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A Deeper Look at the SWAP Movie of the March 2015 Eclipse

To read about the PROBA2 eclipse observation campaign and see images of the eclipse, follow this link.

When ESA posted the video of SWAP’s observations of the March 20 solar eclipse on YouTube a number of viewers shared comments and questions about several unexpected aspects of what they saw. A few viewers were so surprised by what they saw that they even wondered if the images were really authentic. The images were most assuredly real, but nonetheless we on the PROBA2 team were likewise intrigued by similarly unexpected things that we saw in the observations.

Some of the questions commenters asked have straightforward — if not exactly simple — answers, while others required us to dig deeper and do some real research of our own to try to address them.

Among the questions raised in the comments were:

  • Why does the Moon move across the Sun from east to west, the opposite direction of motion from what viewers on the ground observed?
  • Why didn’t the Sun appear to rotate in the movies as it does in many movies from PROBA2 and other Sun-observing spacecraft?
  • Why did the Sun change so little during the movies? Shouldn’t there have been some dynamics visible in the corona?
  • Why did the movie play so quickly? Why were there so few frames showing the eclipse?

Let’s have a look at these questions to see what we can learn about the Sun, solar eclipses, and the PROBA2 spacecraft from them.

PROBA2 Views a Total Solar Eclipse - 2015

Updated (25 March 2015): On 2015 March 20, PROBA2 observed a total solar eclipse — twice! The spacecraft's orbit carried it through the darkest parts of the Moon's shadow two times, first between 08:28 and 08:53 UT and again between 10:24 and 10:50 UT. Eclipse chasers, scientists, media and members of the general public have been following our data closely, so we are collecting all of our results and data products in one place for quick access.

SWAP, an Extreme-Ultraviolet solar telescope, observes the solar corona in a passband centered on 17.4 nm. The structures we see in SWAP images have a temperature of approximately 1 million degrees. LYRA, an X-ray/Ultraviolet radiometer observes the total incoming light levels from the Sun in several wavelength bands.

More information about these instruments is available here: SWAP | LYRA.