Kruger 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…
With a separation that varies from about 2” to 3” Kruger 60 should not be particularly hard to split with telescope apertures of 4 inches (100 cm) or more. What makes Kruger 60 challenging for modest apertures is that the two components are not only relatively faint, but also differ in brightness by nearly two magnitudes: Kruger 60 A is magnitude 9.6, but Kruger 60 B is only magnitude 11.4. You need good seeing, good optics, and a somewhat dark night to split Kruger 60. With my 10 inch (250 cm) Dobsonian (which has “okay” but not really great optics), I usually need a moonless night with pretty steady seeing (at least 4 out of 5) to split it.
The other challenge is actually finding Kruger 60. It sits in a field with plenty of other 9th and 10th magnitude stars. You can generate a good finder chart using your favorite astronomy atlas software (other names for Kruger 60 are HD 239960 and ADS 15972). Don’t use the finder chart in Burnham’s Celestial Handbook: it isn’t accurate anymore due to Kruger 60’s proper motion of about 1” per year.
You can also generate your own finder charts using the AAVSO Variable Star Plotter [2]. I have pre-generated the AAVSO charts at “standard” B and C scales, oriented with north at the top and east on the left. I’ve also labeled δ Cephei. The numeric labels indicate the visual magnitudes of the adjacent stars (as is standard on AAVSO charts decimals are omitted, so “89” means magnitude 8.9).
