Nebula Video Free Download
Terry Chavarin
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Nebula comes to us from Latin, where it means "mist" or "cloud." In its earliest English uses in the 1600s, nebula was chiefly a medical term that could refer either to a cloudy formation in urine or to a cloudy speck or film on the eye that caused vision problems. It was first applied to great interstellar clouds of gas and dust in the early 1700s. The adjective nebulous comes from the same Latin root as nebula, and it is considerably older, being first used as a synonym of cloudy or foggy as early as the 1300s. Like nebula, however, this adjective was not used in an astronomical sense until the mid-1600s.
Ultraviolet radiation from Sigma Orionis causes the clouds behind the Horsehead to glow, while the thick clouds of the Horsehead itself block light from directly behind it; this makes the head look dark. The nebula itself is made up largely of cold molecular hydrogen, which gives off very little heat and no light. Astronomers study the differences in the conditions for star formation between the dark and bright clouds.
For example, in the Carina Nebula, hot, young stars erode and sculpt the clouds into this fantasy landscape by sending out thick stellar winds and scorching ultraviolet radiation. The low-density regions of the nebula are shredded while the denser parts resist erosion and remain as thick pillars.
About 50 years later, Edmond Halley wrote about six different nebulae. For that, he got a comet named after him. (Not really, he was a very accomplished scientist who served as the second Astronomer Royal in Britain).
But, famous names flocked to nebulae over the years. Edwin Hubble helped categorize nebulae based on the spectra of light they produce, also discovering that nearly all nebulae are associated with stars and are illuminated by starlight.
Through advanced space telescopes like the Spitzer and Hubble Space Telescopes, we have plenty of gorgeous imagery of nebulae. Most of these are formed through infrared and false-color images but they all are striking. These images depict the wide variety of nebulae available for scientists to study. All of them cover light years of distance in space. Some are wispy, some are well-defined. All of them are worth your time.
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