Monitoring Solar Activity

Our Sun is a very active star. It not only emits energy as visible light that makes life possible here on Earth, but also radiates infrared, ultraviolet, microwave, x-ray, and gamma ray energy. Luckily, most of the more dangerous radiation is blocked by our atmosphere. Astronomers constantly monitor the Sun using detectors on satellites as well as on ground based radio and optical telescopes. The American Association of Variable Star Observers (AAVSO) has a program for monitoring what are called Sudden Ionospheric Disturbances (SIDs) caused by x-ray and ultraviolet flares on the Sun. A SID is a change in the upper atmosphere of the Earth due to the impact of solar flare radiation. It results in making the ionosphere more ‘reflective’ for very low frequency (VLF) radio waves, and, therefore, to strengthen the reception of these radio waves.

SID monitoring involves a simple antenna and radio receiver tuned to a distant VLF transmitter. Conveniently, the military operate such transmitters for their own purposes that amateur astronomers like myself can use to record SID activity. I have recently been honored to be recognized by the AAVSO as a SID observer who has contributed SID data reports for over 40 months. My SID detection system consists of a small wire loop antenna and a VLF receiver tuned to a 24 kilohertz transmitter operated by the US Navy in Cutler, Maine. The output signal strength of this station is measured once every 30 seconds by a computer that runs every day during daylight hours. When a UV or x-ray flare occurs on the sun, the radio signal suddenly increases and then fades within several minutes. A computer program plots this change in signal strength versus time as a graph and stores it as a file. Once a month, I review these stored graphs and report to the AAVSO the SIDs that I have recorded. I am proud, along with the group of a dozen or so other observers around the world, to make this small contribution to solar astronomy.