sun considered a God in ancient time because People through the ages have worshiped the sun as the source of light and therefore as the source of all life. Our ancestors realized that if there was no sun, the earth would be plunged in perpetual darkness. It would be unbearably cold, and all the water on earth would freeze up. They had no clear idea of how the sun produced light, nor why it moved throughout the sky. They did understand however, that without the sun life would not be possible.
Ancient civilizations were primarily agricultural, and depended on the sun for life, and their crops. Therefore, it is no surprise that they worshipped the sun as a God.