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# Astronomy part 2

## by West Hollow MS Ms. Gill on Nov 28, 2010

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## Astronomy part 2Presentation Transcript

• Astronomy from Earth’s Perspective: Before the invention of technology that enable humans to leave earth’s perspective, astronomers relied solely on their observations of the heavens to make inferences about earth’s motions .
• Models of the Solar System
• Based upon observations of the apparent motion of celestial objects.
• Before our current understanding that the planets revolve around the sun, people actually believe that the sun and other planets revolved around earth.
• Explain the difference between the geo- and helio-centric models of the solar system. Helio-centric Geo-centric Earth- centered Sun- centered
• Models of the Solar System
• Geocentric Model – Earth is the center of the solar system, and all objects revolve around it.
• Used epicycles (small sub-orbits) to explain retrograde (backward) motion of planets
• Models of the Solar System
• Heliocentric Model – The Sun is at the center, and the planets revolve around it
• Geocentric vs. Heliocentric
•
• Coordinates in the Sky On earth we use latitude and longitude to locate places. In astronomy we use _______________ and __________________. Altitude Azimuth
• Coordinates in the Sky Altitude is the angle above the horizon in degrees. (Horizon: imaginary boundary between the sky and the ground)
• Coordinates in the Sky 90° Zenith The highest angle of altitude is ________ and that is the point directly over the observers head called _______
• Coordinates in the Sky 0° 360° Azimuth is direction broken down into degrees from _______ to _______   Altitude and azimuth together form a coordinate grid for locating objects in the sky.
• We draw this grid on a dome model of the sky called a celestial sphere .
• Zenith- directly above 90°
•
• Is the Earth Perfectly round?
• The Earth is NOT a perfect sphere
• It is an oblate spheroid.
• It is flattened at the poles and bulges at the equator
• Earth is slightly out of round or OBLATE.
• The Oblate Sphere
• The difference is small
• We can not see it with the naked eye
• It still appears like a sphere
• Be careful on multiple choice
• Why is the earth not perfectly round?
• Earth’s rotation causes…
• Bulging at equator
• Flattening at the poles
• Why do observations of Polaris help determine the Earth’s shape?????
• The North Star appears lower and lower in the sky as you travel toward the equator because of earth’s spherical shape, where the North Star is just visible at the horizon. The latitude of the equator is 0°.
• Ships appear to sink gradually below horizon
• Lunar Eclipse
• Only a sphere can cast a shadow that appears round. During a lunar eclipse, the earth casts its shadow on the moon during the full moon phase.
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• What proof is there that we are slightly oblate?
• Gravity measurements. Gravity is the force of attraction between any 2 objects. Increase mass of objects = increase gravity Decrease distances = increase gravity
• If Earth were a perfect sphere, it would be expected to exert an equal force on objects at equal distances from the center of earth.
• Weight!!! – measure of gravitational force
• We are further from the center of the Earth at the equator – gravity is less
• This means we weigh LESS!!!
• We are closer at the poles…
• We weigh MORE!!!!
• The least amount of gravity is farther from the center of Earth High Mountains farther from the center of earth – gravity is less
• Summary: How did they prove the Earth to be round?
• Ships appear to sink GRADUALLY below the horizon as they travel away from observer
• Polaris (North Star) changes altitude (angle measured in degrees above earth’s surface) directly with your latitude
• ALT OF POLARIS = LAT OF OBSERVER
• Lunar Eclipses - Earth’s shadow on the moon
• Satellite Imagery – absolute proof
• Gillism #1: “It’s all a matter of perspective! When you change the way you look at things the things you look at change!”
• Celestial Observations
• celestial object : any object in space (outside of earth’s atmosphere) examples: Moon, planet, stars, sun
• The apparent daily motion of celestial objects (like stars) have enabled scientist to create theories about earth’s motions: Rotation and Revolution
• Earth Motions
• Earth's Motions How long is one rotation of Earth? One day
• Rotation Revolution Rising and Setting of the Sun Rising and Setting of the Moon The Seasons Changing Constellations Movement of Stars through the sky
• Earth’s Rotation Earth’s axis is tilted 23.5° from the perpendicular. Earth’s axis is always tilted in the same direction this is called parallelism. AXIS – the imaginary line through the planet from the North Pole to the South Pole
• Earth’s Rotation The earth rotates counterclockwise when looking down from the north pole. Or from west to east when looking at a side view of earth
• Tilt of the axis always stays the same – 23.5 ° from a line perpendicular to the ecliptic plane: Parallelism
• How do you calculate Earth's rate of rotation? One rotation = 360° Time for one rotation = 24 hours 360° ÷ 24 = 15°/hr
• Regents Question
• Earth’s rate of rotation is approximately
• (1)1 ○ per day (3) 180 ○ per day
• (2)15 ○ per day (4) 360 ○ per day
• (4)360 ○ per day
• Finding Polaris
• Polaris North Star
• This is the star that lies in space practically over the geographic North Pole of the earth.
