Trivia Question of the DayTrivia Question of the Day

Astronomy Picture of the DayAstronomy Picture of the Day

Lesson 6: Lesson 6: Celestial Celestial MotionsMotions

Celestial Motions:Celestial Motions:The Celestial SphereThe Celestial Sphere

► Imagine all of the Imagine all of the stars moved down stars moved down onto a big glass onto a big glass sphere around the sphere around the EarthEarth

► Celestial sphere does Celestial sphere does NOT moveNOT move

► Earth rotates Earth rotates counter-clockwise counter-clockwise (as viewed from (as viewed from above the North above the North Pole)Pole)

Celestial Motions:Celestial Motions:The Celestial SphereThe Celestial Sphere

► Effect 1:Effect 1: Stars Stars appear to rise in the appear to rise in the East, move East, move westward, and set westward, and set in the Westin the West

**ZenithZenith*: The highest *: The highest point in the sky that point in the sky that a star reachesa star reaches

Challenge QuestionChallenge Question

Celestial Motions:Celestial Motions:The Celestial SphereThe Celestial Sphere

► Effect 2:Effect 2: When we look When we look up, we see the stars up, we see the stars “fixed” on the celestial “fixed” on the celestial sphere AND rotating sphere AND rotating counter-clockwisecounter-clockwise

Celestial Motions:Celestial Motions:The Earth’s RotationThe Earth’s Rotation

Earth is constanty rotating, Earth is constanty rotating, or spinning, counter-or spinning, counter-clockwise around its axisclockwise around its axis

Axis: imaginary line between Axis: imaginary line between the North and South Poles the North and South Poles

Axis is tilted 23.5°Axis is tilted 23.5° Axis is pointed towards Axis is pointed towards

Polaris (North Star)Polaris (North Star) Rotates 360° in 24 hoursRotates 360° in 24 hours

***Challenge Question******Challenge Question***How many degrees is that per How many degrees is that per

hour???hour???15° per hour 15° per hour

Earth’s RotationEarth’s Rotation

Celestial Motions:Celestial Motions:The Earth’s RotationThe Earth’s Rotation

*Evidence**Evidence*►1. Foucault Pendulum1. Foucault Pendulum

When swings freely, path APPEARS to When swings freely, path APPEARS to change in a predictable waychange in a predictable way

Recall: Time-lapsed Motion of a Foucault Recall: Time-lapsed Motion of a Foucault PendulumPendulum

What causes this apparent change in What causes this apparent change in motion?motion?►Pendulum swings in a fixed direction but Earth Pendulum swings in a fixed direction but Earth

rotates under the pendulumrotates under the pendulum

No force is making the pendulum rotate No force is making the pendulum rotate – so it must be the Earth that is – so it must be the Earth that is

rotating!!!rotating!!!

Celestial Motions:Celestial Motions:The Earth’s RotationThe Earth’s Rotation

*Evidence**Evidence*►2. Coriolis Effect2. Coriolis Effect

The deflection, or curving, of all moving The deflection, or curving, of all moving objects (air, water, planes, rockets) at objects (air, water, planes, rockets) at the Earth’s surfacethe Earth’s surface

Caused by Earth’s surface rotating with Caused by Earth’s surface rotating with respect to the objectsrespect to the objects►Northern Hemisphere: Deflection to the Northern Hemisphere: Deflection to the

RightRight►Southern Hemisphere: Deflection to the Southern Hemisphere: Deflection to the

LeftLeft

In the Northern Hemisphere…In the Northern Hemisphere…

In the Southern In the Southern Hemisphere…Hemisphere…

Challenge QuestionChallenge Question

FYI…FYI…Earth’s Rotation and Time Earth’s Rotation and Time

ZonesZones►Time ZonesTime Zones

Created so that each region in the world Created so that each region in the world could have a standard timecould have a standard time

24 separate time zones in 15°-wide bans 24 separate time zones in 15°-wide bans existexist

***Challenge Question******Challenge Question***

Why 15°-wide bans?Why 15°-wide bans?

