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Celestial Coordinates

Galactic Longitude

The arc distance eastward along the galactic equator from the direction to the center of our Milky Way galaxy to where an object's secondary to the galactic equator crosses the galactic equator; it increases from 0° to 360°.

Galactic latitude b, the arc distance of an object from the galactic equator along its secondary to the galactic equator. Values of b vary from +90° at the NGP to -90° at the SGP. Galactic coordinates of the direction to the center of the Milky Way galaxy are 1=0°, b=0°. Galactic coordinates are usually heliocentric but can also be centered at the center of our Milky Way galaxy.


Resources

Books

Berg, Rebecca M., and Laurence W. Frederick. Descriptive Astronomy. New York: Van Nostrand, 1978.

Bernhard, Hubert J., Dorothy A. Bennett, and Hugh S. Rice. New Handbook of the Heavens. New York: McGraw-Hill, 1948.

Motz, Lloyd, and Anneta Duveen. Essential of Astronomy. Belmont, CA: Wadsworth, 1966.

KEY TERMS


Celestial equator

—The projection into space of the earth's equator.

Celestial merdian

—The circle passing through the zenith, zadir, north celestial pole, and south celestial pole.

Ecliptic

—The intersection of the earth's orbital plane with the celestial sphere.

Galactic equator

—The circle through the middle of our Milky Way galaxy's disk which passes through the direction from the solar system to the center of the Milky Way.

Horizon

—The circle on the celestial sphere 90° from the zenith and nadir.

Hour circles

—Half circles from the north celestial pole to the south celestial pole.

Nadir

—The point on the celestial sphere directly below (by downward extension of the plumb line through the earth) the observer.

North point of the horizon

—The intersection of the horizon and celestial meridian closer to the north celestial pole (NCP).

North (south) celestial poles (NCP, SCP)

—The intersection(s) of the earth's rotation axis extended beyond the north (south) geographic poles, respectively, with the celestial sphere.

Secondaries to the ecliptic

—Half circles from the north ecliptic pole to the south ecliptic pole.

Secondaries to the galactic equator

—Half circles from the north galactic pole to the south galactic pole.

Vernal equinox

—The intersection of the celestial equator and ecliptic which the Sun appears to reach on or about March 21.

Vertical circles

—Half circles from the zenith to the nadir.

Zenith

—The point on the celestial sphere directly above (by upward extension of the local direction of gravity (plumb line) the observer.

Additional topics

Science EncyclopediaScience & Philosophy: Categorical judgement to ChimaeraCelestial Coordinates - Horizon Coordinates, Celestial Latitude B, Galactic Longitude - Equatorial coordinates, Right ascension a, Declination d, Hour angle, Ecliptic coordinate, Celestial longitude l