Ordinary Meeting, 2002 April 27

The deep sky scene of late spring

Dr. Hewitt opened by expressing his gratitude to the University of Wales and Cardiff Astronomical Society for hosting the meeting. He stated that in the summer months there was less time for observation, but more exciting objects. In this talk he would discuss the "Main Corridor" which stretches from Ursa Major to Leo.

The speaker opened his discussion with Mizar and Alcor - the middle stars of the bear's tail in Ursa Major - which was discovered to be a binary of separation 11.8' by Riciolli in 1650. This was not only the first binary to be discovered telescopically, but later the first spectroscopic binary to be found. Pickering showed in 1889 that it was composed of 6 stars. Dr. Hewitt commented that Ursa Major is our nearest star cluster, and that Dubhe (123ly) and Alkaid (106ly) move in the opposite direction to the other five members of the cluster.

In Coma Berenices, the speaker recommended the open cluster (Melotte 111) and described the Coma-Virgo cluster of galaxies (Abell 1656) as possibly the greatest of the Abell galactic clusters. The speaker also suggested the two contrasting globular clusters M53 and NGC5053 as prime observing targets. The latter was described by Walter Scott Houston as "a little gem of woven fairy fire".

Dr. Hewitt commented that the local supercluster is best viewed in spring, since we are close to one side of the cluster, and it is spring when we can see into it. Whereas the autumn sky offers only the Andromeda and Fornax galaxies, the spring sky offers a much richer view. The sedate spiral of M81 is one of the best known, and M109 is also well worth a look. The former is an active star forming region, in the aftermath of a close encounter which stirred up its dust content.

The speaker showed a superbly illustrated tour of many of the most interesting observing targets in Canes Venatici, which includes the whirlpool (M51) and M94, which appears elliptical but has a faint halo and is in fact spiral. Of particular interest were 19th century photographs by Welsh astronomer Dr. Isaac Roberts, who had taken a number of excellent images, often exposing for up to 4 hours using his Cooke.

Dr. Hewitt made brief reference to the work of the supernova patrol, commenting that Tom Boles' recent discovery of three supernovae within a week had brought him to a total of 22 discoveries, whilst Mark Armstrong had 37 supernovae and Ron Arbour 6. To close, the speaker extended "deep sky" to the limit with a Ratledge photograph of the Twin Quasar, which is 5 billion light years distant.

Following much applause for Dr. Hewitt's superb slideshow, the President thanked Cardiff Astronomical Society for hosting the afternoon, and adjourned the meeting until May 28th at Savile Row.

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Dominic Ford

© 2002 Dominic Ford / The British Astronomical Association.