By 2014, 16,000 volunteers had traced solar eruptions across spacecraft images; 38,000 hand-drawn tracks helped scientists catalog 144 coronal mass ejections

The Sun emits enormous clouds of electrically charged particles and magnetic fields into space. These eruptions, known as coronal mass ejections, can travel millions of miles and, when directed toward Earth, may affect electrical flow, satellites, radio communication transmissions, navigation systems, and even power grids when they reach their destination. Recording these eruptions as they move away from the Sun is an important part of understanding space weather, but tracking them is a slow and demanding task.

To solve this problem, scientists launched Solar Stormwatch, a citizen-science project that invited people to examine pictures taken by NASA’s STEREO twins. Instead of letting machines do the whole job, the citizens have tracked solar eruptions by hand, marking them on various images of STEREO spacecraft. As a result, the Solar Stormwatch research team has prepared more than 16,000 volunteers’ hand-made tracks of over 38,000 solar eruptions. By the end of 2014, scientists gathered a catalog of 144 coronal mass ejections.

Why were people needed?


Although computers correctly recognize several attributes in images of spacecraft, coronal mass ejections acted as a complex and puzzling problem. The ejections often appeared as faint and expanding clouds that changed shapes when they moved through the dimensions of space. Bright stars, background light, and other solar activity could also make them difficult to distinguish.

Solar Stormwatch decided not to burden volunteers with complicated scientific definitions and just gave them a simple task. Participants viewed specially prepared images called J-maps. Every event was traced many times by different volunteers rather than relying on a single observation. Now, each volunteer used a range of points to make a visible path of a phenomenon. Instead of just relying on one observation made by one volunteer, every eruption’s path was observed many times. This process of repeating the same study was extremely significant.

The technique

The project yielded a vast collection of observations. More than 38,000 individual tracks were created as volunteers traced out the eruptions through pictures captured by the Heliospheric Imagers tool aboard the STEREO-A and STEREO-B spacecraft.

Researchers then grouped the tracings that belonged to the same eruption. Every person marked the object differently, and this made it possible to get the collective average path of the eruption by using all individual marks. Instead, every work was averaged in order to obtain the consensus path for each eruption, which enabled scientists to calculate the speed and angle of every eruption together with its approximate area of source on the Sun. Using this approach, the team prepared a catalog of 144 coronal mass ejections observed between January 2007 and February 2010. This is a catalog offering the path of the eruption from close to the Sun and at a distance of about 70 degrees from the Sun, and therefore difficult to gather with the help of earlier catalogs.

A citizen science catalog for future research

The Solar Stormwatch team later described the catalog as the only citizen science-generated collection of coronal mass ejections available at the time. The volunteers involved in Solar Stormwatch did not work with telescopes or spacecraft. They contributed to studying the images and tracing images that computers failed to recognize with the necessary reliability.

The purpose of the project was not limited to counting eruptions. Since each event consisted of the original volunteer tracings and the final consensus profiles, the researchers were able to compare information, predict risk, and improve the analysis of solar eruptions in the future. The combined observations from the volunteers provided researchers with a consistent record of solar eruptions during years near the Sun's solar minimum, creating a valuable resource for future studies of space weather.