Cosmology is the study of the universe as a whole.
This includes theories about its origin, evolution, structure, and future. A light-year is a unit of length used to measure distances. It is equivalent to the distance light travels in a mean solar year. A light-year is equal to 9,461,000,000,000km or 5,880,000,000,000mi. A parallax is the apparent displacement of an astronomical object when viewed from different positions.