Astronomy 135: Archaeoastronomy
Classical Astronomy Terms
Altitude
(h) The angle between the horizon and an object in the sky.
Azimuth
(A)
The angle between due north on the horizon and a point on the horizon directly
below an object in the sky.
Celestial Equator
An imaginary circle on the Celestial Sphere that is the projection of the earth’s
equator up onto the Celestial Sphere.
The CE divides the Celestial Sphere into a northern
hemisphere (where Declination measures are positive) and a southern hemisphere (where
Declination measures are negative).
The Declination of the CE is 0°.
Celestial Sphere
An imaginary sphere concentric with the earth but infinitely far away.
The entire
Celestial Sphere rotates around the earth from east to west once per day.
Objects on the Celestial
Sphere have coordinates of Right Ascension and Declination.
The RA and Dec of the “fixed” stars
do not change significantly over short timescales.
The RA and Dec of the Sun changes over the
course of a year due to the orbit of the earth around the sun.
Circumpolar
An object that never sets (i.e., crosses the horizon), but just circles the Celestial
Pole in the sky.
Declination
(Dec, or sometimes
δ
)
The angle between an object on the Celestial Sphere and the
Celestial Equator.
Declination is typically measured in degrees, arcminutes, and arcseconds.
Declination can be thought of as a kind of Celestial Latitude, since it gives the northsouth position
of an object on the Celestial Sphere.
Ecliptic
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 Spring '08
 MichaelFaison
 Astronomy, Solar time, Celestial coordinate system, right ascension

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