Proper motion is motion we detect due to actual relative velocities 
of stars.  As an example lets look at Orion as it is viewed today and then 
see what it will look like 1 million years into the future.
Orion Today

The Hipparcos satellite has recently provided us with our best information to 
date on the proper motions of stars.  Hipparcos was the first ever satellite 
dedicated to the precise measurement of the positions of stars.  Learn more 
about the Hipparcos mission here.  

For an interesting summary of Hipparcos results take a look at "Hipparcos: 
The Stars in Three Dimensions" by Michael Perryman in the June, 1999 Sky and Telescope.
Get more information on Sky and Telescope here.  

The next generation of astrometric satellite, GAIA, is already planned.  
You can find out a little about GAIA. 

Barnard's star shows the largest proper motion of any known star.  
See the motion of Barnard's star as determined with a relatively small telescope.

Find a good simulation of the proper motion of the stars in the Big Dipper here.
I recommend viewing the MPEG movie if you have the capability.  Note also that 
this site has several other good animations of astronomical objects.   


A PROPER MOTION EXERCISE

Visit the above link and make a plot of the Big Dipper's shape every 10,000 years
from 100,000 BC to 1000,000 AD.  You could use tracing paper right on the screen
if you like.

Describe how the shape has changed over the course of recorded human history.

By about what factor is the largest proper motion observed larger than the smallest
proper motion observed?  Discuss the different factors that could lead to the 
different observed motions.


GOING FURTHER

Make a prediction of how you would expect proper motion to depend on distance to 
a star.  Defend your reasoning.

Let's test the prediction.  Go to the Hipparcos proper motion simulator.  
In the boxes below the display enter any valid right ascension and declination. 
Keep the limiting magnitude at 99 so the simulator will display all stars in the 
catalog.

Click on any one of the stars and the display will give you a Hipparcos Catalog 
identifier number and the visual magnitude of the star.

Now click on "Get Info" at the right of the display.  You will get information on
the selected star.

H11 is the measured parallax of the star.

H12 is the proper motion in right ascension

H13 is the proper motion in declination

Record these values.

Use parallax to determine the distance to the star, recalling that the distance 
in parsecs is just the inverse of the parallax angle given in arc seconds.

Square each of your proper motion values ; add them and take the square root to 
get the total proper motion speed.  See Exercise 25 in your lab manual for more 
information.  Record the speed and the distance.

Repeat for each star in the field of view.  move to a different field of view and
repeat for those stars if you want more data for better results.

You are in the process of statistical astronomy.  It should be apparent to you 
the utility of computers for such operations.  A computer program of just a few 
lines would allow you to simply enter (or better yet, download) the data and 
churn out the results you want.

When you have several tens to a few hundred points, make a graph of proper speed 
versus distance.

Is there a trend in the data?  Is it a clear trend?  Would you report strong 
support for your prediction?  Given a proper motion, how confident would you be 
estimating the distance to that star?  Would there be some instances in which you 
would be able to put an upper limit on the distance to a star?  Specifically, 
answer these questions:  Suppose a star shows no proper motion, are you able to 
say anything about its distance based on this information?  Suppose a star shows 
large proper motion are you able to say anything about the starŐs distance in 
this case?

Discuss your results and the answers you gave to the previous questions