PDA

View Full Version : orbiting planets



FRENDALL
2007-Jul-31, 05:49 PM
Do Orbiting planets all go the same way around.
and do orbiting planets have the same angle ie from say 9 oclock to 3 o clock
or does it vary?

Hornblower
2007-Jul-31, 06:41 PM
All of the bodies commonly called planets revolve in the same direction around the Sun. A few small objects such as Halley's comet are in retrograde (opposite directon) orbits.

I do not understand the second question.

FRENDALL
2007-Jul-31, 06:51 PM
hmm I think i should have said do all moons around planets rotate in the same direction.
and do they all orbit around the planet at the same angle?

i can understand u not understanding me i dont understand me most of the time.

Saluki
2007-Jul-31, 07:14 PM
hmm I think i should have said do all moons around planets rotate in the same direction.

All planets orbit the sun in the positive direction using the right hand rule. In other words if you took your right hand, and pointed your thumb in the same direction as the Sun's north pole, and curled your fingers into your palm, your fingertips are "orbiting" your thumb in the same direction as the planets orbit the sun. Most, but not all moons also orbit in the positive direction. IIRC, it is believed that the retrograde moons are likely captured objects.


and do they all orbit around the planet at the same angle?

The planets all orbit in roughly the same plane as the orbit of the Earth. If you set the orbital inclination of Earth at 0.00º, Mercury is at the greatest angle from that plane at 7.00º. Pluto used to hold the record at 17.15º, but Pluto is no longer considered a planet.

The moons of the different planets orbit at various inclinations to their parent planet.

astromark
2007-Jul-31, 07:22 PM
The plain of the solar disk from which the planets colest. That sort of says it all.
The natural satellites ( moons ) lay in the equatorial zone of there planet unless they are captured or have been disturbed.

FRENDALL
2007-Jul-31, 07:32 PM
Thank you both for answering my questions
i found them very educational

grant hutchison
2007-Jul-31, 07:50 PM
The giant planets (Jupiter, Saturn, Uranus, Neptune) all have inner, regular satellite systems, in which the moons orbit more or less in the plane of the planet's equator, and outer irregular systems, probably composed of captured objects, which orbit in all sorts of inclined planes, including orbits that go "backwards" relative to the planet's rotation.

Grant Hutchison

Jeff Root
2007-Jul-31, 07:52 PM
Mark,

I'll translate what you just said because some people might not
be able to figure out that you meant "coalesced".

The Solar System formed from a really big cloud of gas and dust.
(Probably there were many other solar systems or star systems
which formed from the same cloud at the same time, but those
stars and star systems have been spread at least halfway around
the galaxy by now. There's no way to determine which stars were
part of the same cloud we came from, after such a long time.)

The cloud cooled off slowly over time. As it cooled, it shrank and
became more dense. That meant the particles collided more often.
The collisions caused the particles to re-organize in two ways:
Some particles fell toward denser parts of the cloud, banged into
each other, cancelling out each other's motions (because they
were moving in approximately opposite directions), and became
stars. Other particles fell toward the denser parts of the cloud,
but banged into each other long before they got close to the
center, where the star was growing. They cancelled out each
other's motion in one direction (perpendicular to the plane of the
protoplanetary disk), but continued orbiting the large mass at the
center of the disk. As more and more particles ended up in the
disk, the disk became more and more effective at picking up new
particles. Just because the density was high enough for the
particles to bump into each other frequently.

At some point, the disk became dense enough, and cool enough,
that particles started sticking together into lumps, and planets
started growing. They kept growing until the Sun heated up
enough to start giving off a strong solar wind, which blew away
the remaining gas and dust which had not yet become part of
any planet, moon, or asteroid.

The orientation of the disk was a combination of random chance
(which particles happened to bump into which other particles),
and the angular momentum of the cloud. The direction that the
Sun rotates and the direction that the planets revolve around
the Sun probably tells us something about the average angular
momentum in our part of the original cloud. Not a whole lot,
though, because the randomness of the particle collisions tends
to reduce the significance of the direction.

