Cosmology suffered a great loss yesterday with the passing of Andrew Lange, co-leader of the BOOMERang experiment, which provided the first experimental evidence that our universe is flat, and offered strong support to the supernova evidence for dark energy. Lang was a professor of physics at Caltech, and that tight-knit community is reeling from the news that Lange apparently took his own life. I only met Lange once, but my husband Sean, a Caltech colleague, knew him well and offers his own eulogy (of sorts) over at Cosmic Variance:

The only way I can think to honor Lange is to tell you a bit more about his most famous work. BOOMERang stands for Balloon Observations Of Millimetric Extragalactic Radiation and Geophysics, and it's essentially a balloon-borne telescope designed to make measurements of the cosmic microwave background radiation — the "afterglow" of the Big Bang that still pervades our universe. The first flight, in 1997, concentrated on North America, while two subsequent flights in 1998 and 2003 circled the South Pole.

Based on this data, the BOOMERang team made the most detailed map of temperature fluctuations in the CMB — at least as of April 2000, when the first results were announced. (Science always marches on.) The CMB is pretty smooth, so those fluctuations are tiny, with differences of 1 part in 100,000, and hence very difficult to measure.

Those fluctuations provided the "seeds" that eventually grew into the gigantic galaxies, galaxy clusters and cosmic structures we see in the cosmos today. What BOOMERang did was to measure the size of those fluctuations in angular measure (degrees). I'll let these folks explain why that's significant:

BOOMERang's exciting results were the first "to resolve the structures in the CMB, allowing us to 'see' structures that predate even the first star or galaxy in the universe," Lange said in an interview with the European Space Agency in 2001. But he was always looking forward to the next experiment — in this case, the Planck satellite that launched last spring. Planck's instruments have even better resolution than BOOMERang, capable of measuring many more frequencies in the CMB, and it will cover the entire night sky, instead of just select regions. "Planck will be revolutionary!" Lange declared in that 2001 ESA interview. It's a tragedy that he didn't live to see the revolution in action.