In the recent times, the term "blue moon" has come to mean having two full moons in a month. The term "once in a blue moon" implies some kind of a rarity. The year 2018 is in that sense even more rare in the sense that there are two blue moons in the same year. But is it that much of a rare phenomenon? Having two full moons in a calendar month occurs due to a mismatch in the lunar calendar and our standard calendar. But before going there, let's get some basics in. What is actually the lunar calendar? or what is a lunar month? There are two ways to define the periodicity of a body like the Moon. This occurs because Moon revolves around the observer while the observer also revolves around another object. If we measure the time taken to do a full 360 degree cycle around the axis of the Earth, that period is called the sidereal period (or month). It takes 27.3 days for the Moon to complete this revolution. However there is a slight problem here. Sin...
An amateur's attempts at astrophotography.