Mapping the Interstellar Cloud We Live in

We often speak of the Hubble Space Telescope as a unique window on the most distant and ancient galaxies. But the HST can also tell us things we never knew about our most intimate interstellar surroundings. The 10 January Astrophysical Journal brings us the first of two articles, by Jeffrey Linsky, Seth Redfield, and colleagues at the University of Colorado, that offer a three‐dimensional map of the “local interstellar cloud,” derived mostly from ultraviolet absorption spectra recorded by instruments aboard the HST. The LIC, they report, is a rather uniform, egg‐shaped cloud of warm atomic hydrogen, only 20 light‐years long, in which the Solar System and its surrounding heliosphere of solar wind and magnetic field sit like a tiny, offcenter yolk. (See the figure below.)