2011-06-29

Survival Guide: Tell time using the stars

Whenever technology is not immediately available, I try to tell time using the stars. When I say stars I mean either the one closest to us (aka the Sun) or those further away. In today's survival guide, I'm going to show you how to estimate the time using only the stars and a bit of math.

(As I have mentioned in previous Survival Guides, if you are unable to use the techniques below due to weather conditions, I strongly suggest that you be less concerned with the current time and focus instead on quickly finding shelter nearby.)

NORTHERN HEMISPHERE
STEP 1: Find the star Polaris (North Star) and the constellation Ursa Major (Big Dipper). [help]
STEP 2: Imagine a straight line from Polaris drawn through the two stars of Ursa Major which are furthest away from its tail.
STEP 3: Imagine that the line is the hour hand of a clock with Polaris at its center. Estimate what time the hand falls on. For example:
If the line to the two stars is perfectly level to the right, that would be 3:00.
If the line is midway between the bottom and level at right, that would be roughly 4:30.
STEP 4: Add an hour for every month that has passed since March 7th and the current month's 7th. Or subtract an hour for each month between this month's 7th and the approaching Marth 7th.
(For additional accuracy you can add or subtract two minutes for each day before or after the seventh of each month.)
Some examples:
- At midnight on March 7th, our hour hand is also at midnight. So, this is our zero date (in the Northern Hemisphere).
- November 7th is eight months after March 7th, so 8 hours are added to our STEP 3 time.
- January 2nd is two months and five days before our zero date, so we subtract two hours and ten (5*2) minutes from our STEP 3 time.
- March 10th is three days after March 7th so we add six (3*2) minutes to the STEP 3 time.
STEP 5: Double the STEP 4 time. (e.g. 3:00 * 2 = 6:00, 4:30 * 2 = 9:00, 7:45 * 2 = 15:30)
STEP 6: Subtract the STEP 5 time from 24. (Subtract it from 48, if it is initially larger than 24.)
STEP 7: This is the estimated current time. You may choose to make local adjustments (e.g. AM/PM, daylight saving time, timezones, etc.)

SOUTHERN HEMISPHERE
STEP 1: Find the Southern Cross constellation and the pole (imaginary southern point). [help]
STEP 2: Imagine a straight line from the pole drawn through the two stars of the long bar of the Southern Cross.
STEP 3: Imagine that the line is the hour hand of a clock with the pole at its center. Estimate what time the hand falls on. For example:
If the line to the two stars is perfectly level to the right, that would be 3:00.
If the line is midway between the bottom and level at right, that would be roughly 4:30.
STEP 4: Add two hours for every month that has passed since March 29th and the current month's 29th. Or subtract two hours for each month between this month's 29th and the approaching Marth 29th.
(For additional accuracy you can add or subtract four minutes for each day before or after the twenty-ninth of each month.)
Some examples:
- At midnight on March 29th, our hour hand is also at midnight. So, this is our zero date (in the Southern Hemisphere).
- March 19th is ten days before March 29th, so we subtract forty (10*4) minutes from the STEP 3 time.
- June 29th is three months after March 29th, so we add six (3*2) hours to the STEP 3 time.
STEP 5: Double the STEP 4 time. (e.g. 3:00 * 2 = 6:00, 4:30 * 2 = 9:00, 7:45 * 2 = 15:30)
STEP 6: Subtract the STEP 5 time from 24. (Subtract it from 48, if it is initially larger than 24.)
STEP 7: This is the estimated current time. You may choose to make local adjustments (e.g. AM/PM, daylight saving time, timezones, etc.)
Discerning the time from the stars can be a useful skill in non-emergency situations, though it may not be of high importance in circumstances where your survival is threatened. However, it can be a welcomed distraction when needed to keep yourself calm while facing a mentally stressful situation while trying to survive in the wild.
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