Astronomy

**Heliocentric**
-Sun centered system developed by copernicus - modern understanding of the structure of the universe.

__Celecstical 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.

A spinning about the north and south axis. //__EVIDENCE__//: the apparent daily counter- clockwise motion of celestial objects around plaris (north star) is because of earth's rotation toward the east. (rate= 15º per hour)
 * ROTATION**

15º X 24 HOURS= 360º
 * SOLAR DAY**- the amount of time required for the earth to rotate from one noon to the next.


 * STAR TRAILS**

Horizontal deflection undergone by all moving materials on the earth's surface. Northern Hemisphere- deflected to the right (CLOCKWISE) Southern Hemisphere- deflected to the left (COUNTER CLOCKWISE)
 * CORIOLUS EFFECT**

An experiment to demonstrate the rotation of the earth.
 * FOUCAULT** **PENDULUM**

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 and sun)
 * REVOLUTION**

//The earth's tilt is 22.5º __PARALLELISM OF THE EARTH'S AXIS -__ the earth axis remains parallel through out its revolution around the sun. __LOCAL NOON-__ when the sun reaches its maximum altitude. __ZENITH__- the point directly overhead. the sun's rays can only be directly overheade at solar noon between the tropics (23.5º N or S of the equator.)
 * //S E A S O N S//**
 * mental note:** IF YOU WANT TO SEE THE NORTH STAR.. YOU HAVE TO BE AT THE NORTH POLE.....

__EQUINOX__ - the sun is in the zenith position at the equator (march 21s and sept. 23rd) 12 hours of both daylight and darkness.

__SUMMER SOLSTICE-__ the sun is 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 (DEC. 21ST) SHORTEST DAYLIGHT OF THE YEAR IN THE NORTHERN HEMISPHERE.

EARTH'S ORBIT 1.) Parallelism of earth's axis - every position of earth's axis in its orbit is parallel. 2.) earth's distance to the sun - @ perihelion- 147,600,000 km - @ Aphelion- 152,400,000 km //

Kelper's Laws a. planets travel in elliptical orbits therefore they will be at different distances from the sun throughout there revolution. b. the equal area law- states that each planet moves around the sun in such a way that an imaginary line joining the planet to the sun will sweep over equal areas of space in equal areas of time. c. the harmonic law- the farther the planet is from the sun, the longer its period of revolution. ELLIPTICAL ECCENTRICITY a. eccentricity- degree of the out of roundness of the ellipse. b. formula- distance between foci. eccentricity —————————— length of major axis