In Vedic Astrology there are two characters not present in western Astrology that actually hold great power over the planet and our lives, and that is Rahu (Head of the serpent= your future and Ketu, the body and tail of the serpent = your past.)

The legend of Rahu and Ketu

Long long ago Indra, the king of Devtas, was riding on his Elephant. Rishi Durvasa (a sage) saw Indra and he offered him a garland. Indra accepted the garland with a smile and placed it on the trunk of his elephant. The elephant got irritated by the scent of the garland and threw it on the ground, seeing this the enraged sage cursed Indra and all the Devatas to forget their Divya Shakties ( Divya means divine and Shakties means Powers)
In such a condition the Daanavas (rivals of Devtas ) attacked the Heavens and conquered the whole universe. The Devas approached supreme father and creator of the universe, Lord Brahma for help, who guided them to Lord Vishnu, the preserver of universe. Lord Vishnu made a plan and suggested Devas to approach the Asuras and ask them for their co-operation in churning the mighty ocean to obtain amrita, the nectar of immortality.

The Devas approached Asuras who agreed as this task required combined efforts of both Devas and Asuras. They started churning using Mount Mandara as a rod and the Serpent Vasuki as a rope. Lord Vishnu incarnated as a Tortoise to hold up the mountain on his back.
As the churning of the ocean started, several things emerged as a result, starting with poison Halahala which threatened to destroy all the universe but Lord Shiva kept it in his throat, without swallowing it. Kamadhenu, the wish-fulfilling cow, celestial horse Ucchaishravas, Airavata, the celestial elephant, the Kausthubha gem, the Parijataka (wish-fulfilling tree), Apsaras, the beautiful celestials maids, Lakshmi, the goddess of prosperity, Varuni, the goddess of liquor appeared one by one.
Finally Dhanvantari, the god of medicine, appeared holding the pot of amrita. The Asuras forcefully snatched it, and refused to give it to Devas. Lord Vishnu then incarnated as Mohini, the enchantress, the most beautiful female form in the universe. Vishnu’s incanation Mohini was a lady with divine beauty . Mohini came with the Amrit pot to the battle place and she suggested devtaas and danavaas to sit in different rows, so that she can distribute Amrit among them. All the Devtaas and Daanavas agreed.

Mohini started distributing Amrit to the Devtaas. One Danav, Rahuketu, sat in the row of devtaas and drank the Amrit. The Sun God and the Moon God noticed him and they informed Mohini; however, by that time Rahuketu had already became immortal. Vishnu as Mohini cut off his head with Sudarshan Chakra . Rahuketu could not die but his head was seprated from his body , his head came to be known as Rahu and his body Ketu. Now the Devtaas were immortal so they fought the Danvaas and won.
As per Hindu Astrology, Rahu and Ketu denote the two points of intersection of the paths of the Sun and the Moon as they move around the celestial sphere. Therefore, Rahu and Ketu are respectively called the north and the south lunar nodes. The fact that eclipses occur when Sun and Moon are at one of these points gives rise to the myth of swallowing of the Sun.
The Rahu is of feminine and Ketu is of neuter gender, Rahu is the karaka or significator of spiritual knowledge and Ketu is the karaka or significator of Moksha or the final liberation, as relationship significator Rahu governs maternal grandparents and Ketu denotes paternal grandparents.

Rahu is one of the nine well known astronomical bodies in Indian texts. Rahu is a shadow entity, unlike the other eight bodies. It is the one that causes eclipses and is also believed to be the king of meteors. Rahu represents the ascension of the moon in its precessional orbit around the earth.According to some accounts in Hindu mythology, Ketu belongs to Jaimini Gotra. Whereas Rahu is from Paiteenasa Gotra. Thus both are totally different entities having distinct characteristics but are two parts of a common body. Ketu is generally called as a “shadow” planet. It is believed that it has a tremendous impact on human lives and the whole creation as well.
The Rahu is of female and Ketu is of neutral. Rahu is the significator of otherworldly information and Ketu is the karaka or significator of Moksha or the last freedom, as relationship significator. Rahu oversees maternal grandparents and Ketu indicates fatherly grandparents.