Terminology assist

[Allan]

I'm looking for the scientific astronomical term which describes when two planets are at their nearest points to each other in their rotation around the Sun.

I've found

Apogee-the highest or most distant from earth
Aphelion - furthest from the sun
Perihelion - closest to the sun

These terms really don't apply as I need it. I'm thinking there is a scientific term to precisely decribes any event. If you know what the term is I'd appreciate the assist.

Thanks in advance.

 

[jedidia]

I think what you're looking for is "conjunction", which is the nearest point, and "opposition", which is the farthest point. However, watch out: Purely astronomicaly, these refer to visual apearance from earth (i.e. conjunction is when two bodies are seen close together from earth) and must not necesarily mean that they are physically closest. In Science fiction, the terms are often used in the physical sense. I don't know if there is a proper term for the maximum physical proximity of two bodies...

 

[N_Molson]

Not exactly.

Inferior conjunction (heliocentric) : When a planet is aligned between the Sun and the Earth. Only possible for Mercury & Venus (ex. Sun-Venus-Earth).

Superior conjunction (heliocentric) : When the Sun is exactly between the planet and the Earth. Planet is "hidden" behind the Sun. (ex. Mars-Sun-Earth).

Conjunction (geocentric) : When 2 bodies or more are (almost) aligned from a point of view located on the surface of the Earth. (ex : Moon-Mars-Saturn)

Opposition : When the Earth is aligned between the Sun and the planet. Obviously impossible for Mercury & Venus. It's also the moment where the distance between the Earth & the planet is the smaller. (ex : Sun-Earth-Mars).


Allan, the word you are seeking for is "opposition".

If you say that there is an opposition between Mercury and Venus, we know by definition the reference is the inner planet (Mercury), and it's the moment when the 2 planets are aligned with the Sun and then at their nearest point.

Be aware that the distance between 2 same bodies is never the same if you compare several opposition. The absolute nearest point between 2 bodies would be would be an opposition occuring when one body is at its apoapsis and the other at its periapsis (which depend of which one has the most eccentric orbit).

 

[jedidia]

wait...

I thought opposition means that two planets are aligned with the sun, but 180 degrees apart??

 

[orb]

In positional astronomy, for relative position, it can be either inferior conjunction or opposition (for a superior planet).
A drawing from Wikipedia (you may need to click on it or change the forum skin to some with bright background to see it):


The conjunction and [ame=http://en.wikipedia.org/wiki/Astronomical_opposition]opposition[/ame] terms are only defined in a manner of the relative position to the observer.

It's just the closest approach otherwise (i.e. for the absolute distance between planets).

 

[Allan]

You know, I knew I was confused before...now I'm just not sure of the depth of my confusion :lol:

 

[MikeB]

Maybe syzygy? Even if not, what a cool word, with three y's and no other vowels!

From Wikipedia: In astronomy, a syzygy is the alignment of three or more celestial bodies in the same gravitational system along a straight line. The word is usually used in context with the Sun, Earth, and the Moon or a planet, where the latter is in conjunction or opposition. Solar and lunar eclipses occur at times of syzygy, as do transits and occultations. The term is also applied to each instance of new moon or full moon when Sun and Moon are in conjunction or opposition, even though they are not precisely on one line with the Earth.

 

[jedidia]

:rofl:

ok, that did a world of good! Now... Is there anyone that can enlighten us poor earthlings? I can read Wikipedia alright, and I thought I understood it right, but after seeing some more suggestions I'm really not sure anymore!

 

[TSPenguin]

I'd like to expand on the original question and request proper expressions for the closest approach of two bodies within one orbit of the innermost body and the rare occurrence of the inner body being at apoapsis and the outer one at periapses during opposition as seen from the gravity source both are orbiting.

P.S.: I am secretly hoping there is no defined expression for the latter and we get to define it as "probeproach" or something equaly orbinerdy

 

[orb]

The conjunction, opposition, sygyzy terms are used to describe the alignment as seen from the position of observer, and not to describe the distance between observed bodies.

I couldn't find a single word term for the closest approach, closest encounter, closest/minimal distance, as it can be described for the absolute distance between celestial bodies.

 

[Allan]

well, if there is no specific term I can always use creative licence and make something up or work hard to avoid putting that term in play altogether.

When life give your lemons...:tiphat:

 

[N_Molson]

...or call it "the-moment-when-two-planets-are-at-their-nearest-points-to-each-other in-their-rotation-around-the-Sun."

OK, that's a bit long... Why not "Tmwtpaatnpteoitrats" ? Mmh, that isn't a lot better :hmm:

 

[Jarvitä]

...or call it "the-moment-when-two-planets-are-at-their-nearest-points-to-each-other in-their-rotation-around-the-Sun."

OK, that's a bit long... Why not "Tmwtpaatnpteoitrats" ? Mmh, that isn't a lot better :hmm:

I vote for "probeproach".

 

[Allan]

How about "rectilineal caesura" aka a straight line gap?

:tiphat: ..thank you, thank you very much

 

[Izack]

Why not stick with closest approach?
If you want to sound technical, I'm sure 'minimal distance' will suffice.

 

[Lucy]

I wanna name it a "Schweiger Moment".

 

[Allan]

Why not stick with closest approach?
If you want to sound technical, I'm sure 'minimal distance' will suffice.

Just having fun with it really. I'm more than a little surprised there isn't a text book definition for something like this.

 

[Izack]

Just having fun with it really. I'm more than a little surprised there isn't a text book definition for something like this.

Well, in the textbooks I've read, closest approach is the term used.

If we're going to be coining terms, though, my vote goes with probeproach. :hail:

 

[jedidia]

Somebody will have to put an "orbiter dictionary of technical terms in spaceflight" on the OrbiterWiki!

btw, I vote Probeproach! Only problem is, when spoken fast, it sounds a lot like cockroach...

 

[Moach]

i just call it "bob"