Tenth Sign of the Zodiac
In the midst of that region of outer space [antariksa] is the most opulent sun, the king of all the planets that emanate heat, such as the moon. By the influence of its radiation, the sun heats the universe and maintains its proper order. It also gives light to help all living entities see. While passing toward the north, toward the south or through the equator, in accordance with the order of the Supreme Personality of Godhead, it is said to move slowly, swiftly or moderately. According to its movements in rising above, going beneath or passing through the equator -- and correspondingly coming in touch with various signs of the zodiac, headed by Makara [Capricorn] -- days and nights are short, long or equal to one another.

Purport
Lord Brahma prays in his Brahma-samhita (5.52):
yac caksur esa savita sakala-grahanam
raja samasta-sura-murtir asesa-tejah
yasyajnaya bhramati sambhrta-kala-cakro
govindam adi-purusam tam aham bhajami

"I worship Govinda, the primeval Lord, the Supreme Personality of Godhead under whose control even the sun, which is considered to be the eye of the Lord, rotates within the fixed orbit of eternal time. The sun is the king of all planetary systems and has unlimited potency in heat and light."

Although the sun is described as bhagavan, the most powerful, and although it is actually the most powerful planet within the universe, it nevertheless has to carry out the order of Govinda, Krsna. The sun-god cannot deviate even an inch from the orbit designated to him. Therefore in every sphere of life, the supreme order of the Supreme Personality of Godhead is carried out. The entire material nature carries out His orders. However, we foolishly see the activities of material nature without understanding the supreme order and Supreme Person behind them. As confirmed in Bhagavad-gita, mayadhyaksena prakrtih: [Bg. 9.10] material nature carries out the orders of the Lord, and thus everything is maintained in an orderly way.

Srimad-Bhagavatam 5.21.3
A.C. Bhaktivedanta Swami Prabhupada