Polaris
• Since it is located above our axis of rotation– Polaris is a fixed point in our sky above the North Pole. 90º
• Anyone in the Northern hemisphere can see Polaris but where it appears on the observer's celestial sphere depends on their latitude.
• If you stood at the North Pole, Polaris would be at your zenith (directly overhead).
Polaris
• An observer on the equator would find Polaris along the horizon
• Any observer in between would find Polaris has an altitude equal to their latitude. So for NYS, Polaris will have an altitude of approximately 41° .
• Polaris – Fixed Point above the North Pole
• Because of this, in the Northern Hemisphere, the altitude (angle measured in degrees above the horizon) of Polaris tells observer his latitude position.
• If observer’s latitude changes in the Northern Hemisphere, the altitude of Polaris will exactly match observer’s latitude.
• ALT OF POLARIS = LAT OF OBSERVER
•
• Locating Polaris – our latitude is 41 °N , Polaris’ altitude will be 41°
• To find Polaris, look for the Big Dipper.
• Draw an imaginary line from the two end ‘pointer’ stars.
• They will point approximately to the last star in the handle of the Little Dipper… Polaris!
• Am I pointing to Polaris? How can you check to be somewhat sure? To Polaris Zenith = 90 ° above the observer Horizon 42 Degree Angle… Pretty close to 41 Degrees
•
• Apparent Daily Motion
• Apparent Daily Motion
• An apparent motion is a motion an object appears to make
• An apparent motion can be real or an illusion
• Celestial objects appear to move in the sky
• This is due to the earth’s rotation
• Apparent Motion
• Celestial Objects appear to move 15° per hour , because Earth rotates 360° in 24 hours.
• Apparent Motion
• The apparent daily motions of stars changes when the observer’s Latitude on earth changes.
• Therefore, at the poles (90° N or S) stars do not rise or set but at the equator (0° ) all stars rise and set
• Apparent Motion
• At 41° N (New York state) some stars, like the sun appear to rise in the east and set in the west making an arc across the celestial sphere. Other stars such as ones part of circumpolar constellations never set but instead trace out giant circles daily around the poles.
• Apparent Motion
• Using a time-lapse camera we can document this phenomenon. We call these images Star Trails
• Apparent Motion
• Stars are so far away they appear stationary (not moving). Why do they have this pattern? Earth is Rotating!
• Circumpolar New York State Mid October 3 4 2 1 2 3 4
• Since earth is spherical as it rotates greater distances are covered at the equator than at the poles for every degree the earth turns .
• Rotational speed at Poles: 1 cm/day
• Rotational speed at Equator: 1000 miles/hour
•
• The Earth is moving faster at the equator than at the poles
• How many degrees did the stars move from diagram 1 to diagram 2? 30° (2 hours x 15°)
• How can you find Polaris? It’s the only one that didn’t move
• What hemisphere must you be in? Why? Northern Because Polaris can only been seen in the North
• What direction must you be looking? North
• What direction do the stars appear to move?
• What causes the stars appear to move?
• Evidence for Rotation Foucault Pendulum Coriolis Effect
• 1. Evidence of Earth’s Rotation
• 1851, Foucault’s pendulum will appear to change in a predictable way.
• Why is this evidence? There is no force acting on the pendulum to make its plane of oscillation rotate or go around its own axis
• It would continue to swing in the original path if Earth did not rotate.
• No force that makes pendulum rotate – must be earth that is rotating!!!
•
• 2. Evidence for Rotation
• Coriolis Effect – the tendency of objects moving over the earth (air, water, planes, projectiles) to be deflected (curve away) from a straight line path. The French scientist, Gaspard Coriolis, first explained the deflection of objects moving over the surface due to Earth’s rotation
• The deflection is to the right in the Northern Hemisphere and to the left in the Southern Hemisphere.
• This deflection occurs because Earth’s surface is rotating with respect to the objects.
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•
•
•
•
• Rotation Revolution Rising and Setting of the Sun Rising and Setting of the Moon The Seasons Changing Constellations Movement of Stars through the sky
• Regents Question
• Regents Question
• The diagram below shows how Earth is illuminated [lighted] by the Sun as viewed from above the North Pole.
• In which orbital position would Earth be illuminated as shown?
• (1)A (3) C
• (2)B (4) D
• (1)A
• Regents Question
• In the Northern Hemisphere, planetary winds blowing from north to south are deflected, or curved, toward the west. This deflection is caused by the
• (1)unequal heating of land and water surfaces.
• (2)movement of low-pressure weather systems.
• (3)orbiting of Earth around the Sun.
• (4)spinning of Earth on its axis.
