Which way do stars rotate?

Dear Astronomy Experts
I was standing outside, and saw the North star. I remember the photos of
stars rotating around, but I do not know which direction. My best guess
is counter-clockwise, is this correct?
Cordially
ypauls

"ypauls" wrote in message ...
Dear Astronomy Experts
I was standing outside, and saw the North star. I remember the photos of
stars rotating around, but I do not know which direction. My best guess
is counter-clockwise, . . .

Generally, the answer is counter-clockwise, as bwhiting notes. But
the apparent direction of rotation of the sky also is relative to
which direction that you face.

The earth rotates, once a day, counter-clockwise on its axis. The
earth also revolves, once a year, around the sun, traveling
counterclockwise in its orbit.

Whether you see the daily rotation of earth as clockwise or
counterclockwise depends on:

1) whether you are facing north or south;

2) whether you are in the northern or southern hemispheres.

If you live in the northern hemisphere, let's say New York City,
Chicago, Salt Lake or San Francisco, and face to the north, the
circumpolar stars will appear to move in a counter-clockwise
direction. They rise in east on your right-hand shoulder, set in west
on your left-hand shoulder.

If you turn around and face south (the way most people view the Sun
moving across the sky during the day), you can no longer see the north
pole; it is behind you. The apparent motion of the sun during the day
appears clockwise. The Sun rises in the east _on your left shoulder_
and sets in the west _on your right shoulder. This is direction of
travel of the hands of an analogue clock. Not surprisingly, since
most cultures that invented the water clock, first, are located in
the Northen hemisphere, i.e. - China and Greece, the hands of clock
travel in a clockwise direction. This emulates the experience that
most northerners have of looking to the south and seeing the Sun
travel across the sky each day.

If you live in the southern hemisphere, let's say Buenos Aires, the
situation is reversed. When you face south towards the south pole,
the stars appear to rotate around the south pole in a clockwise
direction. When the southern hemisphere resident turns around in
during the day and faces to the northern horizon (the same as our
southern horizon), the Sun appears to travel in a counter-clockwise
direction across the sky. (Or so I'm told, I haven't actually been
there. - )

If this is hard to see in your mind's eye, a couple of visual aids
lying around the house may help.

First, find a clear drinking glass (a suitable plastic one is
available at most Starbuck's) and a basketball or a soccer ball. It
is important that the glass is clear and that you can see through it.
With a magic marker, put dots on the ball at about 40 degrees north
(Salt Lake City) and at 40 degrees south (Buenos Aires) along the same
meridian line.

Let's use the plastic glass first. Hold the glass in your left-hand to
the left of the center of your chest. The open end of the glass
should point horizontally to your right. Use the index finger on your
right hand to continuously trace a counter-clockwise circle around the
rim of the glass. Now, while still moving your finger around the rim
of the glass in a clockwise fashion, move your arms and the glass to
the right of the center of your chest. You can now see the same view,
this time from the perspective of a "southern hemisphere" resident of
the glass. The apparent motion of your finger now appears clockwise
from the relative "southern hemisphere" frame of reference.

The basketball can be used to help visualize the same thing for a
"northern" Salt Lake City or "southern" Buenos Aires resident. Rotate
the ball with your finger tips in a counterclockwise direction of from
the "northern hemisphere" perspective.

If you wish to explore this further, download the outstanding Cartes
de Ciel free planetarium software from:

http://www.stargazing.net/astropc/index.html

With this free, desktop planetarium software you can set your
observing location to cities throughout the northern and southern
hemisphere, digitally "turn around" and face either north and south,
and animate the display to see the apparent rotation of the stars and
Sun.

With respect to the apparent motion of the stars that results from the
earth revolving around the Sun, visualize this like driving your car
down a highway, around a race-track or around a four-square city
block.

If you live in the northern hemisphere, face to the east. This is the
direction that the earth is traveling through space. The southern
horizon is out the passenger side of your "car" off your
right-shoulder. Much like what you see when you drive down the
freeway, the "scenery," the stars, are moving past you and receding
behind you (toward the west). Think of telephone poles or billboards
along the side of the road, coming towards you and then receding
behind you as you drive.

However, you are in the world's "slowest" "car" - the world in fact.
Still facing east, extend your right-hand up level with your right
shoulder with your hand to the southern horizon. Do not face to the
south, remain facing east. Turn your head to the right and look over
your right-shoulder to your right-hand. Extend your index finger
vertically, which now will be silloueted against the southern horizon.
The "scenery", the stars and constellations, and much like the
telephone poles along the side of the road, are moving past your
finger, from in front of you to behind you, at the rate of _one finger
tip per day_.

