Time and Place

1
Time and Place

• Learning Goals
• Understand the Cartesian Coordinate system
• Define and explain latitude and longitude
• Understand how the different motions of the Earth
  and Moon create the day (solar and sidereal), the
  month and the year
• Explain the Earths seasons and their cause
• Describe the precession of the Earths axis and
  its consequences

2
Coordinate System

• There are 3 dimensions you need 3 coordinates
  to locate precisely an object
• As many origins as there are coordinates
• Cartesian coordinates at a right angle
• At the surface of the Earth, 1 coordinate is
  fixed (surface), the other two are necessary
• Latitude
• Origin the equator, halfway between the poles
• Angular measurement in degrees north or south of
  the equator
• Longitude
• Origin Greenwich, or prime meridian
• Angular measurement in degrees east or west of
  the prime meridian

3
Diagram Showing Latitude and Longitude of
Washington, D.C.
Section 15.2
4
Time

• The second is the standard unit of time
• Defined in terms of the emitted frequency of
  Cs-133
• A day can either be
• Solar Defined to be 24h time it takes the SUN
  to come back to the same position
• Sidereal time it takes a STAR to come back to
  the same position

5
Solar and Sidereal days are different because the
Earth goes around the Sun!
6
Lecture Tutorial on Sidereal VS Solar Day

• Work with TWO partners, no more, no less!
• Read the instructions and questions carefully
• Talk to each other and discuss your answers with
  each other
• Come to a consensus answer you both agree on
• If you get stuck or are not sure of your answer
  ask another group
• If you get really stuck or dont understand what
  the Lecture Tutorial is asking ask me for help!

7
Standard Time Zones

• The earth is divided into 24 time zones, each
  containing approx. 15o of longitude or 1 hour.
• How many degrees does the Earth rotate in 1
  hour?
• The first time zone begins at the prime meridian
  and extends approximately 7.5o both east and
  west.
• The centers of each time zone are multiples of
  15o.
• The longitude opposite Greenwich is the
  International Date Line
• Going West same hour tomorrow
• Going East same hour yesterday

Section 15.3
8
(No Transcript)
9
Finding the Standard Time and Date at Another
Location

• It is 6 A.M. on March 21 in Los Angeles (34oN,
  118oW). What are the time and date in Perth,
  Australia (32oS, 115oE)?
• Construct a circle with 24 even divisions on it.
• These divisions represent 15o increments of a
  full circle and each hour of the day.
• Los Angeles falls in the time zone with the 120oW
  central meridian
• Within 7.5o of the central meridian
• Perth falls in the time zone with the 120oE
  central meridian.

Section 15.3
10
(No Transcript)
11
Suns Position in the Daytime Sky

• The Suns noontime altitude changes throughout
  the year due to the Earths inclination of its
  polar axis
• Lowest altitude winter solstice
• Highest altitude summer solstice
• Only reaches the ZENITH for latitudes between
  23.5o latitude
• Tropic of Cancer the parallel at 23.5o N
• Tropic of Capricorn the parallel at 23.5o S

12
The noon-time position of the Sun goes from being
above 23.5oN on June 21st, to - 23.5oS on
December 21st and back again in a year The Sun
travels 23.5o23.5o23.5o23.5o 94.0o in
365.25 days 94.0o/365.25 days0.257o/days
This is an APPROXIMATION! The speed of the Earth
around the Sun is NOT constant
13
Seasons

• Caused by the Earths tilt
• Any planet with a tilt will experience seasons
• The closer you are to the equator, the less
  difference you notice between seasons
• Summer longer days, more direct rays from the
  Sun
• Starts on June 21st in the northern hemisphere
• Starts on December 21st in the southern
  hemisphere
• Winter shorter days, grazing rays at the surface
• Starts on December 21st in the northern
  hemisphere
• Starts on June 21st in the southern hemisphere
• Spring and Fall
• Intermediate period, where on the Equinoxes the
  night and days are of equal length.

14
Class Action Season Simulator!!!
15
(No Transcript)
16
Lecture tutorial on the Seasons
Class action questions 10 Suns Ray 23
Seasons contributor(s) Challenge 2 Sun at the
Zenith
17
Calendar (Gregorian)

• Days Solar day, time it takes the Sun to come
  back to its southernmost position
• Month linked to the time it takes the Moon to
  complete a full set of phases, 29.5 days
• Year based on the time it takes the Earth to
  complete one revolution around the Sun, 365.2422
  days
• Leap year to sum up the 0.25 year left over
• Every 400 years, 3 leap years are skipped

18
Precession

• The Earths rotation axis changes its orientation
  on a 26,000yrs cycle

19
Homework on Chapter 15

• Short-answer question
• 4, 5, 15, 17, 28
• Applying you Knowledge
• 5
• Exercises
• 18, 20