Distance
Until recently the distance to the supernova remnant was estimated at about 2500 light-years. Recent studies, however, have shown that it must be closer. In 1999, William Blair, assuming that the shock wave should be expanding at the same rate in all directions, compared the angular expansion along the sides of the bubble (visible in Hubble Space Telescope images) with direct line-of-sight measurements of the radial expansion towards the Earth. He concluded that the actual size of the bubble was about 40% smaller than the conventional value, leading to a distance of about 1470 ly.
This revised calculation, though it involved some uncertainty and was met with some resistance, has been substantially corroborated by the discovery via the Far Ultraviolet Spectroscopic Explorer (FUSE) of a star behind the Veil. The star, KPD2055+3111, of spectral type sdOBwas, was identified as UV-bright in an image from the Ultraviolet Imaging Telescope, and absorption lines in its spectrum indicate that its light is partially intercepted by the supernova remnant. The emission properties of the star indicate that it lies about 1860 ly away, giving an upper bound for the distance of the loop and supporting the previous estimate of 1470 ly.
The revised distance in turn yields revised estimates of the size of the remnant (to 90 ly, down from 150 ly previously) and for its age (now thought to be between 5000 to 8000 years).
Read more about this topic: Cygnus Loop
Famous quotes containing the word distance:
“By sharing the information and observations with the caregiver, you have a chance to see your child through another pair of eyes. Because she has some distance and objectivity, a caregiver often sees things that a parent’s total involvement with her child doesn’t allow.”
—Amy Laura Dombro (20th century)
“A solitary traveler whom we saw perambulating in the distance loomed like a giant. He appeared to walk slouchingly, as if held up from above by straps under his shoulders, as much as supported by the plain below. Men and boys would have appeared alike at a little distance, there being no object by which to measure them. Indeed, to an inlander, the Cape landscape is a constant mirage.”
—Henry David Thoreau (1817–1862)
“Small, black, as flies hanging in heat, the Boys,
Until the distance throws them forth, their hum
Bulges to thunder held by calf and thigh.”
—Thom Gunn (b. 1929)