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61 Cygni
Nearby Double Star System
HR 8086, HD 201092, PPM 86049, HIP 104217, NSV 13546, TYC 03168-2798 1, GSC 03168-2798
Visual Magnitudes: 5.2 + 6
Apparent Separation: 30.5"

Minimum requirements to view: any telescope under urban skies


This multiple star system is among the most interesting in the sky. A mere 11 light years distant, the stars of 61 Cygni are among our closest neighbors. The primary (A) is a cool K5 main sequence star that is suspected to be variable (from 5.19 to 5.27 magnitude). The B component is a cool K7 dwarf that is also suspected of variability (a tiny variation from 6.02 to 6.09 magnitude). The orbit for these stars is indeterminate, but an orbital period of at least 700 years is indicated.

61 Cygni lies to the southeast of Deneb. Look for a triangle of stars of similar brightness. 61 Cyg is the westernmost. North is up and east is left.
In 2009 these stars are 31.3" apart, making them easy in any scope. The cool surface temperatures give them a ruddy orange hue that really makes them stand out in the field. The fainter star is a slightly darker red-orange. These stars are near enough to us that their motion relative to the sun is visible in just a few short years. When you look at this ruddy pair in the eyepiece imagine them drifting to the northeast against the stationary background stars.

The view in a 6" at 152x. The first image represents the appearance in August 2009. The second is how things will appear in August 2019. North is down and east is to the right.

In addition to their motion across the sky, the two stars orbit one another over a period of about 650 years.  The pair is currently widening slowly as they approach maximum separation in about 2091.

It is a testament to how how much fainter the  low-mass stars such as these are that the components of 61 Cygni appear apprciably fainter than stars of similar distance, such as Sirius (-1.5 magnitude) and Procyon (0.4 magnitude). The low mass stars are also cooler which gives them a distinct reddish hue. The mass of each of the 61 Cygni stars is around 1/2 that of the sun and produce 1/6 as much light. Sirius, on the other hand, has a mass around 2.5 times that of our sun and is 40 times brighter.  

The most massive stars start out with much more fuel to burn, but they burn it so fast that they live very short lives. The components of 61 Cygni will be around for tens of billions of years--long after Sirius and our sun are gone. As such, this pair of stars will be drifting across the sky long after our sky is gone...
 

Millennium Star Atlas Vol III Chart 1146
Sky Atlas 2000 Chart 9
Uranometria 2000 Vol I Chart 121
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