Tuesday, August 5, 2008

How to Tell Time Without a Clock

For many people, knowing the correct time is vital to everyday life. If you're in an unfamiliar environment without any kind of clock, however, figuring out the time could be a matter of safety and survival. Without a clock or watch, finding the exact time may not be possible, but you can figure the approximate time using the sun, moon or stars.
[edit] Steps
Sun Position

1. Make note of the position of the sun. If you're in the northern hemisphere, face the south; if you're in the southern hemisphere, face north. (If you don't have a compass, use one of these techniques.) In other words, look at the equator--that is the line the sun generally follows in the sky. It always rises in the east (which is to your left if you're facing south, to your right if you're facing north) and sets in the west.

* If the sun is in the exact center of the sky, it's exactly noon. A nickname for this is "high noon" because the sun is at its highest at noon and the time will be 12:00 PM, but this assumes no daylight saving time, and that you're in the middle of your time zone. For instance, in Salt Lake City, Utah (US), "high noon" is actually at 1:30 PM in the summer because there's an hour added by daylight saving and another thirty minutes added because the city is that time distance (west) away from the center of the time zone.[1]
* If the sun is not in the exact center, you will have to do more figuring. If it is morning, the sun will be in the eastern half of the sky. If it is afternoon, the sun will be in the western half. You can use fractions to divide the sky into hours, and find the approximate time.
2. Estimate the number of hours between sunrise and sunset. This varies depending on the season and location. Winter days are shorter than summer ones: about ten and fourteen hours, respectively. Spring and fall days tend to be about twelve hours long, especially close to the equinox (late March or late September).
3. Divide the sun's path into segments. If you're looking towards the equator, you can imagine the sun following an imaginary arc from east to west, beginning and ending at the horizon, even if it's obscured. Visualize dividing that arc into equal segments; the number of segments should equal the number of hours in the day. If you know there are twelve hours in a day, you would divide the arc into twelve equal parts, six on the eastern half and six on the western half.

* If you're having trouble visualizing the sky in segments, you can use your hand or fist to "measure" segments. Going hand over hand, count the amount of fists from one end of the arc to the zenith (the highest point of the sky). Take that number as half of a day. For instance, if you counted 9 fists, and you know the day is 12 hours long, nine fists would be equal to six hours. To figure out how much time each fist represents, divide the number of hours by the number of fists. One fist, then would equal 6 divided by 9 - or about 2/3 hours (40 minutes). This is your hours-per-fist.
4. Determine which segment the sun is in. Starting in the east, count how many segments there are before you get to the segment that the sun is in. That will tell you how many daytime hours have passed. The segments that the sun hasn't touched yet indicate how many daytime hours are remaining. If you know the time of high noon, sunrise, or sunset in your area, then you can approximate the current time.

* Using the Salt Lake City example given earlier, let's say there are fourteen segments (because it's summer) and the sun is on the ninth segment (from the east). The eighth segment (right after the highest point) begins at 1:30 PM. The ninth segment begins one hour after that, so if the sun is in the ninth segment, it's probably between 2:30 and 3:30 PM. If the sun was in the sixth segment, the time would be between 11:30 AM and 12:30 PM. With practice, you'll be able to estimate time without consciously dividing the sky.
* If you used the fists method, count the number of fists from the eastern end of the arc to the sun. Multiply that number times the hours-per-fist measurement. Let's say you counted three fists from east to west. Three hours times forty minutes equals 120 minutes, or two hours. So it's been two hours since sunrise. If you know the time of sunrise in your area and season, you can approximate what time it is.

Reading the Moon[2]

1. Find the moon. If the moon is full, stop here and follow the instructions for telling time based on sun position. If it's a new moon (i.e. you can't see the moon) this technique will not work.
Imagine the moon is a circle divided into vertical strips. The number of vertical strips equals the number of hours in the night, with the first hour at the right edge and the final hour at the left edge. As discussed earlier, the number of nighttime hours can vary by season and location. Let's assume twelve hours, beginning at 6 PM and ending at 6 AM, for now.
3. Read the moon from right to left, following an imaginary horizontal halfline. Look for where that line intersects the border between light and dark. Make note of which strip that intersection is in. If as you read from right to left, the moon goes from light to dark, that strip where the intersection is located tells you when the moon will set in the west (moonset). If the transition is from dark to light, then you can determine when the moon will rise in the east (moonrise).

