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Does The Moon Block Radio Waves From The Sun, An Eclipse Experiment

A description of how you can test to see if the Moon blocks radio waves during an eclipse.

Published onMar 01, 2024
Does The Moon Block Radio Waves From The Sun, An Eclipse Experiment


When astronauts were sent to the Moon, they experienced periods of radio blackout with mission controllers here on Earth. Is this a result of weak signals being used, or the structure and properties of the Moon? The Sun produces light across the entire electromagnetic spectrum, including radio. To demonstrate this, a simple satellite radio dish can be attached to a signal finder and aimed at objects known to produce signals (like the Sun). We know that the Moon blocks the Sun’s light during an eclipse. Using this phenomenon, we can conduct a test to see if it blocks more than just visible light, in this case, radio waves.

1. Introduction

For years I have enjoyed the sky and stars. Like many, I began this journey with a simple pair of binoculars, and eventually my first telescope. These tools continue to be my preference, but I began to look at different ways to study the heavens. Years ago, I came across an interesting experiment that used an old TV satellite dish to do entry-level radio astronomy. With a few basic pieces of easy-to-find equipment, I found myself in possession of a new view of space.

2. Radio Waves and the Electromagnetic Spectrum

Radio waves are part of the electromagnetic spectrum and have become the primary form through which we communicate. From cell phones to satellites, we use this range of the spectrum in many parts of our daily lives. Astronomers have found use for studying these waves as well as stars produce light in every part of the electromagnetic spectrum. Since not all wavelengths of light make it through Earth's atmosphere, different areas of astronomy have evolved over time, including radio astronomy. Radio waves pass through all layers of air surrounding our planet, making their study a great tool for us. There are obstacles that can block radio waves though. Understanding these challenges is important to how we explore space. To explore this on my own I wanted to ask a simple question: Does the Moon block radio waves from the Sun?

3. Designing an Experiment

An experiment to test the question of whether the Moon can block radio waves or not requires two main parts; 1) a time where the Moon would be in front of the Sun, and 2) a way to detect radio waves from a specific direction. The first of these two may seem challenging since it requires there to be a Solar Eclipse. It turns out there is a pattern in nature that exists which allows the prediction of these. The next Solar Eclipse will be April 8, 2024. To tackle the second part of detecting radio waves from a specific direction I am excited to try a DIY project on basic radio astronomy. Satellite dishes are perfect for this as they're designed to aim at and receive radio signals from a satellite in orbit; a specific direction.

While there are several setups you can find online, the purpose of this experiment will take less to set up. Since the goal is simple — to see if the Moon blocks radio waves from the Sun — there are only five items needed. Things needed will be; a satellite TV dish, a satellite finder, two coax cables, and a power supply. To make things easier, buy a satellite finder kit (Figure 1) and power supply on either eBay or Amazon. These kits already come with the finder unit, battery pack, and coax cables. The cost is low as well, in general around $35 or so. For the satellite dish, I would recommend checking thrift stores or online auctions. (hint: you may even have a neighbor or nearby apartment complex that might have a spare). Make sure the satellite dish you get has at least the dish and an arm unit with an LNB (low-noise-block) attached.

a box with a compass, cord, and electronics.
Figure 1

Satellite finder kit containing satellite signal finder, battery pack, short coax cable and compass.

3.1 Assembling and Testing a DIY Radio Telescope

To assemble the experiment, attach a coax cable between the satellite dish and finder. On the back of the satellite finder, you'll have one coax side labeled "to rec/receiver" and the other "to LNB". Connect the power supply to the "to rec/receiver" side, and the coax from the satellite dish to the LNB side (Figure 2). With batteries in your power supply, everything is ready! Even without a mounted base for the dish it can be moved and pivoted about with ease. Because the dish is made to reflect radio signals to the receiver, aiming it at the Sun is an important step. If it is a sunny or partly sunny day, finding the Sun will be easy. Aim the dish to point toward the Sun. If the day is clear enough, you should be able to see the shadow of the arm unit on the dish. Continue to rotate the dish in slight adjustments until the least amount of shadow is seen. You should now be aimed at the Sun. Looking at the satellite receiver, the needle will move from no reading to a strong one. If this is not the case, adjust the "-dB" dial on the finder as if you were turning the volume up until you see the needle move.

satellite dish on a table, a hand holding a meter
Figure 2

Final assembly of a DIY radio telescope showing the satellite signal finder connected to the satellite dish and battery pack.

4. Ready, Set, Explore!

With even the most basic radio telescope we are now set to explore our questions and others that may arise. Before the April 8, 2024 Solar Eclipse, take some time to explore and enjoy testing what you can see in the world around. To test and prepare, you will want to make a note or mark on your signal receiver where the -dB dial is set to once you have determined the signal fully drops off when not pointed at the Sun. This will be important in order to have good, calibrated measurements. The day of the eclipse you will want to take measurements with the signal finder just before and several times again leading up to totality. This will allow you to make sure your dish is aimed at the Sun properly, making additional use of the Sun’s shadow while visible. Minutes before totality, stay with your dish the entire time to hold it still as the Moon passes fully between Earth and the Sun.

Does the Moon reflect radio waves from the Sun? Do clouds have any effect on whether you can find the Sun with your radio telescope or not? If you keep your telescope aimed just right, how long does the signal from it last when the Sun passes in front of it? No matter how you chose to experiment or if you are in the path of totality or only have the chance to view a partial eclipse, I hope there are ways to enjoy this amazing event for everyone!

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