View Full Version : moon unit

2004-Jul-30, 07:21 PM
i wonder what the odds are that a planet would have a moon the exact relative size as its star as seen from the planets surface.....u know like our moon and good old sol. certainly no other place in this system....am i right?
theres something fishy about that u think?

Dave Mitsky
2004-Jul-30, 07:56 PM
Not in the least. The Moon is steadily receding from the Earth, albeit at a rather miniscule rate, so total solar eclipses will be a thing of the past in the distant future.

Dave Mitsky

2004-Jul-30, 08:59 PM
but dave u dont address the odds...i know that the odds cant be figured with any real accuracy on a galactic scale. i would think that we know enuf about our system and the bodies within to determine if it happens anywhere else in our system. but surely this is an extremly rare occurance....wouldn't you think?

2004-Jul-30, 10:37 PM

I am not a regular to the forums, but the subject of this thread is interesting.

I also think it is amazing that the Moon appears roughly the same size in our sky as our Sun. Another planet I would never have thought of as able to have the Sun signifigantly eclipsed is Mars with it's tiny asteroidal moons, but here is a view from the surface of Mars http://www.jpl.nasa.gov/mer2004/rover-imag...s/image-22.html (http://www.jpl.nasa.gov/mer2004/rover-images/mar-11-2004/captions/image-22.html). Could Phobos have totally coverd the Sun in the distant past if it occupied a different orbit? This is something of what our future observation of eclipses will look like in the future... very disappointing if you have ever witnessed a total eclipse :-)

Intermittent Lurker

2004-Jul-31, 07:03 PM
it's just our luck that our ability to catalogue solar eclipses came just before the time when total solar eclipses may soon never again occur.

2004-Jul-31, 10:09 PM
Hey, All!

In line with Tony's jump to Mars and it's moons, I was wondering if any calculations had been done to determine what kind of solar eclipses could be observed on the other "mooned" planets.

[Thanks for that link, Tony!]


2004-Aug-01, 03:52 PM
Tony, Phobos is moving closer to Mars. Basically, any moon that has a "month" longer than the planet's "day" will move out, and any moon that has a "month" shorter than the planet's day will move inward (due to tidal forces). Slowly - very slowly. Phobos is, I think, the only moon in the solar system that is in the second category.

So, in the future, (if Phobos can avoid being broken in pieces by those same tidal forces), Mars will get solar eclipses like ours. They'll be very brief, because Phobos moves so fast (and will be moving even faster by then).

BTW, Phobos is already inside the roche limit, which means that anything loose on its surface would have been stripped off by the tides, and the only thing holding it together is its internal strength. (That probably belongs under the interesting facts thread <G>)

Another interesting co-incidence: If I&#39;ve done the math right, for an observer at Earth&#39;s L2 Lagrange point, the earth appears the same size as the sun. Inagine a permanent total solar eclipse. Of course, since the earth has an atmosphere to refract sunlight around it, that eclipse would look different than the ones we see here on earth, caused by the moon. It might even be more spectacular.

2004-Aug-01, 04:14 PM
I wonder if we could get a rocket to see an Earth-sun eclipse, does one exist?

2004-Aug-04, 03:20 AM
Damienpaul, re-
I wonder if we could get a rocket to see an Earth-sun eclipse, does one exist?

Yes, this can happen&#33; I have heard this come up in Space Tourism discussions.

As the Buzz Aldrin style Mars Cyclic Orbiter gets up speed to leave the Earth/Moon system, it might be fun to "schedule" one of these into the itinerary, or a few, if we are lucky&#33; B)