Deep Sky Section Meeting 2004 - Meeting Report

Held at the Humfrey Rooms, Castilian Terrace, Northampton, 2004 March 6th

The 2004 Deep Sky Section meeting marked the retirement of Nick Hewitt as Section Director, after some 12 years in the post. The BAA Council had appointed as his successor Dr Stewart Moore, a keen visual observer well known for his fine drawings of deep-sky objects. The meeting was conducted by Dr Hewitt and the official handover took place at the end of the day.

In his introductory speech Dr Hewitt noted that the Section's membership was a healthy 120. The Section web page had recently been updated by Callum Potter. The archive of visual observations had now been fully scanned and work had begun on the photographic archive. The 2003-4 period had been one of the best years for observations submitted to the Section, the material received including webcam and video work. The small band of supernova hunters had continued to go from strength to strength. Of the 300 supernovae discovered in 2003 by amateur and professional astronomers worldwide a remarkable 50 had been found by UK observers. CCD technology had now progressed to the point where amateurs were discovering novae in nearby galaxies. Martin Mobberley had recently found a nova in M31 and Mark Armstrong had found another in M33.

Nick Hewitt then gave the first of the main talks, on amateur observations of galaxies. He noted that galaxies have come into their own as targets for amateurs only with the advent of the CCD, as galaxies are generally difficult objects for the visual observer and do not impress newcomers. Observing galaxies became popular with amateurs at the beginning of the 1980s, with the publication of books such as Burnham's Celestial Handbook and the Webb Society Deep Sky Observer's Handbook: Galaxies as well as the American Deep Sky magazine. The 1980s were the heyday of the visual observer and traditional film photography, the Section receiving many sketches and photographs at this time. A few dedicated members systematically searched for supernovae. There were no successes, although one amateur narrowly missed the credit for a discovery by submitting his observation by post!

Affordable CCD cameras hit the amateur market in 1991, and from then on fewer 35mm images were received by the Section. Drawings declined as well, visual observers preferring to concentrate on planetary nebulae. The introduction of CCDs led to the UK's first supernova discovery by Mark Armstrong in late 1996. CCD cameras greatly improved in quality during the 1990s and today's amateur images rival those taken by professionals just a decade ago. On the other hand, Dr Hewitt remarked that for all the rapid advances in technology and remarkable discoveries, some of the romance of deep-sky observing had gone. This was particularly true with the advent of computerised 'Go To' telescopes at prices beginners could afford, which removed the incentive for beginners to learn their way around the sky and took away the enjoyment of finding deep-sky objects.

The second speaker was Bob Marriott, who talked about the Palomar Observatory Sky Survey. The Northamptonshire Natural History Society had recently obtained a copy of the POSS prints from Imperial College, London and once the collection had been organised it was hoped to make it available for amateur astronomers to come and use. Imperial College had originally paid £20,000 for the prints back in 1982, but some academic institutions are now giving away such collections at knockdown prices, because they take up space and are being superseded by digital sky surveys. The original sky survey was carried out from 1950 to 1957 with the 48-inch Schmidt camera at Mount Palomar, USA in red and blue light. The fantastically detailed wide-field photographs had a limiting magnitude of 22. The original survey went down to declination -40° and the southern sky was later surveyed by the UK Schmidt Telescope in Australia. A second survey was carried out in the 1980s with improved photographic emulsions and a third survey is now being undertaken with an array of 112 CCD chips at the focus of the 48-inch Schmidt. With the help of a video camera and light box, Bob Marriott demonstrated the amazing amount of detail and faint objects visible on the prints.

An excellent ploughman's-style lunch was then laid on by the Northamptonshire Natural History Society and members had plenty of time to chat and view a fine exhibition of observations from the Section archives.

The first speaker of the afternoon session was Dr Katherine Gunn of Southampton University, whose talk was titled 'Galaxy Clusters and their Use as Cosmological Probes'. Dr Gunn, who is involved in research with the Chandra and XMM-Newton X-ray telescopes, began by saying that galaxy clusters are the largest gravitationally-bound structures in the universe. It was from observations of galaxy clusters that astronomers found that the universe is much more massive than it at first appears. Velocity measurements of galaxies in clusters showed that the total mass of a galaxy cluster was much greater than the masses of all the galaxies in the cluster added together. The invisible mass was originally called 'dark matter' but is now thought to be caused by the as yet unexplained phenomenon of 'dark energy'.

Galaxy clusters can be detected in several ways. Hot ionised gas in clusters causes them to show up in X-rays and synchrotron radiation caused by magnetic fields in the clusters make them good radio emitters as well. There is also the SZ effect, in which light crossing a cluster gains energy due to the expansion of the universe and so the cosmic microwave background is amplified when we look in the direction of a cluster. In optical wavelengths, the use of redshifts to determine distances allows us to confirm that a group of galaxies are all at the same distance and so are a true cluster and not a line-of-sight effect. If galaxies are far enough out, redshift causes them to appear red on colour optical images and groups of such red galaxies betray themselves as clusters.

Galaxy clusters are believed to form when a slightly denser region of the universe causes galaxies to clump together under gravity. Computer simulations show that galaxies cluster together in long filaments, although the exact pattern of clustering varies according to whether the universe is closed, open or flat. A notable feature of galaxy clusters is that most of their members are elliptical galaxies. Astronomers believe that they may have started out as spiral galaxies but had their arms torn off by multiple collisions with other galaxies. The presence of many spiral galaxies on the outer edges of clusters supports this idea.

