Earth and our Solar System
Our planet, Earth, is small, only 7,926 miles in diameter and 24,000 miles in circumference. In volume, it is only 3 millionths the size of our sun. We exist in a solar system comprised of the sun, nine planets, 168 moons (Earth: 1, Mars: 2, Jupiter: 63, Saturn: 59, Uranus: 27, Neptune: 13, and Pluto: 3) with more being discovered all of the time, more than 30,000 asteroids, and countless comets, meteoroids, and newly discovered planetoids (beyond Pluto). Of the nine planets, four are known as the inner (and terrestrial) planets: Mercury (3,029 miles diameter), Venus (7,519 miles diameter), Earth, and Mars (4,223 miles diameter). The five outer planets, which represent 99 percent of the mass of all the planets, are Jupiter (89,000 miles diameter), Saturn (75,000 miles diameter), Uranus (32,000 miles diameter), Neptune (31,000 miles diameter), and tiny Pluto (1,423 miles diameter), which is smaller than our moon. The sun, in comparison, is so large (865,000 miles diameter) that it comprises 99.85% of the total mass of our solar system.
As our planet orbits the sun at 65,000 mph, simultaneously it turns, rotating on its axis, at 1,000 miles an hour. To rotate fully once, it takes what we call a day. As we orbit our sun, our moon, 238,857 miles away, orbits us every 27 days, 7 hours, and 43 minutes. Earth is about 93,000,000 miles from the sun. The closest planet to the Sun, Mercury, is about 36,000,000 miles from it. To give you a sense of the size of our solar system, Pluto, the most distant planet, is 3,666,000,000 miles from the sun. The circuit that we orbit around the sun is 600 million miles. To orbit once, it takes what we call a year.
While all this is going on, our solar system orbits the Milky Way galaxy. Envision this: the Sun (comprised only of exploding gases: 75% hydrogen, 24% helium, and 1% other gases) and its nine planets (four made of gas, five solid), moons, asteroids, meteoroids, and comets all orbit together at 600,000 miles per hour like a huge self-contained space station more than seven billion miles in diameter.
How long does it take for us to orbit the Milky Way galaxy one time? Recall that it takes Earth a year to get around the sun at 65,000 miles an hour. In contrast, our solar system is traveling around the galaxy at 600,000 miles per hour. But even at that speed it takes 225 million years to orbit the Milky Way galaxy one time!
Filed under: cosmology
