This month’s wide-field targets include the Dumbbell and North America Nebulae
1. The Coathanger
Recommended equipment: 10×50
Let’s begin with a summer star party piece. Put mag. +4.4 Alpha (α) Vulpeculae at the north of the field of view, and the Coathanger (or Collinder 399), will be near the southern edge. It lies in a darker part of the Milky Way, so even small binoculars will reveal the 10 brightest stars that give this asterism its name. It was first recorded by Persian astronomer Abd al-Rahman al-Sufi in his AD 964 Book of Fixed Stars.
2. The Dumbbell Nebula
Recommended equipment: 10×50
Next is the easiest planetary nebula for binoculars. Identify Gamma (γ) Sagittae and pan over 3° in the direction of 15 Vulpeculae where, even in suburban skies, you will find a small glowing cloud. This distant object, the Dumbbell Nebula, is 1,360 lightyears away. Initially it will appear rectangular but, with patience, you should discern the narrowing in the middle that gives it its common name.
3. Albireo
Recommended equipment: 10×50
Albireo (Beta (β) Cygni) marks the Swan’s eye. This double star has a separation of 34 arcseconds, a good test for 10x magnification: if you don’t see two stars, make sure that your focus is perfect and try mounting the binoculars. Once you have split it, notice the beautiful contrast between the golden mag. +3.1 primary and azure mag. +5.0 secondary. Albireo was recently revealed as an optical double, a line-of-sight coincidence.
4. M29
Recommended equipment: 15×70
Put mag. +2.2 Sadr (Gamma (γ) Cygni) at the north of a 15×70’s field of view and the mag. +6.6 cluster, M29, will be near the centre. This is a fairly unremarkable target in smaller binoculars but, on a good night, 15x70s will resolve around a dozen of the 50 or so of these hot blue giants, each with a luminosity of over 150,000 Suns. The brighter stars form a ‘cooling tower’ shape.
5. The North America Nebula
Recommended equipment: 10×50
The North America Nebula, NGC 7000, is a large bright patch of nebulosity whose centre is 3.5° eastsoutheast of Deneb (Alpha (α) Cygni). If it’s not immediately visible, try instead to detect the dark nebula that forms the ‘Gulf of Mexico’. This emission nebula is about 100 lightyears across and appears to us as four times the Moon’s size.
6. Barnard 145
Recommended equipment: 15×70
Our final object is another of these intervening clouds of dust. ‘The Man Who Never Slept’, EE Barnard, described them as “holes” and “lanes” cutting through the Milky Way, before he realised their true nature. Identify mag. +3.9 Eta (η) Cygni, and use the chart (above) to find 25 Cygni, at mag. + 5.1. Barnard 145 is the inky-black ‘inlet’ into the Milky Way, 0.75° to the northeast.