Meeting of the Deep Sky Section, 2010 March 6: held at the Humfrey Rooms, Castilian Terrace, Northampton.
Supernova discoveries continued to be made by Ron Arbour and Tom Boles, with Ron reaching a total of 22 and Tom a staggering 128. Tom had once again discovered three supernovae in a single night and during the course of the year had broken Fritz Zwicky's record for the most supernovae discovered by a single individual when he made his 124th discovery (2009ii in UGC 10923) on 2009 August 21.
The Director then showed a sample of images received during the year from members, many associated with the Section's observing programmes. Surprisingly there were still some Messier objects that had not been adequately observed by the Section, although these tended to be the more southerly objects. The programme to monitor variable nebulae, run by Grant Privett, had attracted more interest, but unfortunately Gyulbudaghian's nebula, the one chosen for detailed study, had gone into deep fade the moment observers showed interest in it and was still almost invisible even on deep images. The Director also showed the first image received by the Section of Simeis 147, an extremely faint supernova remnant in Taurus. He noted that the images received had a huge range of exposure times--from a few seconds to an astounding 700 minutes.
The first main talk was by BAA Papers Secretary Nick James, on using remote telescopes. The advent of high-speed internet connectivity now allowed amateur astronomers stuck under Britain's cloudy skies to take images with large telescopes in first-class observing sites thousands of miles away, all from the comfort of their homes. However, remote observing can be expensive and difficult, so the BAA had recently appointed a Robotic Telescopes Coordinator to advise members on this new field. Mr James discussed two remote observing services currently available: Global Rent-A-Scope and Sierra Skies. Global Rent-A-Scope allows real-time observation, but you have to pay for all the time you are using the telescope, including slewing and parking it, so costs can mount up. Sierra Skies does not provide real-time observing --it just e-mails you the image after the resident observer has taken it--but it only charges for the exposure time and not all time on the instrument, and so is the cheaper option. It also has a less restrictive charging system.
Sierra Skies' main telescope is a 60cm reflector sited in California, with a large CCD giving a true field of view of 21 arcminutes. BAA members with a worthwhile project can apply to the BAA to have half the cost of using either service paid for out of the Ridley Grant, which was set up using a legacy left to the BAA by the late Harold Ridley. Sierra Skies' efficient system allows you to set up a list of objects you want the telescope to image, together with your desired exposures and filters. Mr James showed a 60-second exposure of a faint comet that he had recently taken with this system. It had a limiting magnitude of 19 and cost just 50p to take!
Sierra Skies is best for most observing programmes, but Rent-A-Scope is the system of choice if you need to take an image right now. Mr James gave a live demonstration of imaging using Rent-A-Scope, whose New Mexico site was still in darkness at the time of the talk. The globular cluster M3 was selected as the target, an exposure time was chosen, and then 'acquire image' selected. Shortly afterwards an image of M3 appeared on the screen in Northampton. The image can also be saved and downloaded to your own computer.
Grant Privett then spoke on variable nebulae. Defining a variable nebula as a nebula whose appearance varies as a function of time, Mr Privett noted that not many of these objects are known, only five or six being observable in visible light. The first one to be discovered was Hind's Variable Nebula in Taurus, discovered in 1852 with a 7-inch refractor. It then faded out of view and was not seen again until 1890. It is now known to be a very young star interacting with surrounding gas. Hubble's Variable Nebula was originally discovered by William Herschel in 1783, but its variability was only noticed by Edwin Hubble in 1916. It is bright enough to be seen in small telescopes and Mr Privett encouraged members to sketch as well as observe it--though he stressed the importance of using the same equipment each time, as otherwise it is difficult to compare observations to note any variability.
