Why a Charioteer for Surya

When Surya became furious, BRAHMA had to find a way to protect the planets and living beings from his fierce heat and light.

In the Hindu mythology, Surya the Sun God is depicted as riding on a one wheeled chariot drawn by seven horses representing the seven colours of the rainbow.
He is also worshipped as Suryanarayan a manifestation of Lord Vishnu.
It is said that Surya also known as Aditya was born to Kasyapa Maharshi and Aditi, daughter of Daksha. He was gifted with the power of enormous heat and light to sustain the existence of all beings on earth and dispelling darkness and providing energy in the form of heat.
Besides Aditi, Kasyapa had two more wives – Vinita and Kadru. Through Kadru  he gave birth to serpent species and to Vinita was born Aruna, a human being with the upper part of the torso and no legs. A few years later Vinita gave birth to another son with the head of an eagle and a human body who was Garuda. Thus Aruna and Garuda are step brothers of Surya.

Once, while the Ocean of Milk was churned by the devas (heavenly beings) with the help of asuras (demons) to produce amrit (nector).
Lord Vishnu assumed the form of Mohini, a divine damsel to distribute it. The aim however was to see that the asuras did not partake of it and become immortal.
So Mohini with the pot of nectar in hand started dancing and distributing it cleverly in the course of the dance she gave it to the devas only. One asura however was too clever and standing along with the devas, got a little nectar and put it into his mouth.
Surya and Chandra, standing on either side of the asura, hinted this out to Mohini who acted smartly and chopped off the head of the asura. But since a few drops of the nectar had entered his body, he did not die and survived separately as two entities of a snake. The head came to be known as Ketu and tail as Rahu. They joined the row of significant planets and became part of the Navagrahas ( nine planets)
Since then Rahu and Ketu harbored  vengeance on the Sun and Moon and now and then attempt to swallow them. These times when Surya or Chandra would be partially inside the mouth of the serpent there would be partial darkness and such periods were called eclipses. But eventually the Sun and Moon would wriggle out of the serpents mouth.

Shield Against Heat
When the frequency of the attempts to swallow him increased, Surya became livid with rage. He took the form of a furious ball of fire thousand times bigger than the other planets. Blazing fire was flaming around him . Because of this the other planets and lives on heaven and earth found survival difficult. They took refuge under Brahama who got a idea to minimize the heat and radiance f the Sun. He decided to put up a screen before Surya as a shield, so that the intensity of the heat and light would be toned down. That screen would be a chariot driven by Aruna the step brother of Surya who alone could withstand the heat and light of Surya and tone it down.

Arunas torso would act as a shield and filter the heat and light falling on other planets and living beings. Further the chariot was made of fire proof material and the Sun’s rays themselves  were used to create the seven horses with seven colours.

Bhrama blessed Surya and asked him to calm down a little in the interest of the others. Surya was also happy and his brother was given a status and would always be with him. The bright sky at dawn just before sun rise is known as Arunodaya (the rising Aruna) The world sees Aruna first before having darshan of Surya.

Role of the Ramayana

Aruna played a significant role in the Ramanaya also. Sampati and Jatayu, the two divine birds who helped Rama in the search of Sita were the sons of Aruna. Jatayu fought with Ravan to save Sita while he was carrying her away. He sacrificed his life in the process after duly informing Rama about the abduction.
It was Sampati with his powerful eyesight, who spotted Sita in the Ashokavana and informed Rama about her whereabouts.

Aruna had two more sons, who also played significant roles in the Ramayana, but circumstances of their birth were strange.

Once a chaste woman, Silavati undertook ugra tapas (deep penance) to save the life of her husband and requested Surya not to rise till her penance was over. This gave respite for Aruna also. He decided to entertain himself in Dwarkaloka (heaven) for a while, and taking due permission from Surya, left for the place. But it was the order that no male except Devendra could enter the entertainment spot. So he took up the form of an apsara ( celestial woman) and went inside.

In heaven, Indra was attracted to this charming female form with the name Aruni Devi and this resulted in the birth of a beautiful male child. As Aruna had to resume the duty of charioteer when Silavati’s penance ended, he left the child in the care of Ahalaya, wife of sage Gautama and resumed his journey.

On the way Aruna narrated to Surya also became interested to see the charming female form of Aruna. The latter obliged and this resulted in the birth of another male child Aruna left this child also in the care of Ahalaya since he had to resume with the duties of  charioteer.

Though Ahalaya showered affection on the children her husband, sage Gautama, did not relish the idea of Indra’s and Surya’s sons living  in his abode. He cursed them and turned them into monkeys. When  Indra came to knowabout this, he took away both the monkey children with him. The elder one with a long tail, born to him and Aruna Devi, was named Vali (or Bali). The younger one with a beautiful neck, born to Aruna Devi and Surya was named Sugriva.

Raksharaja, the monkey king of Kishkinta, had no children and he prayed to Indra to give Vali and Sugriva to him. Indra was happy to do so. It was these brothers who figure in the Ramayana.

Sugriva  helped Lord Rama in the mission of his avatar and Vali attained moksha at the hands of Rama.