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50&25 years ago.

November 1949 "NGC 5128, a luminous object crossed by dark parallel lanes, has long been the subject of controversy: Is it an external galaxy or strictly a local nebulosity? . . .

"David S. Evans . . . presents results of a photometric study of the object in both red and blue light. The isophotes, or contours of equal brightness, are approximately circular around the center and the variation of brightness outward is close to that of an inverse square law. . . .

"The author suggests that the object consists of a concentrated source hidden behind obscuring matter and surrounded by a spherical mass of gas, and that it is probably not extragalactic."

We now know that NGC 5128 is a galaxy - in fact, at a distance of 16 million light-years, it is the nearest active galaxy to our own Milky Way. Also known as Centaurus A, it is famous for its enormously powerful lobes of radio emission that span some 10[degree sign] of sky.

November 1974 "X-ray astronomy of space beyond the solar system came into existence in the late 1950's and the 1960's. . . . By 1967, approximately 30 discrete sources had been catalogued. . . .

"The main problem in trying to identify these sources was that the positions were not accurate enough. . . .

"[The Uhuru satellite, launched in 1970] made possible several catalogues, the most recent of which lists 161 sources. . . . The best positions are accurate to one or two minutes of arc, and consequently several dozen new optical identifications were made."

Among the objects discovered by Uhuru were X-ray binary stars, the most common source of this high-energy emission in our galaxy. Also found was X-ray emission from gas at temperatures exceeding 1,000,000[degree sign] Kelvin that enfolds clusters of galaxies.

"On October 16th, the Prince of Wales was scheduled to dedicate the new 3.9-meter (155-inch) Anglo-Australian telescope at Siding Spring Observatory. . . .

"The new instrument doubles the present giant-telescope capability of the Southern Hemisphere."

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Publication:Sky & Telescope
Article Type:Brief Article
Geographic Code:1USA
Date:Nov 1, 1999
Words:319
Previous Article:Letters.
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