Ask ARSE: How big would Betelgeuse appear if it replaced the Sun?

Ask ARSE: How big would Betelgeuse appear if it replaced the Sun?

G’day campers, it is I; Kathy from HR at ARSE to answer the questions of our followers yet again. 

Today’s question comes from Michael Slater from one of the more overrated places in Australia, the Gold Coast. 

Take it away Matthew…

“Hey guys how big would Betelgeuse be to us if we replaced the Sun with it?”

First off, don’t call me a guy Mark. 

Secondly, it’s super difficult for most common folk to grasp the size of Betelgeuse. Even though it is large but it is not the largest star we can see. In fact, Betelgeuse is the 10th brightest star on a given night. 

What is Betelgeuse?


Classified as a red supergiant of spectral type M1-2, Betelgeuse is one of the largest stars visible to the naked eye. 

Calculations of Betelgeuse's mass range from slightly under ten to a little over twenty times that of the Sun. For various reasons, its distance has been quite difficult to measure; current best estimates are on the order of 500–600 light-years from the Sun – a comparatively wide uncertainty for a relatively nearby star. Its absolute magnitude is about −6. Less than 10 million years old, Betelgeuse has evolved rapidly because of its large mass and is expected to end its evolution with a supernova explosion, most likely within 100,000 years.

So, it’s big. Real big. 

But how big would it seem if we swapped it for our Sun?

Calculating the difference.

Betelgeuse is 1.234 billion km or (767 million miles) wide. Now we know the Earth is only 149.67 million km or (93 million miles) from our Sun. To get the width of Earth’s orbit you would double that and add a million. 

Why add a million? 

Because we have to consider the current size of the Sun, but it is less than a million miles wide. The Sun is actually only 1.391 million km or (864,364 miles) wide. 

So the Earth’s Orbit is approximately 301 million km or (187 million miles) wide plus or minus 1 million miles due to the elliptical shape of its orbit. Mars’ orbit is 455.44 million km or (283 million miles) wide.

But enough of that…

How big would Betelgeuse look to us on Earth?


Again, really big. But... For about a millionth of a second.

And then everything we ever knew about reality would be dust.

Because Earth would be inside of Betelgeuse, if Betelgeuse was where the Sun is. 

So much so that Earth would be closer to the center of Betelgeuse than to the outer edge. The outer edge of the star would be closer to where the asteroid belt is.

If Betelgeuse were at the center of our Solar System, its surface would lie beyond the asteroid belt and it would engulf the orbits of Mercury, Venus, Earth, and Mars.

The size of Betelgeuse does not come close to the orbit of Jupiter. The orbit of Jupiter is 1.566 Billion km or (973 million miles) wide. So Betelgeuse is 331.52 million km or (206 million miles) less than the orbit of Jupiter.

I hope this answers your question mate.
If it doesn’t, there's something going on with you.

Cheers and keep spreading ARSE,
Kathy from HR

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