Mercury, the smallest planet in the Solar System, is just about to get between us and the Sun. Today, for a few hours, Mercury will trek across the solar disk, a phenomenon known as transit. It will be visible in Europe, Africa, and the Americas starting at 7:35 am EST (12:35 pm GMT) and finishing at 13:04 EST (18:04 GMT). So here’s how to observe it safely and, in case the weather is terrible where you are, where to watch it online.
First of all, under no circumstance try and look up at the sky to get a glimpse of the transit. The only thing you’ll be getting is solar retinopathy, as the sunlight leaves a chemical burn on your retina. You will need binoculars or a telescope with the appropriate filters. Mercury covers about 0.004 percent of the Sun’s disk, so you need magnification to actually see it.
If you don’t have a telescope with a filter handy do not despair. Many libraries (across the US at least) have telescopes to borrow available and several organizations, universities, and observatories are running free events for members of the public to join in. A full list of timings for cities across the US and Canada is available at Eclipse Wise.
There are also plenty of livestreams with expert commentary happening online from the Royal Observatory Greenwich in London, UK to the Griffith Observatory in Los Angeles, California. You can also watch it on the IFLScience Facebook Page as we stream the Slooh broadcast.
Transits of Mercury happen 13 or 14 times every century either in November or in May. This is due to the inclination of the orbit of Mercury with respect to Earth, so those months are the only times the planet is aligned with the Sun from our point of view. Mercury’s orbit shifts around the Sun due to our star’s gravity, so the transits are gradually moving to later in the year. Before 1585, they occurred in April and October.
Try and catch the event today because there’s quite a gap until the next one. We won’t be seeing another transit of Mercury until November 13, 2032.