Galactic distance by triangulation.Triangulation triangulation: see geodesy. The use of two known coordinates to determine the location of a third. Used by ship captains for centuries to navigate on the high seas, triangulation is employed in GPS receivers to pinpoint their current location on earth. is a common method of measuring distances on the face of the earth. Now it has been used for the first time in determining the distance from earth to a faraway galaxy. The achievement introduces a method that may in the long run prove more certain than other methods now is use. It also gives Hubble's constant Hubble's constant Constant used to relate the velocities of remote galaxies to their distances from Earth. Denoted H0 and named in honour of Edwin Hubble, it expresses the rate of expansion of the universe. , the number that measures the rate of expansion of the universe. The triangulation method depends on radio and optical observations of a supernova in a distant galaxy, specifically a supernova that exploded in 1979 in the galaxy M100 located in the Virgo cluster Virgo cluster Closest large cluster of galaxies at a distance of about 50 million light-years in the direction of the constellation Virgo. About 200 bright galaxies and thousands of faint ones reside in the cluster. . A supernova is a stellar explosion. It starts from virtually zero diameter and produces an expanding ball of debris. Optical observation can give the linear speed of expansion, in this instance up to 12,000 kilometer per second. From this the diameter of the ball at any time can be calculated. Radio observation can measure the angle that the diameter makes, as viewed from the earth. From these two data triangle can be set up that gives the distance to the galaxy, in this case 19 megaparsecs. Essential to the procedure is precise, very-long-baseline interferometry, the combining of simultaneous observations by radiotelescopes located across the earth. Participants in the observation are Norbert Bartel of the Harvard-Smithsonian Center for Astrophysics The Harvard-Smithsonian Center for Astrophysics (CfA) is located in Cambridge, Massachusetts. It consists of the Harvard College Observatory and the Smithsonian Astrophysical Observatory. The Center is located at 60 Garden Street. (CFA (Computer Fraud and Abuse Act of 1986) Signed into law in 1986, the CFA was a significant step forward in criminalizing unauthorized access to computer systems and networks. The Act applies to "federal interest computers" that include any system used by the U.S. ) in Cambridge, Mass., A.E.E. Rogers of the Haystack Observatory in Westford, Mass., Irwin I. Shapiro Irwin I. Shapiro is an American astrophysicist. Since 1982, he has been a professor at Harvard University. [1] Shapiro was director of the Harvard-Smithsonian Center for Astrophysics from 1982 to 2004[2][3]. , Marc V. Gorenstein and C.R. Giwnn of the cFA, J.M. Marcaide of the Max Planck Institute for Radioastronomy in Bonn, West Germany, and K.W. Weiler of the National Science Foundation in Washington, D.C. They reported their findings in the Nov. 7NATURE. The value of the Hubble constant determined is 65 kilometers per second per megaparsec meg·a·par·sec n. One million parsecs. megaparsec One million parsecs. with uncertainties of plus 35 and minus 25 km/sec/Mpc. The large uncertainties arise because a long string of assumptions had to be made about the geometric development of a supernova -- whether it expands evenly and spherically, whether it is a thin sell or a filled sphere, etc. Further observations of supernovas in general and of this one in particular ought to lessen some of the uncertainties. The value of the Hubble constant lies between the two earlier "standard" ones, 50 and 100, but the uncertainties do not allow it to distinguish between them. Such a distinction, settling on a single value for the constant, is the ultimate goal. |
|
||||||||||||||||
Printer friendly
Cite/link
Email
Feedback
Reader Opinion