We observed the solar eclipse with our Compact Radio Telescope (CRT) by measuring the total brightness of the Sun in the radio wavelengths (within the range of 1421-1423 MHz). Check out our video below that was recorded live on April 8, 2024 and scroll down for more information.
Why 1421-1423 MHz?
One of the purposes of our radio telescope is to detect the Hydrogen line (rest frequency of 1420.4 MHz) produced by cold hydrogen clouds in our Milky Way galaxy. We designed the feed of our telescope and its electronics to capture the frequency band near 1420.4 MHz. By studying this frequency band, we can map the hydrogen clouds in our galaxy, determine their relative velocities with respect to us, and determine our galaxy’s rotation curve.
What does the vertical axis show?
It is an uncalibrated intensity measurement of the electromagnetic radiation produced by the Sun.
What causes the small variations in intensity?
It turns out it is not very easy to do a long term measurement of total power over an extended period of time. There are a lot of sources of RFI (Radio Frequency Interference). Cell phone towers, individual cell phones, WiFi access points and any devices with WiFi or Bluetooth create interference that affects our radio telescope’s measurement. These source of noise also affect our measurements differently depending on where we point our radio telescope in the sky. The pointing of the telescope also needs to be accurate to a small fraction of the telescope’s beam size in order to track the Sun properly. All these effects cause some additional variations on top of what we expect to see from the eclipse itself. But the dip in the intensity due to the eclipse was clearly visible.
What is the noise in the video?
It is the noise coming from the Sun! Well, kind of. The live stream ran off of a Raspberry Pi, which worked really hard to produce the video. It is in an enclosed box with a webcam and a fan. The webcam captured the noise from the fan which is just a white noise. The Sun would have sounded similar if we had demodulated the electromagnetic waves into sound. Interestingly, you can hear the fan noise going down during the eclipse due to the enclosure getting less light and the Raspberry Pi requiring less cooling. The fan starts working faster again as the Sun comes out after the eclipse.
Results
The plot below shows the final result of our analysis. In the live stream plot, there was a typo in the timing of the maximum occultation. The correct time should be 3:30pm. We also normalized the brightness value to be 1.0 by using the data collected between 12:30pm and 1:30pm.
