Rahu, the immortal head, Q. Cassetti, 2011, pen and inkFrom Wikipedia on Rahu:

RahuIn Hindu belief, Rahu is a snake that swallows the sun or the moon causing eclipses. He is depicted in art as a dragon with no body riding a chariot drawn by eight black horses. Rahu is one of the navagrahas (nine planets) in Vedic astrology. The Rahu kala (time of day under the influence of Rahu) is considered inauspicious.

According to legend, during the Samudra manthan, the asura Rahu drank some of the divine nectar. But before the nectar could pass his throat, Mohini (the female avatar of Vishnu) cut off his head. The head, however, remained immortal. It is believed that this immortal head occasionally swallows the sun or the moon, causing eclipses. Then, the sun or moon passes through the opening at the neck, ending the eclipse.

Astronomically, 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 the swallowing of the Sun.

Rahu is a legendary master of deception who signifies cheaters, pleasure seekers, operators in foreign lands, drug dealers, poison dealers, insincere & immoral acts, etc. It is the significator of an irreligious person, an outcast, harsh speech, logical fallacy, falsehoods, uncleanliness, abdominal ulcers, bones, and transmigration. Rahu is instrumental in strengthening one’s power and converting even an enemy into a friend. In Buddhism Rahu is one of the krodhadevatas (terror-inspiring gods).