The rise of any planet or sun and moon is known as uday in Hindu astrology. The rise of the sun, suryodaya, and that of the moon, chandrodaya, plays an important role in the horoscope of a person. Here is a look at as to how the rise of sun and moon is calculated in Hindu astrology.
‘Rise’ in Hindu astrology means coming up to a level. The rise of sun comes into view two minutes earlier than the actual timing of rising because sun rays undergo refraction. The sun even rises when it is actually half a degree below the horizon. Now, at this virtual rise of the sun, the other planets are yet to rise. So, with reference to other planets, the day has already begun.
The same phenomenon happens when the sun sets. Due to the refraction effect, the sun sets two minutes later than the actual timing. Thus the day is increased by four minutes in all.
The period from one sunrise to another at the same place is called a day in Hinduism. Hence there is a difference between a day at a place and the 24-hour day of a clock. This difference is called velantara. The velantara, the precession of the sun at the vernal equinox (chara period) and the degree of refraction at a place, can determine the rise of sun at that place.
The moon rise in the east after the sun sets. On the new moon day, the sun and moon are in the same nakshatra (asterism). When the moon is at 12 degrees away from the sun and the first tithi, pratipada, of the next lunar month starts, the moon’s rise occurs and a cusp of the moon can be observed.