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Mercury Transit in Trinity on 9 May 2016

Mercury transiting the Sun as seen from Earth in 2006. Mercury is the smallest planet in our Solar System, with a diameter of 4,879 km, while the Sun is an enormous 1.4 million km across — about 109 times the diameter of the Earth (12,742 km) Credit: ESA/NASA/SOHO

CAUTION: Do not look directly at the Sun during the transit or at any other time. Doing so can cause permanent damage to your eyes.

On Monday 9 May 2016 a rare transit of Mercury  across the face of the Sun takes place, and will be visible for us here in Ireland. During the transit, Mercury, the smallest planet in our Solar System, and also the planet closest to our Sun will pass directly between the Earth and the Sun. This gives us the opportunity to see the tiny dark dot that is Mercury transit across the bright surface of our closest star. There are only about 13 Mercury transits that are visible from Earth every century. The next ones are in 2019 and then 2032  - and much longer for us in Ireland.

EuroPlanet YouTube Movie

Animation explaining why the transit of Mercury is visible from Earth on May 9
(Credit: Europlanet)

The School of Physics, Trinity College Dublin will celebrate this rare event, and will be setting up two telescopes in Trinity's Front Square on Monday, 9 May from 12:00 noon. Additionally, a plasma TV displaying real-time observation of the transit will be shown from NASAs spacecraft called Solar Dynamics Observatory. This will let us view the transit even if it’s cloudy or raining.  Mercury will appear as a black dot about 1/150th of the Suns diameter, meaning it’ll be too small to see without magnification. The telescopes, with special solar filters, will let members of the public see what the Sun looks like and to see a planet moving through space across the vast face of our Sun. There will be plenty of expert astrophysicists from Trinity’s Astrophysics Research Group on hand to talk to the members of the public about this exciting event, and to help all view the transit safely. 

Planetary transits were hugely important throughout the history of science such as proving Kepler's revolutionary ideas that all the planets moved around the Sun in elliptical orbits, along with providing estimates of the distance from the Earth to the Sun. The transit of Venus in 1916 was used by Eddington to verify Einstein’s laws of gravity in his General Theory of Relativity. The Irish connection was that the tracking mirror used for this famous expedition was made on Observatory Lane, Rathmines, Dublin by Thomas Grubb’s company (further detail at the Royal Irish Academy )

Scientifically we don’t do much with planetary transits viewed from Earth these days. This is because we have much more advanced technology so we can build spacecraft and satellites that provide state-of-the-art observations. For example, the European Space Agency (ESA) will be launching a spacecraft called Solar Orbiter in 2018 to fly inside the orbit of Mercury, where it will be extremely hot. Irish scientists and engineers play a key role in this new exciting mission. The Irish company, EnBio will be providing the "solar sunblock" for the spacecraft which will protect it from the searing heat of the Sun. The Solar Physics Research group in Trinity College Dublin is part of the science team for Solar Orbiter and Prof. Peter Gallagher and Dr. Shaun Bloomfield are Co-Investigators for the Solar Telescope Imaging X-rays (STIX) instrument on Solar Orbiter.

The event at Trinitys Front Square on 9 May will be an exciting experience for all involved. Join us to have the unique opportunity to observe Mercury’s transit with our telescopes, talk to our scientists about the physics of our Sun, the science of planetary transits along with new and exciting missions we are involved in.

If you can’t make it to Trinity’s Front Square both the ESA and NASA will be web-streaming live images from their spacecraft and telescopes.

Further information, including safe viewing details, and teacher resources can be found at

Royal Astronomical Society Website