Artist concept of NASA's Voyager 1, now
the most distant spacecraft from Earth.
Credit: NASAOne of the hardest things to explain to people is of the astronomical sizes and distances involved in our Universe. It's hard to explain because it’s hard for us–any of us–to really get our heads around the numbers, and what they really mean.
Along the road to understanding all things big and far away, I'll start small: the Earth.
Big as our world is, it's really only relative– but relative to what? It's just shy of 8000 miles in diameter. As a volume of space, that's about 268 billion cubic miles. In other words, were Earth a giant fish-bowl (an empty sphere), we could divvy up that volume between every human on Earth today, and each of us would get a cube of space about three and a half miles on a side.
How about that walk to the Moon? Do you remember from elementary school how long it would take you to walk to the Moon–IF you could walk to the Moon? The Moon is about 240,000 miles away, and while it takes light only 1.3 seconds to cross that distance, walking at a speed of 3 miles per hour it would take you about nine years to get there. That's equivalent to walking around the Earth's equator ten times.
Next step out might be Mars. At least, NASA's talking about sending people to Mars next–after a return to our Moon in 2019 (note that in this plan, it will take us longer to get back to the Moon that it would to walk there…). Walking the distance to Mars, even when it's at its closest (35 million miles) would take well over a thousand years–so the walking tour is out. At NASA-speed, it takes about 7 months to get a spacecraft to Mars.
One of the quintessential distances when talking about the scales of space is that old favorite: "Pluto distance." About forty times farther from the Sun than the Earth, a walk to Pluto would take an appalling 170,000+ years. At the speed of NASA's New Horizons spacecraft, which is currently past Jupiter and heading toward the distant dwarf planet at 50,000 miles per hour, it's about a ten-year journey. And New Horizons is the fastest spacecraft ever hurtled off into space.
To top off this blog (because there isn't nearly enough space in here to go much farther up), I'll leave you with space exploration's greatest up, up, and out story: Voyager 1. After 30 years in space, Voyager 1 is now a hundred times farther from the Sun than the Earth–that's two-and-a-half times farther out than Pluto! About nine billion miles.
Okay, now for the big finale. So, Voyager 1 is nine billion miles out, and it's taken it 30 years to get there. Hypothetically, if Voyager 1 were bound for the nearest star in space to our Sun–the Alpha Centauri system–then the portion of that journey it has now completed is equivalent to someone on a road trip from Oakland to New York City who has gone a single mile!
Coming up in a future blog: Mile Two.
Benjamin Burress is a staff astronomer at The Chabot Space & Science Center in Oakland, CA.