What is a small circle of constant altitude, also called a parallel of altitude?

What is a small circle of constant altitude, also called a parallel of altitude?

• A. Zenith Distance
• B. Declination
• C. Almucantar
• D. Right Ascension

Answer: (C)

Almucantar is the circle on the celestial sphere formed by all points at the same altitude above the horizon. Since altitude is the angle up from the horizon, a plane parallel to the horizon cuts the celestial sphere in a small circle, and that circle is called the almucantar. This differs from zenith distance, which is the angle from the point to the zenith; from declination, which measures north-south position relative to the celestial equator; and from right ascension, which is the along-the-equator angular coordinate.

Almucantar is the circle on the celestial sphere formed by all points at the same altitude above the horizon. Since altitude is the angle up from the horizon, a plane parallel to the horizon cuts the celestial sphere in a small circle, and that circle is called the almucantar. This differs from zenith distance, which is the angle from the point to the zenith; from declination, which measures north-south position relative to the celestial equator; and from right ascension, which is the along-the-equator angular coordinate.