1,153=18,418, which is close to 18,254 (though not 'precisely'), but nowhere near 29,216.

Am I missing something obvious (I'm not very good at space, so I am pretty sure this must be the case) or is Leach using poetic license, or is it a bit of both?

I find it hard to believe that there would be a universal perfect orbit distance, as celestial bodies are of varying mass, and there are also external tidal forces acting on them. However, I also find it hard to believe that there are big balls of rock and ice in mutual orbit, and that these systems are, themselves, in orbit around a huge ball of gas.

Illustrations for child's space-themed mural?

ericbop — Tue, 04 Aug 2009 11:01:56 -0800

Our son is getting too old for the animals on his wall, and we'd like to do a space theme (rockets, the real planets, etc). We've found that by enlarging an image and printing it out on clear label paper, we can make murals using our favorite illustrations, either found online or in books (technique originally posted here). So, we're looking for cool illustrations of the planets, rockets, etc. Preferably with a Mary Blairish, 1950's feel. Any suggestions, either on the internet or book recommendations?

Yey, Moon?

leotrotsky — Mon, 27 Jul 2009 08:51:23 -0800

Planetary magnetic fields and life: Is there any reason to believe that strong magnetic fields on rocky inner planets are relatively uncommon? If so, is there any reason to believe that the hypothetical giant impact 4.5 billion years ago that created the moon could have spun the earth up sufficiently to create that magnetism?

Finally, assuming the first two questions aren't ridiculous, couldn't the combination help explain the apparent dearth of other complex life in the universe?

Not an expert in the field, I'm just curious if I'm completely off base in seeing a connection here.

Where can I find kids tees with nerdy themes like the Solar System outside the US?

pootler — Sun, 07 Dec 2008 12:59:30 -0800

Where do I find nerdy T-shirts and other clothes for a 4 year old in Europe? And by nerdy I mean space, science, alphabet, math all the usual autistic obsessions. :-) My son's autism means that shirts with all the usual kid obsessions, like Spiderman, Ben 10, or Batman, anything with big eyes, humans or animals are absolutely out. They scare the pants off him. I know this is probably silly, but there are so many normal kid things we miss out on that just being able to get a t-shirt that he will love, just lke any other parent might pick up one of the thousands of transformer/power ranger/pokemon shirts out there... well that really is the only thing *I* want for Christmas.

You'd think this would be easy, but I've been looking for a year and not found anything except a couple of pairs of space jammies on ebay and a sold out alphabet shirt on threadless.com. Surely there are other kids outside the USA who would love a t-shirt with planets on it?

I know he's not the only nerdy 4 year old in Europe. There are plenty of cool things to be had in the US, but the customs charges are often as much as or even more than the cost of the shirts themselves if I want to have them sent to Holland.

And he's a big lad - he's wearing size 6/7, so you'd think someone somewhere would be selling something to suit him. Surely?

Which of Holst's Planets Sounds the Best?

bach — Thu, 15 May 2008 17:29:45 -0800

Seeking the definitive recording of Gustav Holst's The Planets. In planning for the 2008 competitive marching season, we have selected music from The Planets. The entire staff has listened to several versions of the work, but thought I'd use my bi-weekly question and query the hivemind as to the best recording of this work since we cannot seem to settle on a particular interpretation.

Where can I find data on planetary positions and velocities?

deansfurniture5 — Mon, 17 Mar 2008 13:33:41 -0800

I'm working on a computer simulation of the solar system, but I need data on the positions and velocities on planets and their moons. (more inside) For a class project, I'm working on a 3D simulation of the solar system. However, I need to get good data on the positions and velocities of planets and their moons. I've managed to find a lot of sites with information about planetary positions as viewed from earth, but the way I'm constructing it, I need to be able to locate them by x, y, and z coordinates with the Sun at the origin.

Any ideas where I might find any good data? Also, anywhere with an analytical solution to the position of a planet with respect to the Sun would be helpful as well.

Thanks!

Would our Sun really eat Earth?

Burhanistan — Tue, 05 Feb 2008 07:29:37 -0800

Would an expanding Sun really swallow the inner planets? Not that it keeps me up at nights, but would the Sun's projected eventual expansion into a red giant actually swallow up the inner planets? Is there actual astronomical evidence of this occurring in other star systems? I have an unfounded theory that the orbits of the planets would somehow be rebalanced further away from the sun by some combination of less gravity from the Sun (red giants are less dense) and other factors I'm not taking into account. Any research to support this?

Distributed Probing?

[insert clever name here] — Sat, 18 Aug 2007 08:05:08 -0800

Why hasn't anyone invented cheap space probes? Some kind of thing that could be sent up en mass to gather just base data we don't have on all the planets/moons/etc . . .? So I've been watching the Universe series on the History Channel. One point that keeps coming up is that they don't know a lot of things about certain planets or moons because we haven't sent a probe there yet, and probably won't for a long time.

That got me thinking, why hasn't anyone, NASA or otherwise, developed "cheap" space probes to do basic information gathering? Relatively speaking of course. Instead of spending millions on a probe, maybe a few hundred thousand. Something that gets it to its destination, takes a bunch of pictures and sends those pictures home.

I'm sure I'm being naive asking this. Please enlighten me!

On the Destruction of Our Neighboring Planets

TwelveTwo — Sat, 24 Dec 2005 02:42:59 -0800

Given our current state of technology and the world's nuclear armaments, I ask the question that the world needs an answer to: Could we destroy Mars? How about Mercury? Could we even take down a gas giant or is that going too far? Which local planetary bodies could we possible annihilate? I am also curious about the repercussions of such actions. (Bonus: What about the astrological effects?)

Take your time, I seek accuracy bordering on technical pedantry!

Darkness at the edge of town

nightengine — Fri, 26 Aug 2005 11:53:49 -0800

How would I determine sunlight levels for the planets in the outer solar system? I've always been fascinated by the exploration of the outer solar system, from Pioneer to Cassini. As an amateur photographer, I've always been particularly interested in the available light levels used to image the planets and their satellites. I realize I can determine light levels with a little physics, but I'm more interested in a source that describes those levels in terms I can relate to. Instead of describing sunlight at Pluto as being 1000 times dimmer than on Earth, the ideal reference would compare it to a moonless night, a dark room with a candle, etc. My Google-fu has failed me, so I've not been able to find such a practical source.

Buying a Telescope for My Son

alexg23 — Mon, 25 Jul 2005 20:36:37 -0800

I want to buy my son, who is turning six, a telescope for his birthday. I don't want to spend a fortune, but one site I looked at for advice said anything less than $300 is a piece of junk. Anyone have any advice (including specific models) on one I can by this budding astronomer for $100 or less?

If the sun's gravity is so strong as to keep whole planets circling it in orbit, how come light and heat can escape?

amberglow — Sun, 14 Nov 2004 15:33:48 -0800

ScientificIlliterateFilter: If the sun's gravity is so strong as to keep whole planets circling it in orbit (even ones million of miles away), how come light and heat (incredibly fragile things compared to planets) can escape as rays (or whatever they are)?