How to calc longitude and latitude of sun?

Question

The website http://www.timeanddate.com/worldclock/sunearth.html displays the location of the sun over the earth. I want to calculate this position myself. I have managed to calculate the latitude but the longitude never calculates correctly. Anyone know the formula for this. Ill give you a 10 if you can show me

Answer 1

The longitude depends on the exact time, as the sun (actually the earth) moves the spot it is over with the rotation of the earth. ~
Thus is it moving a lot more and faster than the latitude position.

Answer 2

Well, the sun passes through 360° of longitude every 24 hours, or 15° every hour. If, say, you are using 12:00 noon Greenwich Mean Time as your starting point, then the longitude at 7:00 PM GMT should be 7 * 15° = 105° West longitude, give or take a fudge factor.

As for what this "fudge factor" is, I'd guess it can't be more than one degree. If you are off by about 15°, Daylight Savings Time may be the reason - don't forget that, when DST is in effect, the sun reaches its highest point in the sky at about 1 PM.

* * * * * *

The next poster's comments vaguely reminded me of something, so I did more research. This is pretty interesting, actually. There is an astronomical term called "equation of time" which basically refers to changes in the time of solar noon for a given location over the course of a year. After Dec 21, the lengths of the days actually don't increase that fast, but the solar noon moves forward roughly 30 seconds each day. The opposite happens after June 21. Play around with the following Web site to get a feel for this:

http://www.srrb.noaa.gov/highlights/sunrise/sunrise.html

As for why it happens, it's due to Earth's elliptical orbit and "Kepler's law of equal areas in equal times", (as the next poster says in a different way).

Answer 3

Longitude is a function of time in the celestial sphere measured in hour angle. in the right of ascension. Latitude is observed relative to Zenith on the celestial sphere however due to the Wobble of the Earth it produces errors depending on which location on Earth you are measuring from. And it is complicated process to make the corrections.
There is a book that was published explaining how lattitude variation is calculated. Its titled "Latitude Variation"Which discusses how Chandler,Newcomb and others etc. confirmed it.
As far as position of the earth during the earths continually changing radius vector moving on the eliptical orbit.There is a simple formula for the Radius as a function of angle. Its found in any calculus book which describes the locus on an ellipse. A good reference book that would give formulas would be Bowdich Handbook" American practical navigation"

Answer 4

Try this page for a start. The accuracy is claimed to be 0.01 degrees, which is about 2.4 seconds of time.