Astronomy - Notes

ASTRONOMY The study of stars and space.

I. Earth’s Place in the Universe Planet Earth – a small dense rocky planet

2. Our Solar System Earth is one of 8 planets that orbit the sun – an average yellow star. 3:47

The Planets Orbits of the planets and their relative distances. 3:41

3. Milky Way Galaxy Our Sun/solar system is one of an estimated 180 billion stars making up this spiral galaxy

4. Universe Our Milky Way Galaxy is one of billions of galaxies in an expanding universe

II. Models of the Universe Geocentric Model About 2000 years ago, the Greek astronomer, Claudius Ptolemy developed a detailed model of the universe based on the idea of revolving spheres.

E. Models of the Universe In this model of the universe, Earth was at the center, and all heavenly bodies moved around Earth in Perfect circles.

3. Ptolemy’s Geocentric model, as illustrated on the next page, can be summarized as follows: Earth is located in the center and does not move. The stars are located on a transparent sphere that rotates once each day from east to west around Earth.

The Sun , the Moon and each planet are carried by separate spheres of different sizes. Each planet is located on an “epicycle” that also rotates. This explained retrograde motion.

d. This model was accepted for almost 1400 years because it explained celestial observations made from Earth and……… it seemed obvious. However – The geocentric model does NOT explain terrestrial (Earth) observations such as: The movement/rotation of a pendulum’s direction. The curvature of the paths of projectiles, winds & ocean currents.

B. Heliocentric Model In the 1500’s, a new model of the universe was proposed in a book by the Polish astronomer Nicholas Copernicus. In this model of the universe, the sun was the center. 2:08

B. Heliocentric Model Copernicus’ heliocentric model can be summarized as follows: The Sun is located in the center of the system and does NOT move. The stars are located on a stationary/unmoving transparent sphere. The sphere is a great distance from the sun. The planets , including Earth , move in circles around the sun. The Moon moves in a circle around Earth . Earth rotates on its axis from west toward east each day.

However….. Copernicus’ heliocentric model does NOT explain the apparent cyclic variations in the size of the Sun, and the cyclic variation in orbital speeds of the planets. This is because in the heliocentric model, the planets orbit the sun in perfect circles .

Brainstorming Rules Inspect the question Develop as many ideas as possible as quickly as you can. Stretch your thinking. Each idea should be new and different (think creatively and divergently), but you can build off of other’s ideas. All responses are acceptable. Do not JUDGE someone’s ideas. Work within the time limit (5 minutes).

STEPS Select a recorder Time limit is 5 minutes Recorder should record each idea as stated. One idea must come from each participant before proceeding to the next. You are encouraged to build on others’ ideas and generate as many possible within the time frame. Examine and group the responses according to their quality (Great, Good and Just OK). Present the BEST idea for solving the problem.

This animation shows twelve images of the sun, each taken through a telescope on Earth, one month apart. The dates range from August 2000 to July 2001. The dark markings on the sun are sunspots—regions where the surface is slightly cooler than the surrounding area. Notice how the size of the sun appears to change in a regular pattern.

SO..The question is: Why does the size of the sun appear to change? Answer : All stars change size over their lifetimes, but the sun is currently very stable. Evidence indicates the sun has a constant diameter of about 1.4 million kilometers. The only reasonable explanation for the change in the sun's apparent size is that Earth's distance from the sun changes in a regular pattern.

C. Kepler’s Heliocentric Model In 1609, Johannes Kepler published a book which included his first 2 “Laws of Planetary Motion”. These laws explain why the apparent size of the sun changed, and why the speed of a planet changes as it orbits the Sun.

This is because….. The orbits of the planets were “elliptical” and not circular.

a. Kepler’s First Law The orbit of each planet is an ellipse with the sun at one focus and an imaginary point in space at the other focus.

An Ellipse – draw the parts in your notes An ellipse looks like an oval, or squashed circle. The longest line drawn from one end of the ellipse (through the center) to the other side is called the major axis . For a circle, the two foci lie on top of each other.

