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Nov 3
Binocular Highlight by Mathew Wedel
T
railing behind the southeastern wing of Cygnus,
the Swan, is one of the most fascinating double
stars in the sky: 61 Cygni, also known as “Piazzi’s
Flying Star.” In 1792, the Italian astronomer Giuseppe
Piazzi noted that his own observations of 61 Cygni
differed from those of 40 years earlier. Piazzi made
repeated measurements and published his own
results in 1806. The system is moving across the
sky at 5′′ per year, which in technical terms is “really
trucking.” This is one of those happy cases in which
a historical discovery can be re-enacted by any inter-
ested amateur today — more on that in a bit.
I have three pie ces of homework for you, each
requiring different gear. The fi rst uses no optical
equipment at all: Try and pick out 61 Cygni with your
naked eyes. It’s not easy, especially if there’s any light
pollution, but it’s doable, and I fi nd that I have a better
gut-level knowledge of where things are in the sky if
I’ve directly laid eyes on them.
The second assignment is to split 61 Cygni using
binoculars. The two stars are currently separated by
31.8′′, which makes them a bit tighter than Albireo
(34.6′′). The split is technically feasible with 10×
binos, but I need 15× to “black-line” this close pair.
See what you can do.
The fi nal step is to follow in Piazzi’s footsteps:
Grab a scope, crank up the magnifi cation, and sketch
61 Cygni and its surrounding star fi eld. Amateur
astronomers armed with webcams have measured
the proper motion of 61 Cygni in as few as four years.
With pencil and paper it might take a little longer — as
it did for Piazzi! — but if you start now, you’ll have a
record you can revisit many times in years to come.
¢MATT WEDEL thinks that any discovery is
thrilling, even if many others have made the same
discovery before.
See for Yourself
skyandtelescope.com • NOVEMBER 2019 43