I Am God

The size of the Universe is unknown; it may be infinite. The region visible from Earth (the observable universe) is a sphere with a radius of about 46 billion light years, based on where the expansion of space has taken the most distant objects observed. For comparison, the diameter of a typical galaxy is 30,000 light-years, and the typical distance between two neighboring galaxies is 3 million light-years. As an example, the Milky Way Galaxy is roughly 100,000 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. There are probably more than 100 billion galaxies in the observable Universe. Typical galaxies range from dwarfs with as few as ten million stars up to giants with one trillion stars, all orbiting the galaxy’s center of mass. A 2010 study by astronomers estimated that the observable Universe contains 300 sextillion (3×1023) stars.

The Milky Way is a barred spiral galaxy some 100,000–120,000 light-years in diameter which contains approximately 100–400 billion stars. It may contain at least as many planets as well. The Solar System is located within the disk, about 27,000 light-years away from the Galactic Center, on the inner edge of a spiral-shaped concentration of gas and dust called the Orion–Cygnus Arm. The stars in the inner ≈10,000 light-years form a bulge and one or more bars that radiate from the bulge. The very center is marked by an intense radio source named Sagittarius A* which is likely to be a supermassive black hole.

The rotational period is about 240 million years at the position of the Sun. The Galaxy as a whole is moving at a velocity of approximately 600 km per second with respect to extragalactic frames of reference. The oldest known star in the Galaxy is at least 13.6 billion years old and thus must have formed shortly after the Big Bang. Surrounded by several smaller satellite galaxies, the Milky Way is part of the Local Group of galaxies, which forms a subcomponent of the Virgo Supercluster.

The Milky Way contains at least 100 billion stars and may have up to 400 billion stars. The exact figure depends on the number of very low-mass, or dwarf stars, which are hard to detect, especially at distances of more than 300 light years from the Sun. As a comparison, the neighboring Andromeda Galaxy contains an estimated one trillion stars.

The Virgo Supercluster or Local Supercluster is the irregular supercluster that contains the Virgo Cluster in addition to the Local Group, which in turn contains the Milky Way and Andromeda galaxies. At least 100 galaxy groups and clusters are located within its diameter of 33 megaparsecs (110 million light-years). It is one of millions of superclusters in the observable universe.

The Great Attractor is a gravity anomaly in intergalactic space within the range of the Centaurus Supercluster that reveals the existence of a localized concentration of mass equivalent to tens of thousands of galaxies, each of which is the size of the Milky Way; this mass is observable by its effect on the motion of galaxies and their associated clusters over a region hundreds of millions of light years across.

• Milky Way
• Virgo Supercluster
• Great Attractor
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