Sirius

Sirius, the Dog Star, is the brightest star in the night sky at magnitude -1.46. It is a white main-sequence star of spectral type A1V located only 8.6 light-years from Earth, making it one of our closest stellar neighbors. Sirius is actually a binary system: Sirius A, the brilliant primary, is about twice the mass of the Sun and 25 times more luminous, while Sirius B is a faint white dwarf companion orbiting with a period of about 50 years. The white dwarf, though roughly the size of Earth, packs nearly a full solar mass into that tiny volume.

Unmistakable as the brightest star in the sky, Sirius dominates the constellation Canis Major during winter evenings in the Northern Hemisphere. It often twinkles vigorously in multiple colors when low on the horizon due to atmospheric refraction. The white dwarf companion Sirius B (magnitude 8.5) is an extremely challenging target, requiring at least a 200mm telescope at high magnification during moments of excellent seeing — the glare of Sirius A normally overwhelms it. The best window is when the pair is near maximum separation (about 11 arcseconds, next around 2025). Best observed from December through March.

Sirius has been significant to virtually every ancient civilization. The ancient Egyptians based their calendar on its heliacal rising, which heralded the annual flooding of the Nile and the start of their new year. The Greeks associated it with the scorching heat of late summer, giving us the term 'dog days.' The companion Sirius B was predicted by Friedrich Bessel in 1844 from wobbles in Sirius A's proper motion and first observed by Alvan Graham Clark in 1862. It was one of the first white dwarfs ever identified.