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A galaxy color–magnitude diagram showing the red sequence (old galaxies, typically elliptical galaxies), the green valley (where the Milky Way is believed to be in), and the blue cloud (young galaxies, typically spiral galaxies). The Milky Way began as one or several small overdensities in the mass distribution in the Universe shortly after ...
- Overview
- Star clusters and stellar associations
- Emission nebulae
- Planetary nebulae
- Supernova remnants
The Milky Way Galaxy takes its name from the Milky Way, the irregular luminous band of stars and gas clouds that stretches across the sky as seen from Earth.
How big is the Milky Way Galaxy?
The first reliable measurement of the size of the Milky Way Galaxy was made in 1917 by American astronomer Harlow Shapley. Assuming that the globular clusters outlined the Galaxy, he determined that it has a diameter of about 100,000 light-years. His values have held up remarkably well over the years.
Is Earth in the centre of the Milky Way Galaxy?
The solar system is about 30,000 light-years from the centre of the Milky Way Galaxy. The Galaxy itself is thought to be about 100,000 light-years in diameter.
Milky Way Galaxy, large spiral system consisting of several hundred billion stars, one of which is the Sun. It takes its name from the Milky Way, the irregular luminous band of stars and gas clouds that stretches across the sky as seen from Earth. Although Earth lies well within the Milky Way Galaxy (sometimes simply called the Galaxy), astronomers do not have as complete an understanding of its nature as they do of some external star systems. A thick layer of interstellar dust obscures much of the Galaxy from scrutiny by optical telescopes, and astronomers can determine its large-scale structure only with the aid of radio and infrared telescopes, which can detect the forms of radiation that penetrate the obscuring matter.
Although most stars in the Galaxy exist either as single stars like the Sun or as double stars, there are many conspicuous groups and clusters of stars that contain tens to thousands of members. These objects can be subdivided into three types: globular clusters, open clusters, and stellar associations. They differ primarily in age and in the numbe...
A conspicuous component of the Galaxy is the collection of large, bright, diffuse gaseous objects generally called nebulae. The brightest of these cloudlike objects are the emission nebulae, large complexes of interstellar gas and stars in which the gas exists in an ionized and excited state (with the electrons of the atoms excited to a higher than normal energy level). This condition is produced by the strong ultraviolet light emitted from the very luminous, hot stars embedded in the gas. Because emission nebulae consist almost entirely of ionized hydrogen, they are usually referred to as H II regions.
H II regions are found in the plane of the Galaxy intermixed with young stars, stellar associations, and the youngest of the open clusters. They are areas where very massive stars have recently formed, and many contain the uncondensed gas, dust, and molecular complexes commonly associated with ongoing star formation. The H II regions are concentrated in the spiral arms of the Galaxy, though some exist between the arms. Many of them are found at intermediate distances from the centre of the Milky Way Galaxy, with the largest number occurring at a distance of 10,000 light-years. This latter fact can be ascertained even though the H II regions cannot be seen clearly beyond a few thousand light-years from the Sun. They emit radio radiation of a characteristic type, with a thermal spectrum that indicates that their temperatures are about 10,000 kelvins. This thermal radio radiation enables astronomers to map the distribution of H II regions in distant parts of the Galaxy.
The gaseous clouds known as planetary nebulae are only superficially similar to other types of nebulae. So called because the smaller varieties almost resemble planetary disks when viewed through a telescope, planetary nebulae represent a stage at the end of the stellar life cycle rather than one at the beginning. The distribution of such nebulae i...
Another type of nebulous object found in the Galaxy is the remnant of the gas blown out from an exploding star that forms a supernova. Occasionally these objects look something like planetary nebulae, as in the case of the Crab Nebula, but they differ from the latter in three ways: (1) the total mass of their gas (they involve a larger mass, essent...
Nov 8, 2017 · Using infrared images from NASA's Spitzer Space Telescope, scientists have discovered that the Milky Way's elegant spiral structure is dominated by just two arms wrapping off the ends of a central bar of stars. Previously, our galaxy was thought to possess four major arms. This annotated artist's concept illustrates the new view of the Milky ...
Sep 23, 2021 · A galaxy is a large group of stars, gas, and dust bound together by gravity. They come in a variety of shapes and sizes. The Milky Way is a large barred spiral galaxy. All the stars we see in the night sky are in our own Milky Way Galaxy. Our galaxy is called the Milky Way because it appears as a milky band of light in the sky when you see it ...
Apr 18, 2023 · The Milky Way is a large barred spiral galaxy, with a relatively small bar compared to most galaxies of a similar size. A central bar (or central bulge) is a circular to oval shaped structure of ...
Nov 1, 2023 · According to Hubble's classification system, the Milky Way is a spiral galaxy, although more recent mapping evidence indicates that it may be a barred spiral galaxy. The Milky Way has more than hundreds of billions of individual stars. It's approximately 100,000 light-years in diameter, and the sun is located about 28,000 light years from the ...
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The Milky Way Galaxy. The Milky Way is our galactic home, part of the story of how we came to be. Astronomers have learned that it’s a large spiral galaxy, similar to many others, but also different in ways that reflect its unique history. Living inside the Milky Way gives us a close-up view of its structure and contents, which we can’t do ...
