This will be the first Mercury Transit visible from Ireland since May 2003, and the next one will occur on 11 Nov 2019, but the Sun will set before the end of that transit.
Of the 12 transits up to 2100, 2 are completely invisible from Ireland, 6 are partly visible, and only 3 more are entirely visible; the next one of those will be on 7 May 2049, so this is a chance that you really should not miss!
And this one will have the longest duration of any visible in Ireland this Century!
Mercury appears much smaller than Venus during a transit; the apparent diameter this time will be only 12.06", and so optical aid will be required. This can be either a proper solar filter on a telescope as used for normal solar observing, or you can project the image through a telescope onto a piece of white paper or card. Mercury will appear as such a small black dot that it will be barely visible with binoculars (also fitted with proper solar filters of course!) unless they are of fairly high power, say 12x or more.
Mercury will first appear as a tiny little black notch (if you use sufficient magnification - say 100x) at the E side of the Sun, and gradually move across the Sun's disc, passing South of the Centre, and exiting the disc on the SW limb. Remember that these directions are relative to the Sun's N Pole, not to its orientation in the sky, which will change during the transit.
Looking for First Contact is the hard part - once the transit is under way it will be fairly easy to follow. Also remember that in an astronomical telescope, directions can be reversed both N-S and E-W depending on the optical design, and whether a diagonal is used at the eyepiece!
The best way is to let the image drift through the field of view (switch off your drive for about 30" or so, and see how it drifts) – the side of the Sun's disc which is leading the direction of motion is the preceding side, and the opposite is the following side.
East will be fairly close to the following side at the start of the event. For more accurate location, at the start of the transit, Mercury will enter onto the Sun's disc just very slightly S of the E limb of the disc as the Sun appears in the sky at that time – say about '8.45' on a clock face. By the time the transit is ending, it will appear just very slightly W of the apparent S point on the Sun's disc at that time – about 5.45 on a clock face.
Do NOT attempt to image with a camera unless the optical system is fitted with a proper filter as above. Above all, do not try to image through a telescope unless it has a proper filter! You will need quite a high effective magnification to get an image showing Mercury clearly.
You can however easily take a photo of the Sun's image projected through a telescope onto a piece of white card: you may need to get in close to see Mercury clearly.
The Sun will be just N of West at the end of the transit, and down to an altitude of only 11 degrees, so make sure you have a good view in that direction if you want to see the whole event.
4. Public lecture, May 10, entitled "Science from High Altitude Balloons" will be held in UCD as part of the ANSRI 2016 workshop. The talk will be given by Prof. Mark McConnell of the University of New Hampshire. Venue is Room 129 Science Centre North, UCD, at 6pm. More details at http://spacescience.ie/ansri2016/publictalk
14. Interesting Weblinks
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