What’s the brightest star in the night sky?

Sirius, also known as the ‘dog star’ or ‘sirius A’ is the brightest sky in the night sky. The name means ‘glowing’ in Greek, which is quite fitting seeing as there are only a few planets, the International Space Station and a full Moon that are brighter. 

It’s certainly hard to miss this glowing spectacle in the sky.

Luminosity in astronomy refers to the intrinsic brightness of a star. Just to be clear, Sirius is the brightest or most ‘luminous’ star in Earth's sky, but it is not the brightest star in the universe. It could technically be described as an ‘ordinary’ star that appears especially bright because it is positioned relatively close to Earth - only 8,611 light years away.

Sirius is located in Canis Major constellation, in the southern celestial hemisphere. The Canis Major looks extraordinarily bright in the Earth's sky, no matter where you live.

Did you know? Sirius is more than 20 times brighter than the Earth’s Sun, and more than twice as big. Sirius is classified by astronomers as an “A” type star. That means it’s a much hotter star than our sun; its surface temperature is about 9,400 Celsius in contrast to our sun’s 5,500 C.

Colours?

Many people have said they can see flashes of colour when they look at Sirius. This happens when the star is low in the sky. The colours are created in a similar way that rainbows are made - by the refraction of light. The colour changes are what happens when such a bright star as Sirius shines through the blanket of Earth’s atmosphere. The varying density and temperature of Earth’s air affect starlight, especially when looking at a star low in the sky.The bright ‘colours’ of of Sirius are more easily visible than other stars because it is brighter. 

If you look, you will notice that Sirius shines less and looks less multi-coloured (more strictly white) when it appears higher in the sky.

Brightest Stars

There are brighter or more ‘luminous’ stars in the universe than Sirius. Many stars in the sky are intrinsically brighter than Sirius but appear dimmer because they are further away.

At least three stars in the constellation of Canis Major are believed to be thousands of times more luminous than Sirius: Aludra, Wezen, and Omicron 2.

Astronomers express the brightness of stars in terms of stellar magnitude. The smaller the number, the brighter the star.

The visual magnitude of Sirius is -1.44, ‘lower’ or brighter than any other star. There are brighter stars than Sirius in terms of actual energy and light output, but they are further away from Earth, which means they appear dimmer.

In conclusion, Sirius, the ‘dog star’ is the brightest star visible in the Earth’s sky.