Sade-Sati is the 7 1⁄2 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 2 1⁄2 years in each sign. To cross these three signs it takes about 7 1⁄2 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. If Saturn is ill-placed in bad houses, he may face challenges that reflect this bad placement. 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 achieve a lot of success during the period of Sadesati. Saturn, the karaka for hard work, discipline, old age and authority, will show results based on how the individual has lived his/her life up till that point. If the person has been disciplined, and worked hard, this is the moment Saturn shows its rewards. Sadesati's heaviest challenges during this time, and how the individual deals with it, sets the tone for the next 22.5 years as Saturn starts to move around the twelve houses again.
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.
Sade Sati is divided into three phases called Rising, Peak and Setting and the results of Sade Sati varies as per the phase native is going through.
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.
Another related astrological transit of Saturn is the Dhaiyya (2.5 years), also known as Small Panoti (Small Trouble), and Kantakshani, or Ashtamshani. This transit of Saturn occurs when the Saturn is transiting through the 4th sign from the birth Moon sign (Kantak Shani), or from the 8th sign from the birth moon sign (Ashtamshani). Vedic astrology says that these two are hazardous periods, though not as much as the Sade-sati. But if there is a proper system then this period of sadisati will not effect any human being.