Stephen Tonkin’s Binocular Tour

There’s a dwarf planet to look out for this month as well as a wide spectrum of stars

Tick the box when you’ve seen each one

1. NGC 2017

Begin by familiarising yourself with the brighter stars of Lepus, then identify Arneb (Alpha (_) Leporis). 1.5° due east of Arneb is a tiny group of stars, the brightest of which shines at mag. +6.4. This is NGC 2017. The NGC describes it as an open cluster, but it is really just a multiple star. How many stars you see will depend on your sky conditions: good conditions yielding will yield a row of three stars and an orange fourth just north of the row in 10x50 binoculars. This is a chance line-of-sight group, with actual distances ranging from 500 to 3,000 lightyears. SEEN IT

2. IOTA AND RX LEPORIS

Nearly 4° south of Rigel (Beta (`) Orionis) lies Iota Leporis, itself a fairly unremarkable mag. +4.5 brilliant white star, but it contrasts beautifully with the fainter reddish star, RX Leporis, which lies 0.25° to the west of it. RX Lep is slightly variable, oscillating between magnitudes +5.4 and +4.9 over a period of 74.5 days, but this main period is overlain by longer periods and it is classified as an ‘unsolved’ semi-regular variable. While you are here, scan around it: Iota and RX Lep are part of a rewarding, colourful star-field that fills the field of view of your binoculars. SEEN IT

3. THE STREAM

While we’re looking at starfields, let’s pan 6° west from Mu (µ) Leporis, where you will find the most northerly of a colourful string of mostly 5th and 6th magnitude stars running down to the southwest. There is a colour gradation from orange 60 Eridani at the top of the chain, through yellow 59 and 58, down to a fainter white star. Then it all changes with the reddish 54 Eri, the brightest star of the group. On a transparent night, see how many fainter stars you can see, especially near the top of the chain. SEEN IT

4. 62 ERIDANI

Go back to Rigel and identify Cursa (Beta (`) Eridani), 3.5° to its northwest. Linger around Cursa for a while and take time to appreciate its rich stellar environment before heading 3° due west to the brilliant blue-white mag. +5.5 62 Eridani. This can be a tricky double star, not because of the separation, which is a substantial 66 arcseconds, but because the companion is so much fainter (mag. +8.9) than 62 Eri. This is not a binary star, but an optical double: the fainter of the pair is four times further away than the primary. SEEN IT

5. ZIBAL

The mag. +4.8 Zibal (Zeta Eridani) might just be visible to your naked eye if your southern aspect is good. It is part of a wide pair, the other member being 14 Eridani (mag. +6.1), which is 0.5° southeast. The ‘pairing’ does not end there; on the northwest of Zibal, a mere 5 arcminutes away, is another companion, shining at mag. +6.6. Both of these companions are line-of-sight associations, although Zibal is part of a binary system, but one that requires spectroscopy to detect; the secondary has an orbital period of only 17.9 days. SEEN IT

6. JUNO

Although only the 10th largest asteroid, Juno was the third to be discovered, thanks to its unusually high albedo, and this is what will enable us to continue observing it two months after opposition. Identifying it will be a bit of a challenge, so familiarise yourself with its region of sky, and note which ‘star’ has moved after a couple of days. At the beginning of January, it is mag. +8.2, so well within range of 15x70 binoculars, but see how long you can continue to observe it before it fades from view. SEEN IT