How Big is space? Part 1

As Douglas Adams writes in Hitchhiker's Guide to the Galaxy, "Space is really, really big. You just won't believe how vastly, hugely, mind-bogglingly big it is. I mean, you may think it's a long way down the road to the chemist's, but that's just peanuts to space"

So, let's attempt to visualize just how big it is.

First, we look at Earth.  One little planet.

A few years back, I took a drive from my hometown of Calgary, Alberta, down to Orlando, Florida, a trip of roughly 5,500 kilometres (3,400 miles).  It took five days.  Five full days of driving.  The trip back took a week, as it included a side trip to Santa Fe.  Before I got my driver's license, though, I would hitchhike.  Which meant that sometimes, I had to walk long distances.  A walk of 20 kilometres only takes 10 minutes in a car, but it took me four hours.  So, I have a pretty good idea just how far it is across America.

Now, 5,500 kilometres is pretty far, but if there were a road stretching around the Equator of Earth, it would be a little more than seven times further.  It would take roughly six weeks of long, full day drives. On foot, it would take you about two years, at twelve hours a day.

At this point, I'll start employing analogies, so you can picture this.

Imagine a perfect, 1:1 million scale globe of the Earth.  At least one such globe exists.  On this scale, the Earth is 12.756 metres (41 feet 10 inches) in diameter.  In my trip across North America, I'd cover about a metre (3.28 feet) a day on that globe.  My 4 hour walk covered about 2 mm (1/12th of an inch).  Just as a side note, the edge of space is defined as 100 kilometres, so on that globe, it would be about 10 cm (4 inches) off the surface.  Of course, it's only breathable to about 5 km (5mm) on that scale.

A trip to the moon and back is the longest "straight line" trip humans have undertaken.  It's 383,000 kilometres to the moon, so a return trip is 766,000 kilometres.  19 trips around the Earth's equator.  On our "big globe" model, the moon is 383 metres (just under 1/4 mile) away.

The next big leap is to the Sun.  Fortunately, that distance will serve as a convenient yardstick for the great distances to come.

The Earth orbits the Sun at a distance averaging 150 million km, about 390 times the Earth-moon distance.  For our big globe model, the 1:1 million scale, this is equivalent to 150 kilometres, or about an hour and a half's drive at highway speed.  If you could equate your highway driving to the model scale, your speed would be roughly a little less than 1/10th the speed of light.  By definition, the Earth-sun distance, actually about 149 600 000 kilometres (92 900 000 miles) is 1 Astronomical Unit, or A.U.

Another thing to consider is that on this scale, the Space Shuttle, in low orbit, moved at about 7.8 millimetres (1/3 of an inch) per second.  Our fastest interplanetary spacecraft, Voyager 1, is currently moving 3.6 A.U. per year.  At 1:1 million scale, that's 61.43 metres per hour, so it covers the real Earth-moon distance every 6 hours and 15 minutes, and 1 A.U. every 101.5 days.

At this point, we have to reduce scale, so that 1 A.U. (Earth-sun distance) is just 25.4 mm, or 1 inch.  I've chosen this particular scale for one simple reason.  It turns out, the ratio of a Light-year to 1 A.U. is almost exactly the same as the ratio of 1 mile: 1 inch.

On this scale, the Sun would be a barely noticeable speck the size of a grain of fine sand.  The Earth would be only visible through a microscope on that scale.  Earth orbits 1 inch away from the sun.  Mars orbits about 1 1/2 inches (3.8 cm) away from the center, and Jupiter is about 5 inches (12.5 cm) out.  Saturn lazily carves its circle, 10 inches (25.4 cm) from the Sun every 29.4 years.  Uranus is about 18 inches (46 cm) out, and the outermost planet, Neptune, is 30 inches (76 cm) from the Sun.  Our furthest probe, traveling since 1976, Voyager 1, is now roughly 130 A.U. from the Sun, or just under 11 feet on this scale.  Light takes 18 hours to traverse this distance.

A light year is defined as the distance light travels in a year, or 9,460,730,472,581 kilometres (5,878.625,373.184 miles), or, on this scale, 5,270 feet, ten feet short of a mile.