Nearest star I
(Proxima Centauri) 4.35 light-years
Distance from center of Earth
On the largest scales, galaxies group together in clusters, and clusters merge into each other to form superclusters, sometimes containing thousands of major galaxies and countless smaller ones in a space a few tens of millions of light-years across.
most likely date for Big Bang: 13.7 billion years ago
The Sun is just one of more than 200 billion stars in the Milky Way. A typical spiral galaxy, the Milky Way has a diameter of at least 100,000 light-years.
_The Oort cloud
The Sun's gravity dominates a region of space with a radius of roughly one light-year, or 5.9 trillion miles (9.5 trillion km). At the outer edge of the solar system lies a vast spherical halo of deep-frozen comets—the Oort cloud.
When astronomers look at distant galaxies in every direction, they find evidence that they are moving rapidly away from us, and from each other. The farther away a galaxy is, the faster it is receding. The only logical explanation is that the universe itself is expanding, and carrying every galaxy cluster farther away from its neighbors. If everything in the universe is now moving apart, then in the distant past, everything must have been gravity holds much closer together, and because it was more galaxies within clusters tightly packed, it would also have been hotter. This is together the origin of the Big Bang theory—that the universe the unjve!se was born in a single vast explosion billions of years ago. today most likely date for Big Bang: 13.7 billion years ago latest possible date for Big Bang: 11 billion years ago earliest possible date for Big Bang: 15 billion years ago densely packed young galaxies latest possible date for Big Bang: 11 billion years ago
The 1,000-light-year sphere
90 percent of naked-eye stars are within 1,000 light-years of Earth
62 trillion miles (1014 km)
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