Chaya Ganita, or Chhaya Ganit, is the calculations based on shadow in Hinduism and has its roots in man’s observation of the changes in his own shadow during daytime. Starting from the gnomon, this science grew to the extent of using sophisticated astronomical instruments. In Atharva Jyotisha, muhurtas (time divisions) are defined in terms of the shadow of gnomon of twelve angula (finger) size. Details of chayaganita for determining accurately the cardinal points, time, seasons, length of year, obliquity, ascendant etc., have been given in all the texts of mathematical astronomy, which appeared around 4 th century AD or even earlier. For instance, when the sun is at the equinox, its meridional zenith distance is equal to the latitude of the observer. This can be obtained by measuring the equinoctial shadow cast by a gnomon, from which declination of the sun can be calculated. Following this, the obliquity of the ecliptic with the equator could be calculated to be 24 degre