Southern Sky Notes

Notes · Binoculars

Binocular Astronomy Under the Southern Sky

A decent pair of binoculars will show you more of the southern sky in a first year than most beginners manage with a cheap telescope. They are quick to grab, they show the sky the right way up, and their wide field makes star-hopping almost easy. If you are still weighing up a telescope, our notes on choosing a first telescope explain why we suggest binoculars first.

7x50 or 10x50?

The first number is magnification, the second is the width of each front lens in millimetres. Both sizes gather plenty of light for deep-sky work.

7x50 10x50
Field of view wide, roughly 7° a little narrower, roughly 5-6°
Exit pupil about 7 mm 5 mm
Hand-held steadiness easier shakier
Best for Milky Way sweeping, big clusters, younger eyes slightly more detail on clusters and the Moon

The exit pupil is the beam of light leaving the eyepiece. A 7 mm beam suits a fully dark-adapted young eye; as we age the pupil opens less, so some of that light is wasted. For most adults a 10x50 is the better all-rounder, and the extra magnification darkens the sky background a touch, which helps under suburban skies.

Avoid zoom binoculars and anything with ruby-coated lenses. Look for fully multi-coated optics and BaK-4 prisms, which show as round, evenly lit circles when you hold the binoculars at arm's length and look at the exit pupils.

Holding them still

Hand shake is the main limit. A few things help:

  • A tripod adaptor. Most astronomy binoculars have a threaded socket hidden under a cap at the front of the hinge. A cheap L-bracket screws in and mounts the binoculars on any photo tripod.
  • A reclining chair. Lying back with elbows on the armrests is surprisingly steady and saves your neck for objects near the zenith.
  • Brace against something. A fence post, a car roof or a deck rail all work in a pinch.

Once steadied, you will notice fainter stars and more detail almost immediately.

Where to start

Get oriented with the Southern Cross and the Pointers first; our guide to finding south with the Southern Cross covers that. Free planetarium software such as Stellarium is handy for checking what is up from your town at a given hour.

Give your eyes 20 minutes away from white light, and use a dim red torch for charts.

Summer (December to February)

  • The Orion Nebula. Below the three belt stars, which from New Zealand means above them in the "upside-down" Orion we see. A misty patch with a few stars buried in it.
  • The Hyades and Matariki. The V-shaped Hyades around Aldebaran and the tight Matariki cluster further along are both perfect binocular fields.
  • M41. A pleasant open cluster a few degrees from Sirius.
  • NGC 2516. A rich, bright cluster in Carina that people often overlook.
  • The Large Magellanic Cloud. High in the south on summer evenings, full of knots and clusters.

Autumn (March to May)

  • The Eta Carinae Nebula. Even in binoculars this is a glowing patch, with the bright orange star Eta Carinae inside it.
  • The Southern Pleiades (IC 2602). A loose sprinkle of bright blue-white stars near Eta Carinae, a fine binocular field in its own right.
  • The Jewel Box. Next to Beta Crucis. Binoculars show a compact knot; the colours need a telescope.
  • The Coalsack. A dark cloud beside the Cross. Sweep across it and notice how the background stars vanish.
  • Omega Centauri. The largest globular cluster in our galaxy, a round fuzzy ball that looks like a star at first glance.

Winter (June to August)

Winter evenings put the centre of the Milky Way overhead, and this is the season binoculars were made for.

  • Scorpius. The open clusters M6 and M7 just beyond the "sting" at the end of the tail, and NGC 6231 in the curve of the tail near Zeta Scorpii, a bright cluster that looks like a scatter of diamonds.
  • The Lagoon Nebula (M8). In Sagittarius, a cluster wrapped in faint nebulosity.
  • M22. A bright globular cluster close to the lid of the Teapot.
  • Star clouds. Simply sweep slowly through Sagittarius and Scutum. The dense patches of stars and the dark lanes between them are the point.

Spring (September to November)

  • The Small Magellanic Cloud and 47 Tucanae. 47 Tuc sits right beside the SMC and is the second-best globular in the sky.
  • NGC 362. A smaller globular on the northern edge of the SMC.
  • The Andromeda Galaxy. Low in the north on spring evenings from New Zealand, so it needs a clear northern horizon. An elongated glow, two and a half million light years away.
  • Fomalhaut and the Sculptor region. Less dramatic, but a good test of how dark your sky really is.

Don't forget the Moon and planets

The Moon in binoculars is beautiful, especially a few days either side of first quarter when the shadows along the terminator are long. Our Moon page has more on what to look for. Jupiter's four large moons are visible as tiny points in a line, and they change position from night to night. Saturn shows as an oval in steady 10x50s, though the rings need more magnification to split. Never point binoculars anywhere near the Sun.

Building a habit

A short session most clear nights teaches more than one long session a month. Pick two or three targets, find them, then sketch or jot down what you saw. After a season you will know the sky well enough to find things without a chart, and when you do add a telescope you will already know exactly where to point it.