Astronomy Apparent Motions Making sense of celestial observations
Astronomy: Apparent Motions Making sense of celestial observations.
How does the Earth move? animation Earth rotates- spins on its axis Earth revolves- travels around the sun
How fast does the Earth Rotate?
How many degrees in a circle? o 360
How many hours in a day? (mean solar day) 24 hours Or one rotation on the axis.
How many degrees does the earth rotate in a day? Which direction? 360° Counter Clockwise
How many degrees does the earth rotate in one hour? 360° divided by 24 hours All celestial objects move at this rate across the sky!!!!!
How long does it take for the Earth to revolve around the sun?
How many days in a year? The length of time for one orbit around the sun. 365. 26 days Leap Year web site
How many degrees does the earth travel in its orbit around the sun in one day? 360° orbit divided by 365. 26 days Approximately 1 degree
Apparent Daily Motion Animation Celestial objects appear to move due to the Earth’s rotation Apparent motion = Earth’s rotation 15 degrees/hr Counter Clockwise rotation
How can you prove that the Earth Rotates?
Foucault Pendulum
Proof of Earth’s Rotation Foucault Pendulum: It changes its position 15 degrees/hour due to Earth’s rotation.
Proof of Earth’s Rotation Coriolis effect video Coriolis effect: Causes objects to deflect (bend) to the right in the N. Hemisphere and to the left in the S. Hemisphere.
Proof of Earth’s Rotation Star Paths: Paths stars appear to make in the sky.
Shape of the Sky • Dome shaped • Celestial objects make an arc across the sky (You are at intersection of N-S, E -W line) • Zenith-directly above at 90°
Apparent Solar (Sun) Motion Arcs across the sky ( like all celestial objects) Sun’s apparent path in the sky varies by latitude and season.
Solar Noon- when the sun is the highest in the sky. The noon sun is never directly overhead anywhere in the U. S. The Sun appears to rise towards the east and set towards the west.
Apparent Motion of the Stars Star Trails in the Northern Horizon Polaris Why do they have this pattern? Earth is rotating.
Star trails in the Southern Horizon Notice that the pattern is different.
Star trails in the western horizon
Star Trails in the Eastern Horizon
Apparent Motion of the Stars Constellations, groups of stars that form a pattern, appear to move east to west.
Are stars the same color? No, look at the different color star trails. Stars also vary in brightness.
Models of the Solar System Based upon observations of the apparent motion of celestial objects. Geocentric Model – Earth is the center of the solar system, and all objects revolve around it. Planet Earth Sun
Retrograde Motion: Explained by Geocentric Model (Epicycles) Explained by Heliocentric Model http: //www. lasalle. edu/~smithsc/Astronomy/r etrograd. html
Geocentric Model: Used epicycles (small sub-orbits) to explain retrograde (backward) motion of planets
Galileo Sun-Centered System. flv
Teachers' Domain: Galileo's Thought Experiment
Models of the Solar System Heliocentric Model – The Sun is at the center, and the planets revolve around it Proof: Movement of constellations and changing of the seasons
What causes seasons? Seasons Song
Comparing the seasons. Summer Solstice Winter Solstice One year on earth
What causes the Seasons? • Revolution of the Earth around the Sun. • Earth’s axis of rotation is tilted 23. 5° and always points at Polaris (North Star).
Is distance important to seasonal change? Farthest away on July 4, Closest on Jan. 3. NO! • Distance does not cause seasons
Name the four seasons and their starting date. • Summer Solstice– June 21 • Autumnal Equinox (Fall)– September 23 • Winter Solstice– December 21 • Vernal Equinox (Spring) – March 21
Label Diagram: Date and Season
What changes do we observe during seasons? • Sun’s altitude changes with the season. • Highest – June 21, Lowest – Dec. 21, • NEVER overhead at our latitude.
What changes do we observe during seasons? • Sun rise / set positions change with the seasons. • Due E/W on the equinoxes • South of E/W in fall and winter. • North of E/W in spring and summer.
What changes do we observe during seasons? Duration of Insolation: (amount of daylight) 1. Shortest on Winter Solstice, Dec. 21 2. 12 hours on Equinox for all. 3. Longest on Summer Solstice, June 21
Apparent Path of the sun Animation
What changes do we observe during summer in NY? What to know about the Summer Solstice. 1. June 21, longest day of the year. 2. Sun at highest altitude at noon, 71. 5°. 3. 24 hrs of daylight at North Pole. 4. Direct sun ray at 23. 5° north latitude. 5. Sun rise – NE, Sun set - NW
What changes do we observe during winter in NY? What to know about the Winter Solstice. 1. Dec. 21, shortest day of the year. 2. Sun at lowest altitude at noon, 24. 5°. 3. 24 hrs. of darkness at North Pole. 4. Direct sun ray at 23. 5° south latitude. 5. Sun rise – SE , Sun set – SW
What changes do we observe during Equinox in NY? What to know about the Equinox. 1. Sept. 23 and March 21. 2. Sun altitude at noon, 48°. 3. 12 hrs of daylight, 12 hrs of night. 4. Direct sun ray at Equator. 5. Sun rise – E, Sun set – W.
What effect does the moon have on the earth? • Revolution around Earth causes the phases of the moon. • Causes the ocean tides. • Reason for solar eclipse and lunar eclipse
Moon’s Motion (video start at 22 seconds • Revolution – Counter clockwise, 1 revolution takes 271/3 days. • Rotation - Counter clockwise, 1 rotation takes 271/3 days. • Always see the same side of the moon. • Phases of Moon- 29½ days long
Phases of the Moon Caused by the positions of earth, moon and sun. Repeat because moon orbits earth. Current Phase of Moon
Phases Moon Phases are apparent changes in shape due to the position of the Moon in its orbit. Phase names: – – – New Crescent Quarter Gibbous Full Waxing – becoming more visible Waning – becoming less visible
Light vs. Dark Only half is lit up at any time. What does this look like from earth?
Why are Phases longer? Moon’s orbit Moon has to revolve for 2 more days to get back to the new moon phase. Earth moving around Sun. This occurs because the Earth is revolving around the Sun. Earth Moon phases demo
Moon’s Orbit Moon appears Elliptical shape larger farther Earth when close and smaller closer when farther away.
Tides Low High Earth Low High Caused by Moon’s gravity pulling Earth’s water. Two of each because the Earth rotates. Tides always High in line with Moon.
Spring and Neap Tides Neap Tide Earth Water being pulled in two directions. Sun Spring Tide Earth Sun Quarter Phase – not a large change from high to low tide. New and Full Phase – big change from high to low tide. Moon and Sun’s gravity pulling in one direction.
Lunar Eclipse
Lunar Eclipse Penumbra Umbra Every one on the night side sees the eclipse. Sun’s Rays • Can only occur during the full moon phase. • Earth blocks light to the moon. • Moon must be in Umbra for a Total Lunar Eclipse. • Does not occur that often, moon orbit is tilted.
Solar eclipse
Solar Eclipse Photo Penumbra Umbra Sun’s Rays • Only occurs during the new moon phase. • Only total eclipse if in the umbra. Only a few people see it. • Moon blocks light to the Earth. Occur less often than lunar.
Phases of the moon rap
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