Jimmy Westlake: The hottest star in the sky | SteamboatToday.com

Jimmy Westlake: The hottest star in the sky

To find the sky’s hottest star, look way down south below the dazzling Dog Star, Sirius, at about 9 p.m. in mid-March. Follow a line from Betelgeuse to Sirius, then keep on going to locate Naos.
Courtesy Photo

To find the sky’s hottest star, look way down south below the dazzling Dog Star, Sirius, at about 9 p.m. in mid-March. Follow a line from Betelgeuse to Sirius, then keep on going to locate Naos.

— Back in my days as a planetarium director, I entertained and amazed youngsters by the busload with stories about the stars, planets and constellations. One of the most unexpected questions I ever got was from a little girl in kindergarten who, after I had gone on and on about the stars in Orion and Taurus, asked me — in the most innocent voice possible — “What would happen if you ate a star?”

Whoa. I had to think fast.

“Well, you would burn your mouth because stars are very, very hot,” I replied.

Then we got into a discussion about just how hot stars are.

“See that red star up there?” I said, pointing to Orion’s shoulder star, Betelgeuse. “Red stars are cool stars. Blue stars are the hottest, like that one in Orion’s foot named Rigel.”

That seemed to satisfy her curiosity.

Stars are assigned a letter of the alphabet to designate their temperature, but not in the usual A, B, C order. The stellar temperature alphabet, from hottest to coolest, is O, B, A, F, G, K, M. The traditional way that astronomy students remember this temperature scale is with the mnemonic “Oh, Be A Fine Girl (or Guy), Kiss Me!” The coolest stars are 3,000 degrees, and the hottest stars are about 40,000 degrees. Our sun, being yellow, is a fairly cool star of temperature class “G.”

That little girl’s question set me to thinking. What is the hottest star you can see with the unaided eye? After a little investigation, I discovered that it is the star Zeta Puppis, also known as Naos. It belongs to the constellation of Puppis, the Poop Deck, and is not far from the sky’s brightest star, Sirius.

To locate Naos, you’ll need an unobstructed view to the southern horizon because Naos never rises very high in our sky. Draw an imaginary line from Orion’s shoulder star, Betelgeuse, to the lower left to find Sirius, then extend that line an equal distance beyond Sirius to the next bright star you see. That’s Naos, the sky’s hottest star.

Hot “O” stars like Naos are exceptionally rare. Recent measurements reveal a surface temperature for Naos of 42,000 degrees, placing it near the top of the list of hot stars, and certainly the hottest visible without a telescope. It emits as much energy as 800,000 suns.

The only reason it looks as faint as it does is because it is so far away — nearly 1,400 light years. If Naos were as close as Sirius (about 9 light years from Earth), it would shine like a second sun in our sky, casting distinct shadows in the night.

Hot stars like Naos also use up their fuel very fast, so they don’t live for long. In just a few hundred thousand years, Naos will go kaboom as a supernova, splattering its innards all over this corner of the galaxy and probably leaving behind the ultimate stellar corpse — a black hole.

Pull out your binoculars and aim them at Naos to appreciate its beautiful blue color, and while you are in the vicinity, scan around for several gorgeous star clusters nearby. This section of the southern Milky Way is loaded with little stellar jewel boxes.

Just be careful not to burn your mouth.

Jimmy Westlake teaches astronomy and physics at Colorado Mountain College’s Alpine Campus. He is an avid astronomer whose photographs and articles have been published all around the world. Visit Westlake’s website at http://www.jwestlake.com.

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