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Alpha Lex
2013-Oct-29, 04:12 AM
Hello. My understanding of solar declination is that it is the angular displacement from the celestial equator according to the observer's latitude. Could someone please explain or confirm, does that mean in order to get a reading of solar declination, one measures the number of degrees north or south of due east or west the sun appears in the sky from the observer's position? Also, would the declination reading need to be adjusted to true north from a compass reading per magnetic north?

Hornblower
2013-Oct-29, 02:05 PM
The declination is the displacement from the celestial equator, period. It can be calculated from the displacement of the rising point from due east by means of spherical trigonometry, provided we know the observer's latitude. If the only direction finder is a magnetic compass, then the correction from magnetic to true north must be applied.

This method requires a true horizon, such as at sea, and in addition is subject to error from atmospheric refraction which distorts the apparent position of the rising Sun. If I had some free time around noon, I would simply track the Sun's elevation and find the highest angle. That could be measured relative to a plumb line without any need for a true horizon or a finding of true north. The elevation of the celestial equator is readily found from the latitude, and the difference gives you the Sun's declination.

Alpha Lex
2013-Oct-29, 05:04 PM
Thank you very much!