√ Eccentricity Eccentricity (e) = the “out of roundness” shape of the ellipse given by the ratio of the distance between the two foci and the length of the major axis. e = distance between foci Length of Major Axis The eccentricity of a circular orbit is zero , and can range from zero to less than one for an ellipse. Reference Table page 1

2. Eccentricity Relationship: As the distance between the focal points increase, the shape of the ellipse becomes more oval (Circle = 0)

B. Kepler’s Second Law describes the fact that a planet moves fastest in its orbit when it is nearest the Sun. If you imagine a line connecting the planet and the Sun, the line sweeps out equal areas in equal times . Area A = Area B = Area C Maximum speed Minimum speed Decreasing speed

B. Kepler’s Second Law Perihelion = point in orbit nearest to sun Aphelion = point in orbit furthest from sun

C. Kepler’s Third Law The further a particular planet is from the sun, the longer it’s period (time) of revolution . 1. Farther planets have longer orbital paths 2. Farther planets have slower orbital paths

Table on Page 15 247 years 3 3675 Pluto * 164 years 3.4 2795 Neptune 84.01 years 4 1784 Uranus 29.46 years 6 887 Saturn 11.6 years 8 484 Jupiter 687 days 15 142 Mars 365.25 days 19 93 Earth 224 days 22 67 Venus 88 days 30 36 Mercury Period of Revolution Speed mile/sec. Distance (millions of miles) Planet

D. Sir Isaac Newton Newton’s Laws of Gravity First Law All objects with mass will be acted on by gravity and will pull all other objects with a certain gravitational force.

Newton’s Laws of Gravity Newton’s Second Law The mass of an object will determine the amount of gravitational force that object possesses. The greater the mass, the greater the gravitational force.

Newton’s Laws of Gravity Third Law The gravitational force between 2 objects changes as the distance between them change. As the distance increases , gravitational pull will decrease .

a. Newton’s Law of Inertia States that an objects motion will not change unless that object is acted on by an outside force . Inertia Gravity Stable Orbit

B. Gravity and Inertia Inertia – causes a planet to move in a straight line . Gravity – pulls a planet toward the sun.

Rotation The spinning of a celestial body (Earth) on an imaginary axis

III. Rotation A. Earth’s Direction of Rotation: WEST to EAST 2. Angular Rate of Rotation: THINK – one complete rotation a. 360 degrees b. 24 hours Rate = 360 0 /24 hours = 15 0 /hour

B. Effects of Earth’s Rotation Day and Night

B. Effects of Earth’s Rotation Apparent daily motion of the sun a. Earth rotates from WEST to EAST b. Sun “appears” to move in an arc from EAST to WEST

B. Effects of Earth’s Rotation Apparent daily motion of the stars Appear to rise in the east and set in the west .

Looking East Looking West Looking North Looking South

B. Effects of Earth’s Rotation The apparent daily motion of celestial objects (like stars) changes when the observer’s latitude on Earth changes.

B. Effects of Earth’s Rotation The apparent daily motion of the Big Dipper, a circumpolar constellation.

4 3:00 pm 3 9:00 am 2 3:00 am 1 9:00 pm Position of the big dipper Mid October Date New York State Location of Observer

B. Effects of Earth’s Rotation Star Trails – a time-exposed photographic image that shows the apparent motion of stars; it appears as a blurry line across the film.

Star trail photographs looking north, south, east and west A. North D. East C. West B. South

Celestial Poles – video clip

IV. Revolution The orbiting of one celestial body around another celestial body. A. Earth’s Angular Rate of Revolution 1. 360 degrees 2. 365 days 3. Rate = 360 0 /365 days ~ = 1 0 /day

B. Effects of Earth’s Revolution Nighttime constellations change in a yearly cycle. Constellation – groups of stars that form patterns of imaginary things such as animals, legendary heroes, and mythological gods

3. Zodiac – a band of 12 constellations that forms a background for the Sun as seen from the revolving Earth.

Continued: Effects of Earth’s Revolution Position of the Big Dipper (and other circumpolar constellations) changes position in a yearly cycle. 1 2 3 4

4 Summer 3 Spring 2 Winter 1 Fall Position of the Big Dipper 12:00 Midnight Time of Day NYS Location of Observer

3. Seasons – a yearly cycle

5. Seasons of the Year Causes: Earth revolves around the sun Earth is tilted/inclined on axis 23 1/2 o Earth’s axis always points in the same direction.

