Millstone Hill Observatory is a Massachusetts Institute of Technology atmospheric sciences research centre in Westford, Massachusetts. It is part of Haystack Observatory, which focuses primarily on radio astronomy. Millstone Hill is the location for two of the most well-known incoherent scatter radars in the world. These include a fully steerable 46-meter antenna, and a 67-meter fixed-zenith antenna. These radars are capable of measuring a vast array of ionospheric components, including temperature, ion concentrations, and solar wind data.