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Betelgeuse's color may have changed from yellow (or possibly orange; i.e. a yellow supergiant) to red in the last few thousand years, based on a 2022 review of historical records. This color change combined with the CMD suggest a mass of 14 M ☉ and age of 14 Myr, and a distance from 125 to 150 parsecs (~400 to 500 light years). [12]
Slipher and Edwin Hubble continued to collect the spectra from many different nebulae, finding 29 that showed emission spectra and 33 that had the continuous spectra of star light. [18] In 1922, Hubble announced that nearly all nebulae are associated with stars and that their illumination comes from star light.
Planetary nebulae, represented here by the Ring Nebula, are examples of emission nebulae. An emission nebula is a nebula formed of ionized gases that emit light of various wavelengths. The most common source of ionization is high-energy ultraviolet photons emitted from a nearby hot star .
Reflection nebula are usually blue because the scattering is more efficient for blue light than red (this is the same scattering process that gives us blue skies and red sunsets). Reflection nebulae and emission nebulae are often seen together and are sometimes both referred to as diffuse nebulae. Some 500 reflection nebulae are known.
A dark nebula or absorption nebula is a type of interstellar cloud, particularly molecular clouds, that is so dense that it obscures the visible wavelengths of light from objects behind it, such as background stars and emission or reflection nebulae.
NGC 7129 is a reflection nebula located 3,300 light years away in the constellation Cepheus. A young open cluster is responsible for illuminating the surrounding nebula. [2] A recent survey indicates the cluster contains more than 130 stars less than 1 million years old. [citation needed] NGC 7129 is located just half a degree from nearby ...
IC 418, also known as the Spirograph Nebula, is a planetary nebula located in the constellation of Lepus about 3,600 ly away from Earth. It spans 0.3 light-years across. The central star of the planetary nebula, HD 35914 , is an O-type star with a spectral type of O7fp. [ 4 ]
The M42 nebula is estimated to be 25 light-years across (so its apparent size from Earth is approximately 1 degree). It has a mass of about 2,000 times that of the Sun. Older texts frequently refer to the Orion Nebula as the Great Nebula in Orion or the Great Orion Nebula. [7]