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Just how high of an apoapsis can comets have?!

Wizard Kerbal


1. What’s plural of apoapsis? I’ll just put a * for plural.

I deployed 3 sentinels, 1 for eve, duna and jool, and holy lord that’s a lot of objects. I’ve captured a few asteroids, so i’m focusing on comets and interstellar interlopers, of which i’ve not found :( . But i have found comets with apoapsis* of <3-10x eeloo height. So, just how far out can these be?!

If anyone says ~Farrrrrr ouuuuuut brooooooo~ I will tell them to go back to California.

Edited by Wizard Kerbal
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The answer is: They can have an infinite sun apoapsis. In other words, they can even be on a escape trajectory out of the solar system.

Comets are usually always on very excentric trajectorys. In real life, the Rosetta mission that went to a comet needed several gravity assists to get to its destination.

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On 2/14/2022 at 9:58 AM, Streetwind said:

One apsis, multiple apses. :)

Apsis is borrowed from ancient Greek.  'Apses' is an attempt to use a Latin pluralisation on a Greek root, which is not correct.  The correct plural is apsides.

Wall of explanatory text in the spoiler:


Normally, I'd be right there with a lot of people in saying that it's really too pedantic to make the distinction, and such people would be right, but I personally find the history of the strange admixture of Greek and Latin to be fascinating:  it occurs in field of astronomy like almost nowhere else and so there are good reasons to make the distinction.  Some of the reasons are pragmatically European, mostly due to the fact that the majority of our English (and a lot of other languages') scientific vocabulary is actually predominantly Latin, but astronomy has deeper and older roots.

Fun fact:  astronomy and astrology were once considered synonyms!  The field of measuring the stars was intimately related to divination, or understanding how the motions of the stars affected people's lives.  Because of a lack of good measuring and observational devices, astronomy was also considered a field of mathematics (as opposed to physics) since no one was able to gather physical observations of the stars (not to be confused with empirical observations; anyone can go outside and look).  This persisted until we had a theory of gravity, and Newton re-derived Kepler's Laws from his own.

Of course, there is still a lot of Greek, especially in the names of fields (anything that ends in -ology or -omy has a Greek name, even though the field itself is likely filled with a Latin technical vocabulary), and this stems from the fact that just as Latin is the source language for a lot of technical, scientific, and academic vocabulary, Greek was the academic source language for the Romans.

Thus the field of astronomy carries unique opportunities to mix the root of one language incorrectly with an affix from another language.  We use the Latin names for the planets (Uranus is close, but the actual Greek is Ouranos), but the term for any scientific study of those planets would normally need a Greek root to have an -ology suffix.  Thus, anything from Mars is Martian, but the study of Mars is arieology.  So, too, is it Venerian if it's from Venus, but aphrodisiology if it's the study of Venus.

But, as in all things, vocabulary is complicated, ancient vocabulary exponentially more so, and nothing is ever always absolutely so.  No one actually uses Venerian or aphrodisiology because these words, or at least words with similar construction, have been taken by others to describe some of the things related to the traditional province of the Greek goddess of love.  In a similar vein, the term martial law could technically apply to a legal code developed on or applied to inhabitants of Mars ... but it doesn't.  All of this stems from the original connection between astronomy and astrology--while we know today that the motions of Venus and Mars do not inspire people to love and war, the terms relating to the products of that supposed influence persist in the language.  Cytherian is an alternative for Venus that was in use a century ago, but for the most part, people have adopted the etymologically-clumsy Venusian.

On a personal note, I don't much like the term Venusian.  It's a bad choice for the same reason that it's bad to call a person from Ireland an Irelandian, or a person from Canada, Canadish.  'Canadish' could, for different reasons, apply to an especially pretty Canadian, but I don't recommend using it.  Irelandian is bad, but you can use the Latin name and get Hibernian which technically derives from a similar root (Hiber and Ire are related).  You may still have trouble if you call an Irish person a Hibernian, but not because the word is wrong.  Its literal meaning as 'the land of winter' isn't very accurate, either, but it makes sense comparatively, considering Rome's climate.

