Astronomy Notes

Astronomy

 day/night -> earth spins on axis, repetition of stars and sun very night

we see the shape of the moon change.

Lunar phases are a consequences of the moons 27.3 orbit around earth (sidereal)

Phases of moon  29.5 day cycle (synodic)

Which is it ? both depends on reference point

Synchronous rotation; the celestial body rotates exactly once with each orbit. When we only see one side of the moon. The moon revolves around us and we only see the one face.

What causes eclipse, earth and moon cast shadows

Solar eclipse: moon blocks sun from part of earth, happens at new moon.

Three types: total: completely blocks sun

                  Partial: on part of sun is blocked

                  Annular: the sun appears as a bright ring around the moon

Lunar eclipse: happens at full moon, earth is between sun and moon. Visible over more of earth, last longer then solar.

When you have solar eclipse, two weeks later you will have lunar.

Chapter 2 can be called motion gravity and energy

Chapter 3 laws of motion: we find out ancient mysteries of the planets. How this all started.

Greek astronomy: they observed the celestial bodies revolving around them.

Ptolemy had most sophisticated version of the geocentric model, used for 1500 years

Plato and Aristotle were the first to say earth is the center and the heavens are a perfect circle around us

Geocentric model says that everything revolves around us, earth was the center the center

Retrograde motion 1 planets usually move

Potolemaic model 1 sun rises orbiting earth 2 moon rises and sets 3 stars rise and set together, rotating about point, centered on earth.

Parallax , and apparent shift in the relative coppostions of 2 objects when viewed from different perspectives  

Copernicus center of solar system is near the sun 1543. Parallax earth sun distance << distance to stars. The apparent retrograde motion is caused by motion of planets around sun. copernicun/heliocentric model = center around the sun. The planets follow circular orbits around the sun.

Tycho brahe compiled most precise measurements of planets positions for his time, with no telescope. Observed supernova (1572), showed it was at distance of stars. Parallax view. He hired Johannes kepler (1571-1630)

Tychos invention: a human sized quadrant

Brahe assigned him the tough problems of mars retrograde motion. Found that planetary orbits were heliocentric and elliptical (not circular)

Keplers first law

the orbit of each planet is an ellipse with the sun at one focus

Keplers second law  

the law of equal areas. As a planet moves around its orbit it sweeps out equal areas in equal times.  Areas: A = B = C ….. time of A = time of B = time of C

Keplers third law

the time for planets to orbit the sun is related to its distance from the sun: P squared = a cubed

Galileo 1564-1642 “the astronomer”

Believed Copernican model.

Demonstrated that keplers and Copernicus ideas were right with his telescope.

1 the heavens aren’t perfect

-the sun had spots

-the moon had geological features

2 moons of Jupiter obey keplers law

-saw four moons orbiting Jupiter, proving not all objects orbit earth.

3 phases of venus, supporting heliocentric theory

4 observed that mars, Jupiter and Saturn had no phases

5 observed individual stars in miky way.

Galileo study on motion

Museum in munich Germany

How to describe motion

Speed: rate at which object moves

Velocity: speed and direction

Acceleration: any change in speed and direction

Isaac newton

1 Invented calculus as necessary tool to solve math problems related to motion

2 Formulated 3 laws of motion

3 Formulated 3 universal law of mutual gravitation

universal law of gravitation

1 every mass attracts other mass

2 attraction is directly proportional to the product of their masses

3 attraction is inversely proportional to the square of the distance between their centers

mass is the amount of matter on the object

weight Is the amount of force on the object

Two types of energy

kinetic energy is motion

potential energy is stored

energy

ENERGY CANNOT BE DESTROYED

KINETIC

electrical- charges

radiant- EM energy

thermal- heat

motion- newtons law

sound-

POTENTIAL

Chemical- stored in bonds

Stored chemical- springs

Nuclear- stored in nucleus

Energy transformations

Chemical -> motion

Etc.

Mass-energy

Mass itself is a form of potential energy

E=mc squared

Universal law of gravitation

1 every masss attracts another mass