Stephen Tonkin’s Binocular Tour

Orion, Canis Major and Lepus point the way to January’s best binocular targets

Tick the box when you’ve seen each one

1 COLLINDER 70

Most amateur astronomers have seen Collinder 70 without realising it: it’s the oval-shaped OB association (a grouping of very young O- and B-type stars) surrounding Orion’s Belt. On a clear night, you should be able to see at least 70 stars in this cluster. They are mostly of a blue-white (O and B spectral type) colour, with a few yellow stars interspersed. They form lots of pairs and some beautiful curved chains, in the swan’s neck chain that weaves between mag. +1.7 Alnilam (Epsilon (¡) Orionis) and mag. +2.4 Mintaka (Delta Orionis). SEEN IT

2 SIGMA ORIONIS

Look about 1º to the southeast of the easternmost star of Orion’s Belt, mag. +1.9 Alnitak (Zeta Orionis) – Sigma Orionis is the brightest star you will see, shining at mag. +3.8. With your binoculars, you will see that Sigma Orionis is, in fact, a multiple star. With a pair of 10 50s you will easily see two of the members, the white primary and the blue, 6th-magnitude component that lies 42 arcseconds away, towards Alnitak. In order to resolve the next two components, you will need at least double this magnification. The fifth member is not visible visually. SEEN IT

3 M42

The Orion Nebula, M42, is a highlight of the winter skies and a superb object in binoculars of any size. It’s the nearest stellar nursery to Earth and is visible to the naked eye as the central ‘star’ of Orion’s sword. It’s extremely sensitive to sky transparency and is usually best observed after rain has cleaned the sky of dust. On these occasions, the longer you look at it, the more intricate detail you’ll be able to see. SEEN IT

4 M50

The easy way to find M50 is to navigate a third of the way from mag. –1.5 Sirius (Alpha (_) Canis Majoris) to mag. +0.4 Procyon (Alpha (_) Canis Minoris). Here you’ll find this lovely cluster, which appears as a heart-shaped glow about half the apparent diameter of the Moon. The glow comes from just over 100 stars, of which you should expect to resolve only four or five, depending on your sky conditions, using 10 50 binoculars. SEEN IT

5 M41

M41 is a bright cluster 4° south of Sirius, visible to the naked eye in a transparent sky. It’s larger and brighter than M50 and, in 10 50 binoculars from a reasonably dark site, you should be able to resolve up to 10 brighter stars against the background glow of fainter stars using averted vision. You may also be able to see that the stars differ in colour, with the brightest one, near the centre of the cluster, being somewhat orange. SEEN IT

6 M79

This month’s challenge is a mag. +8.2 globular cluster. First, identify mag. +2.6 Arneb (Alpha (_) Leporis), mag. +2.8 Nihal (Beta (`) Leporis) and mag. +3.6 Gamma Leporis. Extend a line from Arneb to Nihal southwards for just over 4°, where you will find a mag. +5.4 star. Without looking away from this star, avert your attention to a spot about 0.5º away in the direction of Gamma Leporis. Here you should see what looks like a star that is both fainter and larger than the mag. +5.4 one. This is the combined light of the 150,000 stars that comprise M79. SEEN IT