Direction.

[benzun_1999]

How do you find which direcion you are travelling in space?

-Benzun

[ScionPunk352]

Directions in space are never found by going north, south, east, or west. Instead they use terms like starboard, which is the right side of the shuttle, port, which is the left side of the shuttle, bow, which is the front of the shuttle, and stern which is the back. (If i have any of those terms screwed up, please correct them.) That is my understanding, since there is really no way to figure out north, south, east, and west, in a four dimensional area...all you really have is, up, down, left, right, forewards, backwards...it also depends on your perception. They have something in a shuttle called a gyroscope that helps them keep their perception correct, such as if the shuttle somehow gets set into a flat spin upon its reentry into earth's atmosphere, the gyroscope would come in very handy in regaining control of the ship.
-Bob Smith

[selfAdjoint]

Directions in space are found from the relative directions of distant visual objects. Bright stars are adequate for normal purposes and satellites are programmed to pick up Sirius and some other stars to establish its local frame of reference. Three such lines of sight establish a fixed coordinate system (if no two of them are parallel). If you can identify the stars, and are in theolar system, you can orient your local coordinates to an Earth coordinate system.

[ScionPunk352]

Ah, that's right, I remember that from a telescope that I had used one time. It happened to be an electrical telescope, and i always had to align it to three different stars in the sky at night.

[LURCH]

This may seem a bit wierd but, in space, "speed" and "direction" are the same thing. Actually, that's true everywhere, but in space it becomes really noticable. That's why you'll almost never hear NASA scientists use either term when talking about the progress of their latest deep space probe. They nearly always just refer to the "course" of the vehicle. When it is near some object of interest, they'll sometimes speak of its speed or the angle of approach, but this is only in relation to that particular object.

Speed is entirely relative and, therefore, so is direction.

[benzun_1999]

so if there is no direction space how do we know which plane a planet orbiting in ?

[ScionPunk352]

How do we know what plane a planet is orbiting? Well, we see the gravitational force of the sun, acting on the earth, causing it to orbit around in an elliptical manor. There really is not an actual plane that the planets are in...but if you really think about it, their speed is whatever it is, and their path is an elliptical orbit around a large stellar presense...if you want to think of it that way...
-Bob Smith

[Phobos]

Without an absolute reference frame, you simply need to define your direction/velocity relative to something else.

[LURCH]

Originally posted by benzun_1999
so if there is no direction space how do we know which plane a planet orbiting in ?

Oh no, I'm not saying there's no direction in space. I'm only saying that direction is relative. So, as stated above, the plane of orbit for the planets is "whatever plane they orbit in". If our current models of star-system formation are even close, the planets will occupy the plane originally occupied by the disk of gasses and dust that formed when the initial gas cloud began to spin. Therefore, the ecliptic for most or all star-systems should be close to the plane discribed by the star's equator.

But the location of that plane can only be determined in relation to some other thing. For example; if you are standing on the North Pole of Uranus, the ecliptic for the Solar system is 90o from the horizontal, but if you stand on the Earth's North Pole, the planets orbit on a plane that is parallel to the horizon.

[Nereid]

LURCH wrote: For example; if you are standing on the North Pole of Uranus, the ecliptic for the Solar system is 90o from the horizontal, but if you stand on the Earth's North Pole, the planets orbit on a plane that is parallel to the horizon. LURCH is talking approximately ... the 'axial tilts' (as they are called are ~98o for Uranus, and 23.5o for Earth.

Oh, and there's nowhere for you to stand at the North Pole of Uranus, or anywhere else on that planet [;)]

To change the topic, benzun_1999, I don't recall we saw you come back to that great thread you started on evolution ...