From: Brian Skiff Newsgroups: sci.astro.amateur Subject: Messier 81 naked-eye Date: 10 Jan 1997 18:40:31 -0800 As mentioned briefly in the binocular-observing post, I was able to see M81 naked-eye last night from Lowell's Anderson Mesa dark-sky site. In case others would like to try this, here are some details. For reference, have a look at Uranometria chart 23. The two galaxies lie in a string of faint stars that starts with 24 UMa (also the variable DK UMa) at the west end, and arcs eastward and a bit south past M81 and NGC 3077 to a mag. 6 star appearing on chart 24 (brightest of a triangle). M81 in fact is one element of the string. To have a hope seeing M81, you need first to identify several of these stars. The brighter star about 1.5 degrees west of M81 is HD 83489, at V mag. 5.7. Next identify the fainter star at the east end of the string (the one on U2000 chart 24), which is HD 89343 = EN UMa, a very small-amplitude delta-Scuti star, at V mag. 6.0. Now, between HD 83489 and 89343 I consistently saw (glimpsed is a better term, however) at least three star-like objects. First, about 1.5 degrees east of M81 (and just west of HD 89343), is HD 87703, which is V mag. 7.1. If this star isn't pretty readily visible (at say the 20-30 percent detection level), then you probably won't be able get the galaxy. Much more difficult (at the 5-10 percent detection threshold) is the group of stars shown on the U2000 chart near NGC 3077. These are HD 86458 (V=8.0), HD 86574 (no photometry, but roughly mv=8.0), and HD 86677 (V=7.9). I saw these three (or perhaps just the closer pair 86458/86677) as a single object. Assuming V=8.0 for 86574, the combined brightness of the three stars is V=6.8, but the extended nature of the trio means the surface brightness will be lower to the naked eye than a single star of that magnitude, making it more difficult to spot. The third object, repeatedly spotted in the same (correct) place, is M81! Again, this is a threshold object, which I detected only 5-10 percent of the time with optimally-averted vision together with the other faint stars just mentioned. On occasion I also seemed to pick up another star, HD 85828, which is about 40' south of the galaxy. This star has no published photometry either, but has a rough magnitude of 8.0. My observation is neither all that remarkable nor unprecedented. Appended below is a response to this observation from Brent Archinal. The SAO star he mentions seeing is HD 87703 from the foregoing. I think the three previous visual sightings are not the only ones published. I vaguely recall a brief Sky & Telescope letter or note (late-60s or early-70s?) discussing the visibility of M81 and other bright galaxies, such as NGC 253 and NGC 5128. Perhaps someone with a collection of old S&T's can dig that one out for us. Both NGC 253 and NGC 5128 are somewhat closer than M81, which is probably the most distant discrete object visible to the unaided eye, at something like 3.6 megaparsecs (11.8 million light-years)! Having tried this observation seriously (and unsuccessfuly) twice before, I found the key this time was getting all the field stars sorted out. Because there are several stars of similar brightness nearby, you really must be able to identify each of these in order to securely locate the galaxy. As mentioned in the binoculars post, I was using the 6x30s as a guide, which I don't have a problem with, although it could probably be done using only unaided eyes and a chart such as the relevant field from the Tirion "Sky Atlas 2000", which shows all the necessary stars. \Brian Skiff (bas at lowell.edu) +++++++++++++++++++++ From: Brent A. Archinal Subject: Re: Minor observing milestone To: bas at lowell.edu Date: Fri, 10 Jan 1997 13:34:39 EST > A fine photometric night tonight (10th Jan UT) with typical very-low > wintertime extinction. While doing some binocular observing with my > marvelous Fujinon 6x30s, I spotted M81 quite convincingly naked-eye. > This by the way, from the catwalk of the Lowell 1.1-m on Anderson Mesa. > Yipee! > \Brian Brian - Sounds like a wonderful night! Congratulations on the naked-eye observation of M 81. By my count, this brings to four the number of people who been able to do so, including Stephen O'Meara, myself, and Aristides Tzarellas (Webb Society "Deep-Sky Observer", Oct., 1996, p. 1). Could you also see SAO 15100 (V=7.2) to the east? This was the faintest star visible in the area (10 degrees above the horizon!) when I managed my observation from Colorado. Regards, - Brent ++++++++++++++++++++++