by David Kingsley
I arrived about 6:30 pm and set up my 14.5 inch Starmaster Dob on one of the observing pads by the observatory. John Gleason arrived just behind me, and set up for astrophotography on the flat area down the hill from the observatory. Temps hovered around 45 degrees most of the night. The humidity began around 70% and rose to 90% (enough to make things damp but not soaking wet) There was an occasional little breeze, but no problem at all with gusty wind. John and I both noticed that there was hardly any naked eye twinkle to the stars. The bright constellations of winter made a great sight hanging steady in the sky. I was able to get in about five solid hours of observing before the moon rose and bands of clouds started building up on the eastern horizon after midnight
I headed over to M31 just after astronomical twilight began. When I started my extragalactic globular cluster observing project last fall, I could observe M31 for hours as the galaxy rose, transited nearly directly overhead, and slowly began to fall again in the sky. With spring nearly upon us, M31 is now already positioned lower than 45 degrees in the west before the sky even gets completely dark. Still, I spent an enjoyable hour or so tracking down far away globular clusters while M31 was still 30 degrees or so above the horizon. I was able to find four more extragalactic globs in M31 last night, bringing my total to sixty M31 globular clusters since I began hunting at LSA last October. Extragalactic fishing has been a great way to extend a globular cluster observing project through the winter, and I still have a few targets both in M31 and other local group galaxies that should provide challenge targets for the future.
I also tracked down one of the fainter globs in our own Milky Way, Palomar 1 in Cepheus. This is a sparse, faint cluster whose metallicity and position far from the plane of the galaxy both suggest it is more likely to be a globular than an open cluster. However, the HR diagram and main sequence turn off point for Palomar 1 suggest it is only 6 to 7 billion years old. That is only about half the age of a typical globular cluster in our Galaxy. Palomar 1 thus may have formed much more recently from the bulk of other globular clusters in the Milky Way, and by a different mechanism (see http://www.journals.uchicago.edu/AJ/journal/issues/v115n2/960336/960336.html).
I had tried to find Palomar 1 before from both Dino Point and LSA, but had never been able to convince myself I had seen it. Last night I had a much more detailed print out of faint field stars from a SkyTools observing chart. With lots of quiet staring under a hood at the eyepiece, I could just make out a small threshold glow with averted vision at about the right location, though much smaller than the circle indicated on the Sky Tools chart. Today I compared a Digitized Sky Survey image of the region with the rough sketch I made last night at the eyepiece. The threshold glow I saw last night is located just at the core of the sparse globular, and its shape matches the arc of the brightest individual stars near the core.This is a much harder target than I thought it would be. Although Palomar 1 has integrated an visual magnitude of 13.6, it spread widely over a circle of several arc minutes. Fortunately, the brightest individual stars in Palomar 1 have visual magnitudes of about mag 16.3 ( the peak of the red giant branch). That brings the brightest stars just within my visibility limit with a 14.5 inch scope from sites near the Bay Area.
I tracked down a bunch of other targets last night as well, including:
When the moon was going to come up, I also took a look at Jupiter. The bright dot of Io was obvious against the edge of Jupiter's surface. However, the views were no where near as steady as they had been a couple of weeks ago at Fremont Peak. This surprised me because the naked eye stars had much obvious twinkling last night than on other recent trips, and many of the starfields that I had chased down earlier during the night had looked pretty steady at powers up to 400x. I stayed long enough to watch Io's shadow appear on the edge of Jupiter, then packed up and headed for home about 12:30 am.