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HM Nautical Almanac Office: Transits of Venus

2004 June 8th Transit of Venus

Background

The first of the two 21st-century transits of Venus will be visible in its entirety from the British Isles. Given that the last transit of Venus took place in 1882, it is sobering to note that no one alive today has seen one of these events before! As there are better methods for determining the solar parallax, the scientific significance of this transit is limited. However, it has caused great interest in the area of public understanding of science and scientific education in general.

For observers in the United Kingdom, the main obstacle to foil observing the transit will be the weather. The statistics show that there is only a small chance of the weather being completely clear for the whole event. It is more likely that broken cloud cover will prevail. Sadly, there is also a 20% chance of being clouded out completely. If you want greater certainty of seeing the transit, southern parts of Europe close to the Mediterranean Sea offer a significantly better chance of clear skies. Visiting Saudi Arabia or Kuwait may provide an almost guaranteed view of the transit.

Visibility

Global Visibility of the 2004 Transit of Venus

Venus will cross the disc of the Sun on 2004 June 8th. The map above shows the visibility of the event. The entire transit can be seen from Asia except the extreme eastern part, Africa except the western parts, Europe except the south-western tip of the Iberian Peninsula, Greenland except the southern tip and most of the Indian Ocean. The Sun will set while the transit is in progress in the grey area encompassing north-western Canada, Alaska, parts of north-east Russia, Japan and Australasia. The Sun will rise while the transit is in progress in the grey area taking in western Africa and eastern parts of the Americas. The yellow lines on the diagram show the position of the terminator, where the Sun is either rising or setting, at the key phases of the transit.

Geocentric Circumstances

Geocentric Circumstances of the 2004 Transit of Venus

The geocentric circumstances of the transit are shown in the diagram above. During the transit, the diameter of the Sun is 1890.8 arcseconds and that of Venus is 57.8 arcseconds. In other words, the diameter of Venus is 0.03 that of the Sun, making it look like a rapidly moving sunspot. The whole transit lasts just under six and a quarter hours.

All timings are given in Universal Time (UT).

The Transit from the United Kingdom

To convert to British Summer Time (BST), add one hour to the Universal Time.

In the United Kingdom, the transit begins between one and quarter and two hours after sunrise depending on your location. Taking London as an example, sunrise occurs at 03h45m (UT) in the north-eastern sky. The transit begins with exterior ingress at 05h20m (UT) when the disc of Venus begins to cross the limb of the Sun. Interior ingress occurs at 05h40m (UT), when the whole of the disc of Venus has crossed over the limb of the Sun. Venus then moves across the solar disc, reaching a minimum separation from the centre of the Sun of 641.8 arcseconds at 08h23m (UT). Interior egress, when Venus starts to cross the solar limb for the second time, occurs at 11h04m (UT), and the transit ends with exterior egress at 11h24m (UT).

The progress of the transit is summarized in the diagram below. The left-hand panel shows the movement of the Venus across the solar disc. The top of the diagram points to the zenith, the point directly overhead. The position of Venus is marked every UT hour. The right-hand panel shows the movement of the Sun in the sky. At the beginning of the transit, the Sun is east north east at an altitude of just under 12°. By the end of the transit the Sun is south south east at an altitude of just over 60°.

2004 Transit of Venus as seen from London

Local Circumstances

Summary plots like the one shown above and animations showing the motion of Venus relative to the Sun as seen by someone observing the transit through appropriate eye protection are available for several locations across the UK and Ireland. The summary gif files are ~18Kb and the animations are ~200Kb. To view the animations properly, it may be better to download the animations and view them locally.

Local Circumstances of the 2004 Transit
Location Sunrise (UT)Sunset (UT)Downloadable gifs
London, England03h45m20h15mAnimation Summary
Cardiff, Wales03h57m20h27mAnimation Summary
RAL, England03h49m20h20mAnimationSummary
Preston, England03h42m20h39mAnimationSummary
Leeds, England03h37m20h34mAnimation Summary
Belfast, Northern Ireland03h49m20h57mAnimation Summary
Edinburgh, Scotland03h29m20h55mAnimationSummary

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Last modified: Tuesday, 03 May 2011 at 14:08:53 BST