How big is the biggest star? Freakin’ BIG!

One of the great challenges, and thus joys, of studying the universe is getting a sense of the scale of what you’re looking at. We are very tiny. The universe is very large. Language begins to fail here. Large is the smallest cup of coffee you can get at most American coffee shops. We’re talking larger than that.

I’ve been recently chastising my daughter for using the word “ginormous”. I considered it a new, fake kind of word. Isn’t gigantic good enough? Or enormous? Turns out it isn’t that new. Merriam Webster claims it dates to 1948. I find that interesting. 1948 is about when we got our first photographs of the earth from space (as mentioned elsewhere on this blog, taken from the nosecone of a captured German V2 rocket). So maybe “ginormous” has its roots in humankind’s deepening understanding of our own puniness–and the lack of a vocabulary to describe it. So…the universe is ginormous. It eats gigantic and enormous and Starbucks trentas for breakfast, rather like some whales filter krill out of the ocean in their comb/mouth apparatuses.

Talking about how large things are, or how far away they are, at the telescope eyepiece is challenging. The numbers quickly become unapproachable. The Andromeda Galaxy, the farthest object you can see with the naked eye (if the light pollution isn’t getting in the way) is 2.5 million Light Years away. A Light Year is about 6 trillion miles (that’s a 6 followed by 12 zeros). Unless you study the US budget, that doesn’t mean much. Multiply 2.5 million times 6 trillion…well, it’s a ginormous number.

So let’s back away from that one, close the door and say “Whoa”.

2.5 million x 6 trillion = whoa! (actually, it

Let’s try another approach. Go outside around 9pm and look South/Southwest. Find the constellation Orion. If you want, download a free monthly sky chart to help guide you. It’s easy to use, just hold it up with the direction you are facing reading normally, and you should be able to line up the stars in the sky with the chart. We’re going to look at something called the Winter Hexagon. It’s an imaginary asterism (formation of stars) of 6 stars (hexagon!): Sirius, Procyon, Pollux, Cappella, Aldebaran and Rigel.

These stars are all quite interesting in their own ways; they are some of the largest, brightest, or nearest stars we can see, and by comparing them we start to get a sense of the scale of the universe, even if the picture is far from complete. First things first. All those stars you see? They are in the Milky Way, “our” island city of stars. You can’t see any stars that are in other galaxies with your naked eye, though you see the collected light from a whole mess of them when you’re looking at Andromeda, another island city of stars.

We measure the size of stars using our own sun as a standard measure. Our Sun is about 109 times the diameter of the Earth. If you had a bunch of earths and you strung them side by side on a string like popcorn and cranberries on a Christmas tree, you’d need 109 of them to get a string long enough to equal the diameter of the Sun. The diameter of the earth is 7,926 miles, which would make the diameter of the Sun about 870,000 miles.

Let’s start at Sirius, the “dog star” in the constellation Canis Major, or big dog. Sting sings about it. Legends were told about it. The ancient astronomer Ptolemy wrote that it was red, though it’s clearly white–a blazing, shimmering white fitting the Greek meaning of it’s name: Scorcher. Sirius is the brightest star in our sky, not because it’s so intrinsically bright as much as it’s close to us. It’s only 8.6 light years away, which means at the time of posting the light hitting earth from Sirius started it’s journey around the time of the Salt Lake City Olympics, the beginnings of the Enron Case, the invasion of Afghanistan, and around the time the Larsen ice shelf started peeling away from Antarctic, a whopping 1200 miles of ice cracking into the sea. In that time the light travelled 8.6 x 6 trillion= 51.6 trillion miles.

Whoa!  Get in your space car and start driving towards Sirius at 65 miles per hour (watch out in the Oort Cloud–starship troopers love to hang out there and issue speeding tickets). In 92,307,692,307.7 years, you’ll reach Sirius. That’s 92 billion years. The universe is only about 14 billion years old. We need to raise the mileage standards for cars.

Let’s move on to Procyon in the constellation Canis Minor, the little dog. Procyon is also a sun-like star (twice the diameter of our Sun) about 11.41 LY away. It’s intrinsically brighter than Sirius, but farther away, so it only appears as the 7th brightest star in our sky. Procyon, apparently, means “before the dog” in Greek.

Pollux, our next destination, is part of the head pair of the constellation Gemini, the twins. Pollux is a much different star than Sirius or Procyon. It’s an orange giant about 34 Light Years away. Pollux is about eight times the diameter of our Sun, or 856 earth diameters. Give a good look at Pollux. In 2006, a planet was discovered in the Pollux system, a gas giant 2.3 times the size of Jupiter. When I was growing up planets around other stars were just conjecture. Now we have direct evidence of thousands of them.

Capella in Auriga is the 6th brightest star in our night sky. It’s actually a multiple star system consisting of 2 double stars, two giants and two red dwarves. The system is 42 Light Years away, and the two giants are 12 and 9 times the diameter of the Sun. Big, but not nearly as big as stars can get. How many earths would you need to line up to equal their diameters?

Aldebaran in Taurus is our next stop. It’s also an Orange Giant, and it’s 44 times the diameter of the Sun. It’s 65 Light Years away. Notice a pattern? We’re getting larger stars that are farther away. There’s no order or reason to this pattern, it just happens to be that way and we just happen to be taking them in that order so that you feel like we’re leading up to something. We are.

We arrive at Rigel, the foot of Orion. Rigel is 772 Light Years away, and it’s a Blue Supergiant star 78 times the diameter of the Sun! You could line up 8,502 earths side by side and that’s the diameter of Rigel. Send us a few of those earths, by the way, we’re using this one up at an alarmingly fast rate.

Rigel isn’t the biggest star in the Winter Hexagon. What? Didn’t we got through all six? Yes, but there’s a star in the Hexagon that’s even larger. It’s Betelgeuse, and that word means “armpit of the central one” in Arabic. I prefer to call it The Shoulder Of Orion after a great line spoken by Rutger Hauer in his character’s death monologue at the end of the movie Blade Runner. You can watch that here. Chills!

Anyway, Betelgeuse is a Red Supergiant. If we swapped it out for our Sun, its surface would be close to the orbit of Jupiter. It’s 1,180 times the diameter of the Sun and its 140,000 times as luminous. It’s 640 Light Years away. How many earths would it take side by side to equal the diameter of Betelgeuse?

Here’s a little video that compares the sizes of the planets in our solar system, the Sun and some of the largest stars (including the big ones we’ve talked about), though it does so with volume and not diameter. If you go to you can see a great flash animation that compares the diameters of the earth, other planets, sun and these stars. It’s a bit clearer, and you can scroll through at your own pace. Chills!


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