-- Jeff, in Minneapolis

tony873004
2007-Jul-31, 08:32 PM
The giant planets (Jupiter, Saturn, Uranus, Neptune) all have inner, regular satellite systems, in which the moons orbit more or less in the plane of the planet's equator, and outer irregular systems, probably composed of captured objects, which orbit in all sorts of inclined planes, including orbits that go "backwards" relative to the planet's rotation.

Grant Hutchison
Here's an animation of this:
http://www.orbitsimulator.com/gravity/jovianMoons.GIF
This shows Jupiter and its system of moons from slightly above the ecliptic plane. Jupiter only appears as a single pixel in the middle because of the distances involved. Every known moon of Jupiter is in this animation (unless more were discovered in the past few months). Jupiter's innermost moons, called the Amalthea moons orbit in circular, prograde,equatorial orbits. They are so close to Jupiter, that in this image they are indistinguishable from Jupiter. The Galilean moons, Io, Europa, Ganymede, and Callisto are the maroon moons tightly orbiting Jupiter. They are also in circular, prograde, equatorial orbits. Beyond these 8 moons is Jupiter's extended collection of moons. They orbit in a myriad of directions and inclinations. But conspiculously missing are moons in polar orbits. The highest inclination is about 60 degrees. That is because any moon with a higher orbit would periodically have its perijove perturbed closer than the Galilean moons by the Kozai mechanism, setting up an eventual impact with one of the Galilean moons or with Jupiter.

grant hutchison
2007-Jul-31, 08:46 PM
Interesting how your eye sees all the outer moons going clockwise or all anticlockwise: I can mentally flip between the two views.
In fact, almost all the outer moons of Jupiter go retrograde. The exceptions are all fairly close in, from Themisto to Carpo.
That's probably not surprising: retrograde satellites can get nearer to the Hill limit without being perturbed away. Saturn and Uranus show a similar predominance of retrogrades at the outer edge of the system.

Grant Hutchison

tony873004
2007-Jul-31, 08:55 PM
They're color-coded by group, although at the moment I forget which colors are which groups. Wikipedia has a nice description of the classifications: http://en.wikipedia.org/wiki/Jupiter's_natural_satellites
The Himalia group are prograde moons, but you're right, the bias is towards retrograde as these orbits are more stable.

**edit. Here's the legend to the animation.
http://www.orbitsimulator.com/gravity/images/JupiterLegend.GIF

http://www.orbitsimulator.com/gravity/images/JupiterLegend2.GIF

grant hutchison
2007-Jul-31, 09:06 PM
The Himalia group are prograde moons ...Yes, they sit between Themisto and Carpo :) Neither Themisto nor Carpo is a member of the Himalia group, though (as you indeed show by colouring them differently above).

Grant Hutchison

neilzero
2007-Aug-10, 07:30 PM
Earth's moon orbital plane is tilted about 5 degrees with respect to the orbital plane of Earth. Neil

Krupin
2007-Aug-13, 04:34 PM
The important property of our planetary system are two kinds of commensurability. The first is the orbital resonance, such as beetwin the Jupiter and the Saturn (while the first revolves 5 times, the second revolves approximately twice). http://en.wikipedia.org/wiki/Orbital_resonance
The other type is discovered by me “interplanetary resonance” that are illustrates by follow examples:
1. If we send the interplanetary zond to Venus, it relapses to us through 5 revolutions after 4 years.
2. If saturnian people sends their zond to Neptune, they meets it after 3 saturnian years, through the single revolution.
3. If beetwin the orbits of Jupiter and Venus revolves the asteroid, then it meets with Jupiter after every 7 revolutions (that corresponds 3 Jovian years).
This two kinds of commensurability are the golden keys, that opens the door, that disappears the mystery of the birth of our solar system (and other planetary systems).