BBC Sky at Night Magazine
Sparkling stars: a beginner’s guide to binoculars
A sky safari with binoculars
Discover why binoculars are great for stargazing with our tour
Binoculars are a great way to get into stargazing, and Steve Tonkin’s tour designed especially for them will take you to some of the best targets for two eyes this month
There’s one piece of advice that should be familiar to anyone who is trying to get started in astronomy – buy a pair of binoculars and use them to learn your way around the night sky. But once you have a pair, where do you start? Here, we take you on a trip across the night sky, looking at 10 of the best stellar groups visible in September.
We’ve chosen several large targets that are arguably better in binoculars than anything else – it would be daft to omit these – as well as targets that help you develop useful observing skills, and a couple that push these skills to their limits. There are even several circumpolar objects which will be visible in UK skies throughout the year, so you can continue to observe them if you wish. We recommend 10x50 binoculars for this, but all of the objects are visible with a smaller pair, so dust off whatever you have and let’s get observing!
We get things going with a circumpolar sight that’s easy to find. The Alpha Persei Moving Cluster extends 4° southeast from Mirphak (Alpha (α) Persei). When you track it down, you should see stars shining with an intense blue-rich whiteness that indicates that they are young stars. In binoculars, they are said to ‘sparkle like diamonds on black velvet’. The cluster is said to be ‘moving’ because all the stars have the same proper motion (their apparent movement on the night sky). The reason we’re starting here though is that they’re a great place to ensure your binoculars are perfectly focused: focus them until you get the maximum number of visible stars.
With our binoculars in crisp focus, it’s time to take a trip over to southerly skies to look at a duo of sights, starting with the spectacular Scutum Star Cloud. Located in the southern sky, it’s so easy to find that it has been mistaken for a real cloud on a clear night. Note how there seem to be ripples of stars; these are formed by indistinct dark nebulae that weave through it. The richest part is the densest known open cluster, M11, the Wild Duck Cluster. Were it not so rich, it would be very difficult to distinguish from the background star cloud, which itself forms one of the most densely packed regions of the Milky Way.
About 15° northwest of the Scutum Star Cloud we find another ideal object for binoculars. Poniatowski’s Bull has a diameter of about 4° and so fits comfortably in the field of view of 10x50 binoculars. The brightest stars include 66, 67, 68, 70 and 73 Ophiuchi, which form a V-shape similar to the Hyades cluster in Taurus, hence its common name.
By now you should be getting your eye in, so we’ll leave the southern skies and travel up to Vulpecula and do our first star-hop. Star-hopping is a way of finding a
target by navigating from a bright, easy-to-find object to locate less obvious ones nearby. Start at Anser (Alpha (α) Vulpeculae) and navigate 5° (about one field of view of 10x50 binoculars) south, where you’ll find The Coathanger – a popular star-party piece, because it looks like an everyday object. Even 20mm binoculars will reveal the 10 brightest stars that give this asterism its name. Its formal designation is Collinder 399, but it’s also known as Al-Sufi’s Cluster after the Persian astronomer Abd al-Rahman al-Sufi who first recorded it back in the 10th century, or Brocchi’s Cluster after the astronomer who used it to determine the limiting magnitude of his telescopes.
For our next batch of targets, we’ll need to take a slightly larger trip across the sky, requiring a double starhop to find our next target. Imagine a line from Navi (Gamma (γ) Cassiopeiae) through Ruchbah (Delta (δ) Cassiopeiae) and extend it for 7.5° (about one and a half fields of view). Look for a very close pair of small open clusters, the Perseus Double Cluster (you might be able to see them with your naked eye as a single fuzzy blob). But this isn’t our final destination: from the side nearest Cassiopeia there is a 2° curved chain of stars leading northwards to Stock 2, also known as the Muscleman Cluster. This gets its name from the stick-man figure made by its brighter stars. He stands with his feet to the east in a bicep-flexing pose, wielding the Double Cluster on a leash (the starry chain that led us here). The connection between the Muscleman and the Double Cluster is purely illusory: the Double Cluster is nearly seven times as far from Earth as the Muscleman.
Our next asterism is Kemble’s Kite, named for the prolific Canadian binocular observer, Father Lucien Kemble (1922-99), who observed it with 7x35 binoculars. A line from Segin (Epsilon (ε) Cassiopeiae) through Iota (ι) Cassiopeiae leads to Gamma (γ) Camelopardalis, 8° further northeast. Approximately 1.5° west of Gamma (γ) Camelopardalis, you’ll find a yellowy-orange star, V805 Cassiopeiae. V805 is the brightest of a 1.5° long