Astronomy Motions of the Earth and Sun Review book topic 4 Pages 60-70 Mrs. Cohn

Apparent Motions of Celestial Objects Stars in the Night Sky appear to move EastWest This apparent motion is caused by Earth’s rotation (time it takes earth to spin in 24 hrs). NOT revolution (time it takes earth to orbit around the sun-365 days)

Star Arcs and Daily Motion Stars near the north star (polaris) appear to move in complete circles in 24 hours Parts of a circle are called an “arc” All motions of stars occur at 15º/hour

Arcs Continued If each one of these arcs (star paths) were measured to be 60 degrees from the center, how many hours represents this time elapsed photo…? If each arc is 60 degrees, and Earth’s ROR is =15/hr, Than 60 degrees/15 hr yields a 4 hour time elapsed photograph! How many degrees would a star Arc measure at an exposure of 2 Hours? 2 hours x 15/hr= ________

The view of an arc changes with your horizon (N, S, E, W)

Polaris and Earth’s Axis Earth’s tilt & orientation stay the same as it orbits Sun Axis always points to Polaris 6

3. Caused by Earth’s Rotation or Revolution? Towards which direction must be looking to see these star arcs? N, S, E, W? 2. What star is at center? 3. Caused by Earth’s Rotation or Revolution? 59 7

Star paths and polaris Polaris *remains “fixed” in the night sky *All other stars will move east to west

Q: What direction are we looking at various locations in the video? YouTube star trails in Nevada Q: What direction are we looking at various locations in the video?

Apparent Motions of the Sun in the Northern Mid-Latitudes Our own star, the sun also moves through our sky from EastWest at 15º/hour From Sunrise (E) to Sunset (W), the sun’s path also has the shape of an arc

Our own Star’s path…

To an observer, the sun’s path makes an arc over the course of a day

The sun’s path changes in length and position (angle) over the course of a year Let’s see why…

Seasonal Motions of the Sun Caused by Earth’s _____________ around the _____ . 14

Summer Solstice (June 21) Direct sun over Tropic of Cancer Longest day (in N. Hemisphere) N. Hemisphere tiled TOWARD sun 15

Winter Solstice (December 21) Direct sun over Tropic of Capricorn Shortest day, Sun tiled AWAY from N. Hemisphere 16

Vernal Equinox (~March 21) & Autumnal Equinox (~Sept. 21) Direct sun over Equator (0º) Equal day and night everywhere 17

Again, in summary Due to Earth’s revolution around the sun, and tilt on its axis the sun’s path across the sky changes throughout the year How? Gets higher and lower in the sky Length of path changes Lets take a look…

Changes in Sun’s Altitude (angle above horizon) Increases or starts getting higher in the sky after Dec. 21 (Winter Solstice) to June 21 when highest (Summer Solstice) Decreases or starts getting lower on June 21  and is lowest on Dec. 21 20

Sun at highest altitude Sunrise/set NORTH of Due East-West Summer Solstice Sun at highest altitude Sunrise/set NORTH of Due East-West 21

Vernal (Spring) & Autumnal Equinoxes Sun at middle altitude Sunrise/Sunset due East-West 22

Sunrise/set SOUTH of due East-West Winter Solstice Sun at lowest altitude Sunrise/set SOUTH of due East-West 23

Let’s Look at what the sun’s path looks like at other Latitudes in the celestial sphere model… Sun's path interative...click here! Let’s Look at what the sun’s path looks like in the SKY as the seasons change in NY…. Sun's path in the sky interactive animation

Equator

North Pole

Southern Hemisphere at 42 S

Activities for this section Page 62-63 # 1-14 in review book (HW) Skills Sheets Review Sun’s path Lab with globes Shadow Length and Direction Activity

Shadow length prediction activity Note: The southern hemisphere experiences everything OPPOSITE in terms of the sun’s path We mean that the sun is at the highest altitude and longest path in the sky on December 21st and the lowest, and shortest path on June 21st

Models that Explain Celestial Motions : Geocentric vs. Heliocentric pg

1.) Geocentric Model – people thought Earth was the center of the universe, and all planets and stars moved in orbits around Earth -first proposed by Aristotle (384-322 BC) -explained observations of: *sunrise/sunset, *moonrise/moonset *and other movements of star paths -because they were thought to rotate around Earth -COULD NOT EXPLAIN the behavior of a pendulum…!

2.)Heliocentric Model *Sun is at the center of the solar system -and all the planets and comets move around the sun Proposed by Copernicus (1473-1543) Stars remain fixed in the sky but because earth rotates around the sun, these constellations appear to move throughout the year

Evidence of Earth’s Rotation 1. Foucault Pendulum Freely swinging pendulum whose path appears to change. 33

Foucault’s Pendulum : Evidence for Earth’s rotation The ball swings back and forth, knocking the pegs over. It will also move in a circle as the Earth rotates at 15degrees/hour.

2. Coriolis Effect Deflection of moving particles (ex 2. Coriolis Effect Deflection of moving particles (ex., wind) to right in N. Hemisphere http://www.youtube.com/watch?v=_36MiCUS1ro http://www.youtube.com/watch?v=mcPs_OdQOYU&feature=related 35

3. Day & Night (sunrise, sunset) The prime meridian SUNLIGHT A time meridian A standard time zone is 15° wide. 36

Evidence for Earth’s Revolution Earth Revolves Counterclockwise 1 revolution = 365.26 days (1 year) 37

Evidence of Earth’s Revolution 1. Changing Seasons 38

2. Changing Length of Day 39

Evidence of Earth’s Revolution 3. Changing Constellations 40

Complete Review Questions Page 68 in review book # 21-27 21.) 22.) 23.) 24.) 25.) 26.) 27.)