Hampshire Astronomical Group

Celebrating 50 years (1960 - 2010)

12" Dome

The observatory complex's 12-inch f5.5 Newtonian reflector has been designed for CCD and electronic imaging, although one can use the telescope for visual observing.

The telescope has an aluminium closed tube, whereas all other reflectoring telescopes on site have open surrerier truss designs. The value of a closed tube is it stops any stray light from entering into the very sensitive detectors. The disadvantage is one can sometimes suffer from thermal tube currents which can degrade the image. This problem can be avoided by allowing the telescope and mirror to cool to the ambient temperature before the observing session this can typically take anything up to ½ to 1 hour depending on atmospheric conditions.

The telescope is mounted on a fork mount and is computer controlled through commercial AWR electronics and software. This software does interface with standard PC hardware, although in an observatory as compact as this one, such computers are often felt to be rather bulky and so laptops are brought to the observatory for each observing run. This has the added advantage of avoiding damage to electronic equipment held in the damp unheated conditions that often prevail in an observatory.

The telescope was custom made by the renown telescope maker Ron Arbour, who is well known for making 'one-off' telescopes. The mirror was ground and figured by members of the Group. This has since been independently tested and assessed of having a high quality figure. The mirror cell and flat 'spider' was made by the late Norman Fisher.

Since the installation of the telescope, work has been ongoing to refine the polar alignment. If this is not carried out regularly the telescope will not track stars and other astronomical objects accurately and the object in question will appear to be trailed across the detectors rather than appearing as pinpoints.

The observatory dome, which is home made of fibre glass on plywood rib construction, had had some further engineering refining on the dome rotation system and it now rotates with the push of a couple of fingers making access to the night sky much easier.

Through observational experience, it was noted that there was some thermal dissipation from the concrete walls, they have now been cladded with industrial building cladding and this has made a significant improvement to the thermal properties of the dome and the stars are now much sharper.

The inside of the dome, walls, dome and floor, has been completely painted in matt black. This is to stop any light 'bouncing' around in the observatory and interfering with the electronic imaging detectors. The source of this light is from the computer screens and extraneous light from outside the observatory.

A recent addition to this telescope was the fitting of a 4 inch f10 refractor piggy-backed onto the main telescope. At the same time further rebalancing of the telescope was undertaken.

This was mounted in order to give the telescope further flexibility with the possibility of solar observing through it and also fitting a CCD guide camera to increase the accuracy of the tracking of the main telescope. The telescope has been used to gain images of the moon for use in the clubroom and to ascertain the viability of detecting meteoric impacts on the unlit side of the moon. Recently, during the transit of Mercury and Venus, the telescope was fitted with a special white light solar filter and video images were obtained of the planet moving across the face of the Sun.

Additionally, the telescope has been used in tracking fast moving comets such as Comet Neat in 2004.