Small. Far away.

Sitting out in the garden the other night, for the weather was clement, I had a sort of Father Ted moment. The clouds were clearing and in the darkening sky I could see some stars. Being cognisant of the locations of the constellations I reasoned that the lower bright star was Sirius and the slightly dimmer one higher and further west was Betelgeuse.

Sirius, The Dog Star or Alpha Canis Majoris if you prefer, is the brightest star in the night sky. Sirius is classified by astrophysicists as a Type ‘A’ star, that is to say it is a star that is bright by its very nature and it’s just under twice the size of our sun at around 2,381,000 km in diameter, our Sun measuring in at 1,391,400 km diameter. Sirius is around 8.6 light years away, that’s about 81,360,000,000,000 km.

Then there’s Betelgeuse, an M1-2 red supergiant star that recent observations put at approximately 427 light years away, that’s around 4,039,700,000,000,000 km. Betelgeuse isn’t as intrinsically bright as Sirius, being a Red Giant, it is somewhat dimmer, but it makes up for that in size.

Notice I’m not being too precise with the figures here, that’s because measuring the distances to stars is still not a precise science. Some authorities quote the distance to Betelgeuse as 530 light years, and some say 642 light years but either way it’s still a long way away.

Sirius is bright as seen from Earth because it’s not only intrinsically bright but by cosmological standards it’s only next door. Betelgeuse is bright as seen from Earth, even though it’s so far away because it’s HUGE. Estimates put the star’s diameter at around 860,000,000 km. That means that if Betelgeuse were somehow magically swapped for our Sun, then Mercury, Venus, Earth and Mars would all be swallowed up by it!

Mind-bending figures really but I’ve always been a big fan of stars and I don’t mind it when they brag about size.

In the evening twilight both stars looked similarly bright, not the same, Sirius clearly the brighter of the two, but Betelgeuse was also quite easily visible. As the sky darkened, other stars became visible, thus confirming my earlier suppositions of which stars the two bright ones were.

Sirius, smaller and close. Betelgeuse, bigger and far away.