Here is the transcript for my podcast about how to see Mercury, Rigel, and globular cluster M79.
Check out the Astronomy.com's interactive star chart to see an accurate map of your sky. It'll help you locate some of this week's key targets. Astronomy magazine subscribers have access to a slew of cool functions with StarDome PLUS.
Each week, I highlight three different night-sky targets for you to see:
This week’s naked-eye object is the naked-eye planet few people have seen — Mercury. On New Year’s Day, you can find Mercury 30 minutes after sunset. It sits 9° high in the southwestern sky and shines at magnitude –0.7. This altitude places it high enough for easy viewing if you have a clear and unobstructed horizon.
That same evening, Jupiter joins Mercury. The giant outer planet lies 2° to Mercury’s lower right and appears some 3 times brighter, shining at magnitude –1.9.
Watch these planets over the next three nights. Jupiter will get progressively lower, while Mercury’s angular distance from the Sun grows. Mercury reaches maximum elongation January 4. That evening, it will set 90 minutes after sunset.
A bright star’s companion
This week’s small telescope target is Rigel (Beta [β] Orionis). Rigel marks the brilliant left foot of Orion the Hunter. And it is, indeed, bright. Rigel is the 7th-brightest nighttime star, shining at magnitude 0.12.
Point your telescope at Rigel, and insert an eyepiece that provides a magnification of about 100x. Just 9" to Rigel’s south, you’ll spot Rigel B, more correctly called Beta Orionis B. This magnitude 6.7 star is Rigel’s companion. Although it’s not all that faint, it can be tough to see if you don’t use enough magnification. That’s because Rigel A shines some 436 times more brightly than Rigel B.
When you do spot Rigel’s companion, what color does it appear to you? Magnified through a telescope, Rigel appears white. To me, through my 4-inch refractor, Rigel B has a definite purple cast. Our color receptors vary widely, however, so the color you see could be quite different.
An oft-forgotten Messier object
This week’s deep-sky object is globular cluster M79 in the small constellation Lepus the Hare. Lepus may be small, but it’s easy to find. Just look directly south of Orion.
To find M79, which, by the way, is the most southerly Messier object in the winter sky, use Alpha (α) and Beta Leporis as pointers. Draw a line from magnitude 2.6 Alpha through magnitude 2.9 Beta and extend that line 3.5°, which is just slightly more than the distance between those two stars.
M79 is among the oldest globular clusters in the Milky Way. Situated 60,000 light-years from the galactic center, this object lies 40,000 light-years from Earth. For all of its magnitude 7.8 brightness, M79 is a difficult object to resolve through small telescopes.
A 10-inch instrument shows that the 8.7'-wide globular has a bright, broadly concentrated core nearly devoid of stars. But crank up the magnification beyond 200x, and you’ll resolve scores of stars as bright as 13th magnitude at the cluster’s edges.
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