A different astronomy and space science related image is featured each day, along with a brief explanation.

Artist's rendering of the 4-kilometer wide Comet 67P/Churyumov–Gerasimenko compared to the city of Los Angeles.

Light-year is the distance light travels in one year. Light zips through interstellar space at 186,000 miles (300,000 kilometers) per second and 5.88 trillion

Published images of the Crab Nebula have been scanned and measured to derive proper motions, the age of the nebula, and its point of origin. Astrometric reductions provided rms errors ranging from 0.14" to 0.31" in both axes for a given image. Proper motions of 50 optical filaments with a 53 yr baseline projected backward indicates the mean date of the supernova event as a.d. 1130 +/- 16 yr, in good agreement with previous investigations by Trimble and Wyckoff & Murray but 76 yr after the reported outburst recorded by the Chinese astronomers in a.d. 1054. This result confirms the well-known acceleration in the Crab's expansion. The image-scanning technique demonstrates that accurate astrometric reductions can be achieved on a personal computer.

We present deep images of a region around the Crab Nebula made with the VLA, utilizing new imaging and deconvolution algorithms in a search for a faint radio shell. The existence of a high-velocity, hydrogen-rich envelope has been predicted to account for the low total mass and kinetic energy of the observed nebula. No radio emission was detected from an extended source outside the Crab Nebula. Our limits on surface brightness are sufficiently low to rule out the existence of a shell around the Crab whose brightness is at least 2 orders of magnitude below that of SN 1006, the faintest historical shell-type supernova remnant. We consider models for the progenitor star and the presupernova environment and conclude that if a fast, outer shock exists, then it has a sharply reduced efficiency at accelerating relativistic particles from the kinetic energy of the blast wave. We also looked for a steepening of the spectral index along the boundary of the Crab Nebula itself, the signature of an outer shock. However, contrary to previous claims, no such steepening was found. The absence of any evidence at radio wavelengths that either the Crab Nebula or a hypothetical shell is interacting with the ambient medium leads to an interpretation that the supernova of A.D. 1054 was a peculiar low-energy event.

Learn more about these exploding stars!

Better known as the Crab Nebula, Charles Messier originally mistook Messier 1 for Halley’s Comet, which inspired him to create his famous catalog of objects.