For millennia humans have looked to the stars in search of meaning. We have reconsidered our notions about our place in the cosmos with each breakthrough in astronomy, from the astrolabe to the infrared space telescope, but no amount of technological refinement has satisfied our yearning to understand things beyond what our instruments or our eyes can tell us.
In the observable universe, there are around 200 billion galaxies. The Milky Way alone contains between 100 and 400 billion stars and at least that many planets. Data from NASA’s Kepler Space Telescope conservatively suggest that 300 million of those planets orbit their star in its habitable zone — the distance from a star conducive to the presence of liquid water, which may be a prerequisite for life. It would take nearly eighty thousand years to reach the nearest “exoplanet” — a planet in orbit around a star that is not our sun. In 1975 NASA began funding its Search for Extraterrestrial Intelligence (SETI) program, which used then-recent developments in radio astronomy to monitor radio signals coming from space. NASA’s program was canceled by Congress in 1993, at which point the SETI Institute — a nonprofit research organization based in Mountain View, California — took over the program.
