This article was written and published (in Sagittarius, the newsletter of the Astronomy Section of La Société Guernesiaise) before the 2004 transit. Our observations of that transit are recorded in a report published in the Transactions of La Société Guernesiaise (Vol. XXV, Part IV, pages 600-2). That report is available online here.
An eclipse of the Sun happens when the Moon passes in front of it, as seen from the Earth. Transits are similar in concept, as they happen when one of the two planets closer to the Sun than the Earth, ie Mercury or Venus, passes across the disc of the Sun.
Transits of Venus occur in pairs, with a separation of 8 years between each of the pair. However, pairs are separated by over 120 years. One pair occurs on or about 7 June, and the other on or about 8 December. There is a separation of 243 years between pairs occurring on the same date.
The last pair of transits of Venus occurred in December 1874 and December 1882. So no one alive has seen one. The next pair occurs on 8 June 2004 and on 5/6 June 2012. Their visibility from Guernsey is described below.
08 JUNE 2004
Guernsey is in a good location for observation of the first of the transits.
And it is at a good time of the year!
The transit will be visible from Europe, Africa and Asia.
Venus will cross the southern hemisphere of Sun, at a solar latitude of about -60 degrees.
In Guernsey, the Sun will rise at 04h 05m GMT.
The transit will start at about 05h 21m GMT, when the altitude of Sun will be 9 degrees, and Venus will take 20 minutes to cross the limb of the Sun
Mid-transit will be at 08h 23m GMT.
Venus will again take 20 minutes to cross the limb of Sun, and the transit will end at 11h 16m GMT, when the altitude of Sun will be 61 degrees.
The duration of the transit will be about 6 hours.
The Sun's coordinates will be: RA 05h 07m, Dec +22deg 53min.
The angular diameter of Venus will be 58".6, about 3% of the Sun's 1887" diameter.
6 JUNE 2012
Make the most of the 2004 transit, because Guernsey is very poorly located for the second of the pair! The Sun rises just minutes before the end of the transit.
This transit will be visible from the Pacific, Australasia and Eastern Asia.
Venus will cross the northern hemisphere of the Sun, at a solar latitude of about +45 degrees.
The transit will start at 22h 03m GMT on 5 June, when the Sun is below the horizon.
Mid-transit will be at 01h 28m, when the Sun is still below the horizon.
The Sun will rise at 04h 05m GMT.
Venus will take 18 minutes to cross the limb of the Sun, and the transit will end at about 04h 54m GMT on 6 June, when the altitude of the Sun will be just 5 degrees.
The duration of the transit will be about 6 hours 10 minutes (but in Guernsey we will only see the last 49 minutes).
The Sun's coordinates will be: RA 04h 59m, Dec +22deg 41min.
The angular diameter of Venus will be 58".6, about 3% of the Sun's 1888" diameter.
By the way, the next transit of Venus is in 2117!
Transits of Mercury occur much more frequently. Here is a picture of one taken at the Guernsey Observatory on 07 May 2003. The next one is on 08 November 2006, but will not be visible from Guernsey, as it takes place after sunset. The one after that is not until 09 May 2016, and will be visible from Guernsey.
Text and images copyright David Le Conte
Report on observations of the transit of Venus 2004 by David Le Conte
Transits of Venus by Peter Langford
From 1882 to 2004 - a transit of Venus – by Debby Quertier
Belorussian translation of this page courtesy of WH Geeks
Romanian translation of this page courtesy of WH Geeks
visitors since 25 May 2009.