Corgi, Hound of the Internet ([info]sff_corgi) wrote,
@ 2008-09-23 16:09:00
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Current mood: artistic
Entry tags:holy days, space

'11 Planets'
Belated Happy Mabon, to everyone - naturally, I missed the equinox by a couple of days, 'tis my habit.

And as long as we're on astronomical phenomena, I quote from The RASC Calgary Centre - The Solar System:

Including the 8 "major planets" and the 3 "dwarf planets" (Ceres, Pluto and Eris) we now have 11 "planets".

One old way to remember the names of the planets from the Sun outwards was to use the mnemonic phrase "My Very Educated Mother Just Served Us Nine Pizzas" - for Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, Neptune and Pluto.

Now that there are 11 a new mnemonic phrase was needed - and now we have one.

In 2007, the National Geographic books-for-kids division sponsored a contest for kids (14 and under) to come up with a nifty way to recall Mercury, Venus, Earth, Mars, Ceres, Jupiter, Saturn, Uranus, Neptune, Pluto, and Eris in order.

And - here is the winner: "My Very Exciting Magic Carpet Just Sailed Under Nine Palace Elephants".
Oi! What about Sedna?!

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[info]barsukthom
2008-09-24 02:00 am UTC (link)
Never, ever, EVER, forget about Sedna.

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[info]immovablemover
2008-09-24 02:09 am UTC (link)
At the risk of sounding completely out of the loop, I thought Pluto was no longer considered a planet?

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[info]cerrberus
2008-09-24 04:12 am UTC (link)
It is IIRC classified as a 'dwarf planet' now.

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[info]sff_corgi
2008-09-24 05:04 am UTC (link)
*discreet cough* '...the 3 "dwarf planets" (Ceres, Pluto and Eris)...'.

Here's the quote from Wikipedia: 'A planet, as defined by the International Astronomical Union (IAU), is a celestial body orbiting a star or stellar remnant that is massive enough to be rounded by its own gravity, is not massive enough to cause thermonuclear fusion, and has cleared its neighbouring region of planetesimals.'

That means jagged chunks of rock don't count; very small stars don't count; and it's got to sweep up after itself.

'A dwarf planet, as defined by the International Astronomical Union (IAU), is a celestial body orbiting the Sun that is massive enough to be rounded by its own gravity but which has not cleared its neighbouring region of planetesimals and is not a satellite. More explicitly, it has to have sufficient mass to overcome rigid body forces and achieve hydrostatic equilibrium.'

One of the reasons they specified that is because planets are usually either gas giants or rocky (terrestrials). Most of the dwarf planets so far have a large ice component, which is a different order of mass of course. Haumea is one of the Trans-Neptunian Objects in this class, and it's an interesting case - it got hit by something a while back and knocked most of its ice off... creating a whole flock of TNOs following around in near orbits, including its two moons. And knocked the beastie out of round while it was at it (it's sort of oval).

They don't have sufficient gravity to have a clean orbit all by themselves, though.

This doesn't even touch on whether something's a TNO, a cubewano, a Haumean, a detached object, an Oort Cloud object, in or out of the scattered disk, captured or non-captured, and whether it's in a resonant orbit. But they can all have moons.

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