The Milky Way

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The Milky Way is our home in the Universe on a grander scale than just our planet or solar system. Practically everything we see with the unaided eye in the night sky is a part of the Milky Way, except for a few visible extragalactic objects such as M31, the Andromeda galaxy.

Like a celestial blanket the Milky Way forms an arc high above the antennas of the Atacama Large Millimeter/submilimeter Array. This arc is caused by the panoramic view of the image.Credit: A. Duro/ESO

The arc of Milky Way. Like a celestial blanket the Milky Way forms an arc high above the antennas of the Atacama Large Millimeter/submilimeter Array. This arc is caused by the panoramic view of the image.

ESO’s majestic telescope enclosure at La Silla aligns perfectly with the Milky Way’s central region — the brightest section and the area which obscures the galactic centre. Visible to the left of the Milky Way is the bright orange star Antares at the heart of Scorpius (The Scorpion). Visible to the left of the Milky Way is the bright orange star Antares at the heart of Scorpius (The Scorpion).Credit: ESO/B.Tafreshi

La Silla and the Milky Way. ESO's majestic telescope enclosure at La Silla aligns perfectly with the Milky Way’s central region — the brightest section and the area which obscures the galactic centre.
The Milky Way is an island of hundreds of billions of stars, gas, and dust held together by gravity to form a gigantic disk that is surrounded by a halo of globular clusters, which are smaller spherical groups of stars.

On a clear night we can see the band of the Milky Way in the sky, the fuzzy light that stretches from one horizon to the other. This band of light is made up of a vast number of stars that telescopes can pick out as individuals but our eyes cannot. This is our view of the billions of stars that make up the disk of our galaxy, from a viewpoint inside the disk, about two- thirds of the way out from the center of the galaxy to the edge of the disk. There are dark patches in the band of light, due to dark clouds of interstellar matter. Radio telescopes can see through these clouds of dust and have shown that the material in our Galaxy is distributed in a disk with spiral arms of material trailing through. Our Galaxy has a bulge of stars at the center, wherein there may lie a giant black hole at the center. The galactic center lies in the direction of the constellation Sagittarius.

The Two Micron All-Sky Survey (2MASS) was a survey of the whole sky in three infrared wavebands around 2 micrometres (μm). The observations for the survey were taken between 1997 and 2001 and obtained an unprecedented view of the Milky Way nearly free of the obscuring effects of interstellar dust.Credit: 2MASS/UMass/IPAC-Caltech/NASA/NSF

Two Micron All-Sky Survey (2MASS). The Two Micron All-Sky Survey (2MASS) was a survey of the whole sky in three infrared wavebands around 2 micrometres (μm). The observations for the survey were taken between 1997 and 2001 and obtained an unprecedented view of the Milky Way nearly free of the obscuring effects of interstellar dust.
The stars in the disk of the galaxy orbit around the center in a way similar to the way in which planets orbit around the Sun. The speed of each star depends on its distance from the center. The Sun moves at about 250 km/s in its orbit, and it takes 225 million years to complete one revolution around the center. Studying the way in which the stars orbit gives details of the gravitational field of the Galaxy and ultimately reveals its mass. This total mass is about 1 trillion times the mass of our Sun, which is about 10 times the mass of all the visible stars in the Milky Way put together. This mass that is unaccounted for is strong evidence that there is dark matter in our galaxy, matter that is affecting the gravitational field of the Galaxy but is not visible to us.

Questions About The Milky Way

  • General Questions
  • Dynamics
  • The Sun in the Milky Way
  • The Ask an Astronomer team's favorite links about The Milky Way:

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