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Astronomical/Orbital Maths


aener
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Anyone on here got a grasp on this? I'm trying to set up a hypothetical arrangement to see if it could be physically possible. Tried doing it myself but I'm just going 'round in circles.
I'd assumed there would be half-decent simulators but I can't find any that do what I want.

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Adam, it was definitely a pun. I put it in italics just to make sure everyone knows just how funny I am :lol:

Relatively simple scenario, but I just keep doube-guessing myself.

I'm trying to set up a scenario whereby a planet of roughly earth-like characteristics has a moon roughly similar in appearance in the sky from earth to our own that orbits it either ever-so-slightly more or less than daily.

The result should be that from a given point on earth there's a satellite in the sky visible for about six months both day and night, then disappears for six months, but the timing shifts ever-so-slowly.
Preferably it would be visible during day and night in the "light" months, so something fairly small and close orbiting every 1.(1/366) days, so the "dark" and "light" times invert every 183 years. (That number is arbitrary. The phase just needs to shift around the year slowly.) The trouble is, for a stable orbit that fast you're looking at being at an altitude of ~36,000km, which is close enough that I get the impression anything with a large enough mass to appear roughly equivalent to our moon would either escape stable orbit or become too attracted. This mass-based question is my main stumbling point, because googling only returns calculations for satellites which have negligible mass.

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18 minutes ago, isitafox said:

I remember when people used to make topics asking whether people stood up or sat down to wipe their arse....:blink:

Yep, and I still remember you closing my thought provoking topic so don't think you're off the hook yet. 

So I guess in other words, no, I don't have a grasp on astronaut/orbital maths. 

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If you assume earth weight then you can work out gravitational force on your chosen moon size and then the radius/speed of the moon will follow and I guess you can shift things around to make a nice thing you can plot. 
 

gut feeling - if you start with earth size planet you aren’t going to get a similarly visible earth that goes round 27 times faster. but I’ll try it out later. 
 

edit: soggy mind might be talking shite

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Soggy mind seems to have a better handle on it than mine.

If it's a bit smaller in the sky then no biggie, but it would need to obviously be something different to stars.
I guess even 0.25x the apparent size would still serve its purpose, though preferably it would reflect enough light to still see by, as we get. That's relatively optional though.

No strict requirement to stick to Earth mass, so long as it would be likely human-livable.

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afaik the size of the planet doesn't matter. It all depends on its mass. Think about black holes.

I'll try to find the formulas later, technically it should be a reasonably simple calculation.

You're looking for Kepler's Laws of Planetary Motion I think. :)

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I'm aware it's mass rather than size, but I want it to be physically viable so it needs to be a mass/size that is possible for rock/ice/whatever rather than polystrene or something.
Something that could realistically form as planets/moons do and have the right appearance for this scenario would have to have a pretty large mass, which is my main concern.

Thanks for the namedrop. I'll go have a look.
It's endlessly frustrating when you know what you're looking for, but just don't know the right search terms!

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I imagine size will come into play but to some extent, or rather radius, planetary rotation and axis of rotation... assuming you want to model a point on your planet as an observation point and how the satellite is visible as that point versus time. I think that's the bit that will cause the biggest headache!

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