The SDSS-III BOSS survey is now 50% complete. BOSS Survey Scientist Kyle Dawson and Principal Investigator David Schlegel report that as of January 31, 2012 BOSS has completed 1106 survey-quality plates out of its target goal of 2212 plates by summer 2014. Each plate contains holes matching 1000 targets on the sky. 64% of these targets are galaxies, 11% are quasars, 11% are stars, 10% of these targets are observations of blank sky used for calibration, while 3% were targeted as galaxies, quasars, or stars but we didn’t get sufficient signal to classify them. Completing 1106 plates means that BOSS now has collected spectra of 860,000 astrophysical objects including:

642,000 galaxies
110,000 quasars
108,000 stars
  30,000 objects without secure classifications

This puts BOSS slightly ahead of schedule, largely thanks to the very hard work of the entire observing team, and a bit of luck from some slightly darker skies associated with solar minimum.

A noticeable part of the brightness of the night sky emission comes from emission high in the Earth’s atmosphere that is excited by extreme-ultraviolet (EUV) emission from the Sun. The strength of the solar EUV emission follows with the general solar cycle. Thus the sky brightness of the Earth’s atmosphere shows similar variations, which can be as much as 50% of the sky brightness at a dark site.

But closer to cities, the sky brightness is completely dominated by the glow from city lights, which is why the stars of the Milky Way aren’t visible to most people living in the developed and urbanized world. Increasing light pollution from cities is one of the reasons astronomers are forced to place observatories in increasingly remote locations.