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The shape of the Milky Way as deduced from star counts by William Herschel in 1785. ... with estimates for its half-length and orientation spanning from 1 to 5 kpc ...
The first project to describe the shape of the Milky Way and the position of the Sun was undertaken by William Herschel in 1785 by counting the number of stars in different regions of the sky. He produced a diagram of the shape of the galaxy with the Solar System close to the center .
The nature of the Milky Way's bar, which extends across the Galactic Center, is also actively debated, with estimates for its half-length and orientation spanning between 1–5 kpc (short or a long bar) and 10–50°.
The Orion Arm, also known as the Orion–Cygnus Arm, is a minor spiral arm within the Milky Way Galaxy spanning 3,500 light-years (1,100 parsecs) in width and extending roughly 10,000 light-years (3,100 parsecs) in length. [2] This galactic structure encompasses the Solar System, including Earth.
The rotation curve of a disc galaxy (also called a velocity curve) is a plot of the orbital speeds of visible stars or gas in that galaxy versus their radial distance from that galaxy's centre. It is typically rendered graphically as a plot, and the data observed from each side of a spiral galaxy are generally asymmetric, so that data from each ...
A visible light image of the Andromeda Galaxy. Messier 32 is to the left of the galactic nucleus and Messier 110 is at the bottom right. The Andromeda Galaxy is a barred spiral galaxy and is the nearest major galaxy to the Milky Way. It was originally named the Andromeda Nebula and is cataloged as Messier 31, M31, and NGC 224.
As an example, the Milky Way is roughly 100,000–180,000 light-years in diameter, and the nearest sister galaxy to the Milky Way, the Andromeda Galaxy, is located roughly 2.5 million light-years away.
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).
Structure of the Milky Way disc. Three stellar components with varying scale heights can be distinguished within the disc of the Milky Way (MW): the young thin disc, the old thin disc, and the thick disc. The young thin disc is a region in which star formation is taking place and contains the MW's youngest stars and most of its gas and dust ...
The Orion Nebula (also known as Messier 42, M42, or NGC 1976) is a diffuse nebula situated in the Milky Way, being south of Orion's Belt in the constellation of Orion, [b] and is known as the middle "star" in the "sword" of Orion. It is one of the brightest nebulae and is visible to the naked eye in the night sky with apparent magnitude 4.0.