First discovery: 1981A in NGC 1532 Number of discoveries: 46 Location: New South Wales, Australia Equipment: 25,30, and 40 cm Newtonians
Although Bob Evans, shown in Figure 10.1, was not the first amateur to discover a supernova (he was the fourth) and although there are now four amateur astronomers who have discovered more, namely Armstrong, Boles, Puckett, and Schwartz, Bob Evans is still the only truly legendary figure in supernova discovery. To discover supernovae visually, simply relying on your memory of the galaxy fields, and to haul a telescope manually to each object, with no GO TO facility, is awesome. Not only this, but Evans has discovered some absolutely cracking bright supernovae: a result of patrolling the brightest galaxies. If you are not too keen on patrolling 10,000 galaxies, Evans' strategy of just bagging a couple of bright, visually discoverable, supernovae per year may be one to emulate. Remarkably, Evans has discovered three supernovae in the same galaxy, NGC 1559, in 1984,1986, and 2005. In addition, in the beautiful galaxy NGC 1365, he has discovered two supernovae, in the years 1983 and 2001, and likewise for NGC 1448, where he bagged supernovae in 1983 and in 2003. In 1986, Evans bagged the only discovered supernova in NGC 5128, alias the strong radio galaxy Centaurus A. For most amateur astronomers, discovering a supernova in a Messier galaxy (there are only 39) is about as prestigious as it gets. Most of these are in the Northern Hemisphere
though (as Messier was a Frenchman). Despite this, Evans has discovered four supernovae in Messier galaxies, namely 1983N in M 83; 1988A in M 58 (jointly with Ikeya, Pollas, and Horiguchi); 1989B in M 66 (jointly with Manzini), and 2003gd in M 74. Sixteen of Evans' supernova discoveries are in the brightest 100 supernovae, and he has also bagged 15 very bright, highly prestigious, Type Ia supernovae, an awesome reputation! Bob Evans appeared on a video tape made by Rob McNaught that I used to distribute for Guy Hurst's The Astronomer magazine in the early 1990s. Since then, Evans has written up nearly all of his discovery accounts for The Astronomer magazine. They make fascinating reading.
Bob Evans started serious galaxy observing in the 1960s using his 25-cm Newtonian. In the early 1970s,he considered turning the telescope into a photographic instrument to patrol for supernovae but that did not work out. However, Gus Johnson's discovery of the bright supernova 1979C in M 100 inspired Evans and with help from Queensland amateurs and Tom Cragg at the Anglo-Australian Observatory, he was able to make photographic slides of hundreds of galaxies as a master reference library. Evans' first independent discovery (1980N) was not attributed to him because he spotted it,as a mag 12.5 intruder in NGC 1316 (Fornax A) just a day after the Chilean Observatory's astronomer Wischnjewsky claimed it on December 7,1980. It was a close call, but inspired Evans further. Only 11 weeks later Evans did bag his first official supernova discovery with the 25-cm telescope; the first supernova of 1981, in NGC 1532. That discovery, 1981A, was made on February 24,1981. Coincidentally, the supernova of the century would be discovered exactly 6 years later on February 23/24, 1987, that is, SN 1987A in the Large Magellanic Cloud. Bizarrely,less than 3 months after Evans missed 1980N,he made up for the one that got away in NGC 1316. Another bright supernova appeared in that same galaxy, at magnitude 12.7, and became Evans' second discovery. Two bright supernovae occurring in the same galaxy within a few months is almost unheard of! Maybe the Reverend does indeed have inside information on the workings of the cosmos!
