Canis Major
Canis Major contains Sirius, the brightest star in the night sky, known as the "dog star". It is bright because of its proximity to the Solar System. In contrast, the other bright stars of the constellation are stars of great distance and high luminosity. At magnitude 1.5, Epsilon Canis Majoris (Adhara) is the second-brightest star of the constellation and the brightest source of extreme ultraviolet radiation in the night sky. Next in brightness are the yellow-white supergiant Delta (Wezen) at 1.8, the blue-white giant Beta (Mirzam) at 2.0, blue-white supergiants Eta (Aludra) at 2.4 and Omicron at 3.0, and white spectroscopic binary Zeta (Furud), also at 3.0. The red hypergiant VY Canis Majoris is one of the largest stars known, while the neutron star RX J0720.4-3125 has a radius of a mere 5 km.
R136a1
At around , R136a1 is the most luminous star known, radiating more energy in four seconds than the Sun does in a year. If it replaced the Sun in the Solar System, it would outshine the Sun by 94,000 times (M = −7.6) and would appear from Earth at magnitude −39. Its brightness at a distance of 10 parsecs, the absolute visual magnitude, is −7.6, three magnitudes brighter than Venus ever appears from Earth. Its brightness at the distance of the nearest star to Earth, Proxima Centauri (just over a parsec), would be about the same as the full Moon.