Pluto has mountains and complex geology but is even smaller than the moon. Titan has an atmosphere even thicker than Earth's. We found out that many large moons such as Io are geologically active. But by the end of the 20th century, the simple definition became problematic. When Pluto was discovered in 1930, it was clearly a planet because it was neither an asteroid nor a moon. Asteroids and moons should not be considered planets. This began a gradual shift to the idea that planets were large bodies orbiting the sun. But after a dozen worlds were found between Jupiter and Mars, many astronomers argued that they should be not planets, but asteroids. All were planets because they certainly weren't stars. When astronomers discovered Ceres in 1801, it was clearly a planet. This simple definition held well into the 1800s. As Galileo demonstrated in 1611, stars shine of their own light, while planets only shine through reflected sunlight. Planet and moon were not exclusionary terms. For Galileo, a moon is a planet that orbits another planet, named after the first of that name. The use of "moon" as a general object also dates to this time. When Cassini discovered Saturn's moon Titan, he referred to it as a new planet. When Galileo discovered four moons of Jupiter, he referred to them as the Medicean planets. ![]() Throughout the 1600s and 1700s, this was the standard. With the rise of the heliocentric model, objects that orbit the sun were planets, meaning that Earth was a planet, but so was the moon. Thus, the sun and moon were considered planets, but not the Earth. In historical astrology, there were stars, transitory objects such as comets, and planets. The early definition of a planet was an object that moved against the stars over time. Several alternative definitions have been proposed, but a new study argues we should look to history for the solution. This has stirred all manner of controversy, even among astronomers. It must have cleared its orbital neighborhood.īy this definition there are just eight planets in our solar system, most notably excluding Pluto.The best estimate of the size of the observable universe (given that it has been expanding for 13.7 billion years), is about 93 billion light years (880,000,000,000,000,000,000,000 kilometers) across. Our next closest galaxy is the Andromeda Galaxy, which is about 2.5 million light years away, or roughly 24,000,000,000,000,000,000 kilometers. The center of the Milky Way galaxy is about 26,000 light years, or roughly 246 quadrillion (246,000,000,000,000,000) kilometers. Sirius A and B, in the Sirius star system, are about 81 trillion (81,000,000,000,000) kilometers or 8.58 light years away. The next nearest star to us (other than the Sun) is Proxima Centauri, in the Alpha Centauri star system (still part of our Milky Way galaxy), which is about 40 trillion (40,000,000,000,000) kilometers away or, using the more convenient unit based on the distance light travels in a year (which is about 9.46 trillion kilometers), 4.24 light years. The Sun is about 150 million kilometers away from the Earth (sometimes referred to as 1 astronomical unit, or 1 AU). The nearest planet to the Earth is either Venus, which varies between 42 million kilometers and 258 million kilometers away (its orbit is highly irregular), or Mars which varies between 56 million kilometers and 100 million kilometers away. The Moon is about 360,000 kilometers away from the Earth (and it is receding from us at a rate of about 4 centimeters a year as its orbit gradually speeds up). The International Space Station orbits the Earth about 350 kilometers up (in the thermosphere). “Space” is often considered to start at about 100 kilometers up, known as the Kármán line, where the Earth's atmosphere becomes too thin for aeronautical purposes. Random Facts: How far is it to space, the Moon, the Sun, the stars, etc?Įarth’s atmosphere is divided up into several layers: the troposphere from about 6 - 20 kilometers up the stratosphere from 20 - 50 kilometers the mesosphere from 50 - 85 kilometers the thermosphere from 85 - 690 kilometers and the exosphere out to about 10,000 kilometers. A Few Random Facts Where in the universe is the Earth? How fast are we traveling through space? How fast does light travel? How far is it to space, the Moon, the Sun, the stars, etc? How many stars are there? How does the Sun shine? What different types of stars are there? What is the human body (and the Earth, the Sun, the Universe) made of? How many molecules/atoms are there in each cubic meter? What if the history of the universe were squeezed into the period of one year? What are the coldest and the hottest objects in the universe? What is the electromagnetic spectrum? What is a planet? What is a dwarf planet? Why do the planets orbit the Sun?
0 Comments
Leave a Reply. |
AuthorWrite something about yourself. No need to be fancy, just an overview. ArchivesCategories |