Are they similar to perihelion and aphelion? Also, which is for closest and which is for furthest?

Thanx.

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Same thing, just the -helion indicates Sun and the -gee Earth. If you go around the Moon, its apolune and perilune. Apo is the farthest, Peri the closest point on the ellipse to the planet.

Harald

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"Flying in space is risky business, but just staying on this planet is risky business too." - John Young, astronaut

The -helion is closest to or furthest from the Sun, the -gee is relative to the Earth. Peri- is closest, ap(o)- is furthest. To sum up:
Aphelion: furthest from the Sun
Perihelion: closest to the Sun
Apogee: furthest from the Earth
Perigee: closest to the Earth

There are also the general terms "periapsis" and "apoapsis", which can be applied to any body, and -lune for the Moon and (I've just discovered) -melasma for a black hole. 8)

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And -jove for Jupiter. -apsis is the general term.

Didn't they call it pericyntheon during Apollo?

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In general orbit theory I've heard pericenter, but oddly enough never apocenter. Weird.

I just happened to stumble into this yesterday....

Above from...>>> here <<<

Also...
Apopie - a delightful desert
Peripie - double delight

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Lighten up! This is a stellar board!

Peri is no doubt from the Greek meaning close or nearby. Apo is probably something to do with be far away, hence apsis, the furthest points on the ellipse.

General- periapsis and apoapsis
Earth- perigee and apogee
Moon- perilune and apolune, periselene or apselene, pericynthion and apocynthion for a spacecraft that wasn't launched from the moon's surface
Mars- periares, apoares
Jupiter- perijove, apojove
Saturn- perichron, apochron
Sun- perihelion, apohelion
other stars- periastris, apoastris

Most of suffixes come from the Greek. Gee is definitely based on the Greek word for Earth, which is geos or something like that. Helion is based on the Greek word for Sun, Helios. Chron is from the name Cronus, the Greek name for the god Saturn. Ares is from the Greek name for the god Mars. Selene is from the Greek word for the moon, Selenos. Cynthia was the goddess of the moon in Roman mythology, but the name is obviously Greek. Astris may be Greek. I know it's used in Latin, but I think sidereus might be more Latin.

Just checked Encyclopedia Mythica and realised that I got most of that wrong.

Cynthia is an epithet for Artemis, who apparently has nothing to do with the moon, so I don't know what NASA were thinking. It refers to her place of birth at Mount Cynthus. I could find no mention of Cynthia in Roman mythology. Selene is the Greek goddess of the moon.

Oh wait. The link is in Roman mythology. The personification of the goddess of the moon is Luna, who is identified with Diana, the Roman moon goddess and equivalent to Selene, who is identified with the Greek goddess Artemis, who was Cynthia. And wait, it does say Artemis was identified with Selene.

And Artemis was the twin sister of Apollo, hence the suitability of the name of the space program with that name.

Why is there a "h" in there?

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Artemis is identified with the Moon, particularly when it's new, when her dark avatar Hecate stands in for her.

Cool - I hadn't realised that there was a distinction between '-lune' and '-cynthion'. It's kind of an odd distinction to make, though - by its lights we should have a different word to apogee, say, if it's an object from outside the Earth's atmosphere - 'apotellus' or something...

Also seen: apoastron, perisatron.

You know, this is a real mess. I think the IAU needs to step in...

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Fin
Skep-ti-cult® member #488-28303-790

You're right. That's what I meant. That's definitely Greek.

Meant 'periastron', though.

Anyway, was wondering how to simplify things. I'd want a common term for everything except -gee -helion and possibly -lune. Originally, I'd have voted for, say, 'pericentre', but note my British spelling - this creates too many search problems. You seem to have supplied the answer, Glom:

So I'd humbly propose to use that in almost every case. (I note that Martian ap- and perihelion are among the few cases where '-apsis' is used - it deserves better.)

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Fin
Skep-ti-cult® member #488-28303-790

And what about perijove? Jupiter and Jove are both Latin/Roman, but I've never heard of a "perizeus" or "apozeus". :-k #-o

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You're so right - yet another dumb consistency. Just goes to show what a mess it is.

Ah, but poor little Mercury hasn't posed us any problems so far, has it - no moons. Fraid it won't last, though - the Messenger probe launches to Mercury later this year and it's an orbiter. So what's it to be - perihermion/apohermion, I presume?

And what would it be for Neptune - periposeidonon, anyone?

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Fin
Skep-ti-cult® member #488-28303-790

You mean the same bunch that still insists on calling Pluto a "planet"? :P

Erm... Point taken. OK - I nominate Phil to sort it all out. We could have a BABB glossary/stylesheet, publish it on the net, and then hope it catches on. It's the Internet way of doing stuff, after all.

(Could make it a wiki, but you don't want the terminology changing every other day. What's that you say? It does? That could be a runner, then...)

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Fin
Skep-ti-cult® member #488-28303-790

My APL colleagues on MESSENGER (when I worked there) used "periherm" and "apoherm."

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Nice one, thanx all .

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"Profanity is the one language all programmers know best"

Periherm and apoherm for Mercury and hence we get hermeology. How about periaphrodite and apaphrodite for Venus and hence aphroditeology?

Glom, do I know you at uni?

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"Profanity is the one language all programmers know best"

What course do you do? Something computer related I take it.

For some reason (if you're being classy, that is), all things Venusian are Cytherean. It's an odd usage, because Cythera is not an alternative name for the goddess, it's the name of the island she first set foot on after climbing out of that clamshell.

Have to be cythereology, apocythera and pericythera then I guess...

Sigh - more weirdness.

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Fin
Skep-ti-cult® member #488-28303-790

I like that better actually.

Oh, good for you - nice job. I was sad to hear that the launch delays have added 2 years to what is already a lengthy journey. Must have been a bit of a blow for them. Still, we've waited 30 years, what's another two?

But anyway, this just suggests that, if there are no moons already, the first team to get there gets to name the apo- and peri- points. I ask you, is that any way to do things? (That's just because I like the sound of apohermion better, actually )

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Fin
Skep-ti-cult® member #488-28303-790

But they like to tack an "-on" onto the ends of these apses wherever possible, so it'd probably be "apocytheron" and "pericytheron".

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I tried Googling for that and my version, but both come up blank. Also tried a lot of others like apocythereon, apovenera - no luck. So I'm stumped when it comes to Venus.

Funny old world, though. :wink: So far, the best discussion of all this I have found from Google is here:

http://www.badastronomy.com/phpBB/viewtopic.php?t=5100

Right back to home base...

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Fin
Skep-ti-cult® member #488-28303-790

Since this seems to be Greek mostly, I'd imagine that perigee would mean nearest to Earth etc. I'd expect -on endings mostly because if I can remember my Greek correctly, which is unlikely given I only did it for a couple of months, -on ending is a dative ending, which is the case called for in this context.

Hence, we want peri or apo followed by the dative of the body in question.

Somebody better tell the Messenger team, then [-X

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Fin
Skep-ti-cult® member #488-28303-790