B. Earth’s axis is tilted 23.5 0 relative to the plane of it’s orbit. Draw and label your diagram according to the diagram at the right. Be sure to name the equator, the Tropic of Cancer and Capricorn and note where we live. NYS 43 o Tropic of Cancer Equator Tropic of Capricorn

C. Earth revolves around the Sun in a yearly cycle of 365 ¼ days. D. As Earth revolves, its axis always points in the same direction (parallelism of axis) December 21 March 21 June 21 Sept. 20

E. The apparent path of the sun changes with the seasons and with latitude . N.Y.S. 43 o North Latitude 24 o 47 o 71 o

2. Equator 0 o Latitude 67 o 67 o

F. Length of Daylight (duration of daylight) – changes with seasons and with latitude .

G. Angle of Insolation (Sunlight) and Heating of Earth’s Surface High Angle High Intensity Low Angle Low Intensity 1.

G. Angle of Insolation (Sunlight) and Heating of Earth’s Surface The intensity (strength) of insolation is greatest when sunlight (insolation) is perpendicular to the surface – striking at 90 o because the sunlight is concentrated in the smallest possible area. As the angle of insolation increases , the intensity of insolation increases .

H. Factors affecting Insolation Shape of the Earth (spherical)

2. As latitude increases, the angle of insolation decreases , and the intensity of insolation decreases . a. b. Angle of insolation 0 o Latitude 90 o Intensity of insolation 0 o Latitude 90 o

3. Season of the Year As Earth travels along its orbital path around the sun, the angle of insolation at a given latitude changes with the seasons. This depends on how far a given latitude is from the direct rays of the sun. The direct rays migrate between the Tropic of Cancer (north) and the Tropic of Capricorn (south).

b. Key: Direct Ray of Sunlight (Perpendicular to Earth’s Surface; 90 o ) Ray of Sunlight (striking NYS at an angle less than 90 o )

C. Maximum angle of insolation at 12 noon for mid N.Y.S. (Lat. 43 o N) 1. Dec. 21 2. Mar/Sep. 21 3. June 21 24.5 48 71.5 Low angle Low intensity Medium angle Medium intensity High angle High intensity

4. Time of Day The angle of insolation changes in the course of one day. Maximum intensity occurs at Noon .

b. Angle of Insolation vs. Time

d. Looking South The shadow of a vertical pole indicates how the angle of insolation changes during the day. The higher/greater the angle of insolation, the shorter the shadow, and the greater the intensity of insolation.

V. Celestial Observations Celestial Object = The objects observed in the sky during the day or night (outside of Earth’s atmosphere) Examples: Planets, Sun, Moon, stars, comets, asteroids

V. Celestial Observations Celestial Sphere = Model of the sky

Celestial Sphere Zenith – highest point in the sky directly above the observer’s head. Horizon – imaginary boundary between the sky and ground

E. Location on the Celestial Sphere – THE HORIZON SYSTEM Altitude = angular distance above the horizon. From 0 o on the horizon to 90 o at zenith.

Location on the Celestial Sphere – THE HORIZON SYSTEM Azimuth = Angular distance along the horizon from N (0o), clockwise Mark the rose compass on your notes as you see in the picture on the right!

3. Model problems By careful estimation, determine the azimuth (Az) and the altitude (h) for the star ( ) illustrated in each celestial sphere diagram. Example: Common terms Az h E 1/3 Degrees 90 0 30 o

VI The Moon The moon is a natural satellite of Earth . 1. Luna – Latin for moon 2. Diana – Roman goddess of the moon

B. Physical Properties of the Moon Size Diameter: 2160 miles Compared to Earth Diameter of Moon = 2160 = 1 Earth 8000 4 Gravity 1/6 the gravity of Earth Smaller – less mass

2. Atmosphere The Moon has No atmosphere, so radiation from sun strong Sunburn in seconds Gravity too weak so gases escape into space. Frozen water may exist at the Moon’s polar regions, but none in liquid form

3. Temperatures 240 o F on the lighted side - 240 o F on the far side These large temperature extremes or differences exist because the moon does not have an atmosphere to transfer heat.

