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The Milky Way [c] is the galaxy that includes the Solar System, with the name describing the galaxy's appearance from Earth: a hazy band of light seen in the night sky formed from stars that cannot be individually distinguished by the naked eye.
The debate took place on April 26, 1920, in the hall of the United States National Academy of Sciences in Washington DC. Shapley took the side that spiral nebulae (what are now called galaxies) are inside our Milky Way, while Curtis took the side that the spiral nebulae are "island universes" far outside our own Milky Way and comparable in size ...
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.
This is in contrast to extragalactic astronomy, which is the study of everything outside our galaxy, including all other galaxies. Galactic astronomy should not be confused with galaxy formation and evolution, which is the general study of galaxies, their formation, structure, components, dynamics, interactions, and the range of forms they take.
So, they put their best numbers and uncertainties to the test, running calculations for a two-body system (just the Milky Way and Andromeda), three-body systems (the Milky Way, Andromeda, and ...
Milky Way Galaxy: 30,000 pc 9.26×10 17: Our home galaxy, composed of 200 billion to 400 billion stars and filled with the interstellar medium. [36] [37] Milky Way subgroup: 840,500 pc 2.59×10 19: The Milky Way and those satellite dwarf galaxies gravitationally bound to it. Examples include the Sagittarius Dwarf, the Ursa Minor Dwarf and the ...
The Hubble eXtreme Deep Field (XDF) was completed in September 2012 and shows the farthest galaxies ever photographed at that time. Except for the few stars in the foreground (which are bright and easily recognizable because only they have diffraction spikes), every speck of light in the photo is an individual galaxy, some of them as old as 13.2 billion years; the observable universe is ...
Later in the 1920s, Edwin Hubble showed that Andromeda was far outside the Milky Way by measuring Cepheid variable stars, proving that Curtis was correct. [6] It is now known that the Milky Way is only one of as many as an estimated 200 billion (2 × 10 11) [7] to 2 trillion (2 × 10 12) or more galaxies in the observable Universe.