• (4) spinning of Earth on its axis.
• Apparent Solar Motion
• The sun appears to move across the sky, like all celestial objects.
• The sun’s apparent path in the sky varies by latitude and season.
• Four Seasons Name the four seasons and their starting date.
• Summer Solstice– June 21
• Autumn Equinox– September 21
• Winter Solstice– December 21
• Spring Equinox – March 21
• What changes do we observe during seasons? Sun’s altitude changes with the season. Highest – June 21, Lowest – Dec. 21, But NEVER overhead at our latitude.
• What changes do we observe during seasons? Sun rise and Sun set positions change with the seasons. South of E/W in fall and winter. North of E/W in spring and summer. Sun rise in DC
• What changes do we observe during seasons? Day length – Duration of Insolation Longest on Summer Solstice, June 21. Shortest on Winter Solstice, Dec. 21 12 hours on Equinox for all.
• What changes do we observe during seasons? What to know about the Summer Solstice.
• June 21, longest day of the year.
• Sun at highest altitude at noon.
• 24 hrs of daylight at North Pole.
• Direct sun ray at 23.5° north latitude.
• Sun rise – NE, Sun set - NW
• What changes do we observe during seasons? What to know about the Winter Solstice.
• Dec. 21, shortest day of the year.
• Sun at lowest altitude at noon.
• 24 hrs. of darkness at North Pole.
• Direct sun ray at 23.5° south latitude.
• Sun rise – SE , Sun set – SW
• What changes do we observe during seasons? What to know about the Equinox.
• Sept. 21 and March 21.
• 12 hrs of daylight, 12 hrs of night.
• Direct sun ray at Equator.
• Sun rise – E, Sun set – W.
• Earth's Motions How long is one revolution of Earth? One year
• Regents Question
• Which observation provides the best evidence that Earth revolves around the Sun?
• (1)The constellation Orion is only visible in the night sky for part of the year.
• (2)The North Star, Polaris , is located above the North Pole for the entire year.
• (3)The sun appears to move across Earth’s sky at a rate of 15 ○ /hr.
• (4)The Coriolis effect causes Northern Hemisphere winds to curve to the right.
• (1)The constellation Orion is only visible in the night sky for part of the year.
•
• Regents Question
• If Earth’s axis were tilted less than 23.5 ○ , which seasonal average temperature change would occur in New York State?
• (1)Spring and fall would be cooler.
• (2)Spring and fall would be warmer.
• (3)Winter would be cooler.
• (4)Summer would be cooler.
• (4)Summer would be cooler.
• Is distance important to seasonal change? NO! Farthest away on July 4, Closest on Jan. 3. Earth’s orbit is an ellipse.
• Reasons for the Seasons Video Clip
• Regents Question
• Regents Question
• Which position of Earth represents the first day of summer in the Northern Hemisphere?
• (1)A (3) C
• (2)B (4) D
• (3) C
• Regents Question
• Regents Question
• How many degrees will the Sun’s vertical rays shift on Earth’s surface as Earth travels from position C to position D?
• (1)15 ○ (3) 47 ○
• (2)23.5 ○ (4) 365 ○
• (2) 23.5 ○
• Constellations are groupings of stars that make an imaginary image in the night sky. They have been named after mythological characters, people, animals and objects. In different parts of the world, people have made up different shapes out of the same groups of bright stars. It is like a game of connecting the dots. In the past constellations have became useful for navigating at night and for keeping track of the seasons.
• Tropic of Capricorn Arctic Circle Tropic of Cancer Equator Antarctic Circle 66 1/2 0 N 66 1/2 0 S 23 1/2 0 N 23 1/2 0 S 0 0 90 0 N 90 0 S Orbital Plane
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• Long Island 1 2 3 4 9:00 pm 2 3 4
• Summer Autumn Winter Spring Scorpio, Sagittarius, Capricorn Aquarius, Pisces, Aries Taurus, Gemini, Cancer Leo, Virgo, Libra
• Regents Question
• Which object is closest to Earth?
• (1)The Sun (3)the moon
• (2)Venus (4)Mars
• (3)the moon
• The Moon
• The Moon
• The Moon is Earth’s only natural satellite
• It is estimated to be about 4.5 billion years old
• What are these? Why so many? Why is Earth not like this? Craters No atmosphere weathering, erosion, atmosphere
• Features
• The Moon’s interior is thought to have layers, similar to earth
• The Moon’s surface is covered with craters, caused by meteor impacts.
• The Moon’s Surface
• Dark areas called Maria (from Latin mare, meaning sea). These are ancient lava flows.
• Light areas are Lunar Highlands , which are mountain ranges made of lighter color rocks.
• Moon Rocks
• Rocks on the Moon are made of minerals similar to those on Earth.