Several other variable nebulae offer a challenge to CCD imagers with larger telescopes. NGC 6729 in Corona Australis is too far south to be observed from the UK, but might be a good target for the remote imaging systems described in the previous talk. McNeill's nebula near M78 in Orion was discovered as recently as 2004 by US amateur Jay McNeill. It was found to have been recorded on images taken many years previously, but no one had noticed it before. It faded from view after about a year, and an image taken in 2008 showed practically nothing in its position. Gyulbudaghian's Nebula in Cepheus shows more radical changes in its appearance than do other variable nebulae. At times it shows a fan shape, but it has recently been invisible (as noted by the Director at the start of the meeting). Its variability is caused by obscuring material orbiting close to a young star casting shadows on the outer parts of the nebula. Mr Privett was currently taking one image per month of this object using a remote telescope provided by Sierra Skies.
In his conclusion, Mr Privett noted that for objects of such potential interest, surprisingly little work is being done on variable nebulae, and that they allow us to probe the environment of a fledgling star.
World-leading supernova discoverer Tom Boles gave the third main talk of the day, on the past, present and future of supernova hunting. He began his talk with a brief history of extragalactic supernova discovery. He noted that in the past, many supernovae had been discovered by a small number of dedicated individuals, such as the US-based professional astronomers Fritz Zwicky and Jean Mueller, who had discovered 123 and 100 supernovae respectively. More recently, many supernova discoveries have been made by similarly dedicated amateurs, although the first UK discovery did not come until 1996, when Mark Armstrong found SN1996bo.
But now the field was changing, with the advent of a growing number of automatic supernova surveys by professional observatories. Already the 2.5-metre telescope of the Sloan Digital Sky Survey had made 484 discoveries in the 2005-'07 period. These surveys were becoming more specialised, looking for specific types of supernovae--for example, the Texas Supernova Search is looking for supernovae that exploded when the universe was very young. There is even a proposed satellite dedicated to supernova hunting, though it has now been delayed and there is no guarantee that it will launch before 2020.
There are, however, two ambitious ground-based programmes on the horizon which will dwarf any amateur supernova search. The Pan-STARRS project proposes to scan the sky for supernovae using four 1.8m telescopes and hopes to turn up 300 supernovae per month--though no site has yet been selected for the telescopes. Closer to fruition is the Large Synoptic Survey Telescope, which is expected to carry out its first science in 2015. This mammoth 6.5m telescope will have an imaging sensor an incredible 3 feet wide and will survey the whole sky visible from its location; according to the project's official website, the LSST will see more of the universe than all previous telescopes combined. However, one will only have to look on the internet to see where the LSST is pointed and then look for one's own supernovae in another part of the sky, so the role of amateur supernova hunters is by no means over yet!
After lunch, John McCue spoke about observing double stars. Mr McCue, who is the Deep Sky Section's Double Stars Coordinator, described how as part of his work as a schoolteacher in a planetarium, he had done some remote observing using a 14-inch telescope in Chile. The telescope produced many images that he had not had time to examine, so he set his pupils to work on analysing the images, examining them for changes. In this way, several double stars were discovered that had not been previously catalogued. Then, looking at the Washington Double Star (WDS) catalogue, the global standard catalogue of double stars, Mr McCue came up with the idea of re-observing many pairs listed in the catalogue that had not been observed for many years. He had drawn up some lists of such neglected doubles and encouraged members to try verifying their presence for themselves. Their positions and separations could be measured quite easily using an 'astrometric' eyepiece (a type of eyepiece with an illuminated measuring reticule), but even measurements were not essential, as the publishers of the WDS, the US Naval Observatory, merely wanted to confirm whether these pairs existed.
