IIRC, a good example is Alpha Centauri. Off the top of my head, A and B are in elliptical orbits around a center of gravity with about an 80-year period. (Proxima is much smaller, several light-weeks away, IIRC and may not even be part of the system.)
There is a suggestion that either sun may have a planet within it’s habitable zone (area where sunshine is just right for earth temperatures) and the other sun does not come close enough to disrupt this orbit. This is a good example of Hexnut’s “orbiting one star”.
Of course, in that case, the other star would be a long way out (80 years IIRC is about Uranus’ orbit) and would just be a very very bright star.
For two stars to orbit each other inside a planet’s orbit and not disrupt that orbit, they would probably have to be a tight binary, closer than the sun and Mercury. They you’d get the Tantooine effect.
Don’t forget that binaries are not twins. It is not uncommon for one of the stars to be a very different size from the other.
A really good book if you can find it is Stephen Dole’s Habitable Planets for Man, a world-Building 101 type of book.
ADD = Attention Deficit Disorder; the chronic inability to mentally focus for more than a few seconds on any single topic.
No. They would each independently revolve around the planet. But each would be at a different distance & hence take a different amount of time to complete an orbit.
Picture standing in the center of a circular race track. Now put a man walking, a bicyclist riding, a horse galloping, & a race car all going around the track the same way. You’d see the man slowly passing across the distant background & every so often one or another of the bicycle, horse, and race car would pass the man. Meantime, every so often either the horse or race car would pass the bicyclist. And the race car would also pass the horse every so often. Each time sombody passed somebody else they’d be at different places around the track. Once in awhile there’d be double or triple passes where, say, the race car was passing the horse just as the horse was passing the man. But most passes would be just one-on-one.
Meantime, unlike a 2-dimensionsal race track where everybody is at the same level all the time, the orbits would be slightly inclined to each other. So sometimes when the car passes the bicycle the car would be above (“north of”) the bicycle, and other times below (“south of”).
Exactly right.
Cool. Unless your planet was much larger than Earth it’s unlikely you could have multiple Moons that big. They’d tend to interfere with each other & collide, crash into the planet, or spin off into space within a few million years.
For story-telling purposes what matters most is how big a moon appears in the sky. Which depends on both how big it is physically & how far away it is. Within reason those two issues are not connected. You could have a small close moon & a farther-away bigger moon where the small close one *looks *bigger even though it’s really physically smaller.
On Earth there are two tides, one caused by the Sun & one by the Moon. As the positions of the Sun & Moon change, sometimes the two tides add up, leading to very high high tides & very low low tides. At other times the tides offset each other, leading to very low high tides & very high low tides. And the cycle repeats about once a month.
If a planet has lots of suns or moons, odds are that most of the time they’ll not be all lined up; so each sun or moon’s tidal contribution will be being offset by all the others. This leads to most tides being small most of the time. But IF once in awhile all the moons or suns or both lined up, the total tide could be much larger than normal. Like for many “years” tides are a just couple feet high and then once every couple “centuries” tides increase to 50 feet for a few “days” then recede back to normal.
Probably the opposite, more like frozen Pluto than baking Mercury. Although the Universe is a big place and there are probably many Mercury-like planets in multi-sun systems too.
The big issue with multiple suns is that in order for your planet’s orbit to be stable over the long term, the planet needs to be far enough away that the multiple suns act like more or less one big (though lumpy) source of gravity. So the suns need to orbit each other tightly for your planet to be close enough to be baked. If the suns orbit each other loosely, then your planet needs to be a long way away so it can orbit both of them together. And a planet being a long way away from the suns amounts to it being cold.
You’re writing sci-fi, right? Take some literary license and have some fun with it!
Have a planet with two suns, where the planet orbits in a figure-8 path around them!
(Enlist the rocket scientists of SDMB to help work out the details!)
ETA: You could make the moons half the size of Earth moons: Half the diameter, half the surface area, and half the volume, and half the mass! You’ll need to work out the math on that
Most serious readers of science fiction will nitpick the hell out of “literary license”, that is, not doing your science homework. A writer can get away with writing a story which doesn’t agree with current science facts as we know them…but s/he’d damn well better know those facts, and explain why the story doesn’t follow them. Now, usually the author will wave his/her hands and claim a new discovery, without explaining how the discovery works, in a story. For instance, as far as we know, faster-than-light travel is impossible, but a lot of stories call for an FTL method of travel. So the author simply drops an FTL drive into the story, but declines to explain HOW it works except in the most general of terms.
Writing science fiction is no reason to get sloppy. And a sloppy story won’t be well-regarded. Just about every factual element in an SF story has to be accurate, or it has to be explained. It’s like…if a mundane story had a parent who gave birth to a child, that parent WILL be female. If the parent is male, then no reader would take the story seriously. Now, a science fiction story might very well have a male parent who gave birth to a child…but the male parent might have had a sex change (or several) since giving birth, or he might have had an artificial uterus installed, etc. But there would have to be an explanation given or at least implied.
And fantasy writers also have to write self-consistent stories. Magic systems, for instance…if a fantasy story uses magic, then the magic has to follow the rules that the writer has set up, EVERY TIME. Or else the story fails.
@ Senegoid: lol not sci fi, fantasy. Oh believe me, nothing will ever stop me from writing things the way I want to write them. Nit pick away, see if it’ll make me change anything weg
@Lynn : Good thing I don’t write sci-fi then hunh?
Like I said before not asking the question for anything I’m writing, just asking because writing it made me curious. That and seeing/reading things in movies/books/ video games (anyone have a thought about Morrowind? -Love those moons-)
