The incredible diversity of the cosmos is illustrated in the following examples:

  • About 99% of the stars seen on a typical night are larger, more massive and brighter than the Sun. Each one is cruising through the milky Way Galaxy at about 50,000 kilometers per hour (30,000 mph).
  • The star PSR 1937-214 is no wider than the city limits of a medium-sized city but it weight 500,000 times as much as Earth and is spinning on its axis 642 times a second. This record holder among the twirling stars we call pulsars is rotating so fast, its equator is moving at one-tenth the speed of light.
  • Pulsars are incredibly dense. A thimbleful of pulsar material would weigh as much as all the water in Lake Erie. This density produces enormous gravity. If a spaceship could land on a pulsar, it would be instantly crushed by gravity into a puddle of subatomic particles about the thickness of the nucleus of an atom.
  • A black hole with the mass of earth would be smaller than a golf ball. A black hole with the mass of the entire galaxy would be 10 times wider than the solar system.

How Many Galaxies?

The average galaxy is a colossal island of 100 billion stars, although much larger and smaller galaxies are known. But how many galaxies are there in the universe? To calculate this number astronomers use the longest exposures obtained with the Hubble Space Telescope and count the galaxies-typically a few thousand. That average is then multiplied by the number of photographs it would take to cover the entire sky. Of course, this technique misses an unknown number of galaxies that are either too dim or too remote to be picked up, but it does provide a minimum number of galaxies in the universe: 50 billion! The total number could be twice this.

The Universe Train

The universe is so vast that it’s difficult to establish a scale of reference, but this freight-train analogy might help put it into perspective. Imagine each star in the known universe is represented by a grain of sand. A thimble would hold all the stars visible on a clear, dark summer night. A dump truck would contain the Milky Way, the galaxy in which the Sun resides. To demonstrate all the stars in the universe, we need a freight train with hopper cars filled with sand. The train begins to pass at a level crossing. We count the cars as they roar by at one per second. The minutes pass, then hours, then days. We would have to keep count 24 hours a day for three years before the universe train would complete its pass. The universe train would use all the sand on all the beaches on Earth and would be long enough to stretch around the planet 25 times.

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