Mercury 2

Only a handful of times per century do we get to witness Mercury transiting our Sun. On Monday 11th May we welcomed the public to our telescope dome on campus to see this exciting event for themselves.

We had a 10inch Meade telescope with a solar filter set up to view the event, as well as a smaller solar scope. Happily, we were granted enough breaks in the cloud to snap a picture of Mercury just after it had just begun its journey across the Sun and also a few hours later when it was well on its way.

Our astronomers were on hand throughout the day to chat to the public about the planet Mercury, the transit and some of the fascinating research they are conducting, which ranges from which ranges from the unknown origins of giant “globular” star clusters, through to nature of the mysterious “Dark Matter.”

Despite the cloud and sometimes rain we still had over 250 people come to be part of this event. We hope those who didn’t get to see the transit themselves still enjoyed seeing the images we had taken earlier, viewing our telescopes and meeting the astronomers.

Demonstrating the incredible scale of our solar system

The images for Mercury transiting the Sun really capture the incredible scale of our solar system. Mercury is about a third the size of the planet Earth, but only 1/158 the size of the Sun, so it appears as just a tiny dot against the disk of our Sun. Transits are rare as they require Mercury (or very occasionally Venus), the Earth and Sun to all be aligned in their orbits.

Some of the images also capture some sunspots. These are dark regions, often larger than planets as can be seen here. These spots appear dark compare to the sun’s surface as they are colder, around 3,700° C, a much lower temperature than the Suns photosphere (visible surface) which is about 5,500° C. These spots are caused by the magnetic field of the sun surging up; they can often cause solar flares or coronal mass ejections.

Mercury 1

The tiny black dot of mercury passing over the surface of the Sun also reminds us what a remarkable coincidence it is that the Moon almost perfectly eclipses the Sun. This is most likely just a coincidence, but until we know any better we can dare to dream. Perhaps the Earth’s unusually large Moon is an important factor in the development of life. In that case, our near-perfect Eclipse may be no coincidence after all.

Winter astronomy evenings

We look forward to the autumn term when we will begin regular star gazing evenings on campus. And further into the future, the next transit of a planet is Mercury again on 11 Nov 2019 (then not until 2032)

To find out more about the day, one of our astronomers Dr Ramon Rey-Raposo has produced a video!


This article was written by Dr Heather Campbell of the University of Surrey and first published on in May 2016.