An annular solar eclipse will be visible on 26th December2019 in parts of Kerala and Tamil Nadu. The annular solareclipse will be fully visible in Coimbatore. In this article,we explore a few basic things about the Earth, Moon, Sunsystem and explain how, why, and when solar eclipses happen.We emphasise that using elementary trigonometry anda simple calculator one can understand many important featuresof solar eclipses. In particular, we estimate the durationof the eclipse and the size of the shadow of the Moon on theEarth.