4 Scale of the Cosmos
To simplify distance in our Solar System, astronomers use the Astronomical Unit (1 AU), which equals 93,000,000 miles or the average distance from Earth to the Sun.
As for other numbers, these are the diameters of three Solar System bodies. First, our Earth’s diameter is just less than 8,000 miles. Jupiter’s diameter – the largest planet in our Solar System – is around 88,000 miles. And the Sun’s diameter is about 850,000 miles.
The idea here is not to memorize size and distance; rather, it is to appreciate the grand scale of the Universe within which we live.
Going beyond our Solar System, the closest star is Proxima Centauri, part of the Alpha Centauri triple star system. It is about 24,340,000,000,000 miles (that is 24 trillion, 340 billion miles) away or about 270,000 times more distant than Earth to the Sun. And that is the closest star beyond our Sun. Because of these great distances, astronomers will use another measure: the distance light travels in one year, or the light year. This sounds like a time measure, but it is not.
Light travels 186,000 miles in one second, or 2.99 x 108 meters per second. That is 5,869,713,600,000 miles in a year. So the Sun is about 8 light minutes from Earth and Proxima Centauri about 4.24 light years distant.