Sky & Telescope - September 2021 - 43

M57
ε
γ
χ
CYGNUS
M56
LYRA
β
Albireo
α
VULPECULA
M27
Binocular Highlight by Mathew Wedel
A Delightful Double
I
R
Vega
LYRA
M57
don't know if Albireo is the most popular double
star of all, but it has to be in the running. Also
+20°
known as Beta (β) Cygni, Albireo marks the head of
Cygnus, the Swan. Thanks to its prominent position,
the double is an easy find even for those just learning
their way around the sky. Less easy is glimpsing its
two component stars in binoculars. With a separation
of just 35″, the twosome can theoretically be
split with 10× binos, but I've never been able to get a
clean separation with less than 15×.
Regardless of magnification, the trick is to make
θ
0°
M11
S ERP ENS
( CAUDA )
UTUM
M16
M17
sure you hold your binoculars as steady as possible
- the slightest amount of jiggling will blur the two
stars into one. If you use a reclining lawn chair (advisable,
given Albireo's neck-straining altitude at this
time of year), try resting your elbows on the arms of
the chair. Even better is a binocular mount or a pair of
image-stabilized binoculars.
Albireo A is a K2-type orange giant, and Albireo B
WHEN TO
-40°
9h
g Sou
USE THE MAP
Late July Midnight*
Early Aug 11 p.m.*
Late Aug
10 p.m.*
Early Sept 9 p.m.*
Late Sept Nightfall
*Daylight-saving time
is a hot, massive B8-type bluish star. (As a University
of California alum, I tend to see the pair dressed in
Cal blue and gold.) But is Albireo a true double star,
in which the two suns are gravitationally bound to
each other, or are its stars simply coincidentally
aligned? For the time being, the answer remains (if
you'll forgive the pun) " unresolved. " Even with astrometric
data from orbiting observatories it's tough to
tell. Data from the Gaia satellite suggest the stars
are 30 to 60 light-years apart and moving in different
directions, which would mean they're unrelated. On
the other hand, the margin of error is great enough
that maybe, just maybe, the disparate stars really do
belong together. For some reason that conclusion
makes the binocular view more satisfying.
¢ Close double stars make MATT WEDEL wish he
had steadier hands.
sk yand tele scope .o r g * SEPTEMBER 2021 43
5
S ERP ENS
( CAPUT )
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Moon
Sept 10
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O P H I U C H U S
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Antares
S C O R P I U S
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Moon
Sept 13
AGITTARIUS
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LA
κ
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M19
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M7
M6
M62
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L I B R A
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CORONA
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C O M A
B E R E N I C E S
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CANES
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Arcturus
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Mizar
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Sky & Telescope - September 2021

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