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HM Nautical Almanac Office: Transits of Venus

2004 Transit of Venus Observations at RAL

Dawn broke on June 8th promising relatively clear skies and a good view of the passage of Venus across the solar disc. Sunrise occurred at 4:49 (BST) and the team observing the transit gathered outside R22, the main lecture theatre at the Rutherford Appleton Laboratory (RAL), at just after 5 o'clock. The transit itself was due to begin at 06:20 (BST) when the Sun had climbed to just over 11° above the horizon. The question uppermost in peoples' minds was whether the thin cloud close to the north-eastern horizon would threaten the early stages of the transit.

The team started work by setting up the telescope, an equatorially-mounted 105-mm Meade ETX Maksutov-Cassegrain with a lunar and planetary imager (a CCD detector) and a solar filter. Once assembled and its equatorial mount aligned with the north celestial pole, the prime focus imager was configured to provide a live feed to R22. The field of view of the detector was about 8 arcminutes by 6 arcminutes providing an impressively large image of Venus on the screen in the lecture theatre.

Projection of Venus crossing the disc of the Sun By guiding the telescope on the Sun, many people in R22 could experience the transit in complete safety. The video output from the imager was also saved to a laptop hard disk and to an analogue video tape.

Using a solar filter in the presence of variable amounts of cloud can pose a problem. Without the filter on the telescope, the Sun would be far too bright for the imager. With it in place, too much light would be blocked, making the image too faint for the detector.

A second telescope, a 203-mm Meade LX10 Schmidt-Cassegrain, was set up to project the image of the Sun onto a piece of white card some distance from the telescope. This provided an alternative method of viewing the transit in safety for larger groups of observers. The photograph to the left shows the projection of Venus crossing the disc of the Sun.

Steve Bell guiding the Meade ETX telescope With the notable exception of the weather, everything and everyone was ready. Chris Davis, showing a good deal of foresight and a keen sense of occasion, had even remembered to bring a varied breakfast for the team!

With exterior ingress only a minute or so away, cloud was still interfering with the view of the Sun. Steve Bell monitored the Sun through the eyepiece, ready to switch over to the imager when the cloud cleared. He was watching as Venus started to cross the limb on schedule and alerted everyone to the start of the transit. Fortunately, a few minutes later, the cloud had cleared sufficiently for the imager to be used. The live feed and the Recording started at around 6:35 (BST). The photograph above shows Steve Bell guiding the Meade ETX telescope during the latter half of the transit.

Chris Davis and Steve Bell monitoring the Meade ETX telescope The internal ingress as well as the majority of the transit was recorded on disk without too many problems. As the Sun rose higher in the sky, the cloud dissipated quite quickly. As temperatures climbed to around 27°C or so, keeping the telescope properly focused became more and more challenging.

To add a little extra excitement to the proceedings, the Meade ETX telescope ran into its end stops just before midday. Some quick thinking by Chris Davis suggested reversing the telescope. A rapid re-acquisition of the Sun was necessary to ensure the latter stages of the transit were captured for the audience gathered in the lecture theatre. Fortunately, only a few minutes of coverage were lost. The photograph above shows Chris Davis and Steve Bell monitoring the tracking and the focus of the Meade ETX telescope.

Watching the transit with eclipse viewers

Many people at RAL saw the transit. Some saw it by projection on a screen in the R22 lecture theatre, some by viewing the projected image of the Sun on white card several feet from the telescope. Others saw it by using one of a variety of eclipse viewers provided for the event. The photograph to the right shows people using this type of viewer to watch the transit.

Although little new scientific information could be derived from the 2004 transit, the interest generated by the event could not be underestimated. Many, many people came to watch Venus cross the solar disc, some looking for phenomena such as the "the black drop", others to say they had seen something that no one living today had ever seen before.

Children from Greenmere Primary School Janet Haylett and Natalie Bealing also arranged a visit by a group of children from Greenmere Primary School in Didcot to see the transit and to try and estimate the time of both the internal ingress and external egress. Helen Walker gave a talk to these children on the planets and Venus in particular. They also tried out various activities including painting and making drawings linked with the transit. Their headmaster, Richard Furniss, kindly commended RAL for the quality of the visit. The picture on left shows some of the children pointing at Venus on a projection of the Sun on a piece of card. Perhaps the memories of this event will get some of them up at sunrise on 2012 June 6th to see the latter stages of the only other transit of Venus in the 21st century.

For once, good weather blessed the event which stimulated a good deal of media interest from local newspapers, Six TV - The Oxford Channel and Central TV. In fact, we made the local 6 o'clock evening news on ITV.

Pete Read projecting an image of the Sun The hot weather also encouraged some of us to bring out our more flamboyant shirts! The photograph to the right shows Pete Read aligning the Meade LX10 to project the image of the Sun.

The team involved in the transit of Venus observations were Chris Davis, Pete Read and Steve Bell. The R22 projection and analogue recording of the transit were looked after by Reg Jones. The photographs on this page were provided by Steven Kill and the video clips were produced by Nick Horan.

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Last modified: Tuesday, 03 May 2011 at 13:48:59 BST