andromeda galaxy

Andromeda, also known as the galaxy M31, Messier31 or NGC 224, is the closest barred spiral constellation to the Milky Way. One of the few galaxies that can be seen from Earth.

This constellation is located at a distance of 2.5 million light years from Earth. It has a diameter of approximately 200,000 light years and a mass of about 800 billion times the mass of the Sun.

It was discovered by Edwin Hubble in 1923. He was the first to propose that this was a galaxy. Thanks to this proposal it was possible to broaden the understanding of the size of the universe. Until then we thought that the entire universe was the Milky Way; we now understand that our constellation is only one of about 100 billion other galaxies that coexist in the universe.

The galaxy is surrounded by a large halo of gas. It contains a concentrated bulge of matter in the middle, which is surrounded by a disk of gas, dust, and stars and a huge halo.

It has about a trillion stars compared to the 250 billion in the Milky Way. Which makes our constellation actually more massive, as it is believed to contain more dark matter.

History and discovery of Andromeda

This galaxy has been the subject of much interest since ancient times. The earliest records we can find of Andromeda date from the 10th century, to the early 1900s.

In the first observations it was believed that it was a nebula that inhabited within the Milky Way. It wasn't until Edwin Hubble's proposal that the perspective completely changed.

The first documented photograph that we can find of the constellation was taken in the year 1855. However, it failed to reveal enough details, so it was believed that it was actually a nebula.

The astronomer Heber Doust Curtis made the observation of a supernova within the constellation in the year 1917. This made him verify the previous records about Andromeda. In his investigation he found 11 instances of novae which were 10 times dimmer than other novae we observed in other parts of the sky. Curtis, based on the "island universe theory", made calculations about its distance which would be about 500,000 light years long.

The existence of other galaxies and extragalactic objects outside the Milky Way was again the subject of a great debate known as: the Great Debate.

The first concrete evidence for these hypotheses emerged in 1923, when Edwin Hubble observed a variable star called Cepheid within the constellation. Being also a type of pulsating star known as "standard candle" which is used to calculate the distance between celestial objects. Once he was able to know the pulsation frequency of a star he was able to calculate its intrinsic luminosity and its distance from Earth. Edwin Hubble did just that, putting the distance at 2.5 million light-years. He thereby demonstrating the existence of other galaxies or "island universes" in the cosmos.

Features of the Andromeda Galaxy

  • Andromeda is the largest galaxy in the local cluster, however, many studies infer that this might not be the most massive.
  • Although it is twice the diameter of the Milky Way it is possible that it has about the same mass as our galaxy.
  • It is the most distant object when observed with the naked eye from a place where you are free of light pollution
  • For a long time it was thought to be a cluster of gas clouds or a nebula. It was not until 1923 that it was first suggested that this was actually a galaxy.
  • Thanks to its proximity to the earth, this constellation has served the astronomical community to analyze the origin and evolution of galaxies in the universe.
  • The constellation Andromeda is approaching the Milky Way at a speed of approximately 100 to 140 kilometers per second.
  • This galaxy has a very crowded double nucleus. Where not only does it have a massive star cluster right in its center, but it also has a hidden supermassive black hole in its core. Which has about 100 million solar masses.
  • The galaxy has at least two spiral arms, and a dust ring that may have come from the smaller galaxy M32. Astronomers think it may have interacted more closely with Andromeda several hundred million years ago, when M32 plunged into the heart of its larger neighbor.
  • There are at least 450 globular clusters orbiting her galaxy. Some of them are among the most densely populated globular ever seen.
  • Through the Hubble Space Telescope, it was discovered that Andromeda is surrounded by a giant ball of gas which almost reaches the middle of the Milky Way. This gas is dark, but you can see it in the night sky.
  • The ball of gas in Andromeda is about 100 times larger than our moon.
  • Andromeda is heading towards us at approximately 500 kilometers per hour. However, despite having this speed, it has been determined that these two galaxies will not collide for at least four billion years.

How can we identify Andromeda?

As mentioned, it is a galaxy visible from Earth. To be able to observe it, it is necessary to do it from an area that does not have much light pollution.

This constellation can be seen as a small fuzzy spot just below the center of the Milky Way.

We can orient the observation between the Cassiopeia constellation, which has a characteristic W-shape, and the Great Square of the Pegasus constellation.

The best time to view Andromeda is during the fall and winter in the Northern Hemisphere and during the spring in the Southern Hemisphere. In the northern mid-latitudes it can be found between October and December at the zenith, the highest point overhead.


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