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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 in other arms of the galaxy, which are so far away that they cannot be individually distinguished by the naked eye.
In 1958 the International Astronomical Union (IAU) decided to adopt the position of Sagittarius A as the true zero coordinate point for the system of galactic latitude and longitude. [11] In the equatorial coordinate system the location is: RA 17 h 45 m 40.04 s , Dec −29° 00′ 28.1″ ( J2000 epoch ).
Knowledge of the location of Earth has been shaped by 400 years of telescopic observations, and has expanded radically since the start of the 20th century. Initially, Earth was believed to be the center of the Universe , which consisted only of those planets visible with the naked eye and an outlying sphere of fixed stars . [ 1 ]
The horizontal, or altitude-azimuth, system is based on the position of the observer on Earth, which revolves around its own axis once per sidereal day (23 hours, 56 minutes and 4.091 seconds) in relation to the star background. The positioning of a celestial object by the horizontal system varies with time, but is a useful coordinate system ...
The anisotropy of the star density in the night sky makes the galactic coordinate system very useful for coordinating surveys, both those that require high densities of stars at low galactic latitudes, and those that require a low density of stars at high galactic latitudes.
A galactic orientation describes the spatial orientation of a galactic plane, where such exists for a given galaxy.For a spiral galaxy, this can be obtained from the inclination of the galactic plane to the plane of the sky, and the position angle of the major axis as viewed from Earth.
Due to the presence of an x-shaped bulge, [9] visible in multiple wavelengths, it has been argued that NGC 3628 is instead a barred spiral galaxy with the bar seen end-on. [10] Simulations have shown that bars often form in disk galaxies during interactions and mergers, and NGC 3628 is known to be interacting with its two large neighbors.
Sagittarius A*, abbreviated as Sgr A* (/ ˈ s æ dʒ ˈ eɪ s t ɑːr / SADGE-AY-star [3]), is the supermassive black hole [4] [5] [6] at the Galactic Center of the Milky Way.Viewed from Earth, it is located near the border of the constellations Sagittarius and Scorpius, about 5.6° south of the ecliptic, [7] visually close to the Butterfly Cluster (M6) and Lambda Scorpii.