1. It’s a Long Way to Tipperary – And Even Farther to the Nearest Star

2. This was a bit of a trick title. The nearest star to the earth is, of course, the sun—and we’ll look at how far it is from here to there first. But the really big distance is to the next nearest star, Alpha Centauri, and we’ll take a look at that longer journey, too.

3. Astronomical distances are so vast that it’s often hard to imagine just how far away some celestial object actually is. So in order to get a feel for the distance between the earth and the sun, let’s use an analogy…

4. Imagine that we shrank the sun down to a sphere about the size of a basketball. The sun is 864,000 miles in diameter. A basketball is just over 9 inches in diameter—let’s round that off to 10 inches to make our calculations a little easier.

5. So, if 10 inches equals 864,000 miles, one inch will represent 86,400 miles. And 0.0000115 inch will represent a single mile approximately. At this scale, how big is the earth? Well, the earth is 7,913 miles in diameter. 7,913 times 0.0000115 equals 0.091 inches approximately—in other words, not quite a tenth of an inch! We might think of our earth-sun model as relatively the same size as a bit of buckshot is relative to the size of our basketball. Note: Illustrations not to scale.

6. So how far is it from the earth to the sun? As every school child knows (or should know!) that distance is 93 million miles on average. If we wanted to place our model of the earth and sun at their relative correct distance from each other, we’d multiply 93,000,000 times 0.0000115 in order to get the number of inches apart they should be. The answer is 1,069.5 inches or 89.125 feet. So if our basketball sun is here in the Electronic Classroom, our buckshot earth would be somewhere in the vicinity of the table in front of the Reading Room fireplace! 89.125 feet

7. Let’s look at this another way. If we increased the size of the sun to be that of The Rotunda, our familiar star would now be 77 feet in diameter. 1 foot would now represent 11,220 miles. An inch would be 935 miles. So, The earth would be a ball about 8.5 inches in diameter—or roughly the size of our basketball. On this scale, if the Rotunda was the sun, the earth would be a basketball sitting 8,288.77 feet or about 1.6 miles away—roughly at the intersection of Hydraulic Road and 29 North.

8. Okay, now let’s get really far out…!

9. Here’s a photograph of our quarry, Alpha Centauri, the large bright dot to the left of center. This star, which is very much like our sun, is the closest star to earth* other than the sun. How far away is it? * Technically, it’s close companion Proxima Centauri is the closest—but it never gets much respect, being much smaller and dimmer than its sibling stars!

11. So to make a moderately long mathematical story a little shorter, the distance to Alpha Centauri is usually expressed as 4.3 light years. In other words it takes a beam of light 4.3 earth years to cross the distance between Alpha Centauri and earth. This distance is 2.53 x 10 13 miles or roughly 25.3 trillion miles.

12. If the sun were scaled to a 1 foot radius—roughly the size of the basketball we contemplated earlier—then Alpha Centauri would be another basketball about 5,545 miles away in Ankara, Turkey!

13. Truly, the Universe is a very, very big place! Image copyright Robert Gendler

14. And by the way, it’s a mere 3,409.3 miles from Charlottesville to Tipperary—not all that far, is it?

15. The End