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:
“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)
“The mystery of the evening-star brilliant in silence and distance between the downward-surging plunge of the sun and the vast, hollow seething of inpouring night. The magnificence of the watchful morning-star, that watches between the night and the day, the gleaming clue to the two opposites.”
—D.H. (David Herbert)
“Her personality had an architectonic quality; I think of her when I see some of the great London railway termini, especially St. Pancras, with its soot and turrets, and she overshadowed her own daughters, whom she did not understand—my mother, who liked things to be nice; my dotty aunt. But my mother had not the strength to put even some physical distance between them, let alone keep the old monster at emotional arm’s length.”
—Angela Carter (1940–1992)