Current studies of astronomy is categorized in four branches.
Current studies of astronomy is categorized in a number of branches, namely, Descriptive Astronomy, Astrometry, Practical Astronomy, Gravitational Astronomy, and Astrophysics as follows:
It is a method that puts together facts that generally describe the universe.
This particular branch of astronomy dwells on measurement of positions, distances, sizes and motions of heavenly bodies.
It is the science of related instruments that are used.
Gravitational Astronomy (also known as Celestial Mechanics):
It is the study of how heavenly bodies move, guided by principles of forces and movements.
This is the a new branch of astronomy, detailing the makeup of heavenly boldies, inclusive of temperature, atmospheres, brightness and radiation.
The above categories of astronomy relatively involve the mapping of the universe, as well as the study of cosmogony explaining the origin of the universe including its future.
Distances between stars are measured by a process call triangulation. If you look at the night sky you will see the positions of some stars. Two hours later you will notice that they have moved to the west. A month thereafter, you will see that they moved even farther to the west; at the same time, you will notice some stars that you have not seen before, appearing in the eastern sky, the reason being that the Earth has shifted to a different position. It takes the Earth a full year to complete its orbit, at which time, you will notice that those stars that you have seen originally will look exactly the same again.
The Earth can be compared to a top that turns, half of which faces the sun and has daylight; the other half is away from the sun, causing darkness.