The meeting then turned to a historical theme, with a talk by Lee Macdonald on 'Isaac Roberts, Edward Emerson Barnard and the Nebulae'. Roberts was an amateur astronomer who made a large fortune as a master builder. In 1885 he began using a Grubb 20-inch reflector for celestial photography --first from Maghull, near Liverpool, and after 1890 from Crowborough in Sussex. Roberts was the first deep-sky photographer to go really 'deep'--that is, to use very long exposures to reveal faint detail in nebulae unsuspected by even the best visual observers. Although one major historian has implied that he was amateurish in his methods, evidence from original sources suggests that he was, in fact, a careful and methodical worker. His 1888 photographs of M31 in Andromeda were the first to show that this object was, in fact, a 'spiral nebula' highly inclined to our line of sight, and considerably strengthened the then fashionable theory that spiral nebulae were not 'island universes' but relatively nearby objects, perhaps solar systems in the process of formation. If they were nearby, the spirals ought to show detectable internal motion within a short period, and Roberts carefully measured his own photographs of M31 and several other objects taken several years apart. He could find no such motions, and concluded that the spirals were very distant--though did not come round in favour of the island universe hypothesis.
The idea that Roberts was 'amateurish' stems from a confrontation he had in print with US astronomer Edward Emerson Barnard over the existence of certain nebulae. In fact, Roberts and Barnard had three such confrontations between 1895 and 1903. Barnard, a highly skilled observer but with no scientific qualifications, gained employment at the newly-opened Lick Observatory in California in 1888 and quickly began taking pictures of nebulae using long exposures, soon establishing himself as Roberts' American rival. In 1895, Roberts questioned the reality of nebulosity that Barnard had photographed around the star 15 Monocerotis, which Roberts could not discern on his own image of the same region. Roberts thought that the alleged nebulosity was background stars that were not resolved in Barnard's smaller instrument. Three years later, Roberts similarly dismissed a photograph by Barnard that showed faint outer nebulosity near the Pleiades. Finally, in 1903, Roberts claimed from his own photographic survey that only four out of fifty-two large 'nebulous regions' originally catalogued by William Herschel actually contained any nebulosity. Once more he dismissed nebulosity photographed in several other regions by Barnard and others as spurious. In each case, Roberts never changed his position on the reality of the nebulae, despite growing evidence that they were real. Mr Macdonald used some correspondence between Roberts and the Royal Astronomical Society to show that Roberts' intransigence in the face of evidence that he was in the wrong was due less to any lack of professionalism on his part than to a highly irascible temper and an aversion to criticism--traits that were probably shared by Barnard.
After a tea break, Nik Szymanek presented a survey of how night sky photography is done today. He started by describing how many kinds of short-exposure astronomical photographs can be taken with an ordinary, off-the-shelf digital camera. As an example, he showed an image of a noctilucent cloud display taken with a handheld camera pointed out of a window. Faint nebulae require a dark sky to be captured, and Mr Szymanek showed many images taken on his numerous observing trips to La Palma--where the naked-eye limiting magnitude can reach 7.9 and the zodiacal light is so bright that it is almost a nuisance! Mr Szymanek now uses a Vixen 10-inch modified Maksutov telescope on a Paramount equatorial mount. He also recommended the AstroTrac portable tracking mount for astrophotography while on holiday, as it is compact and light enough to carry onto an aircraft, though it is not cheap.
Mr Szymanek remarked that there has been no better time than now to get into deep-sky imaging, as there are now so many good CCD cameras on the market. Originally he took his images using the RGB method--that is, by combining three monochrome images taken through red, green and blue filters to produce a single colour image. Now he has progressed to LRGB--taking red, green and blue images as before, but combining the colour image with an additional monochrome 'luminance' image, which greatly increases the amount of contrast and detail in the final picture. He recommended the Maxim DL software package for controlling the camera and telescope tracking. Another recent advance has been special narrow-band filters, which allow beautiful images to be taken of emission nebulosity, even from light-polluted sites. Mr Szymanek has also used the Faulkes Telescope on Hawaii for remote imaging, and showed some spectacular shots of nebulae taken with narrow-band filters on this telescope.
Nik Szymanek's talk was the last of the day. Stewart Moore concluded the meeting with a vote of thanks to the Northamptonshire Natural History Society for acting as hosts and especially for all their efforts with the catering throughout the day, which included a splendid ploughman's lunch.