Celestia Forums

Like Jupiter, Earth and Mars are both known to have trojans that share their solar orbits. Earth has no known trojans. Trojan asteroids are co-orbital asteroids that are located in L4 or L5 points, nowhere else. But there are some other Earth co-orbitals and quasi-satellites. Cruithne, which is usu...

When you compare it to Jupiter, I think you are making reference to the L4 & L5 points with respect to Jupiter's solar orbit. I do not believe any of Jupiter's moons are known to have asteroids in their Lagrange Points with respect to Jupiter. Saturn has a few. Jupiter's trojans are in solar orb...

It passed only 130,000 km above the surface of Earth last week.

Never mind... I discovered that you mean "position angle of ascending node", one of the inputs that Grant's spreadsheet can use. Remember that his spreadsheet was intended for calculating STC star orbits, not SSC planet orbits. This ascending node parameter is one often calculated by astronomers wh...

Does anyone know off the top of their head how to calculate the energy output, in joules/sec, from a give star, providing that you have the mass radius and tempature, etc...? I want to know the formula, I know that the Sun is ~3.85x10^26 J/sec. Im too lazy to find it. Thanks. Luminosity is 4 pi r^2...

It's got an autopilot feature, so if you want to give demonstrations like similar to a powerpoint, it makes it easy to create a simulation and let it run "hands-off". If you send me an e-mail or post on my lonely forum board and tell me what kinds of things you'd like to denonstrate, I could help yo...

I looked at Gravity Simulator thinking that it was obviously what I'm looking for. However, the little amount of information on their web site led me to believe that it's geared more to people who understand what gravity model they want to set up, and then send the computer off for a while to calcu...

There's Gravity Simulator , although I haven't got much experience. I believe the interface needs some perseverence to master. I understand that the author's a nice guy who will help you set up your simulation if you e-mail him :wink: The newer version may be a little easier to use than the previou...

You can derive the formula from 2 common physics formulas: acceleration due to gravity a = GM/r^2 and rotational acceleration a = v^2/r set them equal to eachother GM/r^2 = v^2/r after cancelling out one of the r's, and re-arranging to solve for v: v = sqrt (GM/r) v is your orbital velocity for a ci...

I can only see Saturnshine on the smaller moon, the one that passes behind the other moon. But I need to brighten it in Photoshop. Then I can see it in both pictures.

That's so cool to realize that that's a real picture and not something pasted together.

Is the Andromeda Galaxy going to collide with the Milky Way? I've heard from numerous sources that the Andromeda Galaxy is going to collide with the Milky Way someday. I understand how its radial velocity relative to the Milky Way is determined through its blueshift, but how do we know its tangental...

Perihelion = Sun
Perigee = Earth
Perilune = Moon

But what about for a star other than the Sun. Is it also Perihelion, or is there a convention for the word if a star's name is known? (Peripolaris?)Or is there a generic word for any star other than the Sun?

I don't see how the Milky Way's central black hole could eject this star, for the same reason that spacecraft can't use the Sun for a gravity boost. It would have had to receive its escape boost from something else, perhaps another black hole that orbits the central black hole.

Using Horizons data in Gravity Simulator, I can paint a before and after picture on what Earth's gravity will do to this asteroid's orbit.

before
after

Try this. These values are from Horizons. This is the first time I edited one of these for Celestia, so no guarantees! I get a much different number for LongOfPericenter than the two of you. see explanation below. "2004 MN4" "Sol" { EllipticalOrbit { Epoch 2451544.500 # 2000 Jan 01 00:00UT Period 0....

Interesting... Any information on how close it will come to the Moon? Looks like that will be a close call too. Take care, Bob I didn't realize I wasn't logged in last time. Hi, I'm guest! It will pass 97,764 km from the Moon's surface about 18 hours after Earth's close approach. January's estimate...

I've heard of something called a quasi-satellite. It seesm to be a moon orbiting around a planet in a bit of a strangely shaped orbit but it's really orbiting around the Sun close to the planet. Do you think the sattelite could be one of these? Michael Kilderry :) A quasi-satellite has a 1:1 resona...

how much have to change for example the mass of earth to really or sensibly impact the moon orbit then? should be in order of half planet, quarter, or much less is enough? Reducing Earth's mass by 10% will cause the Moon to noticably spiral outward. Reducing it by 10% again will throw it into an Ea...

I think the orbit looks more egg shaped rather than triangular, would an orbit like this be able to last long periods of time? Michael Kilderry :) Surprisingly it is pretty stable. I don't know about millions of years, but in my simulator it lasts hundreds of years and would probably last thousands...

I thought the number I ended up with was a little funny, oh well, I'll just have to do the math again. I've never heard of triangular orbits before! Interesting question: How far away does an object orbiting the Earth beyond the Moon have to be from the Moon to avoid being flung into a different or...