Solar telescopes at the ready! On Monday, November 11, Mercury will take a stroll across the Sun. The transit, as it is called, will be visible in Europe, Africa, and the Americas starting at 7:35 EST (12:35 GMT) and finishing at 13:04 EST (18:04 GMT).

Mercury, the innermost planet in the Solar System, orbits around the Sun in slightly less than 88 days, overtaking Earth every three to fourth months. This also happens during special alignments and, in those cases, we see Mercury crossing the solar disk. The reason it happens only at specific times is due to the orbit of Mercury being at a 7-degree angle with respect to our planet’s orbit. For this reason, the transit can happen either in May or November, and the May ones are half as frequent. Interestingly, Mercury’s orbit shifts around the Sun due to our star’s gravity, so the transits are gradually moving later in the year. Before 1585, they occurred in April and October.

If you plan to observe the event, please remember that it cannot be done with the naked eye. First of all, you risk solar retinopathy, a chemical burn to your retina. Even if it weren’t harmful, you wouldn’t see the transit. Mercury covers about 0.004 percent of the Sun’s disk. You need to have magnification to observe the event, ideally a telescope with the correct solar filter. Many libraries across the US have telescopes available to loan, so you may not need to buy fancy equipment to view it. If you don’t have access to a telescope or solar binoculars, several observatories are planning free events and there will be live streams of the transit as well. 

The Sun is currently in the quietest period of its cycle and has no sunspots, so Mercury will be easy to spot with the right equipment. A full list of timings for cities across the US and Canada is available at Eclipse Wise.

There are about 13 or 14 Mercury transits every century. The last one was just 3.5 years ago, but for the next one, we will have to wait until November 13, 2032. While these events are rare, they are not as rare as the transit of Venus. If you missed the 2012 Transit, that’s it until 2117.