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Nylex
2004-Apr-01, 10:12 AM
Are they similar to perihelion and aphelion? Also, which is for closest and which is for furthest?

Thanx.

kucharek
2004-Apr-01, 10:17 AM
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

JohnOwens
2004-Apr-01, 10:21 AM
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)

Kullat Nunu
2004-Apr-01, 10:21 AM
And -jove for Jupiter. -apsis is the general term.

AstroSmurf
2004-Apr-01, 10:27 AM
If you go around the Moon, its apolune and perilune.
Didn't they call it pericyntheon during Apollo?

Normandy6644
2004-Apr-01, 02:02 PM
In general orbit theory I've heard pericenter, but oddly enough never apocenter. Weird.

George
2004-Apr-01, 02:11 PM
I just happened to stumble into this yesterday....

Apoapsis (apo.'ap.sis; plural: apoapses)
apo = [Latin] related to; apsis = [Latin] orbit
The apoapsis of an orbit of one object around another is the point at which the one object is furthest away from the other object. Apoapsis is the general term for such a point, but there are also many specific terms for specific cases: the aphelion is the furthest point from the Sun in an orbit around the Sun. Likewise, apoastron is linked to other stars, apogee to the Earth, and apojove to Jupiter. The opposite is periapsis. The word apofocus is sometimes used instead of apoapsis, and apse instead of apsis.
Apofocus ('apo.'fo.cus; plural: apofoci)
apo = [Latin] away from; focus = [Latin] hearth
The apofocus is the same as the apoapsis.
Apsis ('ap.sis)
apsis = [Latin] orbit
An apsis is a position in an orbit that is at an extreme distance (either a minimum or a maximum) to the central object. The minimal distance is attained in the periapsis and the maximal distance in the apoapsis. When referred to particular celestial bodies, the "apsis" part may be replaced by the (greek) name of the body. For instance, the position in an orbit that is closest to the Earth is called the perigee. Instead of apsis, sometimes apse is used.

Above from...>>> here (http://www.sunspot.noao.edu/sunspot/pr/glossary.html#apoapsis) &lt;&lt;&lt;

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

Glom
2004-Apr-01, 04:20 PM
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.

Glom
2004-Apr-01, 04:32 PM
Just checked Encyclopedia Mythica (http://www.pantheon.org) 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.

Glom
2004-Apr-01, 04:38 PM
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.

Eroica
2004-Apr-01, 04:44 PM
Saturn- perichron, apochron
Why is there a "h" in there?

Grand Vizier
2004-Apr-01, 04:45 PM
Just checked Encyclopedia Mythica (http://www.pantheon.org) 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.

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

Moon- perilune and apolune, periselene or apselene, pericynthion and apocynthion for a spacecraft that wasn't launched from the moon's surface

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...

other stars- periastris, apoastris

Also seen: apoastron, perisatron.

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

Glom
2004-Apr-01, 05:04 PM
Also seen: apoastron, perisatron.

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

Grand Vizier
2004-Apr-01, 05:33 PM
Also seen: apoastron, perisatron.

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:

General- periapsis and apoapsis

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.)

JohnOwens
2004-Apr-02, 01:06 AM
And what about perijove? Jupiter and Jove are both Latin/Roman, but I've never heard of a "perizeus" or "apozeus". :-k #-o

Grand Vizier
2004-Apr-02, 01:14 AM
And what about perijove? Jupiter and Jove are both Latin/Roman, but I've never heard of a "perizeus" or "apozeus". :-k #-o

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?

tracer
2004-Apr-02, 01:53 AM
You know, this is a real mess. I think the IAU needs to step in...
You mean the same bunch that still insists on calling Pluto a "planet"? :P

Grand Vizier
2004-Apr-02, 02:17 AM
You know, this is a real mess. I think the IAU needs to step in...
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...)

ToSeek
2004-Apr-02, 03:51 AM
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?

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

Nylex
2004-Apr-02, 11:36 AM
Nice one, thanx all :).

