Binocular tour

August brings a jewel, a flower and a scientifically significant double

Tick the box when you’ve seen each one

1 HERSCHEL’S GARNET STAR

10x Just a little southwest of the mid-point of a 50 line between mag. +2.5 Alderamin (Alpha (_) Cephei) and mag. +3.4 Zeta Cephei is mag. +4.0 Mu (µ) Cephei, named for William Herschel, whose description is as appropriate today as it was when it was written in 1783: “of a very fine deep garnet colour and … a most beautiful object, especially if we look for some time at a white star before we turn … to it, such as Alpha Cephei, which is near at hand.” Jupiter would orbit inside this huge red supergiant, which is one of the largest known stars. SEEN IT

2 DELTA CEPHEI

10x Variable star Delta Cephei (mag. +3.6 50 to +4.5, period 5.37 days) gave its name to an entire class of variable stars for which Henrietta Leavitt demonstrated the relationship between the period of variation and luminosity. This relationship allowed them to be used as the first ‘standard candle’ for measuring the size of the Universe. This star is not only here for that

reason, though: it is a beautiful binocular double with a deep yellow primary star and a brilliant white 6th-magnitude secondary. SEEN IT

3 M52

10x Mag. +6.9 open cluster M52 rests on a 50 straight line extended from mag. +2.2 Schedar through mag. +2.3 Caph (Alpha (_) and Beta (`) Cassiopeiae), 6º northwest of Caph. In 10 50 binoculars, M52 appears as a grainy glow in the form of an arrowhead that is 13 arcminutes long and well differentiated from the Milky Way stars. There is a brighter (mag. +8.3) star on the western side, which will probably be the only one of the nearly 1,000 cluster stars that you can resolve. SEEN IT

4 THE QUEEN’S AEROPLANE

10x Just under 1º north of M52 lies the golden 50 yellow mag +5.0 4 Cassiopeiae, which marks the starboard wingtip of our next object, a pretty aeroplane-shaped asterism in which eight stars are mag. +8.0 or brighter, making it

5 CAROLINE’S ROSE

15x Our next object is another 1783 Herschel 70 discovery, but this time by William’s sister, Caroline. Open cluster NGC 7789, also known as Caroline’s Rose, sits 6º west of Schedar, forming a triangle with Caph at the rightangled apex. In 15 70 binoculars it appears as a soft glow spanning about half the apparent diameter of the Moon; even if you use averted vision, you are unlikely to be able to tease out any individual stars. With an age of about a billion years, Caroline’s Rose is unusually old for an open cluster and imagery shows that most of its stars have become red giants. SEEN IT

6 TV CASSIOPEIAE

15x You really need 15x70 binoculars at least 70 to appreciate the variability of our last object, which is 0.25º east of Caph and normally shines at mag. +7.2. TV Cassiopeiae is an Algol-type eclipsing binary star with a period of 1.81 days, when it dims by one magnitude and rises again to its normal brightness during the nine-hour eclipse. Because the eclipses are four and a half hours earlier on successive days, it is relatively easy to observe them every week or so at a convenient time. SEEN IT