Welcome to the PROBA2 Science Center

Update: With exciting science talks and participation from all around the globe, SWT13 was a success. A big thank-you to all who contributed! Meeting notes can be found here.

We are pleased to announce that the PROBA2 Science Working Team has selected 8 proposals for the 2016 Guest Investigator Program.

Celestial transits-where a celestial body is seen to pass across the solar disk from the perspective of the Earth-are relatively rare events. The planet Mercury undergoes around 13 transits a century, and Venus has a pair of transits approximately every 120 years. In 2012 the SWAP EUV imager on the PROBA2 satellite successfully observed a Venus transit of the Sun. On May 9, 2016, it was Mercury's turn! The Mercury transit was seen from Earth starting at 11:13 UT and ending at 18:42 UT. The total transit time was around 7 hours and 30 minutes.

What did we expect to see in SWAP observations? SWAP is an EUV telescope onboard the ESA PROBA2 satelite, it observes the Sun at roughly 1 million degrees from orbit around the Earth. Mercury is expected to be pictured as a small black disk crossing the face of the Sun, which would be seen as roughly 4 pixels in diameter. The PROBA2 team created a simulation of what SWAP was expected to see, which is shown in the video below. This simulation illustrates the path of Mercury as it crosses the Sun from the perspective of SWAP on PROBA2. The path of Mercury appears to 'wobble' as it crosses the Sun, but this is an artificial effect created by parallax from the changing perspective of Mercury in the PROBA2 field-of-view as the spacecraft orbits the Earth.

On 2016 March 8 and 9, a solar eclipse took place over the Pacific Ocean. This eclipse was total -that is, the entire solar disk was covered by the Moon- over Indonesia and the central Pacific, starting at sunrise over Sumatra and ending at sunset north of the Hawaiian Islands. Additionally, large parts of South-East Asia, Alaska and Australia witnessed a partial solar eclipse. The path of totality had a maximum width of 155 km and the maximum duration was 4 minutes and 9 seconds at the point of greatest eclipse, which was over the waters of the Pacific Ocean.

The total solar eclipse observed in March 2015 caught a lot of people's attention, especially as the path of totality passed over most of Northern Europe. There was a great deal of fan-fair and plans to observe the eclipse from the ground. However, due to heavy cloud cover, a lot of people had to turn to space-based observations, such as those made by the sun watching extreme-ultraviolet imager: SWAP, on board the European Space Agency's PROBA2 satellite, which images the Sun from the vantage point of a polar Earth orbit, away from pesky cloud cover. More information about the March eclipse can be found here and here.

SWAP observes the solar corona in a passband centered on a wavelength of 17.4 nm. The structures seen in SWAP images have a temperature of approximately 1 million degrees. More information about the SWAP instrument is available here.

It may come as some surprise, especially for those in Europe, that there was another eclipse observed on 2015-Sep-13. Whether you are able to observe an eclipse from the ground depends on your geographic location, in contrast to the March eclipse which was seen from Northern Europe and the Arctic regions, the September eclipse was observed in the southern hemisphere from Antarctica and southern Africa. In any given year the Earth will experience at least 2 solar eclipses due to the Earth and Moon's orbit.

We are pleased to announce that the PROBA2 Science Working Team has selected 7 proposals for the 2015 Guest Investigator Program.

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.