Sirius is the brightest star in the sky after the sun, and is almost twice as bright as the next brightest star. Sirius appears so bright because of in luminousity and proximity to the Earth.
Though the star appears to be a single star, Sirius is actually a binary star system consisting of a main-sequence star and a faint white dwalf companion. The larger star is twice as massive as the Sun.
Although usually white to blue white in colour, Sirius is called a rainbow star because it often flickers with many colours. This is not unusual for stars, as the Earth’s atmosphere makes many stars appear to flicker. But since Sirius is so bright, it is more noticeable than others.
To find Sirius, trace a line through Orions's Belt away from the Hunter's Bow. The star is about eight times away from the Belt as the Belt is wide.