The nodes of the moon are like signposts that point the way to our destiny, with the South Node describing the influences of the past, and the North Node pointing towards our future.  The Vedic scholars call these points Rahu (North Node) and Ketu (South Node) and while western astrology tends to look at these points as being relatively benign, in Vedic astrology both Rahu and Ketu are considered somewhat malefic.  This is likely partly due to the role that the Nodes play in eclipses (a lunar event is considered an eclipse if it occurs within 15 degrees of one of the Nodes).

Because of the relationship of the Nodes to an eclipse, Vedic astrologers consider both Rahu and Ketu to be malefic (ruled by Mars and Saturn) since they are seen to have swallowed the Sun and Moon during an eclipse.  But hope is on the horizon:

Former Union Minister Shashi Tharoor and his friend Sunanda Pushkar, are the latest celeb couple to visit Srikalahasti temple and perform the famous rahu-ketu puja, that is believed to negate the ill effects in a relationship that is facing obstacles and friction.

Their visit on Saturday injected some much-needed enthusiasm to the temple, which had been in the media limelight for all the wrong reasons since the collapse of the Rajagopuram on May 26.

Also known as Dakshin Kailash, the temple has attracted a host of celebrities over the last decade who have performed the rahu-ketu puja here. Astrologer and palmist Palakkad Narayan Iyer says: “One of the main reasons why couples are advised to visit Srikalahasti is because this temple is a rahu-ketu kshetram. Rahu and ketu are the reasons why couples face a lot of friction in their relationships. Basically, rahu and ketu signify the two nodes of the moon and a serpent represents these. The two grahas are said to symbolise the dark sides of our personalities and that’s why it’s important to perform shanti pujas to appease them. Rahu causes mental problems, anxiety, misfortune, loss of wealth, etc. while ketu is responsible for causing misunderstandings in relationships.

Another reason why people visit this temple is to negate the ill effects of sarpa dosha. According to Indian astrology, any person who suffers from this undergoes a lot of problems in their relationship with their spouse and women who have this dosha are said to face difficulties in conceiving. In fact, this is one of the main reasons why childless couples are advised to visit Srikalahasti. And unmarried girls, whose kundali shows they have a sarpa dosha, will find it difficult to get married.

read more here, and thanks to Astrococktail for the link.