The Meridian is that hour circle which passes through the zenith.
A Vertical Circle is any great circle that passes through the zenith. Is the meridian a vertical circle?
The Declination of a star is its angular distance north or south of the celestial equator.
The Right Ascension of a star is the angle included between its hour circle and the hour circle of a certain point on the equator which is called the Vernal Equinox. From spherical geometry we learn that this angle is to be measured either at the pole where the two hour circles intersect, as is done in the star map opposite [page 124], or along the equator, as is done in the map opposite page 190. Right ascension is always measured from the vernal equinox in the direction opposite to that in which the stars appear to travel in their diurnal motion—i. e., from west toward east.
The Altitude of a star is its angular distance above the horizon.
The Azimuth of a star is the angle between the meridian and the vertical circle passing through the star. A star due south has an azimuth of 0°. Due west, 90°. Due north, 180°. Due east, 270°.
What is the azimuth of Polaris in degrees?
What is the azimuth of the sun at sunrise? At sunset? At noon? Are these azimuths the same on different days?
The Hour Angle of a star is the angle between its hour circle and the meridian. It is measured from the meridian in the direction in which the stars appear to travel in their diurnal motion—i. e., from east toward west.
What is the hour angle of the sun at noon? What is the hour angle of Polaris when it is at the lowest point in its daily motion?