The Sun’s Southern Cross

Comet Hartley 2 passed the open star cluster NGC 1528 in Perseus last night. This 2-minute exposure made with a 200mm telephoto lens clearly resolves the cluster into individual stars. Photo: Bob King

I was surprised to see two “comets” when I pointed my binoculars at Comet Hartley 2 last night. The swift-moving Hartley had a fuzzy companion to its left which I knew must be a star cluster. A quick check in the atlas showed that it was NGC 1528, a cluster of stars in Perseus similar in size and brightness to the comet. Through 8×40 binoculars I couldn’t resolve any stars within the hazy puff at first – that’s why it looked so similar to Hartley 2. I concentrated my vision on a second try and discerned a few tiny twinklings and a granulated appearance common in many clusters viewed through binoculars. The telescope resolved NGC 1528 into lovely arcs of individual stars. I’m always grateful for the wandering ways of comets. As they travel across the sky, they often pass interesting objects I might not otherwise think to view. Tonight the comet will lie about one degree east of another star cluster, NGC 1545. I encourage telescope owners to use the comet to find its starry neighbor. Here’s a detailed map to help get you there.

The sun photographed by the space-based Solar Dynamics Observatory at 9 a.m. today. Each sunspot group has its official number. A large new spot is coming around the east side of the sun, while my boxy "Southern Cross" group is - appropriately - in the sun's southern hemisphere. Credit: SDO/NASA

I got another surprise this morning when checking recent pictures of the sun. Not only is there an exciting new spot coming into view,  but I was struck by the current sunspot group 1112, which is shaped almost exactly like the constellation Crux, better known as the Southern Cross. Of course, it’s only a coincidence, but the resemblance is striking. Since the sun’s bubbly, boiling surface is in constant motion, it’s likely the group will change shape by tomorrow. If you have a telescope equipped with a SAFE solar filter, you might want to check it out today.

Crux and sunspot group 1112 side by side. Crux image: Stellarium; sunspot: SDO/NASA

The Southern Cross is the smallest constellation in the sky, but because it contains two bright first magnitude stars and sports a distinctive and compact shape, it’s known the world over. You’ll find its image on the flags of Australia, New Zealand, Brazil, Samoa, Papua New Guinea and now – briefly – on the sun. The ancient peoples of Greece and Italy knew Crux, but the slow wobble of the Earth’s axis – called precession – has moved the constellation out of view for Europeans and most of the U.S. You can see the Southern Cross from Hawaii without difficulty, but it just clears the horizon for southern Florida during the spring months. Folks living in the southern hemisphere use Crux to point to the southern pole star, Sigma Octantis, the same way northerners use the “pointer” stars in the end of the Bowl of the Big Dipper to point to the North Star. They imagine a line through the top and bottom stars of the cross and extend it southward until it intersects with Sigma.

As long as we’re on a sunny topic, there’s a chance for aurora again tonight for high latitudes. A stream of subatomic particles from a prominence ejection on October 11 is behind the current activity, so if it’s clear where you live, take a look in the north for a telltale green arc.

2 Responses

  1. John Brophy

    What would you recommend for size and brand of binoculars to look at the stars. The ones I have now are 10 x 50 that gives me a shaky view. Even when I brace myself against a car the view is still shaky.

    1. astrobob

      Hi John – if money were no object I’d recommend something like the 10×30 Canon image-stabilized binoculars. They’re around $550 (used on Amazon for $350 or so). Once you aim these at a target and allow the binoculars to “settle” for a second, the view is amazingly still. Someday when I’m rich, I’ll get myself a pair. In the meantime, you might take the magnification down a notch – that’s what’s causing the extra shakiness – and get my old standby 8×40 Nikon 7216 Action binoculars for a whopping $62, new from Amazon. While I’m not a binocular expert, I find that these inexpensive binoculars have excellent sharpness, good field of view for eyeglass wearers and decent light-gathering ability. You can go lower in magnification, but below about 7x, binoculars become astronomically less useful. The 7×50 or 7×35 Nikon Action pair might be other good choices for you. — Bob

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