Another hole was dug into the clay to start the base of the telescope pillar. This is kept completely separate from the rest of the observatory to remove any vibrations. Once the pillar was above the lower room floor level, the floor could be laid. This was done in several segments and called for concrete to be mixed on site. A cement mixer was acquired cheaply enabling work to continue weekly.

Now only sand, gravel, rubble and breeze blocks had to be transported down the hillside. Usual deliveries were 3 tons of sand or gravel, or several hundred breeze blocks, to be moved within a day. This called for a major coordinated effort from most members.

With the concrete floor set, work began raising the telescope mounting pillar to the observing floor. This was built in sections reinforced with steel rods. The shuttering was raised week by week until the required height was reached.

As the outer wall continued upward, work began on the inner wall which would eventually support the centre of the observing floor. The gap between the telescope column and this wall is clearly visible.

With the tops of both walls now over ten feet above the observatory floor, lintels were made for a walkway above the lower entrance hall. Once in position, shuttering was made to enable a reinforced entrance platform to be concreted.

The frame of the observatory dome is made from 8 by 4 feet sheets of half inch plywood. These were cut in the lecture hall into segments approximately 4 feet long with a radius on both the outer and inner edges. A box section was constructed which would be the running surface for the dome wheels. This included a lip so that in high winds, the dome would lift and lock, rather than blow off. This was built upside down for convenience and then turned over.

Rib sections, also made from plywood were cut to form the main dome structure. By now the dome had to be left outside and covered between weekends with plastic sheeting. The outer surface is hardboard, cut into segments to fit the round structure. These were nailed to the ribs. The designer of the dome, Peter Blunden, is seen at the end of fitting all the segments.

The dome was sealed with mastic tape and painted with aluminium paint. The whole structure weighs over a ton and was man handled from the observing platform, over the entrance platform and onto the observatory wall. The structure runs on three wheelbarrow wheels and can be turned by one person.

The shutter is made of hardboard and as with the dome is painted with aluminium paint. A pulley system inside allows the shutter to open by pulling a rope. The dome can be turned using a handle attached to the internal wall. The observatory can be used by one person.

On 2nd September 1982 Patrick Moore opened the observatory. The Pennell-Hammerton observatory is named after the late Walter Pennell-who died before its completion, and one of the founding members of the society, Peter Hammerton-who died 10 years after its opening. The observatory can be seen traveling north on the dual carriageway section of the A46 Lincoln bypass against the dark hillside.

The telescope is a 12inch F6 Newtonian, on loan from the Pennell family. It is equatorially mounted with slow motion drives for photographic work and is attached to the top of the 18 feet high pillar. The observing floor is in wooden sections and like the rest of the observatory, is completely separate from the telescope pillar.

The observatory was originally designed in the 1960's, constructed during the 1970's, and refurbished in 2006/7. Society members use the telescope mainly on Tuesday nights and at the weekend. Key holders have access to the observatory seven days a week. The general public can use the telescope on open nights or as invited groups via the visits organiser when a slide show is followed by an observing session -weather dependent.

The observatory started to develop problems in the early 1990s. The dome was only supported on three wheels and the stresses and weight of the skin had made the observing start to close. By the turn of the century the gap part way up was over 50mm narrower than at both ends. This put pressure on the hardboard skin which started to buckle.

The dome after 25 years of use with the buckled skin

The telescope and old shutter were removed at the start and a steel bar put in place between the two main side ribs to stabilise the structure. This would leave a large gap where the shutter had been but this would be covered with a blue tarpaulin after every work party.

Structural Changes

To try and stop the dome twisting again, two extra ribs were fabricated from a double width of 10mm plywood (centre) and the box ring strengthened under the slot (left). The new shutter design required the old slot to be shortened slightly by a box section.(right).

Replacing the Skin

The skin was then removed, section by section and the new ones fitted. These had been pre painted for extra protection before cutting to size. Some rot was discovered in places on the box ring (right), but the plywood frame was in very good condition considering its age.

None of the 22 sections of skin were the same size To make a new piece, each old one was used as a template and placed over the prepainted 8 by 4 ft sheet and cut around. Extra wood was left to be marked accurately using the dome as a template and each one trimmed to fit.

Final fitting and cutting was done in situ. Each panel was then glued and nailed to the frame with 100 nails. The dome is 18 feet in diameter and so 8 feet sheets would not cover from the box ring to the top. A join was made at the 8 feet level.  It was then just a case of continuing around the structure to replace all 22 petals.

To make the skin waterproof, each joint between the panels was sealed with glass fibre sheet

A second coat of aluminium primer was then painted over the outer surface before a single top coat was applied

Priming the wood before fitting helped as it was not necessary to cover the newly fitted petals between sessions..

Building the Shutter

The new shutter is a plywood cover over a welded galvanised steel frame for strength. The structure moves on six wheels, three on each side, over two steel tracks.

Two sheets of plywood are needed to cover the length whole of the shutter. This is tied to the frame.

 The sides of the shutter are made of two sheets of 6mm plywood, carefully cut to size.

These are then screwed and glued to the frame and outer cover.

The new shutter is finished and ready for painting.

Two coats of primer were used together with aluminium top coat to seal the plywood against the damp.

Shutter Running Tracks

The running track are made of steel welded together to form two tracks nearly 25 feet long. These were then fixed to the dome.
The tracks are wider than the main ribs to form a lip on the inside of the slot. Wheels on the shutter engage this lip in high winds, stopping the shutter blowing off.

Shutter moving Mechanism

The shutter is opened by a system of pulleys and steel rope. The pulleys are plastic and fitted between two plywood sheets with steel bolts.

These are fixed to the two main ribs over the full length of the shutter slot.
The ropes are then fed through these to form a continuous loop on each side. The opening mechanism is the worm and gear from a car trailer- suitably modified.

Here we see the steel ropes in place with the main shutter closed.

Telescope Mount

The telescope had been removed before work began on the dome. Here the original mounting srews are being removed and an extra 12 inches of support added to raise the telecope. It had always been impossible to see below Declination 14 degrees south due to the box ring. This change would enable the centre of the galaxy to be observed.

A new concrete block was added to the top of the 18 feet high pillar. This was then painted.

The telescope was refitted and realigned. During the dome reconstruction we took the opportunity to have the mirrors reluminised.

To use the new dome the top shutter is first opened by rotating a handle on the rear box section.

This tensions two continuous steel rope loops and lifts the top shutter. These loops can be seen left and centre.

The lower shutter is then untied and pushed out. Part of the reason for having a seperate lower shutter was to reduce light pollution from the houses on the street above the society. The dome can be used with this lower shutter still closed.

At the end of the observing session, the lower shutter is closed first.
The handle is rotated until the upper shutter covers the top of the lower shutter and locks it in place. The dome is then rotated to its storage position.

The project started in the spring of 2006, took until September 2007 to complete. The largest cost was the paint and not the skin, but it was completely within the £1000 budget that had been allocated.

Members who worked on the dome refurbishment

Colin Reeve
Dave Castledine
Dave Garbutt
Phil Norton
Bill Booth
Laura Lacey