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Observing Hickson compact galaxy cluster #50

Jane Houston Jones

Hickson 50 as recorded in the digitized sky survey at Palomar Observatory.

Both telescopes Jane used to observe Hickson 50 — in the foreground, the 17.5" f/4.5 Litebox dobsonian, and the 30" f/4.8 Challenger newtonian at Fremont Peak Observatory.


In 1755, Immanuel Kant published Universal Natural History and Theory of the Heavens. He noted that some nebulae have different explanations and might be island universes. In 1877, E. M. Stephan discovered a small dense group of galaxies that now bears his name. Stephan's Quintet consists of five overlapping galaxies of unusual shape with structure of gas and stars that seem to interact with the neighboring galaxies. One large spiral in the quintet is probably a foreground object which happens to lie along the line of sight to the more distant galaxies.

In 1918, H. D. Curtis made galaxy observations at Lick Observatory on the Crossley reflector. He observed islands of stars or spiral nebulae. In 1923 Edwin Hubble made the discovery of Cepheid variable stars in the great nebula in Andromeda. For 30 years, astronomers using the 100-inch telescope at Mount Wilson made nightly discoveries of groups and clusters of galaxies.

In 1948 Carl Seyfert, observing with the 100-inch Hooker Telescope at Mount Wilson, discovered another compact group of galaxies, now called Seyfert's Sextet. These galaxies exhibit violent tidal forces, an intergalactic plume of galactic matter. These apparent interactions led astrophysicists to the conclusion that these are compact dense systems. Geoffrey and Margaret Burbridge studied the spectra of these galaxies and discovered that all but one of the galaxies in the two groups shared the same red shift velocity, but that discordant red shifts are found in many compact groups of galaxies.

In 1957 George Abell presented a paper with a catalogue of 2700 rich clusters of galaxies visible on the Palomar Sky Survey plates. In the early 1980's Paul Hickson, in the interest of taking a large sample of compact galaxy groups, composed a catalogue using these same Palomar Sky Survey plates. The search was intended to find a good cross section for study with the expectation of finding new examples of discordant red shifts, so he employed rigorous criteria to select 100 compact galaxy groups. This group of 100 compact galaxy groups are a popular observing project for amateur astronomers. Hickson 50 in Ursa Major is deemed beyond the limit of almost all amateur telescopes, although it has been successfully observed in amateur telescopes ranging from 17 to 36 inches in aperture. Hickson 50 was my observing project over two recent weekends. First I attempted it May 26, 2003, at Lake Sonoma through my own 17.5 inch reflector. Next, I attempted it May 30 through the Fremont Peak 30-inch Challenger reflector. My 20 other weekend Hickson observations can be read here:

May 26, 2003: 17.5 inch f/4.5 Litebox reflector. 222x 9mm Nagler, 333x 6mm Radian. Hickson 50 in Ursa Major 11h 17m 06.1s +54.55.07. Five components, something fuzzy seen. M97, the Owl nebula, is so close to this object, at the edge of the eyepiece field of view at 125x of my 16mm Nagler, 20 arc minutes away. My 125x eyepiece chart (created with SkyTools 2 charting software, made it a snap to get the field of view in the eyepiece. A distinctive trapezoid (like the Hercules keystone) asterism of stars led the way east of M97. Exactly one asterism further east were the pair of mag 13 stars. Directly between these two and a little north should be Hickson 50. I did get confused because the SkyTools map showed an object that I took for a cluster — a circle with a cross in the middle. It's just a second confusing galaxy symbol it turns out, and this turned out to be Hickson 50a, the brightest component of the group. I did see a smudge of something in the right spot. To me the smudge was more than one object, like two clumps a little lighter gray than the background of the eyepiece view. The only other star in the area is a mag 17 star to the north, and I could see that star as well. These galaxies are in the 18 and 19 blue "B" magnitude range meaning they are a little brighter in the visible magnitude range.

May 30, 2003: 30-inch f/5 reflector at Fremont Peak Observatory. I noticed that Mojo had the 30-inch aimed at M97 at our SFAA night at Fremont Peak. I took over the telescope for about 45 minutes and visually moved the big scope by pushing my hands against the truss poles and peering into the eyepiece while moving the telescope, holding a paper chart in my other hand, and balancing at the top of the tall ladder. Ursa Major was high over head. From M97, I changed the eyepiece from 9mm Nagler (400x) back to the 31mm Nagler (114x), moved the telescope past the trapezoid shaped asterism and voila, a little clump of galactic matter popped easily into view! Then I pumped up the power to 200x with the 16mm Nagler, and then higher using the 9mm Nagler for 400x. At each magnification change, I presented Hickson 50 to a group of about 12 members of the SFAA for their viewing pleasure. Some of the group definately saw more than one clump. I think all were mighty impressed. I distinctly made out 4 components, roughly in a tight circle. Two of the galaxies, 50a and 50c, were brighter than the others, and appeared more elliptical or round. The other two, 50b and 50d, were elongated. I didn't see 50e. The group was ready to move on to other brighter objects. I think mag 13.7 Pluto was the next target. Like Hickson 50, Pluto was also next to a distinctive asterism, shaped just like the constellation Delphinus. On the next night we observed Pluto at Fremont Peak in several telescopes for confirmation. Mike Portuesi confirmed Pluto by starhopping to it in his homemade f/7.1 10-inch dobsonian refector. It was in a slightly different place than the night before, as compared to the mini-Delphinus star group. It was Mike's first time to find Pluto in his own telescope. If you look for Pluto tonight, it will have moved on, being a wanderer in our solar system against a background of stars in our own galaxy.


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