Word: nebula
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Dates: during 1930-1939
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...Gaposchkin said that while it is not yet known what causes the stellar explosion that is called a new star, it is now known what happens to it once the explosion has taken place. The exploding star turns into a planetary nebula...
...achievement, "that both are expanding; that both are centered on very hot stars of the same kind; that both shine with similar spectra; that they are even alike in outward appearance. In fact, they are different stages of the same object--the new star is the bursting chrysalis, the nebula, the butterfly...
...light-years away, and this appears to be the limit of Mt. Wilson's giant telescope. Thus the observable universe is a sphere about a billion light-years across. What Dr. Hubble calls a "preliminary reconnaissance" shows that the sphere probably contains 100,000,000 nebulae composed of stars, the average nebula being about 20,000,000,000 times as heavy as the Sun and shedding 85,000,000 times as much light...
...Hubble is renowned for his discovery that the spectrum lines of distant nebulae are displaced toward the red end, indicating enormous speeds of recession away from Earth. The speeds of the most distant cannot be deduced in this manner, since the spectra are too faint to be analyzed. But it has been observed that speeds are closely proportional to distance, increasing about 1,000 miles per second for every 10,000,000 light-years of space. Few months ago Dr. Hubble measured the fastest nebular retreat at 24,000 miles per second. That one was 240,000,000 light-years...
First recorded super-nova was observed in the Milky Way in 1572. It was visible in full daylight. Another appeared in Andromeda in 1885. Since 1900 about a dozen have been found by chance on photographic plates, mostly in the Virgo cluster of nebulae. Drs. Baade & Zwicky estimate that each galaxy has one super-nova every thousand years. The average nebula contains a billion stars. If one star committed suicide in the super-nova manner every thousand years, the nebula would be exhausted in one trillion years?which happens to be the figure commonly set by astrophysicists as the minimum...