Is there a physics major on here willing to help me with a few things?

[tleilaxu]

ok...

you have an earth sized object orbitting the sun at a distance equal to the earth.

it has two moons, one is a phobos sized object in a phobos-like orbit, the other a mars sized object.

if i want the mars sized object to appear the same size as the sun (as the earth's moon does), how long would it take from new moon to new moon? what would the effect on the tides be?

if i want the mars sized object to complete a lunar cycle in 28 days, what would the effect on the tides be and how big would it appear in the sky?

would the phobos sized object affect the tides in any way?


tleilaxu prepares for this post to plunk off the message boards without response...

 

[Azzemmell]

Ha!! I ruined your preparations!

I'm not a physics major, but why don't you just set up the moons and days and tides how you want them. In any of the games I've run, the players wouldn't have cared. All they will see is the effect of said physics. Unless they are a physics major and do some math on it, they will never know.

 

[Ashwyn]

Ha!! I ruined your preparations!

I'm not a physics major, but why don't you just set up the moons and days and tides how you want them. In any of the games I've run, the players wouldn't have cared. All they will see is the effect of said physics. Unless they are a physics major and do some math on it, they will never know.

I agree. And if they do end up doing the math on it, you get what you wanted anyway.

 

[InvaderSquoosh]

Hmm.. mars sized object orbiting Earth? Hmm... weird. I'm a bored astronomy major, so watch this spot.

 

[Dragongirl]

Seeing as this is halfway down the page I thought I would chime in with my opinion, which will be little better than a bump.

Mars is a 10th of the size of Earth, but I think this is still too large to orbit us. I think the pull between the two would be too great and the orbits would either cause Earth or Mars to go flining through the galaxy. That is my totally non scientific opinion.

 

[Ashwyn]

Seeing as this is halfway down the page I thought I would chime in with my opinion, which will be little better than a bump.

Mars is a 10th of the size of Earth, but I think this is still too large to orbit us. I think the pull between the two would be too great and the orbits would either cause Earth or Mars to go flining through the galaxy. That is my totally non scientific opinion.

I think you're probably right. Maybe it could be set so that it is lighter somehow. Or am I completely being dense?

 

[tleilaxu]

i just want to know. i want to know if it is possible. i want to know what it would be like.

there is a good ursula le guin book (the dispossessed) where there are two planets, urras and anarres, which orbit each other...

 

[InvaderSquoosh]

Don't jump to conclusions!

Mars is twice the radius of Moon, and roughly ten times as massive. Mars is ten times less massive than Earth. I'm working on the implications of Mars as a moon of Earth, which shouldn't be too freaky.

 

[InvaderSquoosh]

Ok, I haven't the time to double check my math, but here it is:

If Mars were to orbit Earth and appear the size of our Moon (1/2 degree), Mars would be around 1.5 million kilometers from Earth compared to 380,000 kilometers for the Moon. Because Mars is pretty massive with respect to Earth, the center of mass of the system is somewhat beyond the earth's surface. I didn't have time to do the math for that part, but it was estimated from the center of mass of the Earth-Moon system being about 1600 kilometers below the surface of the earth. Ignoring the center of mass, the period of Mars' orbit around Earth is 1.8 years. Because this is longer than the Earth's year, Mars would appear to circle the sky in the opposite direction of the Moon (E to W instead of W to E).

The implications of this setup on tides is simple: Tides would occur with the same daily regularity due to the sun, but the high and low tides would occur nearly yearly instead of monthly. So the port at Procampur would experience a high tide once every two years and those conditions would persist for almost half an year!

A moon like phobos would probably not be in a stable orbit at only 10,000 km out. It would need to be at a lagrange point in the system, but then that would be boring as it would appear to be locked in step with Mars.

If you want Mars to orbit the Earth monthly, then there will be incredible consequences. Mars would be the distance of the Moon, roughly speaking, and around twice the angular size. The impact on tides would be devastating. Having Mars at 1.5 million km out is already stretching it. I haven't thought out the gravitational conseuqences of that setup in full, especially the part of having the center of mass of the system beyond the Earth's surface.

 

[Paul_Klein]

InvaderScooch, I have a quick question for you:

You said you were an Astronomy major. Could I ask you what you currently do for a living?

Thanks