Slashdot Mirror
Saturn's New Moons Named
sebFlyte writes "The BBC is reporting that three new moons found orbiting Saturn at the end of last year have been named. 'Two moons detected in August have been given the names Methone and Pallene, while another found in October has been provisionally named Polydeuces.' Polydeuces is also reported as being a very strange object-- a trojan moon. It sits in a spot near a larger moon where the gravitational pull of the other moon (Dione here) and the planet cancel each other out."
At the bottom of the
I believe the way the Lagrange points work (from what I read) is that the object "in it" orbits the lagrange point by being tugged back and forth... it's not just "sitting there at some fixed distance relative to the 2 bodies.
We are one consciousness experiencing itself subjectively. Back to you with the weather, Bob!
The point between to celestial bodies (usually a planet and it's moon) where the gravity of one is equal to the gravity of the other is called the Lagrange point.
Usually closer to the smaller of the two bodies, this point is a common location of sci-fi space stations, as there is no need to use an orbit to keep the station from decaying back into the larger bodies atmosphere.
There are no gods but ourselves.
The lagrange spot isn't an absolute, just as with any field, there will be areas of decreasing influence. The moon can safely deviate within these grey areas, with no fear of crashing down. Seeing as how it's in orbat withing this lagrange area, it is fairly stable, because as per what that means, it's kinda stuck there by opposing forces.
Should some (fairly large) foreign space object crash into it, then you may have cause to worry about it crashing into either the other moon or the planet.
Game Overdrive - Gaming News
I was a bit surprised about the name Polydeuces, because he (the mythological character) had little to do with Troy. However, it turns out that there's another Trojan moon called Helene (now this makes sense!), and Polydeucues is Helene's brother.
Because 'planet' is a greek name meaning 'wanderer.' Thte planets were thought to be the gods. Therefor, they named them with those names. Western civilization is largely inherited from the Greeks and the Romans. We kept the names. Besides, why the hell would we call Jupiter Lugh or Woden? It'd be weird.
In celestial mechanics, Lagrange points come up in the three-body problem, where you have two large bodies (eg Sun and planet, planet and large moon) and one small object (a Trojan asteroid, spacecraft, new Saturn moon).
Lagrange points are the five places relative to the two large objects, where the third object will be held at the same position - relative to those two objects - in its orbit. In other words, there will be a net force on the third object that will result in it accelerating around the largest object at the same rate as the second largest object.*
A Lagrange point is stable if an object near by the L point will tend to be pulled towards or orbit around that point if it's a bit off the exact point. The L point is unstable if the object tends to be pulled further away from it once it wanders a little away.
The L1 point (in between the two large bodies), L4 and L5 points (60 deg ahead and behind the orbiting large body) are stable, the L2 and L3 points are unstable. Many of our solar observing spacecraft get sent to orbit the L1 point.
*(Center of mass discussion left out for relative simplicity)
Because these new moons are very small, and moreover they are very close to a large and bright planet like Saturn, that would outshine it in any telescope field of view.
Apparently not many people paid attention to this in high school.
The title of this article should be: Saturn's New Satellites Named.
Unique.
You can orbit around a stable L-point, and an object "floating" (i.e., little acceleration relative to the point) near it will tend to be attracted to it - and thus be stable (there are unstable Lagrange points as well, which are points in the gravity interaction that don't function like this, but are still usable).
L-1 between Sol/Earth is used by solar telescopes. I don't know that there are any in use in the Earth/Luna, but the classic one for space stations back in the 50s and 60s was L-5 (Didn't Carl Sagan's station in Cosmos use L-5?).
--
Evan
"$30 for the One True Ring. $10 each additional ring!" -- JRR "Bob" Tolkien
We can see light from lightyears away. Moons in our solar system don't give off light, and reflect very little. It's the difference between looking around in full daylight, and trying to find a lost marble in the near total blackness of your bedroom.
How am I supposed to fit a pithy, relevant quote into 120 characters?
Some spacecrafts are in orbits around L1 and L2 point of the earth-sun system, but those orbits are only semi-stable. The spacecrafts use some of their fuel to stay in those orbits longer than they would without propulsion, but eventually they will drift out of their orbits.
One can calculate a gravitational-rotational pseudopotential for the system (see e. g. here). In this pseudopotential, L1, L2 and L3 are saddle points (pseudopotential increases along one axis in both directions and decreases along another axis in both directions), L4 and L5 are maxima - one would expect that a body would move away from them. But the potential cannot include forces which depend on velocity and not on position - in our case the coriolis force - therefore it's called pseudopotential. Coriolis force causes an object to orbit the L4 or L5 point in a complicated path. If the object has more kinetic energy it can get from L4 to L5 via L3 and back again - this is called a horseshoe orbit.
http://en.wikipedia.org/wiki/Moon_(disambiguation) :
The term Moon refers, among other things, to:
1. The Earth's only natural satellite, the Moon.
2. A common term for other natural satellites.
In the end, the International Astronomical Union. Which has not approved these names, as far as I can see. Until they do, it's just the Cassini team suggesting things.