The star Sirius, also known as the Dog Star, is the brightest star in the night sky. The brightness of the star is caused by the amount of energy that the star gives off in all directions.
In 1844, The German astronomer, Friedrich Wilhelm Bessel, first reported Sirius was a binary star, which means two stars orbiting together. He noticed they were on a different path from their neighbor stars and concluded that they were revolving around each other, which takes a period of about 50 years. The companion first was seen in 1862 by Alvan Clark, American astronomer and telescope maker.
The average separation between Sirius and its companion star as they orbit together, is about 20 times Earth’s distance from the Sun. Despite the glare of the brighter star, the companion star can be seen with a telescope.
The ancient Egyptians called Sirius the Sothis star. The Egyptians noticed that Sothis appeared the first time every year at about the same time the Nile River flooded which is at the hottest time of the year. The expression “dog days” comes from the fact that this is the time of year that the Dog Star rises.