Many of us, while still in grade school, learned about the staggering distances to planets, stars and galaxies. The sun is approximately 150 million km or 93 million miles away, a distance that is known as the "astronomical unit" (AU). Venus, our closest neighbor, is 0.72 AU from the sun, while Mars is 1.52 AU from the sun. Neptune, the most distant planet, is 30 AU from the sun (i.e., 44.8 billion km or 27.9 billion miles). The Voyager 2 spacecraft, launched in 1977, reached Jupiter just two years later, but did not reach Neptune until 1989.
The scope of the universe is perhaps best illustrated by an example given by Australian astrophysicist Geraint Lewis. He noted that if the entire Milky Way galaxy is represented by a small coin, roughly one cm across, then the Andromeda galaxy would be another small coin roughly 25 cm (10 in) away. The observable universe would then extend for 5 km (3 mi) in every direction, encompassing some 300 billion galaxies (and roughly 3 x 1022 individual stars). And yet most of the universe is empty space!
So how are these distances measured? How can scientists possibly measure or calculate these enormous distances with any confidence? Watch the Video below for answer!
