Double stars

Urban Orion

The constellation of OrionOrion is not only the best known winter constellation, but it is also a great urban constellation. Thanks to its distinctive arrangement of rather bright stars, Orion shines through in heavily washed-out skies, even when few other constellations can recognized. It is also the home of the Great Orion Nebula (M42) big, bright, and easily visible even in washed-out skies. However, M42 is only the most famous of many interesting astronomical objects in Orion. And best of all for urban astronomers, quite a few of Orion's objects—like the constellation itself—can be enjoyed in light-polluted skies. Here is a run down...


Hunting the Great White Dwarf

In the early 1900s astronomers were stunned to discover that some stars had masses comparable to the Sun's but packaged into earth-sized volumes. The first such stars discovered were spectral type A (white) and thus became known as White Dwarfs. The most famous white dwarf is Sirius B, the companion to Sirius. Most white dwarfs don’t make good targets for washed-out astronomers because they are faint, inconspicuous stars or are hard to see companions to bright stars such as Sirius. But there is one white dwarf that is easy: 40 Eridani B.

40 Eridani A, B, & C by David Darling40 Eridani (also known as ο2 Eridani or Keid) is a relatively bright 4th magnitude star. Even in urban areas, it is easy to find by star-hopping from Rigel going via β Eri, μ Eri, and ν Eri. I recently did it from my light polluted front yard using a 50mm finder. Even looking directly over my neighbor’s very bright holiday lights it was an easy hop. 40 Eridani is a triple star system. The primary has magnitude 4.4. Component B—the white dwarf—has magnitude 9.5 and is widely separated from A (83”, PA 105°) making it easy to see in even small telescopes. (Image courtesy of David Darling)

As a special prize, the third component C is a red dwarf flare star of magnitude 11.2. The B-C separation is much tighter at about 8” but it isn’t hard to split except for the faintness of the C component. You’ll probably need at least a 4 inch (100mm) aperature to see C in washed-out skies, but it’s rather easy with 6 inches (150mm) or more. In my 10 inch (250mm) Dob, it looks pretty much like the photo above.

So don’t miss the chance to “bag” a white dwarf. If you want to learn more about white dwarfs, read the excellent Wikipedia article. Now 40 Eridani is interesting for several other reasons, including a connection to Star Trek....


Kruger 60

Triplet of pictures showing Kruger 60's orbital motionKruger 60 is a particularly interesting binary star system in Cepheus. With a short period of only 44.7 years, you can easily see Kruger 60’s PA change about 8 degrees per year. There’s even a convenient nearby reference star that makes the change in PA obvious. Only 13 light years away, Kruger 60 is also one of Earth’s nearest neighbors. Both components are low-mass red dwarfs, but with only 0.18 solar masses, Kruger 60 B is one of the lowest mass stars known. Finally, Kruger 60 B is also a flare star, irregularly doubling in brightness for periods lasting about 5 to 10 minutes. When it flares, it can match or exceed Kruger 60 A in brightness.

Kruger 60, however, is a challenging target for observers in light polluted environments. If you want to take on this challenge, I have more information for you…


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