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Earth's air has a density of approximately 10 19 molecules per cubic centimeter; by contrast, the densest nebulae can have densities of 10 4 molecules per cubic centimeter. Many nebulae are visible due to fluorescence caused by embedded hot stars, while others are so diffused that they can be detected only with long exposures and special filters.
Box Nebula NGC 6445: 1786 4.5 11.2 Sagittarius: Eye of Sauron Nebula M 1-42: 10 14 Sagittarius
A typical planetary nebula is roughly one light year across, and consists of extremely rarefied gas, with a density generally from 100 to 10,000 particles per cm 3. [42] (The Earth's atmosphere, by comparison, contains 2.5 × 10 19 particles per cm 3.) Young planetary nebulae have the highest densities, sometimes as high as 10 6 particles per ...
The following articles contain lists of nebulae: List of dark nebulae; List of diffuse nebulae; List of largest nebulae; List of planetary nebulae;
The following well-known nebulae are listed for the purpose of comparison. Orion Nebula: 20 ly (6.132 pc) [64] Diffuse Nebula: The closest major star formation region to Earth. [65] Crab Nebula: 11 ly (3.4 pc) [66] Supernova remnant: The remnant of a supernova that occurred in 1054 AD. [67] Bubble Nebula: 6 [68]-10 [69] [70] ly (1.84-3.066 pc ...
The Helix Nebula (also known as NGC 7293 or Caldwell 63) is a planetary nebula (PN) located in the constellation Aquarius. Discovered by Karl Ludwig Harding, most likely before 1824, this object is one of the closest of all the bright planetary nebulae to Earth. [3] The distance, measured by the Gaia mission, is 655±13 light-years. [4]
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The Horsehead Nebula (also known as Barnard 33 or B33) is a small dark nebula in the constellation Orion. [2] The nebula is located just to the south of Alnitak , the easternmost star of Orion's Belt , and is part of the much larger Orion molecular cloud complex .