URL hacking for star charts

October 10, 2008 at 8:26 am Leave a comment

Some star charts are available with addresses like:


But how to find other months?




You can’t find these on the site, or Google for them, you have to notice the pattern in the URL and hack the URL address:


where YY is the month as 01, 02, 03, for January, February, March, etc. and Mmm is Jan, Feb, Mar, etc.

April, May, June, July, August, September, October, November, December

You can also view past year’s charts by changing …08 to …07 for example.  Not sure there are differences between years though?

This is useful since some sites publish the night sky star chart for the current month, but the morning sky can be just as fun to look at as the night sky.  The star chart  for the morning of a given month is the same as the night sky chart three months in the future.  So a chart for October’s morning sky at 9 UTC (5AM in EDT) will be the same 3UTC (10 PM EST) in January (EDT = UTC-4, EST = UTC-5) which differ by six hours. 

Why?  It takes 24 h for the Earth to rotate one complete cycle.  Six hours is a quarter of that.  It takes 12 months for the Earth to revolve around the sun, one quarter of that is three months.  Every night the sky shifts  ca. one degree overhead from East to West; after a year it’s made a complete cycle.

So even though many star chart sites don’t publish other month’s charts they can be useful if you can find them.


Entry filed under: Astronomy, feed my pet brain, information hacks.

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