OUR NEIGHBOR,ANDROMEDA GALAXY
OUR CLOSEST GALAXY ANDROMEDA..
Andromeda is the largest galaxy in the Local Group, which includes the Milky Way, the Triangulum Galaxy, and dozens of smaller dwarf and irregular galaxies. A recent estimate gave Andromeda 700 billion solar masses. Our Milky Way is only 80% the mass of Andromeda.
The Andromeda galaxy was first observed by Persian astronomers, thousands of years ago, and was later cataloged by Charles Messier in 1764. He classified it as M31. In 1912, astronomers calculated its speed to be 300 kilometers per second, moving towards the Sun. Edwin Hubble first calculated the distance to Andromeda, by detecting Cepheid variables in the galaxy. He measured that it was 450 kpc, or 2.5 million light-years away; well outside the Milky Way galaxy.
Recent estimates have calculated that Andromeda Galaxy is about 220,000 light-years in diameter, almost twice the estimate diameter of the Milky Way.
While other galaxies are moving away from us, Andromeda is on a collision course with the Milky Way. Our two galaxies will collide with one another in about 2.5 billion years, and begin forming a giant elliptical galaxy. It’s known to have 14 dwarf galaxies orbiting it in various stages of merger.
Based on its appearance in visible light, the Andromeda Galaxy is classified as an SA(s)b galaxy in the de Vaucouleurs–Sandage extended classification system of spiral galaxies. However, data from the 2MASS survey showed that Andromeda is actually a barred spiral galaxy, like the Milky Way, with Andromeda's bar oriented along its long axis.
In 2005, astronomers used the Keck telescopes to show that the tenuous sprinkle of stars extending outward from the galaxy is actually part of the main disk itself.This means that the spiral disk of stars in the Andromeda Galaxy is three times larger in diameter than previously estimated. This constitutes evidence that there is a vast, extended stellar disk that makes the galaxy more than 220,000 light-years (67,000 PC) in diameter. Previously, estimates of the Andromeda Galaxy's size ranged from 70,000 to 120,000 light-years (21,000 to 37,000 pc) across.
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| IMAGE BY : jpl.nasa.gov |
Recent estimates have calculated that Andromeda Galaxy is about 220,000 light-years in diameter, almost twice the estimate diameter of the Milky Way.
While other galaxies are moving away from us, Andromeda is on a collision course with the Milky Way. Our two galaxies will collide with one another in about 2.5 billion years, and begin forming a giant elliptical galaxy. It’s known to have 14 dwarf galaxies orbiting it in various stages of merger.
Based on its appearance in visible light, the Andromeda Galaxy is classified as an SA(s)b galaxy in the de Vaucouleurs–Sandage extended classification system of spiral galaxies. However, data from the 2MASS survey showed that Andromeda is actually a barred spiral galaxy, like the Milky Way, with Andromeda's bar oriented along its long axis.
In 2005, astronomers used the Keck telescopes to show that the tenuous sprinkle of stars extending outward from the galaxy is actually part of the main disk itself.This means that the spiral disk of stars in the Andromeda Galaxy is three times larger in diameter than previously estimated. This constitutes evidence that there is a vast, extended stellar disk that makes the galaxy more than 220,000 light-years (67,000 PC) in diameter. Previously, estimates of the Andromeda Galaxy's size ranged from 70,000 to 120,000 light-years (21,000 to 37,000 pc) across.
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