Star greater than the Milky Way?

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).

The Beautiful Cosmos: Rhea

The Cassini probe recently caught some new breath taking pictures of Saturn’s second largest moon Rhea, a beautiful astronomical body. Wow. I recently wrote about the beauty of our own moon, and it’s amazing to ponder about the countless number of similar bodies out there.

Click to embiggen.

NASA · Space Daily · Tom’s Astronomy Blog · Yahoo

The Beautiful Cosmos: Jupiter

Jupiter has grown to become one of my absolute favourite planets in the last few months. Not sharing Mars’ potential for life, Saturn’s fantastic rings or Uranus unfortunate name, it’s often an overlooked planet, which is kind of a shame. It’s the biggest planet in the solar system, it’s mass being as much as two and a half times that of the rest of the planets combined. In other words, it’s freaking huge, and for that reason it’s also one of the most visible planets in the night sky throughout the year. Right now, it is clearly outmatched by Venus, and Mars is almost as bright, but throughout most of the year, when you look around and find a really bright spot… that’s Jupiter. If you get a small telescope and point to it, you’ll probably not only see the planet but also the four biggest of its dozens of moons – Io, Europa, Ganymede and Callisto. Europa is visible in the Cassini picture below (the dot in the lower left), and is definitely my favourite moon of the solar system, enough to warrant a future ”The Beautiful Cosmos” post.