In this instance, the intersection is at 8 PM, and the transition from right to left is from light to dark. This tells us that the moon will set in the west at 8 PM.
This moon will set at about 7-8 hours after sunset. If sunset is at 7 PM, you can expect moonset at 2-3 AM.
* If the moon is just a tiny sliver on the right, it sets within an hour or two since the night began. If you see it, you're probably within the first hour or two of nighttime, since the moon hasn't set yet.
* If the moon is just a tiny sliver on the left, it rises within an hour or two before dawn. If you see the moon in this phase, you can expect the night to be over within one or two hours.
4. Observe the moon's position in the sky. Divide the moon's path into segments, as described for the sun above. For the purposes of this example, let's assume twelve equal segments for twelve hours in the night.

* If you know the moonrise time, estimate how many hours (segments) it already passed since it rose in the east. Add those hours to the moonrise time to get your current time. If you know the moon rose at 9PM, for example, and it's right in the middle of a 12 hour path, that means it's completed 6 hours since it rose at 9 PM. 6 hours after 9 PM is 3 AM.
* If you know the moonset time, estimate how many hours (segments) it has to go before it sets in the west. Let's say you know the moon will set at 2 AM in the west. If the moon is positioned about 2 segments away from the western end of the arc, that means it has two hours before it sets. Two hours before moonset (2 AM) is 12 AM (midnight).

North Star Clock

1. Locate the Big Dipper constellation. You'll only be able to do this in the northern hemisphere and if the skies are clear. In the summer, the Big Dipper will be closer to the horizon.
2. Determine the raw time. The two pointers in the Big Dipper (the two stars furthest away from the handle) are in line with the North Star (Polaris). This line is like a clock hand, with Polaris at the center of the clock; as you look North, 12 is at the top of the clock, and 6 is at the bottom. When you imagine this clock, what time is it? Let's say the "hand" falls at 2:30. This is the raw time.

3. Add one hour for every month after March 7. Likewise, subtract one hour for every month before March 7. If it's May 7, two months after March 7, then you'd add two hours to your raw time, making it 4:30. To be more exact, add or subtract two minutes for every day after or before the 7th, respectively. If it's February 2, it's one month and five days before March 7, so you'd subtract one hour and ten minutes from 2:30 (making it 1:20).

* The reason we focus on March 7 is because the star clock always reads 12:00 at midnight on this date, so this is our "base" date, and we have to "adjust the clock" for any other date.
4. Double the time.
5. Subtract the time from 24. If the time from the previous step is more than 24, then subtract it from 48. We do this because the clock actually goes backwards (counterclockwise) and this subtraction corrects for that. The result will be the real time, given in military time. That means that if your result is more than 12, you can convert it to PM.
6. Correct for daylight saving time and time zone variation. If daylight saving time is in effect, add an hour. If you live close to the western edge of your time zone, add a half hour. Likewise, if you live on the eastern edge of your time zone, subtract half an hour. Now you know the time!

[edit] Tips

* If you have the time and materials, you can build a temporary sundial with which to tell time.
* Telling time based on the position of the sun becomes more difficult if you are in a region where the difference between daylight hours and nighttime hours can be dramatic, such as if the sun doesn't set at all for part of the summer. Scandinavians and tribes in the Americas used "daymarks"--they associated the position of the sun in relation to a fixed landmark with a certain time of day.[3]
* Don't forget to correct for daylight saving time.
* Don't stress out about exact numbers. Because of latitude and longitude, the numbers might not be exact anyway. Just use this as a handy estimation tool when you're on a hike or out in your backyard.

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