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The nebular hypothesis is the most widely accepted model in the field of cosmogony to explain the formation and evolution of the Solar System (as well as other planetary systems). It suggests the Solar System is formed from gas and dust orbiting the Sun which clumped up together to form the planets.
The Andromeda Galaxy, for instance, was once referred to as the Andromeda Nebula (and spiral galaxies in general as "spiral nebulae") before the true nature of galaxies was confirmed in the early 20th century by Vesto Slipher, Edwin Hubble, and others. Edwin Hubble discovered that most nebulae are associated with stars and illuminated by starlight.
The nebular hypothesis says that the Solar System formed from the gravitational collapse of a fragment of a giant molecular cloud, [9] most likely at the edge of a Wolf-Rayet bubble. [10] The cloud was about 20 parsecs (65 light years) across, [9] while the fragments were roughly 1 parsec (three and a quarter light-years) across. [11]
Barnard 68 is a molecular cloud, dark absorption nebula or Bok globule, towards the southern constellation Ophiuchus and well within the Milky Way galaxy at a distance of about 125 parsecs (407 lightyears). [2] It is both close and dense enough that stars behind it cannot be seen from Earth.
If more energy is available, other elements will be ionized, and green and blue nebulae become possible. By examining the spectra of nebulae, astronomers infer their chemical content. Most emission nebulae are about 90% hydrogen, with the remaining helium, oxygen, nitrogen, and other elements.
It is approximately 2,500 light-years away. NGC 6326 , a planetary nebula with glowing wisps of outpouring gas that are lit up by a binary [ 3 ] central star A planetary nebula is a type of emission nebula consisting of an expanding, glowing shell of ionized gas ejected from red giant stars late in their lives.
Rho Ophiuchi Region, with the main dark nebula Lynds 1688 (and further L1689) to the left, ρ Ophiuchi at the center of the large blue area (IC 4604), Antares in the large yellow area and Sigma Scorpii in the redish Sh2-9 area, with Messier 4 inbetween the latter two stars. North is up. July 2, 2019 photo by Adam Block.
The Lagoon Nebula is estimated to be between 4,000–6,000 light-years away from the Earth. In the sky of Earth, it spans 90' by 40', which translates to an actual dimension of 110 by 50 light years. In the sky of Earth, it spans 90' by 40', which translates to an actual dimension of 110 by 50 light years.