Or a Loony Game?

You're a contestant in a game. The game is simple enough: be the first among ten contestants  dropped "in the middle of nowhere" to figure out where you are. The only rules? No tools: nothing except camping gear. You and your gear have been x-rayed to make sure you don't have a GPS receiver or other electronics hidden away anywhere. AND the other rule: you can't ask anyone you meet where you are. You can talk to them if you know their language, learn about their ways, but you can't ask where you are. And everyone has been given a rolled-up wall-size map of the world so that the contestants can ponder the possibilities...

You have been picked up in Dallas, Texas on January 23, 2004 at Noon. To keep you guessing, you're kept in a darkened airplane cabin and allowed to sleep. Many hours (or is it a day or two?) later, you are blindfolded and transferred to a helicopter and fly on further. At last, still more hours later, you land and the blindfold is removed. You're on an island! You smell saltwater. You see seagulls. The island seems green and fertile but rocky and certainly it's no tropical paradise. And so the game begins...

Good celestial navigator that you are, you've decided to "cheat". Tucked in your sleeping bag, you've brought with you five carefully folded pages from the Nautical Almanac covering the next week. You aim to win the game before anyone else has even started.

Your Almanac Pages

After finding a good campsite away from the other contestants, you begin your survey of the sky. It's late afternoon and the Sun is headed towards the horizon. As the Sun sets, you spot the thin crescent Moon in the west. Right away you have useful info. The Moon is well to the right of the Sun as you face towards the West. There can be only one conclusion.

Just as the last bit of the Sun dips below the horizon, you look up in the sky and realize that you may have an excellent estimate of your location within just a few hours. Hanging there in the west below the Moon, you see a brilliant star. It must be Venus! It's just a short distance from the Moon, and it's already visible at the moment of sunset. Here's what you see right at sunset (to scale and oriented correctly --Venus is at "5 o'clock" from the Moon):

You get out your almanac pages using them as a crude crossstaff to measure the distance between the Moon and Venus as best you can. How accurate would that be? You note the distance in some units (lines of text on the Almanac page held at arm's length?) and make a quick sketch that would roughly resemble the image above. Later you'll be able to determine that the distance from the Moon's center to Venus is just about 2.5 degrees... maybe a little more, maybe less.  You're hoping you've remembered everything you'll need to turn this observation into a longitude. But before you can think about that, you also need your latitude.

Latitude should be easy. You've got that table of navigational stars on every other page of the Almanac, so it's just a matter of finding one in the right part of the sky. After twilight, it's immediately apparent you're in the southern hemisphere. The North Star is nowhere to be seen. You decide to locate the zenith as best you can with an improvised plumb line. You set up your sleeping bag and wait. Late that night, you see Sirius and Canopus pass high overhead on opposite sides of the zenith with Canopus roughly 45% of the total distance from the zenith (45% of the total distance between Sirius and Canopus, that is). With that, you've got all the information you need. You turn on your flashlight and start drawing and figuring.

Where are you? How sure can you be of your position?

I present this problem as an example of complete position determination using nothing but the Almanac. You can get latitude and longitude within certain limits based on the information provided. The probability that anyone would just happen to have a Nautical Almanac handy in any realistic scenario is very low. That's why I've imagined the game above.

You don't need to know much about celestial navigation to resolve this puzzle. You need to understand the basics and understand them well. Enjoy.

-FER
Dec. '03