There is a Shivaratri in every luni-solar month of the Hindu calendar, on the month's 13th night/14th day, but once a year in late winter (February/March, or phalgun) and before the arrival of Summer, marks Maha Shivaratri which means "the Great Night of Shiva".
09 Mar 2024
Lord Shivan Sanadhi
Third Kala Pooja starts by 12:30 AM
Fourth Kala Pooja starts by 4:30 AM