Mercury | Rare Transit of the Sun

Mercury passes between the Sun and Earth during the day on 9 May 2016 allowing us to see it in silhouette for about 7 hours. It happens only 13 times per century. What is expected and how can it be viewed safely? Full details here for those knowledgeable in the technical bits. This NASA article is also very informative. For the rest who don’t feel technically savvy, follow me farther down below in this post.

Where Visible?

Australia, New Zealand, and easternmost Asia will not be able to see the transit live from their locations because it will take place during the night for them. They can watch online. The rest of the world will see at least some of the transit, weather permitting. Far western Europe and Africa, as well as most of S. America and the eastern half of N. America, may see the entire transit.

For western N. America, the transit will be in progress before sunrise and continue several more hours. For Africa and Asia, the transit will be in progress as the Sun sets.

Sky & Telescope diagram | Source: Fred Espenak

Viewing It Safely

🔹  The easiest way is to watch the progress online. Do a keyword search in your browser. You are likely to find several sites. The best, in my opinion, is the Solar Dynamics Observatory SDO. The SDO spacecraft will not have weather issues since it is in orbit. The SDO site does not show anything at this time prior to the transit. Return to it on the 9th for the show.

The SDO site gives multiple views through various wavelength filters in different screen sizes. It will include a progress movie. More description here of the four special views they will offer.

🔹  You might try to project through binoculars or a telescope onto a sheet of paper. You will need to adjust focus and alignment. Warning! Do not look at the Sun through the binoculars! 

🔹  Some people will have the equipment and skill to view directly. They will use a safe solar filter mounted on their own telescope or camera. I plan to use a safe method with my tripod mounted camera I wrote about recently.

When Should I Look?

It depends on where you live. Fortunately, the entire event takes about 7 hours. Details about the times expressed in Universal Time are here. Suppose I want to see Mercury at the midpoint of the transit. The UT article linked in the sentence above says that will be at 15:00 UT. Scroll down that page for the time adjustment for your part of the world. Send me a comment if you are unsure.

According to this time conversion web site, my local time in the central daylight time zone for Iowa is 15 – 5 or 10 am. I have over 3 hours before and after 10 am in which to see the transit. I’m hoping for breaks in the clouds to allow me to get several images of the progress. I will post those if it all works out as planned.

Now mark your calendar as a reminder.


10 thoughts on “Mercury | Rare Transit of the Sun

  1. There won’t be any direct observation for me, but I’ll check in to see how things go for you. We’re supposed to have clouds and rain, so even those who want to give it a try with telescope and camera are going to have issues. It’s great that there are ways to keep up with the action despite the weather.


  2. I heard about this on radio or television last week (can’t remember which). The weather forecast for Austin today is mostly cloudy, and as of now there’s still nothing on SDO.

    Sic transit gloria Mercuris.


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