4. Lunar Topography – surface features of the moon

“ The Dark Side of The Moon”

a. Craters – bowl-shaped depressions formed primarily as a result of impact of meteors. Examples: Copernicus, Kepler, Tycho, Ptolemaeus Most cratering occurred during heavy bombardment period which gave Earth its early CO2 atmosphere ~4billion years ago Some of these craters filled with lava which is now smooth and glassy There are many more craters on the moon than on Earth because… the moon does not have an atmosphere to 1. burn up incoming meteors and 2. no weathering and erosion!

b. Maria The smooth, glassy regions, which are generally craters filled in by lava, are called maria c. rays – appear as “bright streaks” that radiate from certain craters. The rough regions surrounding them are called “ lunar highlands ”. Consist of craters and mountains

MOON FUN FACTS The moon is actually moving away from earth at a rate of 1.5 inches per year. Only about 59 percent of the moon's surface is visible to us here on earth. The moon is not round, but egg shaped with the large end pointed towards earth. The earth rotates about 1000 mph. By comparison, the moon rotates about 10 mph.

5. The Moon’s Revolution Period of Revolution 1 month OR 29.5 days The moon revolves around Earth in an elliptical orbit, and Earth is at one focus . This causes the moon’s apparent diameter/size to change in a cyclic manner.

6. Phases of the Moon Caused by the moon’s revolution around Earth. Our Earth view of the changing illuminated part of the moon’s surface that face’s Earth.

7. Moon Rotation Does that mean the moon doesn't rotate? No, it does rotate-- one rotation for each revolution around Earth!

Eclipses Lunar Eclipse Solar Eclipse Solar Eclipse – different view

10. Tides Tides are the periodic rising and falling of the oceans . Caused by the moon’s gravitational pull on Earth Affected by Earth’s rotation and distance.

The period from high tide to high tide is normally about 12 hours and 25 minutes. Tides are a cyclic change.

VII. Earth’s Place in the Universe Light Year The distance light travels in one (1) year. 6,000,000,000,000 miles (6.0 x 10 12 ) The speed of light is 186,000 mi/sec. a. We see all night stars as they WERE when the light left that star . When we look at distant stars and galaxies, we look back in time .

B. Galaxies Billions of stars held together by gravity. Shape of galaxies: a. Spiral

D. The Milky Way Galaxy Our sun is only one of the estimated 180 Billion stars that make-up the Milky Way Galaxy. The Milky Way is a Spiral galaxy.

Life Cycle of Stars – H.R.Diagram

VIII. Evolution of the Universe Electromagnetic Energy The sun is the major energy source for weather changes in the atmosphere and many of the changes occurring at Earth’s surface. Energy from the sun comes in many different wavelengths.

Electromagnetic Spectrum (4.5 min)

Radio TV/Radar/micro Infrared Visible/White light UV (ultraviolet) X-Rays Gamma Cosmic

B. Doppler Effect – apparent change in the wavelength of light (or sound) that occurs when an object is moving toward or away from the observer .

The amount of “red shift” is a result of the speed at which the galaxy is moving . Conclusion: As the distance from Earth increases , the amount of red shift of a galaxy increases; this indicates that the farther a galaxy, the faster it is moving .

C. The Big Bang Theory In the late 1920’s, Edwin Hubble discovered that All galaxies were “red-shifted” when viewed from Earth. This meant that all galaxies were moving away from Earth and each other , and thus, the universe must be expanding .

D. Evolution of the Universe Cosmic Evolution Big Bang Origin of Matter Formation of Milky Way Formation of Earth Present

Astronomy - Notes

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Astronomy - Notes