The universe is estimated to have a hundred billion galaxies each with a hundred billion stars! One of them is Our Galaxy (the Milky Way) and, when viewed sideways from the edge it looks like a disc with a bulging middle. It stretches over 100 thousand Light Years from edge to edge. (Light Year = the distance light travels in a year = about 10 thousand billion km).
Our Sun, an average star by cosmic standards, is located twothirds the way from the center of the Milky Way. The sun along with eight planets and innumerable small bodies revolving around it comprise our Solar System. Our Mother Earth is the third planet from the sun at a distance of 150 million km (one Astronomical Unit or 1 AU). Mercury, the closest to the sun, is at about 0.38 AU from the sun and Neptune at 30 AU.
There was a ninth one, Pluto, at 40 AU, which was demoted from the rank of a planet in 2006. Carl Sagan, the renowned astronomer, described the....
