OASI - Roland L T Clarkson

In the early 1950s, a local amateur entered an elite group of distinguished astronomers. The leading mapper of the Moon, H P Wilkins, named a lunar crater in honour of Roland L T Clarkson, FRAS, who at the time lived at The Bungalow, The Avenue, Trimley, Suffolk. The East Anglian Daily Times and the Ipswich Evening Star of 18February 1954 carried articles on Clarkson and his crater.

Today we think of the Moon as being on our celestial doorstep: Neil Armstrong set foot on the Moon's surface as long ago as 1969 and more recently, in 1993, the space probe Clementine mapped the Moon in great detail. Yet when Clarkson was observing, just fifteen years before Armstrong's 'giant leap for mankind' the Moon appeared as much beyond our physical reach as it ever had been. Its study was primarily in the domain of the amateur astronomer often working with very modest equipment. The Lunar Section of the British Astronomical Association (BAA), under the guidance of Section Director H P Wilkins, took a leading role in mapping the lunar surface. Clarkson had a particular interest in the Moon and was a prolific contributor to the work of the Lunar Section. Clarkson developed great skill at sketching details of the lunar surface over 30 years of practice at the eyepiece of his 6½ inch reflector. The dedication and quality of his work earned him great respect amongst his contemporaries.

Born in Suffolk in 1889, Clarkson became interested in astronomy as a schoolboy. He kept notebooks and sketches from 1906, when he began his observation work in earnest, and continued to do so for almost 50 years. The BAA has many of his observations in its archives.

Clarkson was a founder and president of the Ipswich and District Astronomical Society (IDAS). In the early 1950s, IDAS occasionally met at Orwell Park Observatory to use the 26cm refractor. IDAS was a precursor of OASI and some members of IDAS later became members of OASI.

In subsequent re-mapping of the Moon, the International Astronomical Union removed names of some of the contributors to lunar astronomy who were less well-known internationally; unfortunately Clarkson was amongst them. Clarkson's crater has reverted to its original name, Gassendi A. The crater is easily observable, being over 33 km in diameter and ringed by 4000 metre high peaks. The pictures below show the position of Gassendi A on the lunar disk, and a close-up of the crater itself.

	Article about Clarkson in the Ipswich Evening Star, 18 February 1954.
	Clarkson's obituary notice in the Ipswich Evening Star, 10 April 1954.
	Image by James Appleton, 25 June 1999. 250mm SCT at prime focus, 1/125sec exposure on 400 ASA B&W print film.
	Image by James Appleton, 04 August 1998. 250mm SCT, positive projection using 26mm eyepiece, 1/4 sec exposure on 200 ASA colour film.

Nowadays, experienced observers are finding their interest in the Moon revitalised by the use of sophisticated computer-controlled telescopes and electronic imaging. Exciting as this technological revolution in amateur astronomy is, it is important to remember that the techniques that Clarkson used - a pencil and paper and the observer's eye - are still excellent tools for lunar observation. Observing the Moon directly gives a real sense of exploring another world.

However you prefer to observe, take the opportunity to explore the lunar landscape and when you do have a look at crater Clarkson (officially Gassendi A).

Clementine successfully completed its lunar mapping mission in 1993. However, a fault resulted in the spacecraft jettisoning a large proportion of its fuel into space. As a consequence Clementine was unable to continue its intended mission to flyby the asteroid Geographos. Despite this incident, the Clementine probe was highly successful, returning 1.5 million images of the lunar surface including many which show the surface topology in high resolution. Observations made by Clementine appear to indicate the presence of ice in areas of the Moon close to the lunar South Pole which are permanently in shadow. The ice, if it exists, may have been brought to the Moon by meteorites.

Gassendi is well known to lunar observers. It is 100 km in diameter with high walls and a prominent central peak. The presence of a central peak is evidence that the crater has been formed by the impact by a meteorite and in fact most if not all the lunar craters are thought to be impact craters. A meteorite travelling at high speed will explode on hitting the surface of the Moon - the peak is due to the shock-wave rebounding and forcing the surface upwards. The walls are formed by the curtain of material blasted out from the lunar surface by the force of the exploding meteorite falling back down to form a ring around the centre of the impact. Part of the North wall of Gassendi has been demolished by a subsequent impact which formed Gassendi A.

Transient Lunar Phenomena (TLP). Gassendi is famous for the widely observed TLP seen on 30 April 1966. TLPs are strange features - mainly colourations or glows - which are seen from time to time on the otherwise unchanging lunar surface, most often appearing in crater floors. TLPs are somewhat controversial and many observers discount them as optical illusions while others claim they are manifestations of real events - such as the seeping of gasses from beneath the surface. According to Patrick Moore's Guide to the Moon, the Gassendi TLP was a wedge shaped orange-red streak extending from the wall of Gassendi right across to the central peak. On two occasions in 1975, observers at Orwell Park Observatory thought that they observed TLPs, although later considerations suggested that the observations were false alarms.

Lunar Drawing If you want to try drawing lunar surface details here are some brief tips:

More advanced techniques that you might wish to apply include the finishing of sketches using India ink- (diluted with water to get the various shades between black and white) and the use of Schroter's system of grading the brightness of areas from 0 to 10 and producing a labelled contour map of brightness.

CCDs (Charge Coupled Devices) These are electronic cameras which can obtain images of the lunar surface which would be difficult to capture by other means. The fluctuating seeing conditions caused by turbulence in the Earth's atmosphere mean that you are lucky if you manage to take a conventional photograph at the right moment, whereas you can gather CCD images continuously, subsequently saving on computer those which captured the moments of fleeting good seeing when the atmosphere steadies.

Roland Clarkson - Trimley's Moon Man