Page:Aryabhatiya of Aryabhata, English translation.djvu/101

 The sine of co-latitude is the koți (the side perpendicular to the base) or sanku (gnomon).

"24. Subtract the square of the sine of the given declination from the square of the radius. The square root of the remainder will be the radius of the day-circle north or south of the Equator."

The day-circle is the diurnal circle of revolution described by a planet at any given declination from the Equator. So these day-circles are small circles parallel to the Equator.

"25. Multiply the day-radius of the circle of greatest dadting: tion (24 degrees) by the sine of the desired sign of the zodiac and divide by the radius of the day-circle of the desired sign of the zodiac. The result will be the equivalent in right ascension of the desired sign beginning with Mega."

To determine the right ascension of the signs of the zodiac, that is to say, the time which each sign of the ecliptic will take to rise above the horizon at the Equator.

"26. The sine of latitude multiplied by the sine of the given declination and divided by the sine of co-latitude is the earth-sine, which, being situated in the plane of one's day-circle, is the sine of the increase of day and night."

The earth-sine is the distance in the plane of the day-circle between the observer's horizon and the