This month’s highlights include a Double Double in Leo and a galaxy triplet
1. 86 Leo Starfield
Recommended equipment: 10x 50
We’ll start this month’s tour with a colourful starfield. Locate the orange-yellow mag +5.6 star 86 Leonis between Denebola (Beta (β) Leonis) and Zosma (Delta (δ) Leonis), and compare its colour to brilliant-white 90 Leonis that is 2° back towards Denebola. There is also a multicoloured curved string of 7th and 8th magnitude stars that extends 3° eastward from 86 Leo, and the region encompassing 92 Leo and 93 Leo is also very rewarding if you like coloured stars.
2. R Leonis
Recommended equipment: 10x 50
R Leonis is a Mira-type variable star, with a magnitude ranging from +10.1 to +5.9 over a 313-day cycle. To locate it, first identify the mag. +5.6 star 18 Leonis and mag. +6.5 19 Leonis. Next, 8 arcminutes south of 19 Leonis is a pair of stars, with R Leonis more easterly. R Leonis is about to start brightening again, so it’s a good time to start viewing it.
3. 17 and 18 Sextantis
Recommended equipment: 10x 50
Look about 4.5° east of mag. +5.1 Gamma (γ) Sextans where you will find a widely separated (12 arcminutes) pair of stars, which make an easy double star for small binoculars. The more easterly one, orange 18 Sextantis, shines at mag. +5.6, and its white companion, 17 Sextantis is slightly fainter at mag. +5.9. There are three fainter colourful binocular doubles within 1.5° to the north, but none of these are as close in magnitude.
4. Leo’s Double Double
Recommended equipment: 10x 50
Use the chart to identify and locate mag. +4.9 Tau (τ) Leonis. One third of a degree to the north-west is its mag. +6.5 companion, 83 Leonis. Look carefully and you will see that each of these is a double star with a mag. +7.5 companion. Tau Leonis’s pale companion is easier to discern at 1.5 arcminutes but, at only 29 arcseconds, splitting 83 Leonis is a stiff challenge for 10×50 binoculars.
5. Leo Galaxy Triplet
Recommended equipment: 15x 70
You’ll need a dark transparent sky for our final targets. If you put mag. +3.3 Chort (Theta (θ) Leonis) outside the northwest of the field of view of 15×70 binoculars, the galaxies will be in the centre. You may need averted vision at first, but once you are familiar with their appearance they become easier to see, but you will still need averted vision to discern NGC 3628’s different shape.
6. NGC 3521
Recommended equipment: 15x 70
Next is a galaxy that is a bit “off the beaten track”, as there aren’t nearby bright marker stars. You’ve already found Tau Leonis, so use that in conjunction with the chart to find 65 Leonis (mag. +5.5) and 69 Leonis (mag. +5.4). Put them near the north and east edge respectively of your field of view, and NGC 3521 will be near the middle.