Earth rotates 360° in 24 hours, so each Earth rotates 360° in 24 hours, so each

15°-wide ban has a time difference of one 15°-wide ban has a time difference of one hour hour

Earth’s Rotation and Time Earth’s Rotation and Time ZonesZones

Celestial Motions:Celestial Motions:The Earth’s RevolutionThe Earth’s Revolution

Earth is constanty revolving, or orbiting, counter-Earth is constanty revolving, or orbiting, counter-clockwise around the Sunclockwise around the Sun

Earth’s orbit is an ellipseEarth’s orbit is an ellipse

***Challenge Question 1******Challenge Question 1***What is Earth’s period of revolution?What is Earth’s period of revolution?

365.25 days365.25 days

***Challenge Question 2******Challenge Question 2***What does the extra .25 days result in?What does the extra .25 days result in?

Leap yearsLeap years Earth’s RevolutionEarth’s Revolution

Challenge QuestionChallenge Question

Celestial Motions:Celestial Motions:The Earth’s RevolutionThe Earth’s Revolution

*Evidence**Evidence*

►1. Seasons1. Seasons Caused by Earth’s tilt and Earth’s Caused by Earth’s tilt and Earth’s

revolution around the Sunrevolution around the Sun If Earth did not revolve around the Sun, If Earth did not revolve around the Sun,

the same part of Earth would tilt toward the same part of Earth would tilt toward the Sun all the timethe Sun all the time

Important Dates in the Northern Important Dates in the Northern (Southern) Hemisphere(Southern) Hemisphere

Name Dates Characteristic Picture

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 QuestionChallenge Question

Celestial Motions:Celestial Motions:The Earth’s RevolutionThe Earth’s Revolution

*Evidence**Evidence*►2. Changing Constellations2. Changing Constellations

Constellations: Constellations: ►A group of stars that form a pattern in A group of stars that form a pattern in

the skythe sky►Are used to help people locate celestial Are used to help people locate celestial

objectsobjects Different constellations can be seen Different constellations can be seen

during each of the four seasonsduring each of the four seasons

Celestial Motions:Celestial Motions:The Earth’s RevolutionThe Earth’s Revolution

*Evidence**Evidence*

► 3. Sun’s Changing Apparent 3. Sun’s Changing Apparent DiameterDiameter As the Earth revolves around As the Earth revolves around

the Sun, its changing the Sun, its changing distance causes the sun’s distance causes the sun’s size to APPEAR to change size to APPEAR to change

Sun appears largest when Sun appears largest when Earth is closest… When is Earth is closest… When is That?That?►January 3January 3

Sun appears smallest when Sun appears smallest when Earth is farthest away… Earth is farthest away… When is That?When is That?►July 4 July 4

Celestial Motions:Celestial Motions:The Earth’s RevolutionThe Earth’s Revolution

*Evidence**Evidence*

► 4. Doppler Effect of Stars4. Doppler Effect of Stars As the Earth revolves As the Earth revolves

around the Sun, it travels around the Sun, it travels ►TOWARDS certain stars for TOWARDS certain stars for

half the yearhalf the year►AWAY from those stars for AWAY from those stars for

the other half of the year the other half of the year Results in small yearly Results in small yearly

cycliccyclic (happening on a (happening on a cycle) changes in the blue- cycle) changes in the blue- and red-shifts of starlightand red-shifts of starlight

Celestial Motions: The EarthCelestial Motions: The EarthChallenge QuestionsChallenge Questions

Celestial Motions: The EarthCelestial Motions: The EarthChallenge QuestionsChallenge Questions

What would happen if Earth revolved What would happen if Earth revolved around the Sun but was NOT tilted?around the Sun but was NOT tilted?

What would happen if Earth did NOT What would happen if Earth did NOT revolve around the Sun but was revolve around the Sun but was tilted?tilted?