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The first attempt to describe the shape of the Milky Way and the position of the Sun within it was carried out by William Herschel in 1785 by carefully counting the number of stars in different regions of the visible sky. He produced a diagram of the shape of the Milky Way with the Solar System close to the center.
The Milky Way Galaxy, where the Solar System is located, is classified as a barred spiral galaxy. Edwin Hubble classified spiral galaxies of this type as "SB" (spiral, barred) in his Hubble sequence and arranged them into sub-categories based on how open the arms of the spiral are. SBa types feature tightly bound arms, while SBc types are at ...
The Milky Way was once considered an ordinary spiral galaxy. Astronomers first began to suspect that the Milky Way is a barred spiral galaxy in the 1960s. Their suspicions were confirmed by Spitzer Space Telescope observations in 2005, which showed that the Milky Way's central bar is larger than what was previously suspected. Famous examples
The Milky Way has more than 150 known globulars, and there may be many more. Both the origin of globular clusters and their role in galactic evolution are unclear. Some are among the oldest objects in their galaxies and even the universe , constraining estimates of the universe's age .
Galaxies are categorized according to their visual morphology as elliptical, [5] spiral, or irregular. [6] The Milky Way is an example of a spiral galaxy. It is estimated that there are between 200 billion [7] ( 2 × 1011) to 2 trillion [8] galaxies in the observable universe.
Artist's impression of the central bulge of the Milky Way. In astronomy, a galactic bulge (or simply bulge) is a tightly packed group of stars within a larger star formation. The term almost exclusively refers to the central group of stars found in most spiral galaxies (see galactic spheroid).
The Galactic Center is the barycenter of the Milky Way and a corresponding point on the rotational axis of the galaxy. [1] [2] Its central massive object is a supermassive black hole of about 4 million solar masses , which is called Sagittarius A* , [3] [4] [5] a compact radio source which is almost exactly at the galactic rotational center.
According to recent analysis of the data produced by the Gaia spacecraft, it would seem possible to explain at least the Milky Way's rotation curve without requiring any dark matter if instead of a Newtonian approximation the entire set of equations of general relativity is adopted.
The Solar System is located in the Milky Way, a barred spiral galaxy with a diameter of about 100,000 light-years containing more than 100 billion stars. The Sun is part of one of the Milky Way's outer spiral arms, known as the Orion–Cygnus Arm or Local Spur.
Whirlpool Galaxy. The Whirlpool Galaxy, also known as Messier 51a ( M51a) or NGC 5194, is an interacting grand-design spiral galaxy with a Seyfert 2 active galactic nucleus. [6] [7] [8] It lies in the constellation Canes Venatici, and was the first galaxy to be classified as a spiral galaxy. [9]