Any astronomers around?
05-30-2014, 06:08 PM
Post: #3
 everettr Member Posts: 60 Joined: Dec 2013
RE: Any astronomers around?
(05-29-2014 05:17 PM)HP67 Wrote:  I do not understand how to calculate the time of x degrees after some celestial event. For example, let's say sundown occurs at 19:30. How do I figure 5 degrees later? I read that every degree is equal to 4 minutes regardless of latitude. So later should be a simple matter of sundown + (5 * 4) minutes (20 minutes after sundown). But my results don't match up.
It sounds like you are working with equatorial coordinates. These are in reference to the orientation of the Earth. Declination (DEC) is like latitude and measured in degrees, and Right Ascension (RA) is like longitude, but measured in hours, minutes, and seconds.
If you are observing on the Equator, on an equinox, the Sun moves perpendicularly to the horizon at sunset (DEC=0), and would be 5 degrees below the horizon 20 minutes after sunset.
One correction that I know about is for declination. Right now (May 30) the Sun has a DEC of about 20 degrees. This means that it appears 20 degrees up from the celestial equator, and travels in a circle that is smaller than the celestial equator by COS(20°). In order to move 5 actual degrees in the sky would take the Sun 20 minutes / COS(20 degrees DEC) = about 21 minutes 17 seconds.
I also am not an astronomer, but I once was a member of an astronomy club. :-)
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 Messages In This Thread Any astronomers around? - HP67 - 05-29-2014, 05:17 PM RE: Any astronomers around? - Dale Reed - 05-30-2014, 04:03 PM RE: Any astronomers around? - everettr - 05-30-2014 06:08 PM RE: Any astronomers around? - HP67 - 05-31-2014, 06:41 PM RE: Any astronomers around? - HP67 - 06-01-2014, 11:37 AM RE: Any astronomers around? - NetMage - 06-02-2014, 07:11 AM RE: Any astronomers around? - HP67 - 06-02-2014, 09:44 AM RE: Any astronomers around? - Bill (Smithville NJ) - 06-04-2014, 01:54 AM RE: Any astronomers around? - HP67 - 06-04-2014, 06:40 PM RE: Any astronomers around? - htom trites - 06-04-2014, 09:01 PM RE: Any astronomers around? - HP67 - 06-05-2014, 01:09 PM RE: Any astronomers around? - CosmicTruth - 06-07-2014, 01:33 PM

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