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Trivia Question of the Day
Astronomy Picture of the Day
Lesson 6:
Celestial Motions
Celestial Motions:
The Celestial Sphere
► Imagine
all of the stars
moved down onto a
big glass sphere
around the Earth
► Celestial sphere does
NOT move
► Earth rotates counterclockwise (as viewed
from above the North
Pole)
Celestial Motions:
The Celestial Sphere
► Effect
1: Stars appear
to rise in the East,
move westward, and
set in the West
*Zenith*: The highest
point in the sky that a
star reaches
Challenge Question
Celestial Motions:
The Celestial Sphere
► Effect
2: When we look up,
we see the stars “fixed” on
the celestial sphere AND
rotating counter-clockwise
Celestial Motions:
The Earth’s Rotation
 Earth is constanty rotating, or
spinning, counter-clockwise
around its axis
 Axis: imaginary line between
the North and South Poles
 Axis is tilted 23.5°
 Axis is pointed towards Polaris
(North Star)
 Rotates 360° in 24 hours
***Challenge Question***
How many degrees is that per
hour???
15° per hour
 Earth’s Rotation
Celestial Motions:
The Earth’s Rotation
*Evidence*
► 1. Foucault Pendulum
 When swings freely, path APPEARS to change in
a predictable way
 Recall: Time-lapsed Motion of a Foucault
Pendulum
 What causes this apparent change in motion?
►Pendulum
swings in a fixed direction but Earth
rotates under the pendulum
No force is making the pendulum rotate – so
it must be the Earth that is rotating!!!
Celestial Motions:
The Earth’s Rotation
*Evidence*
►2. Coriolis Effect
 The deflection, or curving, of all moving
objects (air, water, planes, rockets) at the
Earth’s surface
 Caused by Earth’s surface rotating with
respect to the objects
►Northern
Hemisphere: Deflection to the Right
►Southern Hemisphere: Deflection to the Left
In the Northern Hemisphere…
In the Southern Hemisphere…
Challenge Question
FYI…
Earth’s Rotation and Time Zones
► Time
Zones
 Created so that each region in the world could
have a standard time
 24 separate time zones in 15°-wide bans exist
***Challenge Question***
Why 15°-wide bans?
Earth rotates 360° in 24 hours, so each
15°-wide ban has a time difference of one hour
Earth’s Rotation and Time Zones
Celestial Motions:
The Earth’s Revolution
 Earth is constanty revolving, or orbiting, counterclockwise around the Sun
 Earth’s orbit is an ellipse
***Challenge Question 1***
What is Earth’s period of revolution?
365.25 days
***Challenge Question 2***
What does the extra .25 days result in?
Leap years
 Earth’s Revolution
Challenge Question
Celestial Motions:
The Earth’s Revolution
*Evidence*
► 1.
Seasons
 Caused by Earth’s tilt and Earth’s revolution
around the Sun
 If Earth did not revolve around the Sun, the
same part of Earth would tilt toward the Sun all
the time
Important Dates in the Northern
(Southern) Hemisphere
Name
Dates
Characteristic
Summer (Winter)
Solstice
June 20, 21
- Most (least) hours
of daylight
- Sun directly over
Tropic of Cancer
(23.5°N)
Fall/Autumnal
(Spring/Vernal)
Equinox
Winter (Summer)
Solstice
Spring/Vernal
(Fall/Autumnal)
Equinox
September 22,
23
-
Equal (12) hours of
day and night
- Sun directly over
Equator (0°)
December 21,
22
-
March 20, 21
-
Least (most) hours
of daylight
- Sun directly over
Tropic of
Capricorn (23.5°S)
Equal (12) hours of
day and night
- Sun directly over
Equator (0°)
Picture
Challenge Question
Celestial Motions:
The Earth’s Revolution
*Evidence*
►2. Changing Constellations
 Constellations:
►A
group of stars that form a pattern in the
sky
►Are used to help people locate celestial
objects
 Different constellations can be seen
during each of the four seasons
Celestial Motions:
The Earth’s Revolution
*Evidence*
►
3. Sun’s Changing Apparent
Diameter
 As the Earth revolves around the
Sun, its changing distance
causes the sun’s size to APPEAR
to change
 Sun appears largest when Earth
is closest… When is That?
►January 3
 Sun appears smallest when
Earth is farthest away… When is
That?
►July 4
Celestial Motions:
The Earth’s Revolution
*Evidence*
► 4.
Doppler Effect of Stars
 As the Earth revolves around
the Sun, it travels
►TOWARDS
certain stars for half
the year
►AWAY from those stars for the
other half of the year
 Results in small yearly cyclic
(happening on a cycle) changes
in the blue- and red-shifts of
starlight
Celestial Motions: The Earth
Challenge Questions
Celestial Motions: The Earth
Challenge Questions
 What would happen if Earth revolved
around the Sun but was NOT tilted?
 What would happen if Earth did NOT
revolve around the Sun but was tilted?