Saturday, April 30, 2016

Mercury Transit in 8 Days!

For about 9 hours starting at 1030 UTC (6:30 a.m. ET) on May 9, 2016, SDO will watch a small black dot move across the Sun. The black dot won’t be a sunspot, it will be the planet Mercury making a rare transit of the Sun.

We will be providing a near-live feed of the SDO images of the transit at The images are delayed a few minutes by the data delivery method, but our website will display the data as self-updating movies. The movies will include a visible channel and most of the EUV wavelengths. You pick the box and wavelength and watch the transit unfold!

The image at the left shows Mercury’s position during the transit plotted on an AIA 193 image from April 9, 2016. The black circles are about the size of Mercury and are spaced 30 minutes apart.

Along with the full-disk view of the Sun we will provide several zoomed views. These views are shown by the boxes that are drawn on the image. You can also see that the EUV telescopes will see Mercury blocking the corona about an hour before it moves onto the disk. All of the boxes are built in a 16x9 ratio that nicely fits into an 1080p screen.

  • The Ingress box will show the images from when Mercury moves over the edge of the Sun at the beginning of the transit;
  • The Tracking box will follow Mercury as it moves across the disk;
  • The Egress box images will show the data when Mercury moves into that box as it exits the Sun. It will not be available until about 1730 UTC;
  • The Full Passage box will be updated throughout the transit so that you can watch the entire path of Mercury across the Sun.

Images will be shown as short movies in your browser that update every few minutes to include the latest data from the satellite. The next image is a movie from our testing in AIA 171. Coronal loops and active regions provide an ever-changing background to the circle with a white cross that was drawn to represent Mercury.

Compared to people on the Earth, the orbit of SDO causes the transit to start and end at different times as seen at SDO. The transit starts when SDO is further from the Sun and ahead of the Earth and ends with SDO in front of and closer to the Sun-Earth line.

Even though the Mercury transits were less useful for measuring the size of the solar system, they are fun to watch. You can also compare how the different telescopes on the ground and in space see the black dot of Mercury move across the Sun. Maybe, just maybe, Mercury will pass over a flare!

Never look at the uneclipsed Sun with unprotected eyes!
Always use sun-safe optics to look at the Sun.

You can safely watch the transit at My thanks to the SDO scientists, engineers, and web programmers that make this SDO Data Event possible.