• Rotation and Revolution
• The Moon’s periods of rotation and revolution are both 27.33 days. The result is that the same side of the Moon always faces Earth (the near side).
• However, it takes 29.5 days for the Moon to completely revolve around the Earth
• Why Two More Days? Moon’s orbit Earth moving around Sun. Earth Moon Moon has to revolve for 2 more days to get back to the new moon phase. This occurs because the Earth is revolving around the Sun.
• Dark Side/Light Side
• Changes in Shape
• Phases of the 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
• Phases Of The Moon
• What causes the phases of the moon? The moon's revolution around Earth.
• How long does one revolution of the moon take? 27.3 days How long does one rotation of the moon take? ESRTs p15
•
• Regents Question
• Which sequence of Moon phases could be observed from Earth during a 2-week period?
• What phenomenon does this explain? We only ever see one side of the moon.
• Why does the moon rise later each day? because as the Earth rotates, the moon revolves
• What phase of the moon is this? New Gibbous New Crescent 3rd Quarter
• How many hours is the moon visible each day? 12 hours Approximate Times of Moonrise and Moonset     moonrise     moonset new moon 06:00 AM 06:00 PM waxing crescent 09:00 AM 09:00 PM first quarter 12:00 PM 12:00 AM waxing gibbous 03:00 PM 03:00 AM full moon 06:00 PM 06:00 AM waning gibbous 09:00 PM 09:00 AM third quarter 12:00 AM 12:00 PM waning crescent 03:00 AM 03:00 PM new moon 06:00 AM 06:00 PM
• What is &quot;waxing&quot;? more of the moon's surface can be seen
• What is &quot;waning&quot;? less of the moon's surface can be seen
• The phases of the moon are what type of event? Cyclic
• Tides & Eclipses Astronomy
• Tides
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• What causes tides?
• Moon’s Effect on Tides
• Tides are the periodic rise and fall of the ocean surface
• Tides are caused by the gravitational attraction of the Moon and the Sun on ocean water
• High tide will occur when the Moon is overhead, as well as on the opposite side of the Earth.
• Tides High High Low Low Caused by Moon’s gravity pulling Earth’s water. Two of each because the Earth rotates. Tides always High in line with Moon. Earth
• Regents Question
• The change in the tides as shown on the graph is primarily the result of
• Earth’s rotation and the Moon’s revolution
• Earth’s rotation and revolution
• The Moon’s rotation and Earth’s revolution
• The Moon’s rotation and revolution
• Earth’s rotation and the Moon’s revolution
• During which phases of the moon do neap and spring tides occur?
• Neap? 1st & 3rd Quarters
• Spring? New or Full Moon
• Phases and Tides
• The alignment of the Moon with the Sun affect tides.
• At the full and new moon phase, both are in line, causing a higher high tide and a lower low tide. This is called the Spring Tide.
• At the quarter phases, the Sun and Moon work against each other, resulting in weaker tides, called Neap Tides.
• Spring and Neap Tides Sun Sun Neap Tide Spring Tide Quarter Phase – not a large change from high to low tide. New and Full Phase – big change from high to low tide. Water being pulled in two directions. Moon and Sun’s gravity pulling in one direction. Earth Earth
• How many tides a day? 2 high tides 2 low tides
• Why are there not exactly 12 hours between tides? because the moon revolves around the Earth while the Earth rotates
• Regents Question
• What is the main reason that the gravitational attraction between Earth and the Moon changes each day?
• Earth’s axis is tilted at 23.5 ○ .
• Earth’s rotational speed varies with the seasons.
• The moon has an elliptical orbit.
• The moon has a spherical shape.
• The moon has an elliptical orbit.
•
• Eclipses and Conclusions Video Clip
• Eclipses
• An eclipse occurs when the Sun’s light is blocked from either the Earth or the Moon.
• Since the orbit of the Earth and the Moon are along different planes, eclipses don’t happen frequently.
• What’s the difference between solar and lunar eclipses? Solar Lunar Earth goes into moon’s shadow moon goes into Earth’s shadow
• Solar Eclipse
• Solar Eclipse – occurs when the Moon blocks the Sun’s rays from reaching Earth. It occurs only at new moon phase.
• Solar Eclipse Sun’s Rays Penumbra Umbra
• 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.
Solar Eclipse Photo
• Lunar Eclipse
• Lunar Eclipse – occurs when the Earth blocks the Sun’s rays from reaching the Moon. Only occurs at full moon phase.
• Lunar Eclipse Umbra Penumbra 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.
Every one on the night side sees the eclipse.
• Solar Eclipse 2010
• Solar Eclipses through 2020
• Lunar Eclipse What phase? Full Moon
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• Lunar Eclipse 2010
• Why don’t we have solar and lunar eclipses every month? The moon’s orbit is tilted 5° from the Earth’s orbit.
• Are We Alone?
• Home Sweet Home You are here!