How Far is the Orion Nebula?

You'd think astronomers would have all the key stats on the Orion Nebula (Messier 42) by now. Visible to the unaided eye, this deep-sky showpiece was first studied with a spectroscope in 1864 and first photographed in 1880. It's the first thing many people look at with their first telescope, and the last that William Herschel wanted to see with his last. The nebula has been studied at all wavelengths, harbors many variable stars, and is home to the Trapezium, the best-known multiple star in the sky.

Yet M42's distance was wildly uncertain throughout most of the 20th century, when estimates varied between 600 and 6,500 light-years! In recent years, astronomers have applied sophisticated techniques to gauge the nebula's distance, but the resulting uncertainties remained stubbornly high.Now an international team of radio astronomers has nailed M42's distance — 1,350 light-years — with an uncertainty of less than 2%!

For the full story, go to: http://www.skyandtelescope.com/community/skyblog/newsblog/11853711.html

Pic Caption: At the heart of the Great Orion Nebula lies the Trapezium, a tight knot of four stars (at center) visible in small telescopes. One of the radio sources recently measured by radio astronomers is a close companion of the Trapezium's component A, the rightmost star in this view. The other three radio sources are outside the Trapezium itself and don't show up in visible-light photographs like this.
S&T: Sean Walker

Srikumar M. Menon