The Sun
When solar flares occur on the sun’s surface, they are often accompanied by a burst of radio energy into space. A small radio telescope can pick up these bursts in real time allowing us to track how active the sun is over time. Other radiation from solar flares and coronal mass ejections can interact with the Earth’s ionosphere in ways that radio telescopes can detect.
For learning about many of the facets of Solar Observing and Solar Effects here on Earth you can peruse SpaceWeather.Com. Another great resource for current status of the Sun and Solar Effects on Earth is the YouTube Channel of "Space Weather Woman" Tamitha Skov where she gives a weekly run down on what is happen on the sun, how it could affect us, and some predictions or statistics relating to what could come in in the days that follow.
This diagram shows the strong correlation between 10.7 cm Solar Flux emissions and the Sunspot Number. 1 Solar Flux Unit is equal to 10^4 Janskys or in communication terms, −190 dBm·m−2·Hz−1
The radio emission from the Sun at a wavelength of 10.7 centimetres (often called "the 10 cm flux") has been found to correlate well with the sunspot number. Sunspot number is defined from counts of the number of individual sunspots as well as the number of sunspot groups and must be reduced to a standard scale taking into account the differences in equipment and techniques between observatories. On the other hand, the radio flux at 10.7 centimetres can be measured relatively easily and quickly and has replaced the sunspot number as an index of solar activity for many purposes.
One emission of interest that can be monitored by a small Radio Telescope is the 10.7 cm wavelength (2800 MHz) where astronomers and geophysicists typically make measurements of Solar Flux. Solar Flux has proven to be a very good indirect indicator of where our Day Star is in its 11 year sunspot cycle and sunspot count, as well as a premium indicator of the status of the Ionosphere here on earth. The 10.7 cm signal is broadband noise that rises and falls with the sunspot count, and often changes abruptly with the advent of a powerful solar flare, Coronal Mass Ejection, or other Solar Storm events on the Sun. The effectiveness of Radio Propagation in the HF and Short Wave bands are strongly influenced by this signal, and the Solar Flux number is used to predict short term propagation. Can you hear your favorite shortwave radio programs this evening? Many enthusiasts turn to the Solar Flux number to predict which Shortwave bands they can listen to at what times of day and from what quadrants of the world. Ham Radio operators do the same for deciding what direction to point their antennas or when they can expect talk to their friends overseas. Military, marine, and airline radio operators are also keenly interested in the ups and downs of 10.7 cm Solar Flux.
For more information about Solar Flux see:
The Australian Space Weather Forcasting Centre: The Ten Centimetre Solar Radio Flux
A Small Portable Radio Telescope like this one can receive and measure 10.7 cm Solar Flux.
Solar Flux measurements compared over two 27 day "apparent" revolutions of the Sun (Bartel Rotation*) and by two different measurement techniques.
Solar Flux measurements are often compared from Earth day to Earth day, Solar Day to Solar Day, or 11 year Sunspot Cycle to 11 year Sunspot Cycle to observe cyclical trends in the status of solar emissions.
*Bartel Rotation is the apparent length of a solar day as seen from earth. More about Bartel's Rotation Number and Solar Rotation here.
The antenna system pictured above is a versatile unit designed to receive signals from 850 MHz to 6 GHz. And we have shown elsewhere that it is suitable for 21 cm Neutral Hydrogen, 18 cm Hydroxyl Radical, and "Water Hole" reception using an inexpensive RTL-SDR. However, 10.7 cm is beyond the normal performance of the RTL-SDR so an SDR with higher frequency tuning performance is required, one that receives at least 2800 MHz.
At VBAS, we have future plans to receive and measure 10.7 cm Solar Flux, but to date we have not addressed this.