Astonomy

__SOLAR SYSTEM MODELS__


 * Geocentric**
 * earth centered system developed by Ptolemy
 * was accepted until the 1960's


 * Heliocentric**
 * sun centered system developed by Copernicus
 * modern understanding of the structure of the universe

Celestial Objects: Objects observed in the sky during the day or night (planets, sun, moon stars...) Constellation: a group of stars that make an identifiable pattern in the sky

ROTATION A spinning about the north and south axis rotation: spin on axis ... revolution: go around something Polaris (north star) is because of earths rotation toward the east. (RATE= 15 degreets per hour) SOLAR DAY: the amount of time required for the earth to rotate from one noon to the next, 15 degrees X 24 hours = 360 degrees
 * **EVIDENCE**: The apparent daily counter-clockwise motion of celestial objects around

//Coriolis Effect// - horizontal deflection undergone by all moving materials on the earths surface northern hemisphere: deflected to the right (clockwise) southern hemisphere: deflected to the left (counter clockwise)

FOUCAULT PENDULUM - an experiment to demonstrate the rotation of the earth

a slightly elliptical orbit around the sun (counter clockwise) 365.25 days for one revolution Evidence: Seasonal change of the constellations. The solar diameter varies in a cyclic pattern PERIHELION: sun is the largest, occurs in the N.H winter (shortest distance between the earth & sun) APHELION: smallest, occurs in the N.H summer (largest distance between the earth & sun) __SEASONS__ the earth tilt is 23.5 Parallelism Of The Earth's Axis - The earth axis remains parallel throughout its revolution around the sun Local Noon - When the sun reaches its maximum altitude Zenith - The point directly overhead Equinox: The sun is in the zenith position at the equator (March 21st and September 23rd) 12 HOURS OF BOTH DAYLIGHT AND DARKNESS
 * REVOLUTION**
 * The sun's rays can only be directly overhead at solar noon between the tropics (23.5 N or S of the equator)

SUMMER SOLSTICE - the sun is in the zenith position at the tropic of cancer (June 21st) longest daylight of the year in the northern hemisphere WINTER SOLSTICE - the sun is in the zenith position at the tropic of Capricorn (December 21st) shortest daylight of the year in the northern hemisphere

3. **KEPLER'S LAWS** 4. elliptical eccentricity
 * EARTHS ORBIT**
 * 1) parallelism of earth's axis- every position of earths axis in its orbit is parallel
 * 2) earths distance to the sun
 * @ perihelion- 147,600,000KM
 * @ aphelion- 152,400,000KM
 * planets travel in elliptical orbits therefore they will be at different distances from the sun throughout there revolution
 * the equal area law- states that each planet moves around the sun in such a way that an imaginary line joining the plant to the sun will sweep over equal areas of space in equal areas of time.
 * the harmonic law- the farther the planet is from the sun, the longer its period of revolution
 * eccentricity- degree of the "out of roundness" of the ellipse
 * formula- distance between foci = eccentricity

VII THE PLANETS AND THE SOLAR SYSTEM 2. the asteroids that orbit between mars and jupiter divide the two groups 3. Jovian (outer) planets > 4. meteoroid: a rock or an icy fragment traveling in space 5. meteor- the light made by a meteoroid as it passes through earth's atmosphere 6. meteorite- part of a large meteoroid that survives its trip through the atmosphere and strikes earths surface 7. The most abundant source of meteorites is the antarctic ice cap
 * 1) terrestrial (inner) planets
 * Mercury, Venus, Earth, Mars
 * consist of a rocky crust, a dense mantle layer, and a very dense core
 * average density is above water
 * iron silicon, oxygen, and other heavy elements
 * huge, gaseous, and much less dense
 * hydrogen and helium
 * have ring systems
 * centered around the plantes equator
 * consist of many particles in independent orbits around the planet
 * 93% are stones (resemble earth's dark igneous rocks but include 10-15% IRON)
 * irons (85-95% iron the rest is nickel)
 * stony- irons (rare mixture of stone and iron)

2. **physical properties of stars** 3. **origin of a star**
 * IX STARS AND GALAXIES**
 * 1) **distance between the earth and sun is a 150 million KM**
 * 150 mil. km = astronomical unit (AU)
 * light-year (ly) = 9.6 X 10 KM/YR, distance that a ray of light travels in one year
 * size- range from smaller than earth to 2000X the diameter of the sun
 * density: differs greatly
 * mass: most stars are fairly close to the sun
 * color: depends on the surface temperature
 * red: cooler
 * blue: hotter
 * elements: contain mainly helium and hydrogen
 * brightness
 * apparent magnitude: how bright a star appears to an observer on earth
 * luminosity: true brightness of a star which depends only upon the size and temperature of a star
 * absolute magnitude: expresses luminosity of stars as if they were seen from the same distance
 * stars form from dense clouds of gas and dust
 * an outside force triggers the attraction of gravity causing particles to move toward each other
 * temperature increases as the area contracts
 * if the cloud is large enough parts of it will start to glow
 * protostars : large glowing cloud sections
 * contraction continues protostars become hotter and brighter
 * the center becomes so hot fusion begins (hydrogen nuclei unit to form helium)

4. **red giants and super-giants**
 * star loses stability
 * the star gets so hot it causes the outer layers to expand, enlarging its surface area
 * the star radiates more light and appears brighter

5. **white dwarfs**
 * most of the fusion is used up
 * temperature and pressure of the core can no longer support the weight of its outside layers
 * glows faintly as it continues to cool

6. **supernova**
 * as the star core cools it begins to collapse
 * pressure and temperature rise dramatically
 * the star explodes violently

7. **black holes**
 * gravitational forces are so powerful that even light can not escape

8. **galaxy** : a group of millions or billions of stars held together by gravity

9. **we belong to the milky way galaxy** 9. **big bang hypothesis** : //DOPPLER EFFECT//
 * spiral: central lens shape and spiral arms which usually contain millions of stars as well as dust and gas
 * 1) universe was packed into one dense spere of hydrogen
 * 2) 15 billion years ago the mass exploded, forming an expanding cloud
 * 3) cloud parts condensed into galaxies

V. EARTHS MOON perigee: moon nearest the earth apogee: moon farthest the earth 2. Phases of the moon
 * 1) the moon revolves in an illiptical orbit around the earth
 * revolution = 27.33 days
 * the moon is seen by reflected light
 * the moon is in orbit around the earth

full moon:

waning gibbous:

last quarter:

waning crescent:

new moon:

waxing crescent:

first quarter:

waxing gibbous:

3) lunar month: the time from one new moon to the next a) length = 29.5 days

VI. ECLIPSE umbra: the total shadow penumbra: the partial shadow surrounding the umbra

1) lunar eclipse : occurs when the moon passes into earth's umbra a) only occurs at the full moon phase b) the moons and earths orbit are inclined to each other by 5 degrees so a lunar eclipse does not occur every month (1 per year) 2) solar eclipse: occurs when the moons umbra reaches earths surface a) locations on the earths surface within the umbra experience a total solar eclipse b) locations in the penumbra receive a partial solar eclipse c) can only occur at the new moon phase