Stephen Tonkin’s Binocular Tour

This month, beautiful blue diamonds, a ride on a coaster and bird-spotting in Cassiopeia

Tick the box when you’ve seen each one

1 MELOTTE 20

Also known as Alpha Persei Moving Cluster, this is a stunningly beautiful binocular target, extending as it does for over 3°. It extends nearly 4° southeast from mag. +1.8 Mirphak (Alpha (_) Persei). It is an association of mostly hot young blue (spectral types O and B) stars which, in binoculars, sparkle like diamonds on black velvet. Only about 60 million years old, the cluster is called ‘moving’ because all the stars share a similar proper motion (motion relative to the celestial sphere) of around 33 milliarcseconds per year. Ĵ SEEN IT

2 BETA CAM

Beta (`) Camelopardalis is visible to the naked eye at mag. +4.0. Its mag. +7.4 companion is a very easy split, even in small binoculars, 84 arcseconds to the southwest, but this is not the main appeal of this star. Beta Cam is classified as a yellow supergiant, which is relatively young at 40 million years old and in transition between being a hot new blue star and a red supergiant. Enigmatically, it has been seen to brighten by a whole magnitude in a flash with a duration of second, possibly its equivalent of huge solar flares. Ĵ SEEN IT

3 STOCK 23

If you pan slightly more than 1 ° due west from magnitude +4.3 CS Camelopardalis, you will find an unremarkable little trapezium of 7th and 8th magnitude stars. This is Stock 23, also known as Pazmino’s Cluster. With 50mm binoculars you can see this is much more than a trapezium and you may be able to resolve about half a dozen stars against a faintly glowing patch of sky about 10 arcminutes in diameter. Ĵ SEEN IT

4 EDDIE’S COASTER

One of the ‘binocular classics’, Eddie’s Coaster is an asterism that is not easily apparent in star charts or photographs, but is very obvious in 10x50 binoculars. To find it, look 3° north of Gamma (a) Cassiopeiae, where you will find a 3°-long wave of 7th and 8th magnitude stars, reminiscent of a rollercoaster, hence its name. Ĵ SEEN IT

5 THE CASSIOPEIA TRIPLE CLUSTER

Look 1˚ to the left (east) of the middle of an imaginary line joining Segin (Epsilon (¡) Cassiopeiae) and Ruchbah (Delta (b) Cassiopeiae) and you will easily find the largest and richest of these clusters, NGC 663. The four brightest stars appear to be separated into pairs by a dark lane. Just shy of 1˚ to the north-northwest is the brighter but smaller NGC 654. The poorest of the trio is NGC 659, a tiny ghostly glow which may need averted vision, just on the NGC 663 side of the mag. +5.8 star 44 Cas. Ĵ SEEN IT

6 THE OWL CLUSTER

Using Ruchbah as your jumping-off point, identify mag. +4.3 Marfak-East (Theta (e) Cassiopeiae) and navigate 2° towards it, where you’ll find an easy double star with its components shining at mag. +5.0 and +7.0, separated by 135 arcseconds. These are the owl’s eyes. Its body and wings are composed of 9th and 10th magnitude stars that span an area about ° in the direction of Gamma Cas. The brighter eye, Phi (q) Cassiopeiae, is not actually part of the cluster: it lies just over half way from us to NGC 457, which is nearly 8,000 lightyears distant. Ĵ SEEN IT