Students in Prof. Kristen Thompson's astronomy class recently spent some time outside observing the sun as part of the laboratory component of the course. The students used a dedicated solar telescope to visually observe the features of the sun in a safe manner. Such a telescope integrates a narrow-band filter into the optics of the system that only allows very specific wavelengths to pass through. In this way, the harmful components of the sun's light are blocked, and only light safe for viewing reaches the eyes of the observer.
In addition to visually observing solar features directly through the telescope, students also learned how to create images of the sun by replacing the eyepiece of the telescope with a CCD camera. The camera, connected to a computer via a USB cable, records a series of images of the sun and writes them to disk as .avi video files. The students learned how such files are processed to create beautiful pictures of the sun. Each student captured a digital image of the sun that they could take with them at the end of the day to share with their family and friends.
While recording images of the sun, students are able to view a live feed of the sun on the screen of a computer connected to the CCD camera. During one solar astrophotography session, Shea Parikh '16, a student in the astronomy course, noticed that an airplane crossed in front of the disk of the sun while he was recording his image. The final image of the plane transiting the sun is stunning. The plane and its contrails can be seen in silhouette against the sun and its features. These features, such as sunspots, filaments, and prominences, are all caused by the sun's chaotic magnetic field.
Sunspots, seen as dark spots on the disk of the sun, appear where the surface temperature of the sun is lower than the surrounding regions. Although the temperatures of these regions are reduced, they are still approximately 4,000 K (3,727 °C), which is cool compared to the surrounding material at approximately 5,800 K (5527 °C).
Sunspots are temporary phenomena that expand and contract over time as they move across the face of the sun. Prominences can be seen on the edge of the sun as plumes of gas that are carried away from the surface of the sun by its magnetic fields.
Filaments, the dark lines on the face of the sun, are the same type of phenomena, but are viewed from a different angle. Filaments are seen against the disk of the sun, while prominences are seen reaching outward from the edge.