Mercury Transit 2016
Below are the last four images of the transit of Mercury as observed by the Extreme-ultraviolet Imaging Telescope (EIT) on board the SOHO spacecraft. They are enlargements of a 64 x 64 pixels region tracking Mercury in the original 1024 x 128 pixels strip shown in the four movies below. The camera of EIT has 1024x1024 pixels but the telemetry rate from the L1 Lagrangian point allows only for downloading a 1024x128 window when EIT observes with a cadence of three minutes.
The blue green, yellow and red images correspond respectively to the four passbands of the instrument centered on four spectral lines of the extreme ultraviolet spectrum: 17.1nm (Fe X), 195. nm (Fe XII), 28.4 nm (Fe XV) and 30.4 nm (HeII). Because the solar corona is visible at these wavelengths, the planet is visible in front of it before it crosses the solar disk itself. The transist provides scientists with valuable information to calibrate the instrument.
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The special EIT observation program is summarized below:
06:20-07:05 UT. Two EIT synoptic sets (full frame, four wavelengths).
07:10 - 18:50 UT. EIT subfield set; 128x1024 pixel field of view [4x32 LOCS block]. The total path of Mercury spans a 8x32 LOCS block field of view. This is split between two (128 pixel) coordinates tables.
Transit of Mercury in the EIT field of view:
07:36 UT East edge of field
09:04 UT East limb
12:45 UT transition from table 2 to table 3 coordinates
16:53 UT West limb
18:36 UT West edge of field
The program consists of a ~1 hour block repeated for the duration of the transit as shown:
4 images of 284A at 3:50 minute cadence
5 images of 195A at 3:00 minute cadence
5 images of 304A at 3:00 minute cadence
5 images of 171A at 3:00 minute cadence
19:00 - 19:50 UT. Two EIT synoptic sets (full frame, four wavelengths).