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Stars: A Size Comparison


When people find out that I work in a planetarium they sometimes have questions.  Some of the most frequently asked questions is about stars: what are they, how far away are they, are they explosions or just balls of burning gas.

Basically, what is up with those things we call stars?

Most of the time people think that every star they see in the sky is just like our own star, the Sun.  They know the Sun is a star and that it appears to be larger than the other stars because it is so close to us.  The other stars in the sky are further away, obviously, but they just assume that they’re still relatively the same size as our own Sun.  It’s true that they’re all far away (in varying degrees) but it’s not true that they’re all the same size.

Stars come in a variety of sizes.  The smallest star currently discovered is OGLE-TR-122b. This star is around 96 times more massive than Jupiter. This type of star is called a red dwarf.  The largest star discovered so far is called VY Canis Majoris and has a diameter of about 1,975,000,000 kilometres (1.227×109 mi).  This star is known as a red hypergiant.

This might be hard to wrap our heads around.

For example, the Earth is about 26,000 miles in circumference.  If you were to fly on a commercial jet airliner all the way around the Earth (having to stop to refuel, of course) it would take you about 47 hours.  All the while our own Earth (in its own orbit) takes a year to travel around the Sun.

So how long do you think it would take to fly all the way around the circumference of VY Canis Majoris in that same jet airliner?

Well, I saw a video online a couple of years ago that blew my mind.  It was about star comparisons and it helped illustrate just how big some of these stars are.  If you want to know just how big VY Canis Majoris is and how long it would take you to fly around it in a jet then check out the video.  You might be amazed by the answer.

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