Renewable energy comes from the Sun. The energy of the Sun is nuclear energy generated by the fusion process. The Sun is one of the billions of stars in the universe. Thus, there are enormous sources of energy in outer space. The Sun is a medium-sized star with a diameter of about 1,400,000 km. Some stars are smaller than the Sun, whereas some stars are much larger. However the size of the Sun is insignificant when compared with other larger stars, for example, Eta Carinae with a diameter of about 239,400,000 km, which is the largest star in our Mercury galaxy and is five million times larger than the Sun. The Sun, planets, and other objects together are called the solar system. The Sun is the richest source of electromagnetic energy in the solar system. The Earth revolves around the Sun in an elliptical orbit at a moving speed of about 30 km/s, making one revolution every 365.25 days.