Declination
in astronomy, the distance of a heavenly body from the celestial equator (equinoctial), measured on a great circle passing through the pole and also through the body. It is said to be N. or S. according ng as the body is N. or S. of the equator. Great circles passing through the poles, and cutting the equator at right angles, are called circles of declination. Twentyfour circles of declination, dividing the equator into 24 arcs of 15° each, are called hour circles or horary circles.
Declination of the compass or needle, or magnetic declination, is the variation of the magnetic needle from the true meridian of a place. This is different at different places, and at the same place at different times.
DECLINOMETER (dek-li-nom'e-ter), an instrument for determining the magnetic declination, and for observing its variations. In magnetic observatories there are permanent instruments of this kind, and they are now commonly made self-registering. Such instruments register the small hourly and annual variations in declination, and also the variations due to magnetic storms .