Sometimes the planets in outer space are called islands. We have experience of various types of islands in the ocean, and similarly the various planets, divided into fourteen lokas, are islands in the ocean of space. As Priyavrata drove his chariot behind the sun, he created seven different types of oceans and planetary systems, which altogether are known as Bhu-mandala, or Bhuloka. In the Gayatri mantra, we chant, om bhur bhuvah svah tat savitur varenyam. Above the Bhuloka planetary system is Bhuvarloka, and above that is Svargaloka, the heavenly planetary system. All these planetary systems are controlled by Savita, the sun-god. By chanting the Gayatri mantra just after rising early in the morning, one worships the sun-god.