Free Astronomy Magazine January-February 2022

8 JANUARY-FEBRUARY 2022 ASTRO PUBLISHING A ndrew Zic stud- ies radio-contin- uum observations of pulsars, radio tran- sients, and multi- wavelength stellar activity. Here he is pictured near the Antenna C2 of the Giant Metrewave Radio Telescope, lo- cated in the state of Maharashtra, India. T his artist’s im- pression shows a view of the surface of the planet Prox- ima b orbiting the red dwarf star Prox- ima Centauri, the closest star to the Solar System. The double star Alpha Centauri AB also ap- pears in the image to the upper-right of Proxima itself. Prox- ima b is a little more massive than the Earth and orbits in the habitable zone around Proxima Cen- tauri, where the tem- perature is suitable for liquid water to exist on its surface. [ESO/M. Kornmesser] signal due to the Doppler effect. For this reason, the first creaming off performed by the search algorithm applied by the Breakthrough Listen team concerned all signals inconsis- tent with a transmitter that might be placed on the surface of Proxima b, the only planet that we know ex- ists in the habitable zone of Proxima Centauri. The second selection criterion that was applied to the initial screening of the collected signals concerned the direction from which they came. If by pointing the radio telescope at a certain target we receive a signal, it is sufficient to point the instru- ment towards a different region of the sky to check and see if the signal persists, if it is perhaps weakened, or if it disappears completely. In the first case, it is almost certain that it is from a local source or is local in- terference; in the second case, the signal could come from the target or from a source that is prospectively close to it. A single radio telescope guarantees a rather low spatial res- olution, and it is therefore not possi- ble to precisely locate a source. As for the Parkes dish, the mar- gin of uncertainty is as wide as half a full moon, and it is there- fore necessary to move the antenna by more than half an an- gular degree to carry out the “ON-OFF” control of the signal sources. At the end of these first automated procedures, a few unidentified sources remained that required a “human” verification of their characteristics. Usually, these