Regal Regulus

May 11, 2015

Regulus in Leo the Lion

  This is “Looking UP! in southern Colorado,” from the Colorado Springs Astronomical Society. I’m Hal Bidlack, and there are lots of reasons to look up!

As you look up in the southern Colorado sky, did you know that you can see a lion? 

The constellation Leo soars in the southern sky this time of year. The brightest star in Leo is the star Regulus. While Regulus is not one of the brightest stars in the sky, it comes in at number 22, it’s fairly easy to find, as it appears to be the dot at the bottom of the backwards question mark, which you will find a little to the left of the very bright planet Jupiter.

Regulus is a fascinating star. It’s about 77 light years away and we are glad that it is. If Regulus were to swap places with our sun we only have a few minutes to wonder what the heck was going on before all life on earth was extinguished. Regulus is about four times bigger than the sun and is much hotter, putting out more than 350 times as much energy.

But the really strange thing about Regulus is how fast it spins. While our sun takes just about a month to complete one rotation, Regulus, even though it’s much bigger, rotates once in less than 16 hours!

Let me give you a sense of how fast that spin really is. If you were to fly down to Ecuador and stand on the equator, the Earth would be spinning you around at about 1000 miles an hour. If you could stand on the equator of the sun, you would be spinning at about 4500 miles per hour. But if you are standing on the surface of Regulus, you would be spinning at 700,000 mph.

Regulus is spinning so fast that it bulges out at the equator like a partially squashed tennis ball. It is so squashed that the gravity is different at the poles than it is at the equator. If it were spinning even 10% faster, it would tear itself apart.

All that violent, hot spinning comes at a cost. Stars like Regulus burn through their fuel much faster than our sun does. Happily, our sun may live to be about 10 billion years old, but Regulus, a baby star at only a few hundred million years old right now, will burn out fairly soon, astronomically speaking.

If you’d like to take a closer look at the Regulus or any of the other wonderful and amazing things in the sky, please visit or for a link to information on our monthly meetings and our free public star parties! 

This is Hal Bidlack for the Colorado Springs Astronomical Society, telling you to keep looking up, Southern Colorado