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Measuring Stellar Distances

Started by youngb, 12/30/2007 05:03PM
Posted 12/30/2007 05:03PM | Edited 12/30/2007 05:07PM Opening Post
Is it possible for an amateur to trignometrically measure distances to neighboring stars? I understand that this would require stars near enough to exhibit significant "proper motion".

I also take proper motion to mean movement of a star relative to the background sky/stars as a result of earth's orbital motion. Is this correct?

If it is possible, what technique, equipment, measurements and calculations should be used?

Having a big time on a small scale grin
Posted 12/31/2007 02:51AM #1

The answer is yes, it should be possible for an amateur to get good distances to nearby stars. What you're looking for is trigonometric parallax, i.e. a "wobble" in the location of a star due to the changing location of the earth through the year. This is different than proper motion, which is a steady motion of the star across the sky due to the different velocities (both speed and direction) of the star versus the solar system through the galaxy. If you plot the position of a star versus time, you'll get a helical or corkscrew curve, which is the sum of the parallax and the proper motion.
You also need to take into account the aberration of star light, which looks like parallax (i.e. it causes the location of a star to wobble with a 1 year period). This is due to the fact that the speed of the earth's orbit is a non-neligable fraction of the speed of light. It's just like if you're driving through rain, the rain looks like its coming down at an angle from in front of you when it's actually falling straight down. And then there are all of the instrumental affects, like any changes in the focal length of the scope with temperature, etc. If you're interested in this, the book "Parallax" is a great read, and is very well written. The CCD has made precision astrometry available to amateurs, so a mathematically inclined amateur with the right equipment who understands the problem should be able to get a good measurement.

Mike Connelley