YOU LIVE ON PLANET EARTH
It is probable that the universe expands into infinity, having no boundaries, no end. Its size is certainly beyond human comprehension. If you were able to travel through the universe non-stop at the speed of light for a trillion years, you would not have made any significant gains. The universe you live in is s-o-o-o-o vast.
There are millions (perhaps billions) of ‘clusters’ (or ‘groups’) of galaxies out there. A galaxy is a maze of stars that either orbits around its own center in a systematic fashion, or a group of stars having no obvious order. One of these clusters of galaxies astronomers refer to as the Local Group. The Local Group is not particularly large compared to other clusters, consisting of about 1100 galaxies. One of these galaxies is called the Milky Way.
The Milky Way is immense. Shaped somewhat like a disk, the distance from one end to another is estimated to be about 100,000 light-years (a light-year being the distance light travels in a year). The Milky Way consists of many billions of stars orbiting its nucleus, and could be compared to a gigantic phonograph record that never stops spinning. The Milky Way, like all galaxies in the Local Group, is itself traveling at a very high speed. This is because the entire universe is expanding, stretching, reaching out, perhaps at the speed of light or even faster.
One of the billions of stars orbiting the nucleus of the Milky Way is the sun, located about halfway between the center of this galaxy and its outer edge. Though traveling at 12 miles per second, it takes the sun about 200,000,000 years to make a single orbit, so immense is the Milky Way galaxy. The sun is about 866,000 miles in diameter – not particularly large – almost perfectly round, self-illuminating, its surface heat about 6,000°C. The sun and the other cosmic bodies held by its gravitational pull is referred to as the solar system. The solar system consists of a number of comets, swarms of meteors and also nine planets complete with their own satellites. One of these planets is Earth on which you live.
The earth is a globe of rock, not quite round, about 25,000 miles in circumference at its equator. The fifth largest of nine planets, it is about 93,000,000 miles from the sun, a distance exactly right to sustain life on earth, not too hot, not too cold. The earth has one satellite, the moon. 71 % of the surface of the earth is covered in water. It is water that makes this planet most rare in the Milky Way. The earth is blanketed by an atmospheric layer of mostly nitrogen and oxygen which traps the earth’s heat and protects you from dangerous rays from the sun. The earth spins on its axis every 24 hours, causing rotating darkness and light, and orbits in an almost perfectly round path around the sun, producing varying seasons.
On the surface of the earth there is always motion. Surface water in the oceans are in continuous motion because of the pull of the moon. Rain and snow constantly fall from sky to earth. Atmospheric action causes violent storms. Clouds crisscross the sky. Rivers continuously carry water to the seas. The movement of the earth’s crust results in earthquakes, and internal pressures cause volcanoes to spew liquid lava to the surface.
As far as astronomers can tell, it is only planet Earth that sustains life. You share the earth with over 5 billion other humans, a myriad of animals, insects, reptiles, birds, and marine life. Life on earth is intertwined in such a way that it must be termed wondrous and miraculous. The earth produces an abundance of fruit and vegetables, so varying in color and taste. There is plenty of drinking water, a necessity for every plant and creature. Trees and foliage produce the oxygen you breathe and material to build shelters. Animals and birds and fish supply meat and clothing.
In perspective, you are a unique and tiny creature, a mere speck, spinning at about 500 miles per hour on a global rock we call Earth. Every year you travel 590,000,000 miles in orbit around the sun. In addition, you are traveling 12 miles per second in another orbit around the nucleus of the Milky Way. Also, because the universe is expanding, you are moving at probably an even faster speed away from other galaxies and other clusters of galaxies.