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Errantry: Novak's Journal
...Words to cast/My feelings into sculpted thoughts/To make some wisdom last
Random: Another Childhood Daydream On Its Way To Fulfillment 
19th-Jan-2006 05:38 pm
Self-Portrait 2004
An Atlas V rocket carrying the New Horizons spacecraft on a mission to the planet Pluto lifts off from the Cape Canaveral Air Force Station in Cape Canaveral, Fla., on Thursday, Jan. 19, 2006. The spacecraft is estimated to reach Pluto as early as July 2015. (AP Photo/John Raoux)

Copyright 2005 Associated Press. All right reserved. This material may not be published, broadcast, rewritten, or redistributed.


Patricia Tombaugh, 93, attends a press conference at the Kennedy Space Center in Cape Canaveral, Fla. on Thursday, Jan. 19, 2006 after the launch of an Atlas V rocket that will carry the New Horizons spacecraft on a mission to the planet Pluto. Her late husband, Clyde Tombaugh, discovered the planet Pluto in 1930. The spacecraft, which is carrying some of Tombaugh's ashes, is estimated to reach Pluto by July 2015. Tombaugh, of Las Cruces, N.M., was in tears as she watched the launch from four miles away. "I got emotional. I really did. I just got carried away," she said. "It was so beautiful and we've waited so long." (AP Photo/John Raoux)

Copyright 2005 Associated Press. All right reserved. This material may not be published, broadcast, rewritten, or redistributed.
(Deleted comment)
20th-Jan-2006 12:43 am (UTC)
No, the argument is that Pluto is what is called a Trans-Neptunian Object. There are a number of objects the size of small planets--though none as big as Pluto--in the space beyond Neptune's orbit. These are part of what's called the Kuiper Belt: a ring of dust-to-these-small=planet-sized objects orbiting the Sun, from which the inner, frequently-orbiting comets originate. This mission should settle the Pluto question once and for all. Perhaps what you recently heard about was the discovery of another moon (or captured object) orbiting Pluto. To further confuse things, I might also point out that our moon isn't really a moon, but a planet, making the Earth/Moon (or maybe "Earth/Luna" is better-sounding, even if it means the same) system what's called a "double planet" system.

20th-Jan-2006 04:15 am (UTC)
Wasn't there recently a discovery of an object in the Kuiper Belt larger than Pluto? It seems like I've read that somewhere.
20th-Jan-2006 11:57 am (UTC)
I believe it was called Sedona.

Here is some info.


20th-Jan-2006 08:47 pm (UTC)
Mm. Sedna. And we're sick of hearing questions about it from the general public since someone said it was uncertain whether it should be classed as a planet or a Kupier belt object, and if the latter, Pluto should also be demoted, being very small and likely of Kuiper belt origins, unlike the rest of the planets.
20th-Jan-2006 08:50 pm (UTC)
Then I certainly won't ask any such questions! :-D

Oh, and by the way, I hearby stake a claim to it as my personal property.
20th-Jan-2006 09:08 pm (UTC)
You're welcome to it!
(Deleted comment)
20th-Jan-2006 04:30 am (UTC)
Perhaps--I can't remember the details, myself: I think I've somewhat put all this planetary-definition fuss on "hold" in my mind until the astronomers sort it out to their satisfaction. Until then, I'm not overly-inclined to re-draw my map until theirs is settled. Other than the Earth/Moon bit, of course, because I think that technically is settled, and because it's just fun to rattle people with it....
(Deleted comment)
20th-Jan-2006 05:53 am (UTC)
Yes, I think I've heard that line of argument, too: I guess I would just say "not a term grounded in or originating from our science." I'm sure the Babylonian astronomers were entirely content in having sufficiently distinguished those odd, moving lights that could so commandingly change directions....
20th-Jan-2006 11:37 am (UTC)
I think I heard that the definition of a moon is that the common centre of mass of the two objects is within the radius of the larger, which is definately the case with us and our Moon. But I could be wrong. There's so much debate that no-one really knows!
20th-Jan-2006 05:09 pm (UTC)
Really? Because I understood it that the Earth/Moon system orbited a common center of gravity and that is wasn't a clear orbit of the Earth. I agree with you that orbital dynamics seem to be the clearest way to a definition here.
20th-Jan-2006 09:02 pm (UTC)
I investigated some more: the centre of mass of the Earth-Moon system is located @4700km from the Earth's centre (i.e. ~1700km below the surface). Whereas if you consider Pluto and Charon, the centre of mass it outside Pluto. Charon is called Pluto's 'moon' simply because it is the smaller of the two. All other bodies in the solar system are like Earth-Moon - centres of masses with moons are inside the planets (those that have moons that is).

