In May, students and staff at Loreto College observed a rare transit of the Sun’s disc by the smallest planet in our Solar System, Mercury. At a mean distance from the Sun of 58 million kilometres, Mercury travels quickly around its orbit in just 88 days, at a mean speed of 47 km/s. Even so it took 7 ½ hours for the tiny black silhouette to travel across the face of the Sun. Students were warned not to look at the Sun directly but were allowed to use an appropriately filtered astronomical telescope. Those who saw the event will remember it for a long time.
Transits of Mercury occur either in May or November when the planet crosses the plane of the ecliptic. They occur at intervals of 7, 13 or 33 years. We will have to wait until 2049 to witness another May transit. Transits of Mercury are not as rare as those of Venus – the next one will not be until 2117. The next transit of Mercury will be on 11th November 2019, but it will probably be cloudy! Thanks to Mr Thomson for arranging for our students to view this piece of fascinating science.