Units of Time Based on Astronomical Motions and Objects
Day:New: Time required for the earth to complete one rotation.
Week: Based on 7 celestial bodies observable to ancients, Sun Moon, and 5 planets: Mercury, Venus, Mars, Jupiter, and Saturn.
Month: Based on time for Moon to complete one set of phases.
Year: New: Time required for Earth to complete one orbit around the Sun. 1 year = 365.24 days
The calendar year usually has 365 days. To account for the .24 days, once every four years there are 366 days, with the extra day added to the month of February.This is called a Leap Year
A Leap Year is any year exactly divisible by 4 and/or any century year exactly divisible by 400.
Old: Time between two consecutive sunrises
Old: Time for one cycle of the seasons
12 Noon Local Solar Time
Your Meridian
Sun rises in the eastand moves westward
Post Meridian, PMAnte Meridian, AM
Local Solar Time, LST
Your Meridian
One Solar Day
. . .
Time Zones•Differ by One Hour
•24 Time Zones
•Based on Longitude
•15° of Longitude in width
•Time equal to LST at central meridian of time zone
•1st Time zone centered on the Prime Meridian
(24 hours in one day)
(sun appears to move from east to west)
(earth spins 15° in one hour)1rev
24hrs= 360°
24hrs= 15°
1hr
7.5°W 7.5°E
15°E15°W
75°W90°W120°W105°W
67.5W82.5W97.5W112.5W127.5W PST MST CST EST90W105W120W
12 NOON11 AM10 AM9 AM
U.S. TIME ZONES
Sun
67.5W82.5W97.5W112.5W127.5W PST MST CST EST90W105W120W
12 NOON
U.S. TIME ZONES
Sun
1 PM11 AM10 AM
67.5W82.5W97.5W112.5W127.5W PST MST CST EST90W105W120W
12 NOON11 AM
U.S. TIME ZONES
Sun
1 PM 2 PM
67.5W82.5W97.5W112.5W127.5W PST MST CST EST90W105W120W
12 NOON
U.S. TIME ZONES
Sun
1 PM 2 PM 3 PM
Traveling Westward Go Back One Hour For Each
Time Zone Crossed
Traveling Eastward Go Ahead One Hour For Each
Time Zone Crossed
1:00PM 9/15 Atlanta, GA (EST)
___________ Tokyo, Japan (141°E)
7:00 AM 9/15 Beijing (Peking), China
_____________ London, England 0°E
116°E
3:00AM 9/16
11:00PM 9/14
Atlanta, GA Tokyo, Japan
Moving Eastward, Moving Ahead in Time
W E
?
W E
Beijing, ChinaLondon, England
?
Traveling WestwardGo Back in Time
1:00PM 9/15 Atlanta, GA (EST)
___________ Tokyo, Japan (141°E)
7:00 AM 9/15 Beijing (Peking), China
_____________ London, England 0°E
116°E
3:00AM 9/16
11:00PM 9/14