To make this cosmic "road trip" even more "boring," your "car" is not
driving down a straight highway with ever changing scenery. It is
moving on a roughly circular track. Once a year, you come back to the
same point on the road and the scenery starts repeating itself. Much
the same experience can be had by driving your car around the
four-squares of a city block, again, driving in a counter-clockwise
direction. Your left-should is toward the center of the city block
that you are driving around. On your right shoulder, outside the
passenger window of your car, the buildings on the "outside" of your
route go past and correspond to the constellations in the sky.

If you stay up all night, the astronomically agreed "starting line" of
this cosmic race-track, is in the constellation Pisces, which
currently (summer 2003) can be seen to the south of Andromeda, a
couple of hours before sunrise.

Regards - Kurt

(PrisNo6) wrote in message . com...
"ypauls" wrote in message ...
Dear Astronomy Experts
I was standing outside, and saw the North star. I remember the photos of
stars rotating around, but I do not know which direction. My best guess
is counter-clockwise, . . .

Here's another demonstration of the relative motion of the stars,
depending on which way you are facing. When the northern hemisphere
observer faces north, stars appear to rotate counterclockwise, but
then appear to rotate clockwise when the northern hemisphere observer
faces south.

First, I'll do this for right-handed persons and then repeat the
instructions for left-handed persons.

Right-handers:

Get a chair. If you know which directions are north, east, south and
west while sitting inside, stay inside. Otherwise take the chair
outside to where you can see the four compass points.

Your left-arm will remain stationary and is not involved in this
demonstration.

Sit in the chair facing east and with your right-shoulder to the
south. With your right-arm, make the "body builder" or "muscle-man"
arm that shows off the biceps. The venacular is "showing your guns."
Make a fist with your right-hand.

Now start moving your right-arm and fist in a circular _clockwise_
motion in the vertical plane (from in front of you to behind you).
This simulates the Sun or stars rising in the east and setting in the
west, when you are facing _south_.

Image a broom stick suspended horizontally in front of your chest,
about two-hand widths away from your chest. Keep rotating your
right-arm and fist clockwise in the vertical plane.

Now, continuing to rotate your right-arm clockwise, move your
right-arm across the front of your chest. Continue circling your fist
around the imaginary horizontal broomstick. Image pedaling the crank
arm of a bicycle with your right-hand. This motion makes a helical
path around imaginary broom stick - like the threads of a screw. Your
right-arm will cross your chest and be nearly horizontal.

Eventually, this will result in fist of your right-hand being to the
left, or north, of your head. You will be looking at the back of your
right-fist as it continues in the same circular motion that you
started when your hand was on your right-side.

Look at the relative motion of your right-fist. Now that it is to the
left-side of your body, your fist will now appear to be traveling
counter-clockwise, even though you started out, and have continued to
move, your right-fist in the clockwise direction that it was traveling
in when on your right-side.

Left-handers:

Get a chair. If you know which directions are north, east, south and
west while sitting inside, stay inside. Otherwise take the chair
outside to where you can see the four compass points.

Your right-arm will remain stationary and is not involved in this
demonstration.

Sit in the chair facing east and with your left-shoulder to the north.
With your left-arm, make the "body builder" or "muscle-man" arm that
shows off the biceps. The venacular is "showing your guns." Make a
fist with your left-hand.

Now start moving your left-arm and fist in a circular
_counter-clockwise_ motion in the vertical plane (from in front of you
to behind you). This simulates the Sun and the stars rising in the
east and setting in the west, when you are facing _north_.

Image a broom stick suspended horizontally in front of your chest,
about two-hand widths away from your chest. Keep rotating your
left-arm and fist counter-clockwise in the vertical plane.

Now, continuing to rotate your left-arm counter-clockwise, move your
left-arm across the front of your chest. Continue circling your fist
around the imaginary horizontal broomstick. Image pedaling the crank
arm of a bicycle with your left-hand. This motion makes a helical
path around imaginary broom stick - like the threads of a screw. Your
left-arm will cross your chest and be nearly horizontal.

Eventually, this will result in fist of your left-hand being to the
right, or south, of your head. You will be looking at the back of
your left-fist as it continues in the same circular motion that you
started when your hand was on your right-side.

Look at the relative motion of your left-fist. Now that it is to the
right-side of your body, your fist will now appear to be traveling
clockwise, even though you started out, and have continued to move,
your left-fist in the counter-clockwise direction that it was
traveling in when on your left-side.

- Kurt