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HM Nautical Almanac Office: Transits of Venus

1275 May 25th-26th Transit of Venus

Background

It is feasible that a transit of Venus could have been seen shortly after sunrise or shortly before sunset by observers who did not have access to modern observing aids like solar filters, aluminised mylar or even smoked glass. During IAU Colloquium 196: "Transit of Venus: New Views of the Solar System and Galaxy", it was suggested by one speaker that the Mayans may have known about the transits of Venus. Artifacts thought to have been made between 1200 AD and 1350 AD allegedly show Venus being "consumed" by the Sun. If we accept this speculative premise, then a small part of the transit of 1275 could have been seen by Mayan observers from the city of Mayapan just before sunset on May 25th.

Visibility

Global Visibility of the 1275 Transit of Venus

Venus crossed the disc of the Sun on 1275 May 25th-26th. The map above shows the visibility of the event. The entire transit could have been seen from the western half of the United States, Canada except the eastern part, Alaska, the Hawaiian Islands and the islands of the central Pacific Ocean, northern Japan, northern and western Russia and the northernmost parts of Scandinavia. The Sun set while the transit was in progress in the grey area encompassing western Europe including the British Isles, the eastern part of North America, Central America and South America. The Sun rose while the transit was in progress in the grey area taking in Australasia, Southern Asia, and the easternmost parts of Europe. 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 1275 Transit of Venus

The geocentric circumstances of the transit are shown in the diagram above. During the transit, the diameter of the Sun is 1889.0 arcseconds and that of Venus is 57.7 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 seven and a quarter hours.

All timings are given in Universal Time (UT).

The Transit as seen from Mayapan

Local time in Mayapan is 6 hours behind Universal Time.

Taking the city of Mayapan on the Yucatan peninsula as our example, sunrise took place in the north-eastern sky at 11h14m (UT). After the Sun had crossed the meridian nearly eight hours later, the transit began with exterior ingress at 19h02m (UT) when the disc of Venus began to cross the limb of the Sun. Interior ingress occurred at 19h18m (UT), when the whole of the disc of Venus had crossed over the limb of the Sun. Venus then moved down across the solar disc, reaching a minimum separation from the centre of the Sun of 443.6 arcseconds at 22h35m (UT) when the Sun was still 25° above the horizon. In the quarter hour or so before sunset, Venus would have been visible in the lower-left quadrant of the Sun. Sunset occurred in the north-western sky at 00h32m. The final stages of the transit would have been invisible to observers at Mayapan as interior egress, when Venus started to cross the solar limb for the second time, occurred at 01h55m (UT), and exterior egress, the end of the transit, occurred at 02h11m (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.

2004 Transit of Venus as seen from Mayapan

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 worldwide. 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 1275 Transit
Location Sunrise (UT)Sunset (UT)Downloadable gifs
Mayapan, Mexico11h14m00h32mAnimationSummary

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Last modified: Tuesday, 03 May 2011 at 13:55:54 BST