THE SOUTHWORTH PLANETARIUM

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43.6667° N    70.2667° W  Altitude:  10 feet below sea level Founded January 1970

2021-2022: CXXXVI

"Education is not the filling of a pail, but the lighting of a fire."

-William Butler Yeat, who, if he were still alive, would be celebrating his 157th birthday today!

THE DAILY ASTRONOMER Monday, June 13, 2022

Red Star Rising

Betelgeuse, often dubbed the "Winter sky red supergiant," is now so close to the Sun in our sky as to be completely hidden from view. In fact, it will remain concealed by the solar glow until late July. However, Antares, known as the "Summer sky red supergiant" is now rising in the southeastern early evening sky. Marking the heart of Scorpius the Scorpion -see image below- Antares, like its counterpart Betelgeuse, exudes a distinctive reddish glow.

We can perceive the colors in both stars because they are unfathomably enormous. One could fit 160 million Suns within Betelgeuse and 330 million Suns inside Antares. (Remember that 1.2 million Earths could fill the Sun's interior.) The graphic below, taken from Earthsky.org, gives one a notion about these sizes. The Sun, or Sol, is that one-pixel wide dot at the far left of the lower row.

Antares and Betelgeuse never appear together in our sky because they are almost diametrically opposed in the galaxy relative to the Sun's position.      Betelgeuse is 620 light years farther away from the galactic center than the Sun, while Antares is 440 light years closer.       Mythologically, Betelgeuse and Antares are separate because their respective host constellations, Orion and Scorpius, were placed at opposite ends of the sky.    At the insistence of Artemis, goddess of the moon and protector of wild animals, Scorpius slew Orion before he made good his promise to kill every animal on Earth.    Concerned that Orion would seek to avenge his own death on Scorpius, they were set so far apart that they'll never appear in the sky simultaneously.    In mid-spring, Orion sets with the Sun while Scorpius moves into the eastern evening sky.  In late autumn, Scorius will vanish into the dusk while Orion ascends in the eastern evening sky.

Although they look similar to each other in our sky, a couple differences distinguish  Antares and Betelgeuse.  First, as Betelgeuse is about 8 degrees north of the celestial equator, it spends about 12.5 hours above the horizon each day. (Yes, including those days when it is not visible.) Antares, located about 25 degrees south of the celestial equator, is only above the horizon for about eight hours.    In our sky, it glides along a low path through the southern sky.     Even when it reaches its highest altitude -when crossing the meridian- Antares only rises 21 degrees above the southern horizon.  In contrast, Betelgeuse passes 55 degrees above the due south point when attaining its highest altitude.     Whereas the winter red supergiant remains a prominent evening sight from late autumn to early spring, Antares creeps inconspicuously along the evening sky from late spring to mid autumn.    Secondly, Betelgeuse is also the brighter of the two stars.  At magnitude 0.5, Betelgeuse is the 10th brightest star in our sky.  Antares, at magnitude 0.96, is the 15th brightest star.   (As both stars are variable, these magnitude values are averages.)

Although it might be the more obscure of the two bright supergiants,  Antares is now open to view low in the southern evening sky. 

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