Live streaming a radio-telescope observation of the solar eclipse

Millions of people were in the path of totality of the Great North American Eclipse on 8 April. They had a rare opportunity to witness the corona, which is visible only during a total solar eclipse, as explained in Jay Pasachoff’s August 2019 Quick Study (page 66 ). At Northeastern University in Boston, the eclipse provided us with a unique outreach opportunity involving our new Compact Radio Telescope (CRT), which is mainly used for 21 cm hydrogen-line observations in undergraduate and graduate physics teaching laboratories.

Starting a couple of hours before the eclipse, we tracked the Sun with the CRT and periodically measured the total power received in a bandwidth of a few megahertz around 1.42 GHz, the frequency of the 21 cm hyperfine transition in neutral hydrogen. The signal started to decrease close to the moment of optical Sun–Moon contact and reached a minimum of about 40% of what was measured before and after the eclipse. The visible solar photosphere occultation in Boston was 93%. We observed a smaller dip because additional radio emission comes from the vast solar corona, ¹ which is normally concealed from the human eye by the blue sky.

The 2.5-hour solar eclipse gave plenty of time for us to engage and motivate students to learn more about astrophysics and radio astronomy. Many Northeastern students who watched our live stream ² were curious about the difference between the optical and radio observations. The students were quite enthusiastic about the real-time radio tracking of the eclipse, so we plan to continue live streaming radio-telescope observations in the future.