Free Astronomy Magazine January-February 2022

9 JANUARY-FEBRUARY 2022 ASTRO PUBLISHING are sources that in the “OFF target” position do not produce signals strong enough to be recognized by the search algorithms. Even the transit of satellites and air- planes can generate interference that is not immediately recogniza- ble, as can the simple passage near the antenna of vehicles and people equipped with electronic devices. When all reasonable sources have also been excluded, usually there is no signal left that can be inter- preted as an alien technosignature. Instead, when Shane Smith com- pleted the preliminary processing of the data acquired during the Prox- ima Centauri observations in 2020, T his infographic compares Proxima b’s orbit around Proxima Centauri with the same region of the Solar System. Proxima Centauri is smaller and cooler than the Sun and the planet orbits much closer to its star than Mercury. As a result it lies well within the habitable zone, where liquid water can exist on the planet’s surface. [ESO] he was faced with a signal that did not seem to be eliminated by any fil- ter and which appeared to come from the region of the sky centered on Proxima Centauri. Being the first alien signal candidate recorded by the Breakthrough Listen program, it was called “BLC1.” The first in-depth verifications of BLC1 indicated that the signal had many of the characteristics we might expect from an alien technosigna- ture. First, it became visible only when the radio telescope pointed towards Proxima Centauri. More- over, it occupied a narrow band of frequencies (982 MHz), a typical property of an artificial source, whereas natural sources “transmit” over a wide range of frequencies. BLC1 also met the frequency varia- tion requirement: on the only day the signal was recorded (April 29, 2019), its spectral position varied