The Greenwich Time Ball has been a popular attraction for visitors to Greenwich Park and the Royal Observatory since its construction in 1833. It was built to broadcast a daily one o’clock time signal to mariners on the river and in the docks so that they could check the rate of their chronometers before heading out to sea.

Since its installation there have only been a few brief periods during which the ball has not operated. Perhaps the most dramatic of all was in late 1855 when the ball and mast were blown down from the roof after ingress of rainwater had rotted the base of the mast.

Unfortunately, due to recent bad weather the mast has iced up and this prevents us from operating the ball. The build-up of snow and ice in the channel that guides the ball can be seen in the photograph below.

Writing in The Observatory in 1958, P.S. Laurie recalled that when the ball became iced up ‘the expectant public was on rare occasions treated to the sight of the unfortunate Assistant in Charge (or, probably, more expendable material, such as a supernumerary computer) attempting to scale the mast.’

Fortunately for staff at the Royal Observatory today, lives at sea are protected by modern technology and so we will not have to send anyone up to shift the ice.

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.

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 summer solstice occurs today, 20 June 2012, at 23.09 UTC (GMT).

The summer and winter solstices mark the times when the Sun is at its furthest from the celestial equator (the projection of the Earth’s equator onto the sky) – or in other words, when the Sun reaches its highest position in the sky (as seen from the North pole for the summer solstice). Unless you happen to live in polar regions, the summer solstice is also the day with the longest daylight.

The world solstice comes from the Latin solstitium meaning ‘Sun stands still’ because the apparent movement of the Sun’s path north or south stops before changing direction.

The summer solstice usually falls on 21 June, but not always. Because the Earth takes approximately 365.25 days to go around the Sun, the precise time of the solstices occurs about 6 hours later each year, with a jump of a day backwards on leap years (such as 2012).

Find out more about solstices and equinoxes in our fact file. And enjoy the long daylight hours!

Don’t forget to change your clocks this weekend! At 1.00 am GMT (2.00 am BST) on Sunday 25 March 2012, clocks go forward one hour as civil time changes from Coordinated Universal Time (effectively the same as Greenwich Mean Time) to British Summer Time or BST.

Unfortunately this also means that we all get a one-hour shorter weekend, but at least we get it back in October when the clocks change again.

Find out more in our British Summer Time fact file.