[Ski]

okay so I was out in the back yard this last week looking up at the stars and it got me to wondering.... just how is it that Polaris is always north? I mean... we're going around and around - spinning on our own axis - and hurtling through space at quite a high rate of speed in an elliptical orbit about the sun - and all the while the earth is tilting back and forth back and forth on its own axis - like a toy top when it starts losing momentum - but somehow Polaris is still always north. are there any star-gazer type people here who can explain this in simple layman's terms so I can get my tiny little brain wrapped around it? and yes, I've considered the infinite enormity of space, but it seems to me rather odd that while all these other stars are flying about the night sky - Orion rising over Mt. Rainier and then dropping off into the southwest, for one - Polaris still just kind of hangs out there and is still always north.

[I'm Pysht]

It doesn't go back and forth like you seem to be imagining. The axis of rotation is constant, though there is some very slight wobble. Due to precession (~26,000 year cycle), Polaris will no longer be north pole star in several thousand years. Eventually, Vega will be.

[meandering Wa]

Orion rising and setting over Mt Rainier proves our movement, not the stars. It is the rotation of the earth that makes them move. our movement in relation to the magnitude of the distance to the stars is nothing and Polaris, for now is the center of our spin. multitudes of thousands of years from now, the constellations, as we know them, will cease to be as their stars move on their own courses and distort what we see. There are videos that show how the familiar constellations will change.

[IanB]

The axis of the earth's rotation remains relatively constant. (We are titled to one side somewhat in relation to the sun, but that orientation remains the same throughout the year - the origin of our seasons.) The diameter of the earth's path around the sun each year, +/- 186 million miles, is peanuts compared to the distance to Polaris, so no noticeable shift in perspective on that account. The sun, and all the other stars we can see, are indeed in motion about the center of our galaxy, but that takes something like 200 million years (?) to make one circuit. So again, no change that we can measure with human senses in human lifespans. What does change, within the time frames of human history, is the orientation of the tilt of the earth in relation to the sun. It's called precession, and takes 26,000 years to make one cycle. When the Egyptians were building the pyramids, Thuban was their north star, and as was mentioned above, eventually Vega will be the direction that axis is pointing. (If you wait 13,000 years, early March will be in what would be called late summer.) So the simple answer as to why Polaris seems so dependable, is that space is really, really, really big - and that human lifespans are so utterly inconsequential that we are unable to notice the extremely subtle pace of change.

[Ski]

[wolffie]

north celestial pole Polaris is not precisely at the north celestial pole (imaginary point of Earth's axis of rotation). When you line up a telescope with a clock drive, you point the axis of the turntable at Polaris, but you must make the correction; then the clock drive's axis is parallel to Earth's, and moving with sidereal time, it holds the stars stationary for time exposures. This is fun: how long does it take for a star to return to a meridian? Try it. Sirius (brightest star) makes a good target. Find walls of two widely separated buildings, position yourself so they form a slit, and time it. "Nearby" stars actually do apparently wobble in a 6-month cycle due to Earth's orbital movement (parallax). This allows triangulation of their distance using 1 astronomical unit (our radius from the sun) as the baseline. Other stars are too distant to show perceptible movement. parsec, wikipedia A parsec (symbol: pc) is a unit of length used to measure the astronomically large distances to objects outside the Solar System. One parsec is the distance at which one astronomical unit subtends an angle of one arcsecond.[1] A parsec is equal to about 3.26 light-years (31 trillion kilometres or 19 trillion miles) in length. The nearest star, Proxima Centauri, is about 1.3 parsecs from the Sun.[2] Most of the stars visible to the unaided eye in the nighttime sky are within 500 parsecs of the Sun.

[mike]