Armagh Observatory, 11th May 2016: Observers in Northern Ireland were fortunate last Monday 9th May to have clear skies to observe a rare astronomical event, namely the transit of Mercury, in which the smallest terrestrial planet, Mercury, the one closest to the Sun, passes in its orbit directly between the Sun and the Earth. Approximately 70 visitors to the Observatory, including families and children, and some from as far away as Austin (Texas, USA), Dublin, Newry and Bangor, and various towns in County Armagh, used the Observatory´s special equipment to enable safe solar viewing.

The small black "dot" of Mercury, with an apparent angular diameter of just 1/157th that of the bright solar disc, took more than seven hours to slowly crawl across the face of the Sun. During this time it passed two small sunspot groups, which gave skywatchers an interesting opportunity to compare the blackness of Mercury´s dark shadow with the nearly equally black, but faintly luminous, umbral, or central part of a sunspot. Although patchy cloud-cover interfered with observations for an hour or two in the early afternoon, patient visitors were subsequently rewarded by being able to follow Mercury´s tiny black disc right up to the end of the event at Armagh, around 19:41.

People remarked how great it had been to see the planet, describing the whole event as "Wonderful", "Excellent", "Brilliant", and "Amazing". Images of the event taken by Observatory astronomers are attached. The next transit of Mercury visible from Northern Ireland, weather permitting, will be on Friday 11th November 2019. It will start around 12:35 and continue until after sunset, approximately 16:30.

FOR FURTHER INFORMATION PLEASE CONTACT: Mark Bailey or Apostolos Christou at the Armagh Observatory, College Hill, Armagh, BT61 9DG. Tel.: 028-3752-2928; FAX: 028-3752-7174; E-mail:; URL:

Image Caption: Images of the 9th May 2016 transit of Mercury taken by Armagh Observatory astronomers.


(image 1) Click on image for larger version.

(image 1) Clockwise, from upper left: Mercury soon after it appeared in front of the Sun; the appearance around mid-transit; and then late afternoon, and finally showing the end of the event with a tiny black dot close to the south-western part of the solar limb. The red image shows the appearance of the Sun during the second half of the transit in the red emission line of hydrogen-alpha.


(image 2) Click on image for larger version.

(image 2) People attending the event and the associated free public tours of the Observatory.


(image 3) Click on image for larger version.

(image 3) Photograph taken from an hydrogen-alpha telescope by Rok Nezic at Armagh Observatory at 16.57 (BST) 9th May 2016.


(image 4) Click on image for larger version.

(image 4) Photograph taken by Rok Nezic at Armagh Observatory at 18.23 (BST) 9th May 2016.

Web Links
Original transit of mercury press release

Last Revised: 2016 May 13th