Sidereal Time

Sidereal time is "true" time measured from the movement of the planets wherein a normal day is slightly shorter (approximately 4 minutes) than a clock day. Birth time is converted into sidereal time for the latitude of the birth place in order to calculate the house cusps.

Sidereal time is needed to find the sign and degrees of the Ascendant and Midheaven in order that the rest of the chart can be calculated. Astrological time data is listed in sidereal time units. 

Sidereal Month      Sidereal Zodiac