Unit III: The Earth in Space

Celestial Objects Any natural object “outside” the earths

atmosphere (seen in the sky)

Celestial Sphere

The imaginary sphere on which all objects in the sky appear on.

How do celestial objects move in the sky?

ApparentApparent Daily Motion Daily Motion: the : the apparent apparent motion motion of celestial objects in a path from of celestial objects in a path from east to westeast to west in the sky over a 24 hour period.in the sky over a 24 hour period.

Why is it called “apparent motion”?

The objects themselves DO NOT MOVE—The objects themselves DO NOT MOVE—the Earth ROTATES (spins)the Earth ROTATES (spins)

Tractor Trailer Effect

Celestial objects Celestial objects appear appear to move along a to move along a curved path called an curved path called an ARCARC..

ConstellationsConstellations: groups of : groups of a few starsa few stars that form that form a pattern in the skya pattern in the sky

Examples- Big Dipper, Little Dipper, OrionExamples- Big Dipper, Little Dipper, Orion

Models of the Night Sky

Geocentric Model: shows the Earth in the center of the universe and everything else revolving around it.

(Earth does not move)

THIS IS WRONG!!!!!

Heliocentric Model: sun in the center of our Solar System and the Earth and other planets revolving around it.

This is Correct!

The Heliocentric Model Takes Two The Heliocentric Model Takes Two Earth Motions Into AccountEarth Motions Into Account

1.1. The Earth The Earth rotates rotates (spins) on its axis at a (spins) on its axis at a rate of 15rate of 15° per hour (daily motion)° per hour (daily motion)

2. The Earth revolves (orbits) around the Sun at a rate of 1° per day (annual motion)

Period of Revolution: amount of time it takes an object to go around the sun once.

How do we know that Earth really rotates on its axis?

Foucault Pendulum: swinging weight that is free to rotate as it swings back and forth. As the Earth rotates, the pendulum changes direction.

Coriolis Effect: apparent curving of objects to the right in the Northern Hemisphere (counterclockwise spin)

How do we know that Earth revolves around the sun?

1.1. SeasonsSeasons

2.2. Changing ConstellationsChanging Constellations (at different times of (at different times of the year you see different constellations)the year you see different constellations)

Apparent Motions of the Sun

***The Sun, just like other stars, rises in the east and sets in the west because of Earth’s Rotation

Apparent Solar Day: the interval of time during which the Sun passes from its highest point on one day to its highest point on the next.

Solar Noon: sun’s highest point in the sky during the day

**the Sun’s apparent speed never changes

Shadows….Shadows….

The higher the sun is in the sky, the The higher the sun is in the sky, the shorter the shadowshorter the shadow

Shadows occur opposite the sunShadows occur opposite the sun

morning / evening

afternoon

This shows up all the time! This shows up all the time!

Which direction do the Sun and stars appear to move?

When looking east, west, or south, stars will appear to move to the right

Eastern Sky

Western Sky

When looking north, stars will form circles around Polaris (remember Polaris NEVER moves)

Seasons

What causes seasons on Earth? What causes seasons on Earth?

1.1. Tilt of the Earth’s Axis of 23 ½ Tilt of the Earth’s Axis of 23 ½ ºº

2.2. Parallelism of the AxisParallelism of the Axis: regardless of : regardless of the Earth’s position the axis always the Earth’s position the axis always points in the same direction as it points in the same direction as it revolvesrevolves

****the cause of the seasons ****the cause of the seasons IS NOT DUEIS NOT DUE to to the fact of how close the Earth is to the the fact of how close the Earth is to the Sun—in fact the Earth is Sun—in fact the Earth is closest to the closest to the SunSun in in January January because of Earth’s because of Earth’s elliptical orbitelliptical orbit

Tropic of Cancer: Tropic of Cancer: an imaginary line that an imaginary line that is located 23 ½ degrees is located 23 ½ degrees northnorth of the of the EquatorEquator

Tropic of CapricornTropic of Capricorn: an imaginary line : an imaginary line that is located 23 ½ degrees that is located 23 ½ degrees southsouth of the of the Equator Equator

**the Sun will only get directly overhead (Zenith) **the Sun will only get directly overhead (Zenith) between the Tropicsbetween the Tropics

**the equator always gets 12 hours of daylight!!!**the equator always gets 12 hours of daylight!!!

Four Important Days in Earth Science:

1. Summer Solstice: June 21st

Northern hemisphere is tilted towards the Sun Insolation (incoming solar radiation) is most

direct (sun highest in the sky) Longest Day of the year in the Northern

Hemisphere Sun is directly above The Tropic of Cancer at noon Sun rises north of east and sets north of west

Summer Solstice

2. Autumnal Equinox

September 23rd

Day and night are equal (Equinox: “Equal Night”)

Sun is directly over the Equator at noon Sun rises due (exactly) east and sets due

west

Autumnal Equinox

3.3. Winter Solstice:Winter Solstice:

December 21December 21stst Northern Hemisphere is tilted away from the SunNorthern Hemisphere is tilted away from the Sun Insolation is least direct (sun lowest in the sky)Insolation is least direct (sun lowest in the sky) Shortest day of the year in the Northern HemisphereShortest day of the year in the Northern Hemisphere Sun is directly above Sun is directly above The Tropic of CapricornThe Tropic of Capricorn at at

noonnoon Sun rises south of east and sets south of westSun rises south of east and sets south of west

Winter Solstice

4. Vernal Equinox:

March 21st

Day and night are equal (Again, Equinox means “equal night”)

Sun is directly over the equator at noon Sun rises due east and sets due west

Vernal Equinox

 Winter Spring Summer Fall

Date of First Day       

Scientific Name       

Direct Rays of the Sun Hit       

What is Happening Inside the Arctic Circle?        

What is Happening Inside the Antarctic Circle?        

How much daylight do we get on First Day in NYS?        

How many degrees is the Earth Tilted?        

Altitude of noon sun in NYS       

Seasons Review The tilt (or “inclination”) is the reason for the seasons Temperature changes because the Sun’s rays strike the

earth at different angles (high altitude = high temp.) Insolation = Sunlight On the equinoxes, the Sun is directly over that equator at

noon On the summer solstice, the Sun is directly overhead

The Tropic of Cancer at noon On the winter solstice, the Sun is directly overhead The

Tropic of Capricorn at noon The Lower the Sun is in the sky, the longer the shadow The equator always has 12 hours of daylight

**Remember**

**The Sun ONLY gets 90° (directly overhead in the tropics (23 ½º N

and 23 ½º S)**