I always find it interesting that the centre of mass of the solar system is only a few metres from the centre of the Sun (which has a radius of about 700,000,000 m) - i.e. the Sun is an incredible portion of the mass of the solar system; everything else is pretty insignificant.

Unfortunately, there is not official definition of what a moon actually is, nor is there one for a planet.
20th-Jan-2006 09:08 pm (UTC)
I've also read, or likely this was the same thing and I putzed it up, that the argument for the Moon being part of a double-planet system is that the orbit of the Moon isn't going around the Earth per se. I think this is what I took to mean that they were orbiting a common center of gravity that I assumed to be outside of the Earth.

I'm still impressed from what you found, though, that the common center is still within the Earth: I wouldn't have guessed that, given how large our Moon is.

So, as far as this orbital dynamic I'm half-remembering: does that ring a bell? Or am I just muddled?
20th-Jan-2006 09:14 pm (UTC)
I haven't heard that argument I'm afraid. However, it doesn't hold up at all - nothing orbiting abother body can orbit it's centre exactly. The orbiting body has mass therefore there is a common centre of mass that cannot be the exact centre of one or the other.

There is a confusion with the centre of gravity sometimes - that is the place where the mass of an object is exactly balanced. For example, a perfectly spherical body would have a centre of gravity exactly in it's centre, or at another extreme, a dumbell shaped object would have a centre of gravtiy half way between the ends. A two body system could also have a centre of gravity, but this is not necessarily the same as it's centre of mass, I think.
20th-Jan-2006 09:33 pm (UTC)
Ah, got it. Yes, messy on my terms there, so thanks for making that distinction.

So, I just Googled "Earth Moon Double Planet" to try to figure out what types of things I might have seen before and found various quotations of this sort:

The Earth and the Moon are relatively close in size (4:1 in diameter, 81:1 in mass), unlike most planet/moon systems. Many people consider the Earth and Moon to be a double planet system (rather than a planet/moon system). The moon does not actually revolve around the Earth; it revolves around the Sun in concert with the Earth (like a double planet system).

Oh, but this seems to be what I'd really gotten: I looked at Wikipedia's articles on "Double Planet" and "Moon" and found this in the former:
The late Isaac Asimov suggested a distinction between planet-moon systems and double-planet systems based on what he called a tug-of-war (TOW) value that describes whether or not the presumed satellite is more firmly under the gravitational influence of the presumed planetary primary or the Sun. In the case of the Moon, the Sun "wins" the tug of war, i.e., its gravitational hold on the Moon is greater than that of Earth. The opposite is true for other presumed satellites in the Solar System (with a few exceptions), including the Pluto-Charon system. By this definition, the Earth and Moon form a double-planet system, but Pluto and Charon represent a true primary with a satellite.

This definition has not received wide attention in the professional literature.
I think that this was the orbital dynamic that I had in my head, rather than the location-of-the-common-mass one you mentioned, and which was prominent in this article. The orbital movement of the Moon, being more determined in relation to the Sun than to the Earth, I think was presented in what I had read as determinative in the definition.
20th-Jan-2006 09:48 pm (UTC)
Ah, I hadn't heard that. Interesting, but like it says, a very loose definition and not widely acknowleged. You could then ask questions of the Sun and us orbiting the centre of the galaxy. It's too vague for my liking! Doesn't generalise well.
20th-Jan-2006 10:56 pm (UTC)
Good point! "Is a star not a star if it's orbiting a black hole, etc. ...?"
20th-Jan-2006 01:22 am (UTC)
Not about Pluto, but, have you heard of Richard B. Hays? His book "The Moral Vision of the New Testament" is the main text for a theology course I'm, and I'm curious to know your opinion of it, if you have one.
20th-Jan-2006 01:32 am (UTC)
None, I'm afraid. Is he English? Burn it.
20th-Jan-2006 01:40 am (UTC)
He's a professor at Duke Divinity School... so far, it's been mostly tedious and, in a way, representative of some Protestant problems regarding the interpretation of Scripture that prompted one of my friends to convert. He seems, at the outset, to want to create, in a vaccuum, a modern application of the New Testament, specifically regarding the ethical teachings.
20th-Jan-2006 11:35 am (UTC)
It'll be cool to get proper detailed shots of Pluto and Charon instead of the usual fuzzy blobs.
20th-Jan-2006 12:04 pm (UTC)
I can't remember if I knew you were into astronomy. Doesn't surprise me though :). I am lucky enough to have a 10 inch Meade SCT, but unlucky enough to be too damn busy to have used it for the past year. I am also lucky enough to have access to a 16 newtonian within 15 minutes drive. Plus I am extremely fortunate to live within an hour's drive of a dude that has a 32 inch dob. I've seen some pretty cool stuff through that beast!

I did take some pics through my 10 inch and some through the 16 inch. If ever I get a round tuit, I'll upload them :)

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