The immense gravity of galaxy clusters causes them to bend light coming from objects beyond them. This 'gravitational lensing' effect can sometimes be used to amplify more distant galaxies and so allow us to detect galaxies well beyond the normal range of our telescopes. A recent image of galaxy cluster Abell 1835 taken with the ESO Very Large Telescope shows a galaxy with a redshift of 10. If this result is confirmed it will prove to be much the most distant galaxy known.

Nick Hewitt and Stewart Moore then led a general discussion on the future of the Deep Sky Section, during which Bob Marriott presented Dr Hewitt with a bottle of wine in recognition of his 12 years' service as Director. There was much support for the suggestion of a joint meeting of the Deep Sky Section and the Webb Society, which has similar aims to the Section. More controversial was the idea of reviving a Section publication - the problem being to get members to send in contributions!

Two talks for visual observers followed the afternoon tea break. The first was by Owen Brazell on the Local Group of galaxies. The Milky Way and M31 in Andromeda are the two principal members of our local cluster of galaxies, which contains between 35 and 40 members, most of them dwarf elliptical and irregular galaxies. Observing these small galaxies in the local group is important, because they are the only examples of dwarf galaxies observable - further out in the universe they are too faint to be seen.

M31 is a typical spiral galaxy, with bluish spiral arms where stars are forming and a yellow core dominated by older stars. The low surface brightness of its outer regions makes it a disappointing object for newcomers to astronomy. The next largest galaxy in the local group is M33, nearby in the sky but more difficult to see because it has a large apparent size and its light is spread over a wide area, making it appear faint. It is often easier to see in binoculars or a small telescope than in a large instrument. However, the brightest nebula within this galaxy can be seen in quite small instruments and has its own NGC designation, NGC 604. More difficult again is Barnard's Galaxy, NGC 6822 - another large, low-surface-brightness object that is made even more difficult by its low altitude in the UK. Well below the British horizon are the two Magellanic Clouds, satellites of the Milky Way that are visible to the naked eye. The Large Magellanic Cloud shows intense star formation, due to a close pass with the Milky Way in the past and astronomers believe it will eventually merge with the Milky Way. Some dwarf galaxies, such as M31's satellite galaxies M32 and M110, can be seen in small instruments while a number of others are challenging objects for owners of large telescopes.

A few years ago astronomers discovered a galaxy in Sagittarius in the process of being destroyed by colliding with the Milky Way. The bright globular cluster M54 is thought to be its core or one of its star clusters. The great globular cluster Omega Centauri may also be the core of another galaxy 'swallowed' by the Milky Way in the remote past, as unlike other globular clusters it has two stellar populations and shows rotation. In addition, Hubble Space Telescope images of M31 show it to have two nuclei, making this another possible example of galactic cannibalism.

The last of the main talks was by incoming Director Stewart Moore, on the seasonal topic of galaxies in the 'Sickle' asterism of Leo. Located far from the Milky Way, this region contains many galaxies for both small and large telescopes. The brightest is the 9th-magnitude spiral NGC 2903, so bright that one wonders why it was missed by Messier in his survey. It is easily visible in 10x50 binoculars and shows an elongated core at high power in a telescope. For owners of larger telescopes there are two notable clusters of galaxies - Hickson 44, which Stewart finds easy in his 14-inch Dobsonian, and the more challenging Hickson 57 or Copeland's Septet. One of the most notoriously difficult objects in Leo is the galaxy Leo I - a low-surface-brightness object that would be reasonably easy to see were it not just 15 arc minutes south of 1st-magnitude Regulus. Dr Moore has picked out this difficult object with the 20-inch reflector at the COAA observing site in rural Portugal.

There were three short items at the end of the meeting, two of them by Owen Brazell. In the first he compared the performance of various deep-sky filters that he had tested with the help of Maurice Gavin using a spectroscope. The performance of the classic filters made by Lumicon - even some that had seen 20 years of use - had not degraded, though Mr Brazell had not yet succeeded in obtaining any filters from the recently-relaunched Lumicon company. Some filters recently introduced by Tele Vue had given disappointing views visually and this was borne out by their very loose passbands as determined spectroscopically.

Mr Brazell then spoke about the remarkable discovery of a new nebula near M78 in Orion, by US amateur Jay McNeil on CCD images taken with just a 76mm refractor. When he spotted the new object he could not find any corresponding object on Palomar Observatory Sky Survey images. He contacted noted astronomer Brian Skiff, who asked the University of Hawaii to image it. These professional images confirmed the presence of the new object, which was not visible on images taken in late 2003. However, it may have been observed in 1966 and so may be a recurrent object; moreover, the IRAS satellite noted an object at this position when it surveyed the sky in 1983-4. The object, informally named 'McNeil's Nebula', could be important in our understanding of stellar evolution and amateur CCD monitoring of it could be of much scientific interest. Paul Whitmarsh then showed a CCD image of the nebula he had taken with a 300mm telephoto lens.

The meeting concluded with a few words of thanks to the speakers from Stewart Moore and the presentation of a second bottle of wine to Nick Hewitt! Thanks were also given to Cyril Sampson of the Northamptonshire Natural History Society for his sterling work in preparing the refreshments.

Lee Macdonald