3
$\begingroup$

When a satellite is orbiting a planet (which itself is orbiting the sun) there are periodic points when the satellite is closest to and farthest from the sun, once where it is interposed between the sun and the planet and next when the planet is interposed between it and the sun.

What are the names for these two points?

Improve this question
$\endgroup$
14
  • 2
    $\begingroup$ @Phiteros I keep running into perihelion and aphelion, which are not correct. Every search I put into google returns this. $\endgroup$
    – Kaushik Ghose
    Sep 29 '18 at 23:29
  • 1
    $\begingroup$ Ah, I see. The satellite is orbiting a planet which is orbiting the sun. I misunderstood what you were asking. I'm not sure if there is a term for those situations. The closest I can think of is a conjunction. $\endgroup$
    – Phiteros
    Sep 29 '18 at 23:38
  • 1
    $\begingroup$ I think you could call it opposition? Usually meant for planets tho. $\endgroup$
    – Antzi
    Sep 30 '18 at 9:52
  • 1
    $\begingroup$ Thank you for doing research @uhoh! Search engines seem to fully fail on this topic. $\endgroup$
    – Kaushik Ghose
    Sep 30 '18 at 11:48
  • 1
    $\begingroup$ @uhoh neat question! I made an attempt there, but it has no appeal to authority, just "common sense". $\endgroup$
    – Kaushik Ghose
    Oct 3 '18 at 19:22
1
$\begingroup$

There are some serious problems with the OP's own answer, and so I think conjunction won't do for a satellite in Earth orbit, at least in LEO (where many/most of them are). While Archimedes could move the Earth with the proper fulcrum and a large lever, I'm not sure this can apply to the aforementioned "shoe-horn" as well.

There are two problems actually:

  1. In the context of artificial satellites, the term "conjunction" is frequently used for a three dimensional event; a very close approach of the variety that might result in collision. Satellite conjunction detection and conjunction reports have to do with scenarios where two spacecraft may collide resulting in "end of mission" and a whole lot of brand new space junk.

    To read more about this, see what the letter "C" stands for in Celestrak's SOCRATES; Satellite Orbital Conjunction Reports Assessing Threatening Encounters in Space as well as the questions

  2. Parallax! for satellites that are not in absurdly large distances from Earth, their apparent solar conjunction wanders all over the place depending on the location of the observer. Even in 2D, for satellites in LEO (the ISS for example) there's a ~140° difference between apparent solar conjunction as seen from one side of the Earth compared to as seen from the other. With a significantly inclined orbit, formulating the way that a definition can be worded based on apparent solar conjunction becomes even more difficult, as does even trying to draw it correctly in 3D.

    Here's a sketch of the 2D problem for a 400 km altitude circular orbit lying in the plane of the ecliptic, showing that the effects of parallax are huge!

parallax

Improve this answer
$\endgroup$
4
  • $\begingroup$ Hi @uhoh this is an interesting comment, and makes sense if you define this visually rather than geometrically. Two points 1. It's not clear if conjunction and opposition are defined visually (like syzygy) 2. While it is a critique of the answer, it does not propose an answer itself. $\endgroup$
    – Kaushik Ghose
    Oct 20 '18 at 16:29
  • 1
    $\begingroup$ @KaushikGhose as far as 2. occasionally answer posts are used as space for extended, thoughtful, technical comments where the conventional comment function is insufficient. I've seen this allowed in several SE sites, on a case-by-case basis. Search SE sites for things like "extended comment" or "long comment" or similar(keep the quotes). I found ~40 in Physics SE, ~400 in Math SE, and a few in Space SE and Astronomy SE. As far as 1. The question asks for "the name" rather than a potential name or a name candidate. Your answer is unsourced, it looks like you've just made it up, then accepted. $\endgroup$
    – uhoh
    Oct 20 '18 at 17:21
  • $\begingroup$ @KaushikGhose So in place of Archimedes, let's go with Hippocrates and say "desperate times call for desperate measures. It's not a perfect fit, but I think I can shoehorn it in. If you can produce a source that shows that opposition is correct for an artificial spacecraft no matter the shape of the orbit, that's great! But take a Sun-synchronous orbit with say an ascending local time of 17:00 and a) try to draw that and the Sun on a 2D piece of paper and then b) make a "geometrical argument" and I think you'll... $\endgroup$
    – uhoh
    Oct 20 '18 at 17:28
  • $\begingroup$ @KaushikGhose ...see that terms like "conjunction" and "opposition" are completely unworkable, and that's why your answer is not correct, and why there isn't a word. It's a 2D answer in a 3D world. $\endgroup$
    – uhoh
    Oct 20 '18 at 17:29
0
$\begingroup$

Based on comments by @phiteros and @carlos-n under the question, the closest terms seem to be Conjunction and Opposition. As described in the wikipedia article these are meant for apparent positions as observed from a given location - like the Earth, and meant for planets and natural satellites, but the diagram suggests they can be shoe-horned for this purpose.

Conjunction and Opposition as illustrated on Wikipedia

Improve this answer
$\endgroup$
1
  • 1
    $\begingroup$ do you mean inferior conjunction? Also, I've left another answer that addresses this term. $\endgroup$
    – uhoh
    Oct 17 '18 at 9:09

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.