Since antiquity, the sky has been thought of as a bowl, or celestial sphere, that's directly overhead.
The equatorial coordinate system that astronomers use to find stars and other objects is based on that sphere.
Here are a few common terms to help navigate the night sky:
Celestial is derived from the Latin word caelum, which means heaven or sky.
The celestial sphere's highest point is the observer's zenith.
The north and south celestial poles are the points in the sky directly above the North and South Poles.
The celestial equator is that imaginary line in the sky directly above the Earth's equator. It divides the celestial sphere into the northern and southern skies.
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The celestial meridian is an imaginary circle in the sky that passes through the north and south celestial poles and the zenith. It is the imaginary line that divides the sky into eastern and western halves.
The equatorial coordinate system's coordinates are:
Right ascension, which is the equivalent of longitude.
And declination, which is the equivalent of latitude.
More commonly, however, this column will use a horizontal coordinate system to define an object's place in the sky. In this system, altitude is simply an object's angular distance above the horizon — going from 0 degrees at the horizon to 90 degrees at the zenith. Due east is 90 degrees, due south is 180 degrees, and due west is 270 degrees.
Tim Hunter has been an amateur astronomer since grade school. He is a prime example of someone whose hobby has run amok, spending more time and money on it than common sense would dictate. Contact him at skyspy@azstarnet.com.