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:
“The particular source of frustration of women observing their own self-study and measuring their worth as women by the distance they kept from men necessitated that a distance be kept, and so what vindicated them also poured fuel on the furnace of their rage. One delight presumed another dissatisfaction, but their hatefulness confessed to their own lack of power to please. They hated men because they needed husbands, and they loathed the men they chased away for going.”
—Alexander Theroux (b. 1940)
“We have been told over and over about the importance of bonding to our children. Rarely do we hear about the skill of letting go, or, as one parent said, “that we raise our children to leave us.” Early childhood, as our kids gain skills and eagerly want some distance from us, is a time to build a kind of adult-child balance which permits both of us room.”
—Joan Sheingold Ditzion (20th century)
“A petty reason perhaps why novelists more and more try to keep a distance from journalists is that novelists are trying to write the truth and journalists are trying to write fiction.”
—Graham Greene (1904–1991)