Astronomical nomenclature question
Joseph Groene
Marshall Perrin
> I have a question. Consider an orbit around the
> Earth. The point in an elliptical orbit around the
> Earth that is nearest to the center of the Earth is
> called perigee. The point in an elliptical orbit
> that is farthest from the center of the Earth is
> called apogee. For an orbit around the Moon, the
> terms are perilune and apolune. For Jupiter,
> perijove and apojove. What are the proper terms
> for Mars? For Saturn?
'pericenter' and 'apocenter' or the equivalent 'periapsis' and
'apoapsis' are applicable in all cases. The appropriate Greek
suffixes for Mars and Saturn are '-ares' and '-chron', but I've
never heard anyone use those.
- Marshall
Steen
> I have a question. Consider an orbit around the
> Earth. The point in an elliptical orbit around the
> Earth that is nearest to the center of the Earth is
> called perigee. The point in an elliptical orbit
> that is farthest from the center of the Earth is
> called apogee. For an orbit around the Moon, the
> terms are perilune and apolune. For Jupiter,
> perijove and apojove. What are the proper terms
> for Mars? For Saturn?
I usually just use the terms periapsis and apoapsis.
/steen
Bill Higgins
> Joseph Groene wrote:
>
> > I have a question. Consider an orbit around the
> > Earth. The point in an elliptical orbit around the
> > Earth that is nearest to the center of the Earth is
> > called perigee. The point in an elliptical orbit
> > that is farthest from the center of the Earth is
> > called apogee.
Correct so far.
> > For an orbit around the Moon, the
> > terms are perilune and apolune. For Jupiter,
> > perijove and apojove.
One does see these sometimes, but they are incorrect in the sense that they
mix Greek prefixes (peri- and apo-) with Latin stems.
> What are the proper terms
> > for Mars? For Saturn?
>
> I usually just use the terms periapsis and apoapsis.
This is a pretty sensible strategy.
We had an interesting discussion of this question around here in 1989, which
is a century ago in Internet years, so you might have missed it. See Steve
Willner's response to a similar question:
<http://groups.google.com/groups?hl=en&lr=&ie=UTF-8&c2coff=1&selm=192%40cfa.HARVARD.EDU>
Ask Google to "view complete thread" to see the rest of the discussion.
[begin quote from Steve Willner:]
The generic terms are apoapsis and periapsis. The plural, in case you
want to speak of both, is "apsides." (Pronounced with three syllables:
aps'-uh-deez.)
By the way, the apsides of lunar orbit are the "aposelene" and
"periselene;" the Greek prefixes should be used with the Greek root
words helion, gee, and selene rather than the Latin roots sol, terra,
or lune. (Or something similar; my lack of proper classical education
may be showing here.) The incorrect terms "apolune" and "perilune" are
often used, though.
[end quote from Steve Willner:]
One response was from Jonathan McDowell, now famous for "Jonathan's Space
Report."
[begin quote from Jonathan McDowell:]
Steve points out that we should use Greek roots:
> By the way, the apsides of lunar orbit are the "aposelene" and
> "periselene;"
I thought it was "pericynthion" and "apocynthion"?
(These ones I know:)
Generic: periapsis apoapsis
Generic star: periastron apastron
Earth: perigee apogee
Sun: perihelion aphelion
How about the rest of the solar system? I think that it's
Mercury: perihermes aphermes
Venus: ?
Mars: periares apoares
Jupiter: perizenon?
Saturn: perikronon?
Any offers from classical scholars?
[end quote from Jonathan McDowell:]
Might actually be fun to start a conversation about this among scholars. I
have actually heard someone say "perikronon" in the run-up to Cassini's
injection burn. But sticking to "periapsis" and "apoapsis" is the practical
thing to do.
Geoff Landis has coined "perimelasma" for "low point in the orbit around a
black hole.
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C. F. Leon
While it's perhaps an interesting exercise, the practice of each body
having a particular term for orbital elements can nowadays be carried
to rediculous extremes. What if something goes into orbit around Puck
(moon of Uranus)? Or the minor planet Mr. Spock? Or an unnamed
TransNeptunian or comet? Do you REALLY want terms like apo-P/283
Yokohama-Manichevski-Wszuasckman-al'Qeadf? And how about un-named
stars? "The new planet's peri-HD 24*1111 BD 11*123 is only 0.5 AU." as
a news item becomes rather silly. Let's just stick with the generic
terms 'peri-/apo- gee' for a planetary body, and 'peri-/apo- astron'
for a star. Much simplier and easier to remember. Perhaps, we should
add galaxies and black holes, but every single body in Creation should
not get it's own term.
Jorge R. Frank
news:b428af52.04070...@posting.google.com:
> Let's just stick with the generic
> terms 'peri-/apo- gee' for a planetary body, and 'peri-/apo- astron'
> for a star. Much simplier and easier to remember.
Perigee/apogee are not generic; they are specific to the Earth.
Even simpler and easier to remember would just be to use periapsis/apoapsis
for everything.
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Henry Spencer
Jorge R. Frank <jrf...@ibm-pc.borg.retro.com> wrote:
>> Let's just stick with the generic
>> terms 'peri-/apo- gee' for a planetary body, and 'peri-/apo- astron'
>> for a star. Much simplier and easier to remember.
>
>Perigee/apogee are not generic; they are specific to the Earth.
Perigee/apogee are theoretically specific to the Earth, but in practice
are widely used for other planetary bodies. As are other nominally Earth-
specific terms like "geology".
>Even simpler and easier to remember would just be to use periapsis/apoapsis
>for everything.
Extra syllables for no particularly good reason.
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"Think outside the box -- the box isn't our friend." | Henry Spencer
-- George Herbert | he...@spsystems.net