Phil Harrington's Cosmic Challenge

Cosmic Challenge: Abell 70

Of the more than 80 planetaries listed by George Abell in his 1966 paper "Properties of Some Old Planetary Nebulae," Abell 70 (also known as PK38.1-25.4) is one of the most unique. Actually, the planetary itself is a stereotypical example of a ring nebula, like M57, with a round shell of gas expanding away from the dim progenitor star. But look carefully and there is clearly more here than just that.

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Cosmic Challenge: Barnard's Star

The curtain opened on this challenge in September 1916, when a pair of articles written by Edward Emerson Barnard appeared in the journals Nature and The Astronomical Journal. Both recounted Barnard's discovery of a faint star in the constellation Ophiuchus that appeared completely unremarkable except for the fact that its proper motion was faster than any other star ever found.

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Cosmic Challenge: NGC 6369

One of the more interesting, and at the same time, challenging of Herschel's planetaries to view through 3- to 5-inch (7.6- to 12.7-cm) instruments is NGC 6369 in southern Ophiuchus. Nicknamed the "Little Ghost Nebula," NGC 6369 is an example of a ring-type planetary nebula, a faint version of M57. That is, if you can find it.

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Cosmic Challenge: Plato's craterlets

One of the great challenges facing even the most devoted lunar observers is trying to see the many small craters that dot the lava-covered floor of the walled plain Plato. Plato itself is a prominent impact scar measuring 62 miles across. It takes no more than 10x binoculars to see Plato once the Sun is up in its sky. In general, the best times to view Plato and its environs are about 1.5 days past First Quarter and again near Last Quarter.

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Cosmic Challenge: Abell Galaxy Cluster (AGC) 1656

The Coma Galaxy Cluster, Abell Galaxy Cluster (AGC) 1656, contains more than 800 galaxies brighter than photographic magnitude 16.5. It’s a real galactic forest that will take great patience to make your way through. There is no rushing this one. Unless you have enough time to devote to the task, best to push on to another target and come back here when you do. In fact, you will never get through this huge collection of galaxies in one sitting. Or even two, three, or four sessions, for that matter. AGC 1656 could well take years before every galaxy in view is recorded and identified.

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Cosmic Challenge: NGC 2976 and NGC 3077

M81 and M82 form perhaps the most famous pair of galaxies north of the celestial equator. Johann Elert Bode bumped into both quite by chance on New Year's Eve 1774. His discovery is commemorated today by M81's nickname, Bode's Galaxy. But his discoveries went unknown by his contemporaries. Both galaxies went unobserved for another 5 years until they were independently rediscovered by Pierre Méchain. Charles Messier incorporated Méchain's find into his burgeoning catalog some 19 months later. Bode, Méchain, and Messier missed fainter companions that are found nearby. Two more decades would pass before William Herschel discovered their dim glows, yet both of this month's challenges - NGC 2976 and NGC 3077 -- can be spotted through small backyard telescopes given good skies.

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Cosmic Challenge: Abell 33

Several of the challenges I have profiled over the years have involved hunting down tiny planetary nebulae. Many planetaries appear very small as seen from Earth, which can make them difficult to tell apart from surrounding stars. This also works in our favor, however, since their small size focuses all of the available light into small discs with high surface brightnesses. Their existence is also accented nicely by using narrowband and oxygen-III filters, which help suppress light pollution. That's why planetary nebulae are far better targets for urban observers than some other types of deep-sky objects.

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Cosmic Challenge: Palomar 2

Most globular clusters associated with the Milky Way are positioned around the galactic nucleus, and so are referred to as "inner-halo globulars." There is a second family, however, whose members lie far beyond the Galaxy's center and so are known as "outer-halo globulars." Of all the outer-halo globulars known, Palomar 2 is the most extreme, located almost directly opposite the Galactic center in Sagittarius, separated by 85,400 light years.

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Cosmic Challenge: IC 418

If you have ever glanced at a compendium of images taken with the Hubble Space Telescope, then chances are you have seen this next challenge. You may not know it by its catalog number, IC 418, but instead may recognize it by its nickname, the Spirograph Nebula. That nickname came about because the Hubble images show an amazingly complex cloud of entangled filaments that create a strange, oval cloud that looks like it could have been drawn using a child's Spirograph toy. Remember those? You would trace intertwining arcs by rolling a color pen in a circle along the inside or outside of another circle.

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Cosmic Challenge: WLM and WLM-1

If you thought last month's challenge, IC 1613, was just too easy, try your luck with another member of the Local Group that is also within Cetus.

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