To visualize how far away the Sun is, think about it like this: the Sun is 100 Suns away from us. So if the Sun were a basketball, you could imagine lOO basketballs lined up, and that’s how for away the Sun would be. This distance is known as an AU, or Astronomical Unit. If planes could fly through space, going to the Sun would be an 18—year flight.
We can also use the AU to visualize the size of the Solar System. Mercury, Venus Earth and Mars are 1/3, 2/3, 1 and 1.5 AU from the Sun. Jupiter is 5 AU away while Saturn, Uranus, Neptun and Pluto are conveniently about 10, 20, 30 and 40 AU from the Sun, respectively.
Enif is a massive dying star, which doesn’t mean it is calmly enjoying the rest of its old age. Enif — or Epsilon Pegasi — is known for its erratic and violent behavior. In 1972, the star was observed to release some kind of enormous flare, five times brighter than normal. These kinds of events are only poorly understood and only about 24 of them are documented, so we don’t know what irritated it. But if we were constantly stalked by gawking researchers we’d probably be grumpy too.
A blue-white supergiant in the constellation Cygnus, Deneb is over 50,000 times brighter than the Sun. It’s pretty far from us though — 2,615 light years — so it’s only the 19th brightest star in our sky.
This blue hypergiant with the catchy name is one of the brightest stars in the Milky Way and led the list of the largest stars for a while. Unfortunately, it can’t be seen with the naked eye since it is hidden behind interstellar dust. The brighter a star is, the more mass it ejects constantly, and every 20 seconds the Pistol Star radiates as much energy as the Sun does in one year.
Rho Cassiopeioe is one of the very rare yellow hypergiants. They live hard and die fast — our Sun in comparison is much more grown-up and is a hundred times older than the average yellow hypergiants can get. Rho Cossiopeiae is a whopping 3,400 light years away from us. But it’s insane luminosity — 500,000 times that of our Sun — means we can still see it with the naked eye.
The Romans thought the reddish star looked similar to the red planet Mars, which is called Ares in Greek, so they named it Antares, the Anti—Mars. Antares has reached the final stage of its lifespan and will possibly explode within the next ten thousand years. On Earth this would be seen as bright as a full moon that would be visible even during the day for a few months. So let’s root for it to explode soon because that would be cool.
Betelgeuse, aka Orion’s left shoulder, is an unfathomably large red hypergiant star and one of the brightest stars in our night sky. Betelgeuse has a diameter 887 times that of the Sun, and you could fit 700 million Suns inside of it or around a quadrillion Earths. Betelgeuse is rapidly shrinking, and scientists expect it to run out of fuel and go supernova within the next 100,000 years. When it does, it won’t hurt us — it’s on safe 640 light years away — but it will become as bright in our sky as a full moon!
This fatso is 1,420 times the diameter of our Sun. To put that in perspective, if VY Canis Majoris were the height of a 50—story skyscraper, the Sun would be a grapefruit, and the Earth would be a grain of sand 1 mm across.
Picture a grain of sand on top of on SUV. That’s what the Sun would look like on top of Stephenson 2—18. If you wanted to fly in a passenger plane around this star once, it would be a 9-million—hour flight — a little over 1,000 years — and even in a lightspeed ship, the journey would take 8.7 hours. And if our home star were Stephenson 2—18 instead of the Sun, it would be bigger than Saturn’s orbit, and Uranus would be the new Mercury.
Stephenson 2—18 was probably born as a main sequence star a few tens of times the mass of the Sun and has likely lost about half its mass by now. While typical red hypergiants are in the ballpark of 1,500 times the size of the Sun, the largest rough estimate places Stephenson 2—18 at an absurd 2,150 solar radii and shining with almost half a million times the power of the Sun.
Stephenson 2—18 is the largest known star… kind of. The tricky thing is, red hypergiants are extremely bright and far away, which means that even tiny uncertainties in our measurements can give us a huge margin of error for their size. Worse still, red hypergiants are Solar-System—sized behemoths that are blowing themselves apart, which makes them harder to measure. As we do more science and our instruments improve, whatever the largest star is will continue to change.
Keishinrei 