Is this page a copy?

Since there are now many copies of my astronomy material scattered over the web, it is easy to come across an old version of a web page that may have an error in it or missing material. So you will need to verify that you have the updated version.

If your web browser's URL does not have

http://www.astronomynotes.com/ or https://www.astronomynotes.com
at the beginning of the astronomy material you are reading, the page was copied from Nick Strobel's Astronomy Notes web site. He does not take responsibility for any errors and incomplete material in copies or mirrors of any part of his web site.

Use your browser's ``Back'' button to go back to the astronomy material you were reading or select the following link to go to the official Astronomy Notes web site.

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Author: Nick Strobel