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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 counter- clockwise (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 Earth’s Rotation 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 Time-lapsed Motion of a Foucault PendulumTime-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, counter- clockwise around the Sun  Earth’s orbit is an ellipse ***Challenge Question 1*** What is Earth’s period of revolution? days ***Challenge Question 2*** What does the extra.25 days result in? Leap years  Earth’s Revolution Earth’s Revolution Earth’s Revolution

Challenge Question

Celestial Motions: The Earth’s Revolution *Evidence* ► 1. Seasons 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 NameDatesCharacteristicPicture 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 September 22, 23 -Equal (12) hours of day and night -Sun directly over Equator (0°) Winter (Summer) Solstice December 21, 22 -Least (most) hours of daylight -Sun directly over Tropic of Capricorn (23.5°S) Spring/Vernal (Fall/Autumnal) Equinox March 20, 21-Equal (12) hours of day and night -Sun directly over Equator (0°)

Challenge Question

Celestial Motions: The Earth’s Revolution *Evidence* ► 2. Changing Constellations Changing ConstellationsChanging 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

 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?