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\u2019t imagine is something that resembles a TV dish in your neighbor\u2019s 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.<\/p>\n
<\/p>\n 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\u2019s 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\u2019t 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.<\/p>\n The emission is caused by a spin flip of the hydrogen\u2019s electron. It\u2019s a hyperfine emission, which means the line is very sharp. If you see the line shifted a bit, you know that\u2019s 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\u2019s rotation. Early observations of the line pointed to the existence of dark matter in our galaxy. And now you can do it at home.<\/p>\n 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\u2019s a cool hobby. Even if you don\u2019t intend to build a radio telescope of you\u2019re own, it\u2019s worth checking out the paper just to see how accessible radio astronomy has become.<\/p>\n Reference:<\/strong> J. Phelps. \u201cGalactic Neutral Hydrogen Structures Spectroscopy and Kinematics: Designing a Home Radio Telescope for 21 cm Emission.\u201d arXiv preprint<\/em> arXiv:2411.00057 (2024).<\/p>\nLike this:<\/h3>\n