Sun is the most important star among all heavenly bodies as it is the source of energy. So, people hold him in high esteem.
The Suryopanishad says Gods, Gandharvas and Sages reside in Sun rays.
In the Skandpuran, it is scribbled as a sin to eat without offering Sun the libation. Sun is involved in every auspicious work. Sankranti and Surya Shashthi (the sixth day of a fortnight) are the most important and fruitful days to appease the Sun. Prayers needs to be offered on Sundays otherwise.
Sun is offered water mixed with red sandalwood, rice, red flowers and kusha every morning in a copper vessel. While offering water, Surya mantra or Gayatri mantra needs to be chanted.
In the Shivpuran, 6/39-40, it is said:
0 Master! You look beautiful with the colour of sindoor. Adorned with diamonds and other gems, your eyes are like lotus flowers. Holding the lotus in your hand it appears that you are the cause of Brahma, Vishnu, Indra and the entire creation. 0 Aditya! Please accept my salutations. 0 God. Please accept from this golden vessel the mixture of sindoor, kusha and flowers mixed with red water as a libation and be pleased.
Pleased Surya blesses with good health and long life, wealth and prosperity, sons and friends. He also blesses with knowledge, intelligence, wisdom and fame.
In the Brahmpuran, it is said:
Whoever prays and makes offerings to Surya attains whatever they desire. Surya comes close to them and fulfils desires. With his blessings all physical, oral and mental sins are absolved.
The Rig-Veda says praying Surya blesses you with vigor, vivacity, strength, and divinity. It helps you earn a life free from sins, diseases and poverty. It brings happiness and prosperity.
In the Brahmpuran, chapter 29-30 says, Surya lends brightness to the other Gods. So, every offering to Surya comes back to the devotee as boons.
In the Skandpuran, Kashi Khand, 9/45-48, there are instructions to achieve wealth, prosperity, good health and children by performing Savita Surya Aradhana (prayer of Surya).
In the Yajur-Veda, 13/43, it is mentioned, being the witness of all good and bad deeds of the people, Surya needs to be pleased. For that purpose, the Savita Surya Aradhana is performed.
In the Agnipuran, it is said, Chanting of Gayatri mantra during a prayer pleases the Surya.