Binocular tour

Our wide-field gems include objects near the Keystone asterism and Northern Crown

1. M92 10x 50

M92 is a fine cluster, but tends to

be under-observed owing to the proximity of a more famous one. Start at Eta (η) Herculis, the northwestern corner of the Keystone asterism in Hercules, and imagine a line going northeast to Iota (ι) Herculis. Two-thirds of the way along this line, the 150,000 or so stars of M92, concentrated into an apparent diameter about one-third that of the Moon, shine at mag. +6.4.  SEEN IT

2. The Great Cluster in Hercules 10x 50

The more famous cluster, M13, lies one-third of the way down the western side of the Keystone asterism in Hercules. You might even be able to see it with your naked eye in transparent skies. In binoculars, this globular cluster looks like a comet, brightening towards the core. This is why Charles Messier included it in his list of objects that comet-hunters should not be fooled by.  SEEN IT

3. Nu (ν) Coronae Borealis 10x 50

Nu (ν) Coronae Borealis appears

double to your naked eye and is easily split in small binoculars. The stars of this optical double (a chance line-of-sight pairing of stars that aren’t gravitationally bound) are similar, both being giants with masses about 2.5 times that of the Sun, but the more distant star, Nu1 (ν1) Coronae Borealis, is at a later stage of evolution and more luminous than its partner Nu2

(ν2) Coronae Borealis.  SEEN IT

4. Tau (τ) Coronae Borealis group 10x 50

Navigate 4° northwest from Nu Coronae Borealis to find Tau (τ) Coronae Borealis, the brightest star in a straight line of five stars running eastwest for 2.6°. All but the central one shine brighter than mag. +6, and binoculars reveal their colours. The stars at each end are a deeper yellow than the others, while the star next to the eastern end is almost white by comparison.  SEEN IT

5. R Coronae Borealis 10x 50

Lying in the middle of the Northern

Crown is an enigmatic variable star. It usually shines at mag. +5.9, but its brightness randomly plummets as low as mag. +15, like a nova in reverse. When this happens, it does so very quickly, so it’s worth watching every clear night. R Coronae Borealis is a ‘sooty’ carbon star; it puffs out carbon which, if it is in our line of sight, obscures the star.  SEEN IT

6. 50 Boötis 15x 70

Our final target is a triple star. Start at Delta (δ) Boötis, a fine binary star, and pan about a degree and a half eastwards. 50 Boötis is a hot blue-white star that shines at mag. +5.3. Its two companions, which are mag. +9.5 (174 arcseconds southeast) and +10.4 (118 arcseconds northeast) are yellowish, making this a pretty group.  SEEN IT

✓

Tick the box when you’ve seen each one