At a party a few days ago, I was standing outside with a couple of friends viewing the incredible night sky when we started talking about the magnificent vastness of space. One of them brought up having heard of a single star that was greater than the entire Milky Way galaxy – which is pretty freaking huge! I was skeptical, seeing as from what I know of stars there is a top limit of both mass and size, when the star will collapse onto itself, exploding into a supernova. Stars can be incredibly huge, but as large as the Milky Way, which itself contains several hundred billion stars?

See the Earth dwarfed by our Sun, and it dwarfed by the ginormous VI Canis Majoris, the greatest star discovered. (ill. D. Jarvis)

Stars can indeed be pretty huge, but it’s impossible to keep track of the big numbers. The standing fact, I confirm after a few minutes of researching, is that while stars are huge, the galaxy is a lot huger. In the end it’s like comparing an A2 poster to North America – surely a poster can be pretty big, but an entire continent plays in a different league altogether.

Our own star, the Sun, is about 1 392 000 km in diameter, 109 times the size of the Earth. That’s a tad smaller than your random star in the universe, and there are lots of different kinds of stars both smaller and greater. Our Sun is very much a dwarf, and there are many stars that are several orders of magnitude larger. The greatest star discovered in the universe is VY Canis Majoris, a red hypergiant 2000 times the size of the Sun!

Our Sun as compared to the largest known star. (ill. Mysid)

That’s large. That’s large enough to stretch through a great deal of our solar system. If VY Canis Majoris for some reason suddenly replaced our star, the entire Earth would be engulfed in its flames, as would Mercury, Venus, Mars, the Asteroid Belt, Jupiter and Saturn. Cool, but not nearly as big as the galaxy – that’s several hundred billion times larger.

Illustrations: ”Comparison stars and planets” by David Jarvis (CC BY-SA 3.0), ”Sun and VY Canis Majoris” by Mysid (public domain).

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