Observing the Fraternal Twins (M53 & NGC 5053)

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I imaged these clusters with iTelescope T21 on the night of April 26th with a waning gibbous moon in the sky. Image Details

These two globular clusters are separated by less than a degree in the sky. They provide a wonderful study in contrasts, for it is difficult to imagine two more different clusters. M53 (right) is your classic globular with a bright rich center. On the other hand, NGC 5053 (left) is a most unusual globular cluster. It's stars are spread much more loosely and irregularly, appearing more like an open cluster.

M53 was discovered by Johann Bode in 1775. Smyth reportedly called M53 an "interesting ball of innumerable worlds." Visible in binoculars, small telescopes, and even finders as a small ball of haze, it is only in 6-inch or larger scopes that it begins to grudgingly give up a few of its myriad stars. As you move to larger apertures and higher magnification, more and more stars become resolved. Sir William Herschel said of M53 that is was "one of the most beautiful sights I remember to have seen in the heavens." In larger scopes at magnifications of 250x or greater, this cluster is quite beautiful. It is somewhat asymmetrical for a globular, with a tight core that is resolved when the seeing is good.

M53 is clearly visible in my 8x52 finder scope, appearing as a big fuzzy star. In my 18-inch at 94x it appeared as a round haze with bright center overlaid with a smattering of resolved stars. At 270x the view was very different. It now filled 1/2 of the field of view and my eye was met by a myriad of countless stars. My notes began with a single word, "Spectacular!" The brighter inner region now resolved into many stars, very regular in appearance and distribution. But across the face of the cluster lies another population of brighter stars. These stars are scattered very irregularly and extend far away from the cluster center. It must be these stars that are first resolved at low magnification or in smaller apertures. Perhaps this dichotomy is what Smyth was talking about when he described M53 as "a mass of minute stars 11-15 mag. and from thence to gleams of star-dust, with stragglers." Increasing the magnification still more, M53 appeared absolutely wondrous in my 4.8mm Nagler (425x), filling the field with myriad, tiny points of light.

Of NGC 5053 Walter Scott Houston wrote , "In large instruments it is a little gem of woven fairy fire." It was discovered by William Herschel in March of 1784. As globular clusters go, NGC 5053 is pretty faint. It didn't jump out at me like most do. In my 18-inch at 94x it appeared primarily as a faint, mostly round, smattering of stars embedded in a large very faint glow. The entire cluster appears diffuse--there is no bright core of tightly bound stars as seen in most examples of its type. At 270x NGC 5053 resolved into an irregular smattering of faint stars. At that magnification it appeared much more like an open cluster than a globular.

Oddly, the fainter NGC 5053 is actually the closer of the two (although not by much). Both are located far above the plane of the Milky Way. In fact, NGC 5053 is one of the intrinsically faintest of the known globular clusters, shining perhaps with the light of a mere 16,000 suns. It is also one of the most metal-poor, indicating that it formed from interstellar gas that had not been significantly enhanced with the byproducts of many generations of stars.

Planning Your Observation

Note that we have made the window as small as possible to fit the space here.

The SkyTools 3 Nightly Planner is set up (above) for May 2 at Tierra Del Sol for a 10-inch (25 cm) telescope. This location has a naked-eye limiting magnitude of 6.9. The red-dashed line in the graphic at the top displays the altitude of M53 during the night. The shading is the actual brightness of the sky taking into account moonlight, twilight, and light pollution. By looking at the line we can see that the best time to observe M53 (and NGC 5053) will be after 11 PM.

SkyTools has calculated that you can go ahead and start looking at 20:45 (the Begin column in the planner). The best view will be at 23:12, and the good views will last until 03:21, when it is low enough in the sky that we are now looking through too much air. These calculations are unique to SkyTools, which samples the visual contrast of the object as seen in the eyepiece over the course of the night.