Free Astronomy Magazine September-October 2021

34 SEPTEMBER-OCTOBER 2021 ASTRO PUBLISHING plane containing the axis of our line of sight. The similarity at low radial speeds of the effects produced by stellar activ- ity and those produced by a plane- tary system is the main difficulty that planet hunters face − only a precise characterization of the star and long periods of observation allow them to distinguish false sig- nals generated by stellar activity from the gravitational interactions attributable to any orbiting planets. What is worse is that the most inter- esting planets, i.e. those of terres- trial size orbiting in the habitable zone of their stars, gravitationally attract their star by less than 0.5 m/s, a limit that is rarely reached by the best spectrographs and only under of the pulsation, when instead the geometric center of the star has not changed speed and direction in space. By inverting the order of the addends, the sum does not change, but the substance does change, which produces the observed varia- tion in radial velocity. If a non-vari- able star cyclically approaches and recedes from us, what we observe is very similar to the effect of a mod- erate pulsation, but in this case it is the result of one or more masses in orbit around the star − probably planets with orbits more or less in a S teps in the transfer of NEID to the truck that took it to Kitt Peak National Observatory for installa- tion on the WIYN telescope. As with the acronym NEID, the acronym WIYN is also difficult to under- stand - it stands for “(University of) Wisconsin, Indi- ana, Yale, and NOAO (consortium),” where NOAO stands for “National Optical Astronomy Observa- tory.” [NSF’s National Optical-Infrared Astronomy Research Lab./KPNO/NSF/AURA]