Relation To Latitude
When an object is directly overhead its declination is almost always within 0.01 degree of the observer's latitude; it would be exactly equal except for two complications.
The first complication applies to all celestial objects: the object's declination equals the observer's astronomic latitude, but the term "latitude" ordinarily means geodetic latitude, which is the latitude on maps and GPS devices. In the continental United States and surrounding area the difference (the vertical deflection) is typically a few arcseconds (1 arcsecond = 1/3600 degree) but can be as great as 41 arcseconds.
The second complication is that assuming no deflection of the vertical, "overhead" means perpendicular to the ellipsoid at observer's location, but the perpendicular line does not pass through the center of the earth; almanacs give declinations measured at the center of the Earth. (An ellipsoid is an approximation to sea level that is mathematically manageable). For the moon this discrepancy can reach 0.003 degree; the Sun and planets are hundreds of times more distant and for them the discrepancy is proportionately smaller (and for the stars is unmeasurable).
Read more about this topic: Declination
Famous quotes containing the words relation to and/or relation:
“It would be disingenuous, however, not to point out that some things are considered as morally certain, that is, as having sufficient certainty for application to ordinary life, even though they may be uncertain in relation to the absolute power of God.”
—René Descartes (1596–1650)
“Skepticism is unbelief in cause and effect. A man does not see, that, as he eats, so he thinks: as he deals, so he is, and so he appears; he does not see that his son is the son of his thoughts and of his actions; that fortunes are not exceptions but fruits; that relation and connection are not somewhere and sometimes, but everywhere and always; no miscellany, no exemption, no anomaly,—but method, and an even web; and what comes out, that was put in.”
—Ralph Waldo Emerson (1803–1882)