Looking Up: Betelgeuse, dimmer but no less awesome - McDonough Voice

Winter nights are always full of celestial treasures. There are more of the brightest stars (magnitude +1.0 and brighter) in the evening sky than at any time of year. The spectacle makes it worth bundling up and braving the chill if you live in typically cold winter regions as I do. This winter, one of the most famous of these stellar beacons has mysteriously dimmed!

Yes, it is Betelgeuse, topic of one of these columns a few weeks ago but still attracting a lot of attention from casual stargazers to professional astronomers sharing the awe and asking, “what happened?”

Surely we all ask, “when will it come back?”

Betelgeuse is the famed red-orange supergiant star marking the upper left (east) corner of the figure representing the constellation Orion the Hunter. Although well known as a slow but fairly slight variable star, it’s never been this dim.

It’s still easy to see Betelgeuse; it isn’t THAT dim. It’s just its curious change has enthralled us.

Typically, Betelgeuse is around magnitude +0.5. It started dropping last October; as of Jan. 28, the American Association of Variable Star Observers (AAVSO) reported its brightness as +1.64.

This is very close to the blue-white light of Bellatrix, the star marking the top right (west) corner of Orion. Magnitude +1.6 is getting very close to 2nd magnitude, the brightness of most of the stars of the Big Dipper, the North Star and the three “belt stars” of Orion’s mid-section.

Don’t get me wrong, 2nd magnitude is very respectable although fairly common as naked-eye stars go. We give thanks for stars of 2nd magnitude and brighter. With the abundance of light pollution in populated areas, and on any bright moonlit night, it is these stars that are seen the best, and they allow the most well-known constellations to be recognized by the populace, inspiring us to “look up” for a closer look.

On the magnitude scale, the lower the number, the brighter the star. It would seem to make sense that the night sky’s brightest star would be “0 magnitude” but it isn’t; the brightest is Sirius, to the lower right of Orion (magnitude -1.58). Planet Venus, very prominent in the southeastern evening sky this winter, is around -4.0. The full Moon is -12.0. Our sun is -27! On the lower end of the scale, the faintest star you can typically see with unaided eyes in a rural location is around +6.0. A 6-inch telescope easily takes you to really dim, +12 magnitude stars. Each magnitude is 2.5 times brighter than the one below it.

An article by Bob King posted at skyandtelescope.com relates theories about Betelgeuse’s behavior. The star has made an unusual drop in temperature and luminosity; as it fades, the already massive star had expanded its radius by about 9%.

Others suggest that the star has expelled enough gas and dust clouds to partially obscure its light. Given its known approximate 420-day variability, one astronomer predicts its unusually low point is bottoming out.

There’s a lot more technical data and information on the AAVSO website (aavso.org). In the “Pick a Star” box, type “Betelgeuse” and then click the action you want.

Meanwhile, don’t miss the rest of the sky. Mercury, the planet closest to the sun, is well placed right now, low in the bright dusk. From a site with a low horizon acing southwest, start looking about 30 minutes after sunset. Binoculars will aid you! Venus is much brighter and higher, to the upper left.

Enjoy the first quarter moon, Feb. 1.
Keep looking to the sky!

Peter Becker is managing editor at The News Eagle in Hawley, Pennsylvania. Notes are welcome at news@neagle.com. Please mention in what newspaper or website you read this column.