We have a similar problem with the Moon and the Sun, because unless it is called the Moon or the Sun, it could mean any moon or sun.  We do use the Latin word, Sol, for our sun when we need to make that distinction, and probably any future interstellar colonists will call their local star sun as well, until they need to make the distinction (because no one will find it romantic to watch the Gliese 581-set), but other than a brief aside with Cynthia in the Apollo program, we mostly use lunar for things relating to a moon, with occasional departures to the word selene- for anything relating to our Moon.  Be glad that we didn't call Earth the Planet.

It will likely only get worse:  the Greek form of Saturn is Chronos, which not only has use in many words in the vernacular, but also in scientific study for anything to do with time--when we do get to the point of making more detailed studies of Saturn and its environs, we're probably going to need a new root term just to tell things apart.  Until then, a chronograph can be either a clock or a picture from, or maybe of, Saturn.  A pictorial clock from Saturn is a graphical chronochronograph.  And if we ever do colonise Mars, a hippy living there who wants to celebrate what would technically be martial love will probably be deeply conflicted about that.

It only gets more complicated from there.  Astron is Greek for star, and it was borrowed by the Romans, with a slight modification.  Thus astra is Latin for stars, but so are stellae and sidera.  The singulars are astrumstella, and sidus, respectively, though technically sidus refers to a group of stars, or constellation--which has stella in the middle of it, and literally means something like 'stars appearing in the same place' which makes it about as literal a term as one could expect.  Sidus also appears in astronomy:  sidera is the root in terms describing motion with respect to the celestial sphere (as opposed to the sun), also called sidereal motion.  It was also proposed, briefly, as part of the name for the newly-definitively-discovered planet Uranus, which was named 'Georgium Sidus' (King George's Star) by its British discoverer.  Thankfully, that name did not persist:  imagine trying to describe the study of it!  (Georgian Astrology?  Ugh.  No.)  Astrum is essentially the same as stella, but more poetic.  Latin uses Greek-derived words to convey a sense of heightened importance or poetry, in a somewhat similar manner to the way English does with Latin:  consider, for example, the distinction between the words godly and divine, or eat and dine.

Lastly, we have the 13.2 septillion-pound elephant in the room:  Earth.  People from here are called Earthlings, not Earthians.  Many are aware that geos is the Greek for Earth, so it's not Greek in origin.   Some others may be aware that terra is Latin for dirt, but while earth can mean dirt, does that relationship hold from the Latin?   We don't call this planet Ground.  In truth, our dirt is different, after all:  Earth is one of the vanishingly few examples of a bona fide English term in astronomy (other notables on this list are moon and sun).

In the end, though, languages--even dead ones--change over time, so eventually, apses is probably going to be accepted as a legitimate plural of apsis.  However, if you do decide to use the correct Greek form, then please be aware that the pronunciation is ap-si-DEES, not ap-SIDES.  It rhymes with keys or freeze, not rides or hides.

On 2/13/2022 at 10:06 PM, Wizard Kerbal said:

So, just how far out can these be?!

In theory, they can be anywhere.  Of course, an escaping comet or asteroid has no apoapsis because it is not on an elliptical orbit, but escape is not a function of position; it's a function of speed.  There is no magic line where an object on one side is captured and an object on the other side is escaping.  You see this on any interplanetary launch from low Kerbin orbit:  with enough speed, you escape Kerbin from a, for example, 100 km orbit and go to Duna.  Burn in the retrograde direction and your orbital speed drops to zero and you land (or 'land', in the sense that the char and ash will eventually hit the ground).  Do nothing and you orbit until the hard drive fries.  It has nothing to do with being in low Kerbin orbit:  all three scenarios are possible.

Another way to look at it is in terms of eccentricity.  An elliptical orbit has an eccentricity strictly less than 1, but the problem is that the formula for eccentricity is this:

e = √(1 - [b2 / a2])

Where e is the eccentricity, a is the semi-major axis, and b is the semi-minor axis.  The problem with this is that eccentricities less than one are achievable for arbitrary values of a and b, because a can tend to infinity and b can tend to zero while keeping the b2 / a2 term nonzero.  A parabola, which has an eccentricity of exactly one, can be seen as an orbit where a is exactly infinite.  A radial orbit, which while not a parabola also has an eccentricity of one, is the case where b is exactly zero.

Practically, comets are going to have some nonzero speed which will constrain the possibilities for apoapsis if they have an elliptical orbit, but I don't know the range of those possibilities.

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