Stephen Tonkin’s Binocular Tour

The keyword this month is ‘colour’ in a journey around Cetus in search of some unusual stars

Tick the box when you’ve seen each one

1 THE PISCES PARALLELOGRAM

Binoculars are ideal for enhancing the colours of stars as a look at the 3°x1° Pisces parallelogram proves. The northeast corner is 29 Piscium, a brilliant, blue-white star while, diagonally opposite, is the bright orange 30 Piscium. The other two corners – 27 and 33 Piscium – are a muted yellow in comparison. The northern part of the parallelogram appears empty of stars, but very dark skies or larger apertures show this to be an illusion, as a smattering of fainter stars come into visibility. SEEN IT

2 POXON’S TRIANGLE

Starting at 33 Piscium, drop down 5° to 3 Ceti, then about the same distance again to 6 Ceti. This is the northern point of a triangle that has 2 and 7 Ceti at its other points. This is a lovely starfield containing stars with a wide range of magnitudes and colours no matter what size binoculars you use. Even when it is quite low, 10x50s should reveal a dozen or more stars, but you may see 30 or more in good conditions. SEEN IT

3 T CETI

From 7 Ceti, navigate 2° to the southeast, where by far the reddest star in the region is the unusual, semi-regular variable T Ceti. It is a red giant with technetium in its spectrum. Technetium’s most stable isotope, Tc98, has a half-life of 4.2 million years, which – since the star is billions of years old – provides irrefutable evidence for stellar nucleosynthesis. Its semiregular nature (with a mean period of 159 days) means that it is not entirely predictable but, with a magnitude range of +5.0 to +6.9, it is always accessible to small binoculars. SEEN IT

SILVER COIN GALAXY

Slightly more than 4° to the south of Diphda (Beta (`) Ceti), you will find a right-angled triangle of 5th magnitude stars. NGC 253, the Silver Coin Galaxy, is an elongated glow nearly 3° to the south of this triangle. Its major axis is about half a lunar diameter, and it has a noticeably brighter core. Despite its low altitude viewed from the UK, this galaxy is still a relatively easy object for small binoculars as long as you have a decent southern horizon. This is the best time of year for us to observe it in the evening. SEEN IT

5 NGC 288

From the Silver Coin, pan about 2° towards Alpha (_) Sculptoris. Here lies the mag. +8.1 globular cluster, NGC 288, another easy object so long as you have a clear southern horizon. In a pair of 15x70 binoculars it appears as a dim circular glow, which, with averted vision, grows to about half the diameter of NGC 253. NGC 288 is a good marker for the Milky Way’s south pole, which lies slightly more than 0.5° away to the south-southwest. SEEN IT

6 BLANCO 1

Stick with larger binoculars for the final object to compensate for its low altitude. Identify Zeta (c) Sculptoris and get it in your field of view. Notice how it is the brightest of a sparse, indistinct grouping of white stars that span a region about 1.5° wide? Seventy years ago, Puerto Rican astronomer Victor Manuel Blanco did exactly that, and realised that he was looking at a dispersed open cluster. This sole Blanco object is thought to be less than 150 million years old and is 850 light years away. SEEN IT