Understanding the Night Sky

As the sun sets in the west, the stars appear to shine in the sky. The starry skies are called the night sky. The night sky as seen from a big city comprises of Moon, Planets (if visible) and a few bright stars like Vega, Sirius, Arcturus and Capella. From a dark sky location, the night sky will offer views of over 6,000 stars, Pleiades, Beehive and Perseus star clusters, Andromeda Galaxy and Orion Nebula along with Milky way arm in the sky. The night sky has been categorised in 7 different scales called Bortle Scale. “The Bortle scale is a nine-level numeric scale that measures the night sky’s brightness of a particular location. It quantifies the astronomical observability of celestial objects and the interference caused by light pollution. John E. Bortle created the scale and published it in the February 2001 edition of Sky & Telescope magazine to help amateur astronomers evaluate the darkness of an observing site, and secondarily, to compare the darkness of observing sites. The scale ranges from Class 1, the darkest skies available on Earth, through Class 9, inner-city skies. It gives several criteria for each level beyond naked-eye limiting magnitude (NELM).”