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

Why is it called “apparent motion”? The objects themselves DO NOT MOVE—the Earth ROTATES (spins) Tractor Trailer Effect

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

Constellations: groups of a few stars that form a pattern in the sky Examples- 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 Earth Motions Into Account The Earth rotates (spins) on its axis at a rate of 15° per hour (daily motion)

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? Seasons Changing Constellations (at different times of 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…. The higher the sun is in the sky, the shorter the shadow Shadows occur opposite the sun

afternoon morning / evening

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? Tilt of the Earth’s Axis of 23 ½ º

Parallelism of the Axis: regardless of the Earth’s position the axis always points in the same direction as it revolves

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

Tropic of Cancer: an imaginary line that is located 23 ½ degrees north of the Equator

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

**the Sun will only get directly overhead (Zenith) between the Tropics **the equator always gets 12 hours of daylight!!!

Four Important Days in Earth Science: 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

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

Winter Solstice: December 21st Northern Hemisphere is tilted away from the Sun Insolation is least direct (sun lowest in the sky) Shortest day of the year in the Northern Hemisphere Sun is directly above The Tropic of Capricorn at noon Sun rises south of east and sets south of west

Winter Solstice

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)**