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