When a candle gets 'crabby'

Here's a new story about what is standard and what isn't — in astronomy. Incidentally, setting and adjusting to new and old standards is a topic which I recently find more and more interesting when applied to a number of other contexts as well...

The Crab Nebula: standard candle no more?

Teaming up with other telescopes monitoring the Crab Nebula, ESA's INTEGRAL observatory has made a significant contribution to demonstrating that this source, previously believed to be a standard candle, might not be so reliable, after all. The small, but measurable dimming of what was until now considered to be one of the brightest and, most importantly, the steadiest source in the high-energy sky calls for a re-examination of how X-ray and gamma-ray observations are calibrated. More...

Image credits: X-ray: NASA/CXC/SAO/F. Seward; Optical: NASA/ESA/ASU/J. Hester & A. Loll; Infrared: NASA/JPL-Caltech/Univ. Minn./R. Gehrz