1. Determining Latitude 90°
90° 
The position of the north star relative to the horizon depends on my latitude. At the north pole, it’s directly overhead (90 degrees from the horizon)
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2. Determining Latitude 40°
40° 
The position of the north star relative to the horizon depends on my latitude. At the 45 degrees lat, it’s 45 degrees above horizon
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3. Determining Latitude 0°
The position of the north star relative to the horizon depends on my latitude. At the equator, it’s at horizon
0° 
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4. Determining Latitude 90° 40° 0°
90° 
40° 
0° 
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5. Determining Latitude When the North Star is at 90°
You must be at the North Pole (Latitude = 90°)

6. Determining Latitude When the North Star is at 45°
You must be at the halfway (Latitude = 45°)

7. Determining Latitude When the North Star is on the horizon
You must be at the equator (Latitude = 0°)

8. Determining Longitude
30°
20° 0°
10°
While there must be one and only one equator (90 degrees from each pole), where we put the prime meridian is inconsequential
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9. Determining Longitude0°
10°
20°
30°
While there must be one and only one equator (90 degrees from each pole), where we put the prime meridian is inconsequential
Image:

10. Determining Longitude0°
10°
20°
30°
While there must be one and only one equator (90 degrees from each pole), where we put the prime meridian is inconsequential
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11. What is my Longitude? Boston, MA Greenwich, England Sun: noon
So if we choose zero as Greenwich, England, then TIME is the method of calculating how far we are away from the prime meridian. In NYC, 5 hours behind the time in Greenwich, we are at (5 hours) * (360 degrees / 24 hours) = 75 degrees West
Boston, MA
Greenwich, England
Sun: noon
Sun: noon
Watch: 5:00 pm
Watch: noon
Image by Strebe

12. What must my current longitude be?
“Speed” of the Sun
360° 𝑑𝑎𝑦 = 15° ℎ𝑟
The sun is at the “noon” position, but my watch says it’s 5:00pm in Greenwich, England (0° longitude).
What must my current longitude be?

13. What is my Longitude? 60° 30° 0° 75° 45° 15° Boston, MA 1 hr
So if we choose zero as Greenwich, England, then TIME is the method of calculating how far we are away from the prime meridian. In NYC, 5 hours behind the time in Greenwich, we are at (5 hours) * (360 degrees / 24 hours) = 75 degrees West
Boston, MA
1 hr
Greenwich, England
Sun: noon
Sun: noon
Watch: 5:00 pm
Watch: noon
Image by Strebe

14. Try it out!
What is your longitude if your Greenwich watch says 10:30am but the sun is at local noon?
In what city is the Sun in the noon position when it is 4pm in Boston (longitude 75°)?
2 hours before = 22.5 degrees East of Greenwich = Sweden, Poland, Greece, Libya, Rwanda, South Africa
4pm Boston = 9pm Greenwich which means the sun has traveled 135 degrees from Greenwich noon. It’s now noon at 135 degrees West  Juneau, Alaska