The transit of Mercury, 2016 May 9

2016 January 26

Richard McKim

On Monday May 9 there will be a transit of Mercury across the Sun’s disk. This relatively rare phenomenon is always an interesting spectacle to watch, though the planet’s little disk is small compared to that of Venus, and of course no effects arising from the presence of a planetary atmosphere can be seen. By contrast the solar surface adjacent to the planet will appear brighter than elsewhere. The Director will be pleased to receive any images and drawings. It is interesting to compare the blackness of the disk of the planet with the umbrae of any sunspots that happen to be present.
Few observers will probably choose to go abroad to watch the event, but relying upon the UK weather is often hazardous. I was clouded out for the 1973 November transit, but after 30 years of waiting I had very good luck in 2003 June for the entire transit of Mercury, and in the following year for that of Venus too. For the 2012 Venus transit I was again clouded out. Of course some transits, such as that of Mercury in 2006 November, cannot be viewed at all from the longitude of the UK, but the 2016 event will be visible from the Americas, Europe and Africa. In 2003 I made a series of observations by projection with a 102mm OG, and some of these are illustrated here (Figures 1 and 2). The transit of Mercury on 2006 Nov 8-9 was previously described in a short note (R. J. McKim, J. Brit. Astron. Assoc., 117(4), 168 (2007)).
Circumstances of the 2016 event are fully detailed in the BAA Handbook, and very conveniently by Peter Macdonald in last October’s Journal, 125(5), 263 (2015), so there is no need to repeat them here other than to write that they are extremely favourable, and that in the UK the event will last from 12:12 BST till 19:41 BST.** Another useful source is the article by Nick James in the Yearbook of Astronomy 2016, edited by John Mason (MacMillan, 2015).
The safety sheet issued by the Association on the occasion of the last Venus transit is also relevant. Members may also like to look at the ESA’s webpage about the transit, which has been created a year ahead of the launch of the BepiColombo Mercury mission: http://bit.ly/1K5nJXz
BepiColombo also has a useful website, and Professor David Rothery who is a member of the mission team informs me that the site will be streaming live images during the transit both from space and from solar telescopes in Spain and Chile: see http://www.cosmos.esa.int/web/bepicolombo.
Prof Rothery adds that the website intends to collect (and thereby publicise) all opportunities for the public to see the transit by finding a transit viewing event near to them.
I look forward to receiving any successful observations, and to compiling a report upon them for the Journal.

Richard McKim, Director, Mercury & Venus Section

** Observers should note that these times are incorrectly given as being in UT in the printed Journal.