Thanet Observatory

Tags: observatory, history, equipment

The Thanet Observatory is being run by the Monkton Stargazers group, who are scientists and engineers willing to give up their free time to educate the public in scientific matters.

The Observatory houses a 12 inch Newtonian Reflecting Telescope with a parabolic mirror of focal length 68 inches (1.7 metres). It is controlled by a drive system built by [AWR Technology][1] in Deal.

The telescope had an overhaul in the summer of 2013 with cleaning and realignment of the mirrors using a green laser collimator. The mechanisms for the drives were also cleaned, greased and rechecked.

When we acquired our 12″ Newtonian reflector it was in a very sorry state, having been built in the 1950’s and for the last 10 years subject to all weathers in the back of a garden.

As a charity, we had to ensure that the instrument was worth spending the money that would need to be generated to modernise the telescope. With that in mind the primary mirror was sent for testing by Alan Buckman, B.Sc, FRAS of AWR Technology.

Alan removed the mirror from it’s old three-point welded steel (9kg.) mirror cell. (the new cell is a much lighter nine point cell) The rear of the blank contained a message from Mr G. Hole of Brighton:

Refigured by G. Hole and Son Ltd. Brighton.
Astronomical papabola of 68″ focal length
When properly mounted its performance cannot be excelled.

(signed) G Hole (no date)

A very brave claim, to be sure, and not one that a manufacturer would dare make today, however Mr. Hole’s confidence was largely justified. When the testing was carried out we were very pleased to find that the mirror is capable of resolving a tenth of a light wave – an extremely respectable figure.

Having assured ourselves that the mirror was worth utilising we made plans for modification of the mount, adding a motorised drive with full computer control, and ordering a skeleton tube, etc. Work then began on the observatory which had to be suitable for public access and also ascetically pleasing.

A seventeen foot diameter trench, three feet deep was dug, together with a six feet long by three feet wide by six feet deep telescope pier cavity. The spoil was used to infill old lorry (truck) ruts leading past the site.

The large volume of the pier below ground was thought necessary to support the telescope mount, the base of which had to be raised about three feet in order that at 7° the telescope view was not obstructed. One obvious advantage in going as deep as this was that this pier cavity extended well into the rock substrate thus aiding stability.

The central pier support excavation still had to be taken down another three feet. This had to be done through chalk rock, which though soft offers a surprising resistance to the pickaxe. We resorted to breaking up the rock with a iron bar and sledge hammer and then shovelling out the resulting chalk rubble.

Four holes were then dug around the central pier (not shown in photograph) to provide supports for the suspended floor which must not be allowed to come into contact with the telescope pier. This is to ensure that vibration is not transmitted to the telescope. Note that the work has been carried out without much disturbance to the surroundings. It is hoped that construction can be completed without noticeable detrimental effects to the flora and fauna of the reserve.

A long section of 12″ plastic water pipe was lowered into the pier cavity and height adjusted to bring the top of the pier to the required level.

This was then levelled and held in place with two by fours. Very careful measurements were made to find the level for the main dome wall foundations and sections of iron pipe were driven in at intervals to show the depth of concrete needed. Wooden shuttering was added around the trench to complete the job.

The plastic pipe was added as an un-rustable re-inforcing. At this time we had a site meeting with the manufacturer of the dome to ensure that the components would mate up with the dome base.

The most stressful part of this job was the estimate of the amount of concrete required. We calculated the volume several times and in several different ways. It would have been bad enough to over-order but the nightmare was getting three-quarters of the way through filling the pier cavity and running out! As it was, our calculations were just about right and we had only a little left over.

Another important decision was over the type of concrete used. We left this in the hands of the technical advisor of Brett Concrete Ltd. The mix used was similar to that used in bridge piers with a small alteration in aggregate size to allow easy flow into our pier support. Some extra water was added into the chute to aid us in moving the concrete around the trench. Note the lengths of iron piping indicating the required level for the main dome wall foundations.

Great care was needed when we filled the central pier and especially the 12″ diameter pipe. First we had to fill the first foot of the pipe with concrete, making sure there were no air spaces formed, then the telescope mount bolt assembly was lowered into place. This was then carefully ‘polar aligned’ and the whole tube filled in.

The site was then left to overwinter until the last frosts had gone and dome wall construction could begin.

During this period planning was going ahead concerning the construction of the 16′ diameter dome, and details were finalised with Beacon Hill Telescopes regarding the construction of the skeletal tube.

Below are a few more photographs from the build.

Monkton Nature Reserve is owned and operated by the Thanet Countryside Trust, a not-for-profit charity established in 1982.

The reserve is situated in an old chalk quarry, last excavated in 1958. It was rescued from becoming a county council rubbish tip in 1985 on the condition that it became a nature reserve and study centre. The Trust was particularly anxious to keep one of the last natural assets on Thanet – apart from the coastal cliffs and seashore there are very few areas of natural habitat left on the island.

The Trust’s aims, as set out by the Charity Commission are:

The advancement of public education on ecology, natural history and related subjects.

Thanet Conservation Trust

A 16 acre site set inside an abandoned chalk quarry on the Isle of Thanet in East Kent. Monkton Nature Reserve is managed by the Thanet Countryside Trust. There are over 350 species of flowering plant including 8 species of orchid. 25 species of butterfly have been recorded, and innumerable other species of insect, mammal and bird-life. The reserve is also home to the first artificial bat cave to be constructed in the UK.

There are two ponds inside the reserve, one of which is on the quarry floor and is a water-table pond with a fluctuating water level, while the other is a butyl-lined pond in a secluded location overlooked by a small bird hide. Both ponds are visited by grass snakes on hunting expeditions. Great Crested Newts even make an appearance in one of our ponds. The water-table pond is used by a small number of the rare water vole.

There is a small young woodland in land above the quarry, and this is becoming well used by the bird population. Breeding numbers of Turtle Dove in this woodland have risen from one to five pairs over the last ten years.

A Bronze Age Barrow has been constructed in the woodland. This is a long term experimental project to obtain data for the Thanet Archaeological Unit.

The quarry cliffs are of Late Cretaceous age (Santonian) and contain some good chalk fossils. Collecting can only be carried out with supervision. The cliffs act as home to a number of bird species including Jackdaw, a pair of Little Owls, and occasionally nesting Kestrels.

On-site is a well resourced Field Study Centre, which contains a number of different exhibitions, including a large geological collection. Fossils, rocks and minerals from the Mesozoic, Cainozoic, and Pleistocene are on display, including unusual

The Thanet Observatory is situated in the centre of the nature reserve. It houses a 12″ f5.89 reflecting telescope.

Please visit our articles page to see more about the history of the reserve