Radio Astronomy

You Can Build a Home Radio Telescope to Detect Clouds of Hydrogen in the Milky Way

If I ask you to picture a radio telescope, you probably imagine a large dish pointing to the sky, or even an array of dish antennas such as the Very Large Array. What you likely don’t imagine is something that resembles a TV dish in your neighbor’s backyard. With modern electronics, it is relatively easy to build your own radio telescope. To understand out how it can be done, check out a recent paper by Jack Phelps.

He outlines in detail how you can construct a small radio telescope with a 1-meter satellite dish, a Raspberry Pi, and some other basic electronics such as analog-to-digital converters. It’s a fascinating read, and one of the most interesting features is that his design is tuned to a frequency of 1420.405 MHz. This is the frequency emitted by neutral hydrogen. Since it has a wavelength of about 21 centimeters, the hydrogen emission line is sometimes called the 21-cm line. Neutral hydrogen comprises the bulk of matter in the Universe. The 21-cm emission isn’t particularly bright, but because there is so much hydrogen out there, the signal is easy to detect. And wherever there is matter, so too is the hydrogen line.

Observations of hydrogen in the Milky Way (red dots). Credit: Jack Phelps

The emission is caused by a spin flip of the hydrogen’s electron. It’s a hyperfine emission, which means the line is very sharp. If you see the line shifted a bit, you know that’s because of relative motion. Astronomers have used the line to map the distribution of matter in the Milky Way, and have even used it to measure our galaxy’s rotation. Early observations of the line pointed to the existence of dark matter in our galaxy. And now you can do it at home.

There are other radio objects you can observe in the sky. The Sun is a popular target given its strong radio signal. Jupiter is another somewhat bright source. It’s a cool hobby. Even if you don’t intend to build a radio telescope of you’re own, it’s worth checking out the paper just to see how accessible radio astronomy has become.

Reference: J. Phelps. “Galactic Neutral Hydrogen Structures Spectroscopy and Kinematics: Designing a Home Radio Telescope for 21 cm Emission.” arXiv preprint arXiv:2411.00057 (2024).

Brian Koberlein

Brian Koberlein is an astrophysicist and science writer with the National Radio Astronomy Observatory. He writes about astronomy and astrophysics on his blog. You can follow him on YouTube, and on Twitter @BrianKoberlein.

Recent Posts

A Space Walking Robot Could Build a Giant Telescope in Space

The Hubble Space Telescope was carried to space inside the space shuttle Discovery and then…

1 day ago

New Report Details What Happened to the Arecibo Observatory

In 1963, the Arecibo Observatory became operational on the island of Puerto Rico. Measuring 305…

2 days ago

We Understand Rotating Black Holes Even Less Than We Thought

The theory of black holes has several mathematical oddities. Recent research shows our understanding of…

2 days ago

Habitable Worlds are Found in Safe Places

When we think of exoplanets that may be able to support life, we hone in…

2 days ago

New Glenn Booster Moves to Launch Complex 36

Nine years ago, Blue Origin revealed the plans for their New Glenn rocket, a heavy-lift…

2 days ago

How Many Additional Exoplanets are in Known Systems?

NASA's TESS mission has turned up thousands of exoplanet candidates in almost as many different…

2 days ago