As seen from Earth, only transits of the inner planets Mercury and Venus are possible. Planetary transits are far more rare than eclipses of the Sun by the Moon. On average, there are 13 transits of Mercury each century. Nowadays, all transits of Mercury fall within several days of May 8 and November 10. During November transits, Mercury is near perihelion and exhibits a disk only 10 arc-seconds in diameter. By comparison, the planet is near aphelion during May transits and appears 12 arc-seconds across. However be aware that the planet Mercury is too small to be seen with the naked eye in front of the Sun. It’s therefore essential to magnify the image using a telescope or any appropriate device to detect the black ball pinned in the foreground of the photosphere of our star.
On the 2016 Transit of Mercury visibility map you can see that all the transit was visible from western Africa, the Canary Islands and northern Chile where the weather prospects are the best in May. This is why I finally observed once again from the Atacama desert in northern Chile. In about seven and a half hours time the planet Mercury crossed the solar disk from east to west. It was the first transit of Mercury since the previous one in November 2006 and was visible at least partially from Europe, Africa, the Americas and part of Asia. The next Mercury transit will occur in November 2019. There were a few outreach initiatives to which occasional observers, students, teachers, could participate. For example the Mercury transit project. Do not hesitate to join those.
As you can see the sky over San Pedro de Atacama was quite cloudy during the Mercury transit at sunrise. On the altiplano we experienced a snow storm the night before.
Sky from sunrise to maximum in San Pedro de Atacama, Chile, during the 2016 May 9th transit of Mercury
Weather satellite imagery during the 2016 Mercury transit
Equipment setup at my viewing location in San Pedro de Atacama at 2,400 meters (8,000 feet) elevation
Licancábur volcano at sunrise
First sunrays behind the Licancábur volcano
Solar disk hidden by clouds and the Licancábur volcano
You can see that the visible horizon and terrain elevation were correctly predicted by my local circumstances computation webtool.
Study of the terrain elevation profile at sunrise from my tentative location in the Atacama desert
First glimpse of Mercury at 11:27:35 UTC over 10 minutes after ingress
Mercury at 11:59:05 UTC
Mercury at 13:00:52 UTC
Mercury at 13:57:06 UTC
Mercury at 14:58:45 UTC (maximum)
Mercury at 15:59:56 UTC
Mercury at 16:52:15 UTC
Mercury at 18:38:50 UTC approaching internal egress
Mercury at 18:41:06 UTC approaching external egress
Composite of the 2016 Mercury transit in equatorial coordinates (approximately every hour when the clouds were not obscuring the solar disk)
Composite of the 2016 Mercury transit in horizontal coordinates (approximately every hour when the clouds were not obscuring the solar disk)
Same location at sunset later that day
Multiple transits of the ISS in front of the Sun occurred during the Mercury transit. A checkbox on the interactive map was showing you the locations to be at and the times as well (information provided by John Irwin).
Here are the results in a video by Thierry Legault shot from the Harriet Wetherhill Park outside Philadelphia, PA, USA. From the actual pictures one can notice the accuracy of the prediction map is about 350 meters (1,200 feet).
First Mercury transit ever photographed from Philadelphia, USA, with a transit of the ISS