Figure 1. SWAP eclipse image sequence from the first passage of the 2017 August 21 eclipse.
UPDATE: The SWAP images are received from the satellite. Check out the pictures and movies below.
Monday, 21 August 2017 has marked an important celestial event, a total solar eclipse. This was a well observed event, as the eclipse transited the whole of North America. The path of the eclipse can be seen here. People along the path saw a total eclipse, and those outside this path witnessed a partial solar eclipse where the moon covers part of the sun's disk. The eclipse was visible for about two and a half minutes from any location along the path of totality, and first seen on the west coast of the USA in Oregon at around 10:19 am PDT and finally in South Carolina at around 02:44 p.m EDT (more timing information can be found here). For more information on other types of eclipses, visit here.
Solar physicists and space weather monitors (see here for more information) often observe the sun from the vantage point of space, where they can avoid the absorbing and distortional effects of the earth's atmosphere. From this position it's possible to observe the sun in different wavelengths including the extreme-ultraviolet (EUV). ESAs PROBA2 SWAP telescope is one such instrument, which observes the sun in near real time at a wavelength of around 17.4 nanometers. At this wavelength SWAP observes a part of the sun's hot atmosphere (the corona), at a temperature of around 1 million degrees. The series of eclipse images shown in Figure 1 were produced by SWAP during the 21 August 2017 eclipse. By looking at the images at either end of the sequence you will see how complex the sun's atmosphere can be, containing regions of hot bright structures, outlining tightly wound magnetic fields, and darker regions believed to be the source of the sun's solar wind. These bright features can be seen extending off of the edge of the solar disk giving you an impression of the height of the structures in the sun's lower atmosphere. The sun's solar corona, although hot, is very tenuous and is therefore not normally visible from the earth, as the emission from the sun's bright disk dwarfs that of the solar atmosphere. The off-limb solar atmosphere can only normally be seen from earth during a total solar eclipse, when the moon passes between the earth and the sun blocking the bright solar disk allowing us to see the tenuous solar atmosphere. The rareness of these events and the unique observations that can be made, make them interesting and awe-inspiring events, as well as giving us valuable scientific observations.
What did PROBA2 see during the eclipse?
PROBA2 orbits the Earth at a height of approximately 700 km, tracing the dawn-dusk line, Movie 1 shows an animation of PROBA2's projected orbit on 21 August 2017.
Movie 1. Simulation of the path of PROBA2 on 21 August 2017.