Sade-Sati is the 7½ years long period of Saturn (Shani). This astrological phase is much feared by those in India who give credence to Indian Astrology. According to those beliefs, this is a period with many challenges.
The period of Sade-sati starts when Saturn enters the zodiac sign immediately before the zodiac sign of Moon at the time of the birth of the individual. That is, if the Moon sign (Ayamsha) at the time of birth of the native was Taurus, then the Sadesati will begin when Saturn enters sign Aries. The Sadesati will continue while Saturn transits over this sign and the next two signs, i.e. the birth sign and the sign after it. Saturn spends around 2½ years in each sign. To cross these three signs it takes about 7½ years. Thus the name Sadesati which literally means seven and a half.
According to one school of Vedic astrology this is a troublesome time for the individual who is going through it. There may be a lot of challenges in a person's life, and he may face accidents, sudden failures, money and health problems. However, there's another school of astrology that believes that though the sadesati period is challenging, it is not as damaging as many astrologers claim, and that many people actually achieve a lot of success during the period of Sadesati. Sadesati is development of the brain its a learning curve.
The impact of Sadesati is supposed to be felt differently by people of different moon signs. It is said that people of Moon sign Aquarius do not have any ill effects from Sadesati, while people of Moon sign Leo feel the most impact.
Vedic astrology also prescribes certain remedies and mantras that can be recited to please the lord Saturn and limit the effect of Saturn's Sadesati.