While the penguins were gazing at the total eclipse on December 4, the instruments onboard the PROBA2 satellite worked overtime to image and measure not one, but four passages of the moon in front of the sun. One of these occultations was nearly total for the SWAP EUV imager: as much as 96% of the solar disk was covered by the moon during the second passage (middle image below). The fourth time that the moon was in SWAP’s field of view, it did not touch the solar disk, which made it difficult to observe the moon in the images. The pictures below show the three first transits of the moon observed by SWAP.
LYRA Observations
Also the LYRA radiometer onboard was ready to measure the extinction of the solar light as it was blocked by the moon. As for all eclipses, LYRA activated one of its backup units, which measured together with the regular unit. The instrument monitored the progressive extinction of the solar light in its channels that observe in the ultraviolet (red and green curves) and extreme ultraviolet (black and blue curves). As can be seen in the figure below showing the second and third passage, the extreme ultraviolet curves have an asymmetric profile. This is caused by the fact that the sun, in those wavelengths, doesn't emit uniformly over its surface. Active regions appear much brighter than the rest of the solar disk. The distortion of the extreme ultraviolet curves is caused by the sudden occultation of an active region located at the right limb of the sun (see image above on the right). Interestingly, that active region produced several flares of moderate amplitude (C-class) on the day of the eclipse (see the list of flares).
Eclipses in 2022
This was the 28th eclipse observed by the PROBA2 instruments. In 2022, two eclipses will take place: on April 30 and on October 25. This last one is a special one. Not only because it is the 30th eclipse that PROBA2 will observe; a partial eclipse will be visible from Belgium around midday! Let’s hope the weather will cooperate so that we can also observe this spectacle from ground.
