Learn more physics!
Q:
How long an exposre would a photographer need to photograph star trails that are complete circles? why?
- Anonymous (age 12)
Lousianna,USA
A:
Hello, and thanks for your question!
We see star trails because of the Earth's rotation. So it would
take a whole day, or 24 hours, to see complete circles because we have
rotated all the way around.
It is very difficult to make good pictures of star trails because
you need to expose the film for a long time. If you expose the film
during the day time you might not be able to see anything you exposed
during the night. So the best way to do this if you are interested in
looking at star trails is to put a camera on a tripod and keep the
shutter open for maybe 10-15 minutes. You will definitely see some star
trails. Then when you are comfortable with using the camera and film
you can try for longer times. It's hard to do star trails unless you
are in a very dark place. There's a lot of extra light from cities, or
the moon if it is up, that film will pick up that we can't see very
well. Good luck stargazing!
Thanks again!
(published on 10/22/2007)
Follow-up on this answer.