So, can anyone copy this Australian observer's visual trick? Well, before we get too excited, I think it is important to remember that there is less competition in the Southern Hemisphere, there are more clear nights than in most other countries, and, most importantly, winter nights in Australia are rarely as cold as in most other patroller's countries. However, there is little doubt in my mind that emulating Evans' visual discovery technique does not require a photographic memory. Every human brain has a remarkable ability to recognize patterns and spot something new. This ability has actually been traced to a specific part of the brain, which, if damaged, can result in the victim being unable even to recognize a picture of himself or herself. Amongst a crowd of thousands of Christmas shoppers, we can easily identify a friend or relative (or an enemy for that matter). Other astronomers have also exploited the power of the human memory to make discoveries. Foremost amongst these was the U.K.'s George Alcock who, in the 1960s, decided to build on his already formidable familiarity with the night sky (from three decades of meteor observing) and commit to memory all of the Milky Way stars he could see through his 80-mm binoculars! Essentially, he memorized, in patterns, some 30,000 stars. As a result he discovered five novae in the years 1967, 1968,1970,1976, and 1991. The last of these was discovered from indoors, while observing through double-glazed windows, at the age of 78! As someone who knew George, my explanation of how he achieved this phenomenal memorizing feat is simply that he combined a lifetime of sky watching with a nightly ritual and the already formidable powers of the human brain. If you asked him to draw any region in the Milky Way, to, say, 8th magnitude, from memory, he would find it almost impossible. However, if something new appeared, especially something of 7th magnitude or brighter, he would spot the change in a pattern instantly. Most people could not accurately draw their neighbor's face, but they could spot a change in their appearance. Similarly, they could spot something that was out of place in their home, like an ornament that had moved by a foot or so. It is all about spotting changes in patterns. Obviously, any visual patroller has to have good eyesight and a good memory. However, I would place a love of the night sky, ritualistic behavior, and superhuman patience as the top priorities, not a so-called photographic memory. People with photographic memories, excluding the genuinely rare savants, have simply trained their memories better than the rest of us.
Any visual patrol system has to be sustainable over long periods and, because the observer is outside in the dark, damp, and cold, ergonomics has to be a top priority. A telescope with an uncomfortable observing position, one that is complicated to set up, and weighs half a ton, is not suitable for hauling around the sky from galaxy to galaxy. One of the reasons that Schmidt-Cassegrain telescopes have become such a great success is because they can be stored in a small observatory and the eyepiece position moves very little as you move the telescope around the sky. Seemingly trivial issues like this can become all important when trying to find 14th magnitude specks of light in dozens of galaxies each night.
The vast majority of Bob Evans' supernova finds have been made with relatively modest amateur telescopes. First he used a 25-cm Newtonian, then, from January 1986, at Coonabarabran, a 41-cm equatorially mounted Newtonian (provided by the Commonwealth Scientific and Industrial Research Organisation) and, finally, a 31-cm Dobsonian. But he also used a 1-m telescope belonging to the Australian National University at Siding Spring on just over 100 nights from 1995 to 1997 (three supernovae were discovered visually with that instrument, from around 10,000 galaxy patrols). Evans has always made discoveries from New South Wales but his precise observing location has varied slightly. When using the 1-m telescope, he lived close to the Anglo-Australian Observatory in Coonabarabran, and he was a minister of the local Warrumbungle Parish of the Uniting Church in
Australia. In the late 1990s, he moved to a retirement villa at Hazelbrook in the Blue Mountains but kept his 41-cm Newtonian stored at a friend's farm at Mudgee. Initially, Evans' work was with a 25-cm Newtonian. Then he used the 41 cm with occasional access to the 1-m telescope at Siding Spring. However, his recent discoveries from the Blue Mountains site have all been with a 31-cm Dobsonian (or a Dobson mounting Newtonian as he more correctly calls it). From reading all of his postdiscovery reports in the British magazine The Astronomer run by Guy Hurst, it would appear that Evans usually works with a list of around 1,000 galaxies (depending on the season) and he works through them at a rate of one or two galaxies per minute, moving the telescope by hand from galaxy to galaxy, using a straight-through finder but no setting circles. Evans has stated that the most galaxies he has ever star-hopped to in a single night was 570, in 10 hours in March 1984. Normally, his observing sessions are only a few hours long. In the first 5 years of serious patrolling (i.e., 1981 to 1986), he made 14 discoveries from 50,000 galaxy patrols (i.e.,roughly one discovery for every 3,600 patrols),which is a similar patrol success rate to the best amateur CCD patrollers, except at a slower speed, and Evans' discoveries were much brighter.
Other successful visual hunters seem to use a similar strategy. In the 1996 December edition of The Astronomer magazine, the Italian visual supernova hunter Stefano Pesci reported that in a 4-year search program by himself and his Italian colleague Piero Mazza (using 40- and 51-cm telescopes), 30,000 galaxy observations were made on a database of 600 to 800 galaxies within about 130 million light-years. Two supernovae were discovered in that time and three were missed (one by 20 hours, one by 3 days, and one overlooked). Stefano reported that each galaxy was checked in 2 to 3 minutes but only 20 to 30 nights per year were used for patrolling. If my math is correct, this works out at roughly 150 galaxies per night per observer. Crucially, Stefano stressed that he and his colleague just enjoy observing galaxies: the supernovae are a bonus, not the single aim. By sticking to relatively nearby galaxies, they tried to ensure any supernovae would be brighter than magnitude 15.5.
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