The star of the show: maintaining the 28 inch Great Equatorial telescope

Part one – an astronomer’s tale

A true heavyweight in our collection at the Royal Observatory Greenwich is the 28 inch Great Equatorial telescope. It sits underneath a green dome that bulges beyond the confines of the building’s walls. The telescope is 118 years old, still has its original lenses intact and best of all – it is still available to the public to use between the months of November and March. As an astronomer here at the Observatory, I’m lucky enough to use this amazing instrument on a regular basis.

The interior of the dome is undergoing repair works at the moment. Despite what you might imagine, it is not the century-old telescope that needs attention, but in fact the forty year old dome mechanism. The dome has gone through two iterations; the original was an iron frame covered with papier-mâché (the staple of primary school art classes worldwide!) and, after being bombed in World War II, the replacement was made from fiberglass as it sits today.

Until recently the telescope has been under wraps to protect it from the cleaning going on around it.

The main task with this round of maintenance has been to replace a chain that opens the shutter doors so that the telescope can gaze into the night sky, but the accompanying scaffolding is also being used to help give some tender loving care to the telescope itself. Our Scientific Instruments Conservator Anna will explain the trials and tribulations of conserving such an iconic instrument and building in a later blog post, watch this space…

One aspect of my job is using the Great Equatorial telescope to show visitors the stars, the Moon and occasionally a planet or two at our Evening with the Stars events in the autumn and winter months. Looking through the UK’s largest lensed telescope for the first time is going to be a memory that I will cherish forever. Lunar landscapes, double stars, and the most distant planet in our Solar System, Neptune, have been just a few of my highlights over the past two years.

The light that reaches the telescope passes through a pair of lenses sandwiched together that are wider than a dustbin lid. The light is channelled down eight and a half metres of empty telescope tube before reflecting off a flat mirror at the bottom so that an observer can see the result through an eyepiece. The mammoth telescope tube is simply there to hold the lenses in place!

Often, this light that has travelled thousands or even millions of kilometres is stopped by cloud cover. Although this may seem disappointing, I’ve been making a concerted effort to show visitors on cloudy nights a rare glimpse of the film and photo footage we can take through the telescope on a clear night. So, as well as conserving the dome and telescope, new equipment will be installed in the coming weeks to allow us to do this on a regular basis. This, coupled with a new high resolution camera, is sure to produce some beautiful images that we can project onto the inside of the dome – a unique cinema screen we hope you’ll agree.

I hope that you share my excitement for the coming Evening with the Stars season starting in November when, clear skies or not, the Great Equatorial will open once again and bring the heavens into focus for one and all.

http://www.rmg.co.uk/royal-observatory/flamsteed-house-and-meridian/28-inch-telescope/

The cleaning of the inside of the dome has made a vast improvement!

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