Our sun is pretty small
Our sun is pretty small

Compared to other stars, our Sun is very, very small

If you look at the size of our Sun, compared to the planets in the solar system, you’d be forgiven for thinking that it’s a tad on the large side. After all, it has a diameter of approximately 864,400 miles (1,391,000km), which is 109 times the diameter of the Earth. In fact, it is so amazingly massive that you could fit about 1,300,000 Earths inside it. And in case that comparison wasn’t ridiculous enough, if you flew a jumbo jet (a fire proof one, obviously) around it at 600mph, it would take over half a year to do a complete circuit.

So yes, our Sun is pretty big. Or is it? Well, so far we have discovered many, many stars and we have managed to get a fair approximation of their respective sizes. The measurements are not entirely accurate due to factors such as their uncertain distance from Earth and some stars being surrounded by thick atmospheres or dust shells. However, even taking on board a realistic margin of error, we still get a pretty good idea of just how massive some of these stars are.

 The unit of measurement used to denote their size, commonly used by scientists, is the solar radii, which is equal to the radius of our Sun. So, just to be clear, one solar radii is the same as the radius of our, supposedly massive, Sun. Which is 695,700km (432,288 miles).

Let’s just jump right on in there and pull out the brightest star in our night sky, Sirius. It is about 1.7 solar radii. Nearly twice the size of our Sun. I could keep on creeping up the size charts in this way but I’d like to go home before Christmas if that’s ok. So, let’s leap up to a fairly cool sounding star, The Pistol Star. Known as a blue hypergiant, it’s size is approximately 306 solar radii. In case you missed it, that’s 306 times the size of our Sun.

But we’ve only got started. So, hold on to your hats because I’m going to step it up a bit. Betelgeuse, which is the ninth brightest star in our sky, is called a red supergiant. It measures about 887 solar radii. It should be pointed out that there is a possible margin of error : ± 203 solar radii, but even taking that into account it’s pretty blooming big.

Not quite the largest though.

Let’s stop mucking about with twinkle twinkle little stars shall we. The largest known star discovered so far is called EY Scuti. EY Scuti comes in at a massive, wait for it, 1708 solar radii. Like Betelgeuse, it is also a red supergiant. The measurement has a possible margin of error of ± 192 solar radii, but quite frankly, who cares? It’s massive!

Comparing the largest star with our Sun, when you’re on the beach

While playing on the beach and talking about the universe with my 6 year old son (we do this a fair bit), I had an idea of how to show him just how big EY Scuti is compared to our Sun. I found a tiny stone approximately 1mm in diameter. “This”, I said, “will be our Sun. Now, I’m going to draw a circle next to it. This circle will be EY Scuti”. I drew the circle in the sand next to our 1mm Sun. It was just shy of 2m in diameter.

By Graham Foster
Graham is a graphic designer with a passion for science

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