The Milky Way is a blocked spiral galaxy, one of hundreds of billions in the observable universe. It is also our home.
Like other galaxies, the Milky Way is an isolated collection of stars and other material bound together by their common gravity. In addition to the 100 billion to 400 billion stars in our galaxy, there are probably a similar number of planets in the Milky Way – some of which are part of solar systems and others float freely. Between the stars sit innumerable mists, there are clouds of gas and dust. The vast majority of interstellar gas is hydrogen and helium.
However, more evidence ̵
Who Discovered the Milky Way?
From our vantage point on Earth, the Milky Way looks like a band of diffused light that curves across the night sky. This is where the English name comes from: the Romans called it Via Lactea and imagined it as a wasted milk band. Astronomers and philosophers discussed the nature of the Milky Way until Galileo Galilei first observed it with a telescope and found that the light of the Milky Way comes from countless distant stars. The stars themselves are too far away to see them all individually, but their combined light gives the familiar band.
Until the beginning of the 20th century, astronomers assumed that the Milky Way contained all the stars in the universe (either the Milky Way stretched to fill the entire cosmos, or it was a finite size and surrounded by an infinite void). In the early 1920s, however, astronomer Edwin Hubble made detailed observations of the Andromeda Nebula, revealing that it was his own “island” of stars – a galaxy in its own right – located millions of light-years away from us, according to Britannica.
What does the Milky Way look like?
The Milky Way is a relatively thin, flat disc. This explains why it looks like a band in our sky. When we look in the direction of the disk, Earthlings see the combined light from all the stars in the galaxy. When we look in a direction away from the disk, we only see the stars close to our solar system.
The Milky Way has three main parts: the core, the disc and the halo.
The nucleus is not spherical; it is elongated in the form of a bar anywhere from 5,000 to 20,000 light-years. Up to a quarter of all the stars in the Milky Way lie in the core; the star density is up to a million times greater than it is near the sun, according to the Space Telescope Science Institute. At the center of the galaxy sits Sagittarius A *, a supermassive black hole with a mass 4.1 million times that of the Sun, according to the UCLA Galactic Center Group.
The Milky Way’s star disk has a radius of 75,000 to 100,000 light-years, but it is only about 1,000 light-years thick. Inside the disk are several large spiral arms, according to NASA, where the density of stars and gas is higher than average, and star formation occurs at a higher rate, making these arms stand out in visual observations.
Our solar system sits on the counter, approx. 27,000 light-years from the galactic center, near the inner edge of the Orion arm.
In addition to the disk of the Milky Way is its halo, which is a spherical area with a radius of approx. 100,000 light years. Halogen contains ancient stars and globular clusters that all orbit the galactic center in random directions. The dark matter extends even further up to 400,000 light-years from the center, according to a study published in 2019 in the journal Astronomy & Astrophysics.
Where is the Milky Way?
The Milky Way has two large satellite galaxies – the large and small Magellanic clouds – and dozens of smaller satellites. Our nearest neighbor is the Andromeda Galaxy, located approx. 2.5 million light years away. Together with Andromeda and about 80 smaller galaxies, the Milky Way is part of the local group, which is a group of galaxies, approx. 10 million light-years across, bound together by their common gravity, according to Swinburne University.
The local group is a member of a larger structure called the Virgo Supercluster, which is surrounded by several large intergalactic cavities, according to Durham University. At the center of this supercluster sits the Virgo Cluster, a massive collection of 1,000 to 2,000 galaxies about 54 million light-years away. Virgo Supercluster itself is believed to be a component of an even larger structure called the Laniakea Supercluster.
How big is the Milky Way?
It is difficult to estimate the true size of our galaxy because we live inside it, and all clouds of gas and dust obscure our observations of it. Astronomers estimate that the total mass of the Milky Way is about a trillion times the mass of the sun, according to NASA. By far most of this mass is in the form of dark matter; stars represent only approx. 1% of the mass of the galaxy, and interstellar gas accounts for only 0.1%.
Is the Milky Way moving?
Compared to the general expansion of space, which pulls galaxies apart (on average), the Milky Way moves at about 630 kilometers per second (391 miles per second), researchers reported on the preprint server arXiv in 2005. Our galaxy is on a collision course with Andromeda, and our two galaxies will collapse and begin to merge in about 5 billion years.
Both the Milky Way and Andromeda are moving together in the direction of what is called the big attractor, the University of Hawaii Institute for Astronomy reported. The Great Attractor is believed to be the center of the Laniakea Supercluster. However, observations of this region in the local universe are difficult because it lies beyond the direction of our galactic center, obscuring our view.
—California Academy of Sciences has this amazing teaching video that lets students tour the Milky Way.
—This National Geographic book “Visual Galaxy” has beautiful images of the Milky Way.
—Check out these activities and resources about the solar system and the night sky at the McDonald Observatory.