Astronomers surmise dark matter's existence from its gravitational effects, prompting a quest to understand its nature. It's now possible to detect dark matter using a small radio telescope, like a homemade pyramidal-horn antenna. This antenna, similar to one used in 1951 to detect interstellar hydrogen emissions, is key because these emissions reveal galactic motions and thus the distribution of mass.

The author constructed a larger horn antenna using a $25 roll of roof flashing and a paint can for better angular resolution. Signals are captured by a Nooelec SAWBird+ H1 low-noise amplifier and an RTL-SDR V4 dongle. The core principle for dark matter detection is observing that orbital speeds in the Milky Way do not decrease with distance from the galactic center as expected if mass were concentrated centrally. This suggests the presence of invisible matter.

By measuring Doppler shifts in the 1,420-MHz hydrogen line from clouds at various distances, speeds can be calculated. The tangent-point method, using trigonometry and measurements from specific galactic longitudes, helps determine these speeds and distances. Analysis of these orbital velocities revealed they did not diminish with distance, indicating the influence of dark matter, detectable even from a backyard.