1/17/2024 0 Comments Example of reflection nebula![]() However, we now know that emission nebulae and reflection nebulae are made visible by the light from nearby stars. Since gas and dust aren't luminous, nebulae were difficult to study. The Orion Nebula, for example, is about 150 light years across – that's at least 25 times the diameter of our Solar System. There is nonetheless a lot of matter in them because they're spread out over many light years. The material in the nebulae is so tenuous that an industrial vacuum on Earth is denser. Some of the “nebulae” turned out to be star clusters and some were distant galaxies, but what about true nebulae, the clouds of gas and dust in the spaces between stars? He was the first to discover spiral structure in some of the nebulae. Birr in Ireland saw such a telescope in 1845, built by William Parsons (1800-1867), the Earl of Rosse. Yet except for realizing that some nebulae were star clusters, more powerful telescopes were needed to learn more. William's son John Herschel (1792-1871) later added nebulae of the southern hemisphere. William Herschel (1738-1822) and Caroline Herschel (1750-1848) were the first to take the nebulae seriously, cataloguing nearly 2500 of them from southern England. Charles Messier (1730-1817) only catalogued them so that they wouldn't be mistaken for comets. Viewed in 17th and 18th century telescopes, they were just cloudy bits of sky, and most astronomers paid little attention to them. The word nebula - plural nebulae - is Latin for cloud. ![]() The Helix Nebula (also known as NGC 7293 or Caldwell 63), is a planetary nebula located in the constellation Aquarius.
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