Forty-Seven

The Tropic of Cancer and the Tropic of Capricorn are exactly 47 degrees apart from one another. Well, not exactly. More like 46.87362. But who’s counting?

What are the Tropics of Cancer and Capricorn, anyway? And what do I mean by “degrees”? I’m glad you asked. They are latitude lines, lines that run parallel to the Equator. The Tropic of Cancer is at just around 23.4 degrees north of the Equator, and the Tropic of Capricorn is about 23.4 degrees south. That means that they are about 3,250 miles north and south of the Equator, respectively. The Tropics actually move a little bit from year to year, but it’s always in that range. What’s so special about these latitude lines? Take a look at this picture.

It might be a little confusing, but I’ll try to explain it. The circles on the left and the right are both the earth, at different times of the year. The center circle, of course, is the sun. (I love how the image says “not to scale.” True. The sun in reality is just a bit bigger than the earth, believe it or not. Anyway, the image on the left shows the way the earth is in relation to the sun at the June solstice (known in the northern hemisphere as the summer solstice). The red, purple, and blue lines on the earth are particular lines of latitude. What might surprise you is that those lines are angled — they’re not shown here as horizontal. Well, the reason for that is quite simple: the earth is tilted at approximately 23.4 degrees. Ever notice how globes are made like that, how the earth doesn’t spin “horizontally” on a globe?

It’s the same angle. Anyway, the earth spins on the dashed black line, marked “polar axis.” This line connects the North Pole to the South Pole, straight through the center of the earth. Now, if you notice, the sun’s rays are pointing directly at the Tropic of Cancer on the June solstice. That means that if you live at that latitude, the sun is directly overhead at noon on that day. (And quite, quite hot and sunburn-causing, to boot.) Swing around to December, and you’ll see that the sun is directly overhead if you live on the Tropic of Capricorn. If you live between the two Tropics, the sun will be directly overhead at some point during the year. (On the Equator at the March and September Equinoxes.) So the Tropic of Cancer marks the farthest points north where the sun will be overhead, and the Tropic of Capricorn marks the farthest points south.

Now, how about those blue lines, the Arctic Circle and the Antarctic Circle? Have you heard of the “midnight sun”? There are places in the far north where the sun never goes below the horizon for a time during the summer. Depending on how far north you are, it can last days or weeks around the summer solstice. At the North Pole, there are six months of daylight, followed by six months of night. Poor Santa! Anyway, the Arctic Circle marks the line where midnight sun begins. If you live right on that line (about 66.5 degrees north), you will have exactly one 24-hour period a year of total sunlight, on the solstice. (And one 24-hour period of darkness on the winter solstice.) The Antarctic Circle does the same thing in the south, but nobody lives south of the Antarctic Circle except scientists on stations in Antarctica.

I like to think that this divides the world into three distinct segments:

1. The Oh My God It’s Too Hot Zone between the Tropics. I mean, come on. That’s just hot. And I can’t stand sunny days. (This zone, by the way, is 47 degrees of latitude wide.)
2. The Why Won’t the Sun Go Away? Zones between the Poles and the Circles. I mean, come on. That sounds terrible. No night at all? (Or no day at all six months later?) That hurts.
3. The Thank Goodness for Temperate Zones in between. You know, where I’ve always lived. So of course I like this one best — it’s what I know.