Glom
2004-Apr-02, 12:19 PM
Periherm and apoherm for Mercury and hence we get hermeology. How about periaphrodite and apaphrodite for Venus and hence aphroditeology?

Nylex
2004-Apr-02, 12:27 PM
Glom, do I know you at uni? :)

Glom
2004-Apr-02, 01:21 PM
Glom, do I know you at uni? :)

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

Grand Vizier
2004-Apr-02, 03:56 PM
Periherm and apoherm for Mercury and hence we get hermeology. How about periaphrodite and apaphrodite for Venus and hence aphroditeology?

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.

Glom
2004-Apr-02, 04:05 PM
I like that better actually.

Grand Vizier
2004-Apr-02, 04:30 PM
My APL colleagues on MESSENGER (when I worked there) used "periherm" and "apoherm."

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 :) )

JohnOwens
2004-Apr-02, 04:55 PM
Have to be cythereology, apocythera and pericythera then I guess...

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

Grand Vizier
2004-Apr-02, 05:19 PM
But they like to tack an "-on" onto the ends of these apses wherever possible, so it'd probably be "apocytheron" and "pericytheron".

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:

Right back to home base...

Glom
2004-Apr-02, 06:00 PM
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.

Grand Vizier
2004-Apr-02, 06:43 PM
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

Nylex
2004-Apr-06, 06:20 PM
Glom, do I know you at uni? :)

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

Oh, my mistake (I thought you were doing Space Research). I'm doing Physics and Astrophysics.

ngc3314
2004-Apr-06, 08:52 PM
Waitaminnit - don't forget those ever-popular terms for larger-scale orbital motion. These are actually used in the technical literature:

perigalacticon
apogalacticon

Glom
2004-Apr-06, 10:11 PM
Oh, my mistake (I thought you were doing Space Research). I'm doing Physics and Astrophysics.

I am doing Physics and Space Research.

Grand Vizier
2004-Apr-06, 10:33 PM
Waitaminnit - don't forget those ever-popular terms for larger-scale orbital motion. These are actually used in the technical literature:

perigalacticon
apogalacticon

Nice - I will try and drop those into conversation - but I thought that, orbits around the galactic centre being non-Keplerian, stars wouldn't have exactly the same peri-/apogalacticon two orbits running - though for some like the Sun it must be *fairly* constant, give/take a few light years, I guess.

I wasn't aware, though, until you supplied the word to be Googled, that the Sun is now near to perigalacticon.

http://www.site.uottawa.ca:4321/astronomy/index.html#perigalacticon

How and when was that determined? And do we have any idea how far it gets from the centre at apogalacticon?

And here we go again - isn't 'galaxy' Latin? (Though I must admit I haven't the foggiest as to the Greek equivalent. Depends what they called the Milky Way - assuming that myth wasn't specifically Roman.)

Nylex
2004-Apr-06, 11:41 PM
Oh, my mistake (I thought you were doing Space Research). I'm doing Physics and Astrophysics.

I am doing Physics and Space Research.

Then I know you :) (we're in the same lab group, for one thing).

Peter B
2004-Apr-07, 02:14 AM
Someone might care to search for an earlier thread where these terms were discussed.

Someone there came up with the appropriate terms for an object orbiting Io, and in the process I think set a joint record for the greatest number of consecutive vowels in an English word: Periioion and Apoioion.

:o

Eroica
2004-Apr-07, 07:20 AM
And here we go again - isn't 'galaxy' Latin? (Though I must admit I haven't the foggiest as to the Greek equivalent. Depends what they called the Milky Way - assuming that myth wasn't specifically Roman.)
Galaxy (http://www.hellskitchen.com/inkwor4.htm) is Greek.
Wikipedia (http://en.wikipedia.org/wiki/Milky_Way)

Eroica
2004-Apr-07, 07:27 AM
Someone might care to search for an earlier thread where these terms were discussed.

Someone there came up with the appropriate terms for an object orbiting Io, and in the process I think set a joint record for the greatest number of consecutive vowels in an English word: Periioion and Apoioion. :o