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.

GRAVITY EXPRESS

"When I was in high school", writes physicist, A. Zee*, "I read about how gravity might be exploited to create a new mode of travel. Suppose a tunnel could be dug straight down through the center of the earth to the other side. Look down into it. Scary! An apparently bottomless pit. We have bought our ticket and now we are invited in. We take a deep breath and we jump." "Whoosh! We fall straight down, just as Alice once fell into the rabbit hole. We go faster and faster. It is that falling dream come true! We go rushing past the center of the earth. The moment we go past the center, gravity starts to act as a brake. It tries to pull us back to the center. We start to slow down. Will our momentum carry us through? Yes! Provided there is no friction, we would just make it to the exit hole on the other side. We would also need help getting out of the hole, lest we fall right back in."

"In practice, there is friction, and we need a little boost to get us to the end. Of course, we would also need to be inside a capsule strong enough to withstand the searing heat at the center of the earth, not to mention the lightning speed we will get up to as we zoom past the center." "Since we know the strength of the gravitational force, we can easily figure out how long the trip would take. It turns out to take forty-two minutes! No airplane with current technology could possibly get you there that fast. Better yet, no fuel is needed for this ’gravity express.’ We just let gravity do its thing." "You are suspicious. What is the catch? There is no catch, aside from the expense and engineering difficulty of building a heatproof tunnel that would not collapse through the center of the earth. The physics is perfectly sensible. Gravity always is trying to pull us down; we will just let it."

*An Old Man’s Toy--Gravity at Work and Play in Einstein’s Universe, Macmillan Publishing Company, N.Y., 1989.