In Hindu astrology there are nine grahas or ‘planets’ and they are Surya, Chandra, Angaraka (Mars), Buddha, Brihaspati, Shukra, Shani, Rahu and Ketu. There also12 rashis or moon signs, corresponding to the 12 sun signs of the zodiac. Of all the grahas, Shani is a mischief maker and Hindu scriptures suggest that even gods are not spared from Shani’s effect. Shani’s effect is believed to be for seven and half years.
Shani or Saturn revolves around the Sun in about 30 years. Thus it passes through all the 12 rashis in 30 years, spending an average of 2.5 years in each rashi.
The astrology associated with Hinduism assigns a specific moon sign to each individual, which is calculated based on the date, time and place of birth.
Shani’s effect starts when Shani enters the rashi just before your particular rashi and ends when he leaves the rashi that’s after yours. This works out to 2.5 x 3, a total of seven-and-a-half years. This is popularly known as Seven and a half Shani.
This seven and a half year of Shani is considered to be the toughest phase in an individual’s life.