1. TIME!!!

2. Time-keeping on earth is tied to rotation and revolution.

3. A year is
The time the earth takes to orbit the sun days

4. A day is
The earth ROTATING once.

5. A month is
(roughly) one orbit of the moon.

6. Time of Day: It takes about 24 hrs for the earth to rotate once.
Since there are 360⁰ a circle, the Earth turns 15⁰ in one hour.

7. This means an hour difference for each meridian.

8. a.m. means “ante (before) meridian” P.M. means “post (after) meridian”
Note:
a.m. means “ante (before) meridian” P.M. means “post (after) meridian”

9. Since the earth rotates west to east,
points to the east of us go into the sun’s light first.

10. Since points to the west enter the sun’s light after we do…
Their dawn happens later—their time is behind ours.

12. GENERAL RULE: Time changes one hour for every meridian crossed.
Going East—ADD an hour.
Going West, SUBTRACT an hour.

13. THE PROBLEM:
If we keep adding and subtracting hours, we will wind up in the future or the past!

14. OR….
Two dates at the same location!

15. SOLUTION:
The international date line—the meridian at 180⁰ (E or W) , adjusts dates adds or subtracts days to avoid such problems.

16. Add day
I.D.L W E
P.M

17. As you ponder the problems, keep in mind:
12 P.M. is noon (midday)
12 a.m. is midnight, considered the beginning of the new day.