Lecture 4: Introduction to the Solar System, Lecture notes of Astronomy

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TO THE SOLAR SYSTEM

INTRODUCTION

LECTURE 4

Believed that some stars orbits the Sun and others orbits Earth. 30 years of observations right before the telescope was developed.

I. TYCHO DE

BRAHE

II. JOHANES

KEPLER

Kepler’s Laws: Law of Ellipses: orbit of planets around the Sun is not a perfect circle but rather in elliptical/oval shaped.

=> The ellipse are called foci. The bigger the eccentricity, the elongated the circle. => The least eccentricity, the more circular the planet and the closer it is to the Sun.

2. Law of Equal Areas: A line joining a planet and the Sun sweeps out equal areas in intervals of time. => Sun is the focal point => when the planet is further away from the Sun, it moves slower (orbit slower); closer to the Sun, the planet moves faster.
3. Law of Harmonies: the square of a planet’s orbital period (time it takes to complete an orbit) is directly proportional to the cube of its average distance from the Sun. => The further it is from the Sun, the slower and further it orbits. Created models from Tycho’s data about how the solar system works.

G

FORCE

Mass 1 x Mass 2

(radius)^2

III. ISAAC

NEWTON

Law of Universal Gravitation: Every object in the universe pulls on every other object with a force. Force depends on the masses of the object and the distance between the two or more objects. Mass: The bigger the mass of an object, the stronger its gravitational pull will be. Distance: If 2 objects are closer to each other, the gravitational pull will be stronger. F O R M U L A : is the force gravity between two objects. is the gravitational constant. are the masses of two objects. is the distance between the centers of the two objects.

F

G

m1 m

r

IV. THOMBOUGH

A farmer boy who discovered Pluto in 1930. Pluto is a small planet that was considered the ninth planet in the solar system, but was demoted as a “dwarf planet” in

American astronomer.

1.Sun

2. 8 Planets

3. Moons

4. Asteroids

5. Dwarf Planets

6. Comets

V. THE SOLAR

SYSTEM

T H E S O L A R S Y S T E M C O N S I S T S O F :

The total mass is 100%

=> 99.8% mass of the solar system belongs to the Sun (biggest

mass).

=> 0.1% for Jupiter.

=> 0.1% for Others.

Jupiter, Saturn, Uranus, Neptune are Gas Giants.

=> No solid surfaces; low density; big mass; big size.

=> Often spread apart in the outer solar system.

=> Very dense gas; has many moons that is like ice and reflect light;

has rings and atmosphere; are huge magnetic spheres.

=> Uranus was discovered in 1781 by William Hershel via telescope.

Earth, Pluto, Mercury, Venus and Mars are Terrestrial Planets.

=> Small mass; small size; rocky solid surface; have high density.

=> Crowded in the inner part of the solar system; has few to no

Moons.

Radiometric dating can help distinguish the age

of the solar system.

=> Zircors (tiny crystals in meteorites and moon

rocks) is approximately 4.3 billion years ago (bya);

Oldest moon rocks is ~4.48 bya; meteorites from

Mars is ~4.5 bya and oldest Meteorites is ~4.57 bya.

All planets orbit the Sun in the same direction

when viewed above the North Pole (except

Venus and Uranus - they rotate above their axis,

counterclockwise).

Most of the major Moons orbit the same

direction that their planets rotates in because

they are both commonly formed from the same

rotating disk of dust and gas.

The orbit of all planets lies very close to a single

planet.

Many meteorites are formed from broken

pieces of comets and asteroids.

The higher the mass of a planet, the bigger the

force will be.

=> Earth vs Mars: a spacecraft will start moving

towards Earth because Earth has bigger mass than

Mars and will be moving quickly.

V. THE SOLAR

SYSTEM

Only metal and silicates can exist in solid form due too their

atomic structures and chemical bonds.

Terrestrial planets are composed of rocky and metallic materials.

The Outer part of the solar system is cooler and composed of icy

bodies, gases and solid elements.

Hydrogen compounds are like water.

The inner solar system consists of rocky planets while outer is

mostly gas giants.

There are more solid/rocky debris and icy substances in the

outer solar system than the inner solar system which forms

protoplanets faster.

Sun’s core triggers a nuclear fusion reaction that convert

hydrogen into helium, overtime help releases massive energy

that help sustain life on Earth.

The more craters there is on the surface of a planet, the older it

is.

=> If the surface is smoother, it is a young planet.

=> Craters are called “Maria” from the Latin word for “seas” (early

astronomers mistook the craters on the Moon as seas)

V. THE SOLAR

SYSTEM