‘The Universe’

Many discoveries are credited to scientists from Greece

1. Geocentric Model

◦People once thought Earth was the center of the Universe

◦They thought the moon, Sun, and other planets orbited Earth

Geocentric Model:

In this 1st model, the Sun revolves around the EARTH.

*Scientists in the 16th and 17th centuries made observations that made this model difficult to accept – it did not make sense based on what they were seeing.

So they came up with:

2. Heliocentric Model

◦People changed their thinking to the Sun being the center of the solar system instead of the Earth

◦So, they finally believed that the planets and moons orbit around the Sun

Heliocentric Model

In this model, the earth revolves around the SUN.

Objects in space are in motion – they move!:

A. Rotation

◦Spin of a body on its imaginary axis◦On Earth: Rotates once every 24 hours Causes day and night

Spinning in place; like a dradle

B. Revolution

◦Movement/orbit of a body around a larger one Earth revolves around the Sun and the

moon revolves around Earth

Earth revolves around the Sun once a year (every 365 days)

◦Orbit is elliptical (oval-shaped) so the distance from the sun changes

1. Perihelion – Earth is closest to Sun (1/3)

2. Aphelion – Earth is farthest from Sun (7/4)

C. Force of Gravity

◦Gravity = the force of attraction between 2 objects

◦Depends on the mass of each object and the distance between them

◦Greater mass = greater force of gravity

◦Less of a distance between objects = less force of gravity

◦Gravity holds planets and other space objects in their orbits

 

2. Measuring Distance in Space

A. Light year – unit of measure for the distance between objects in space

◦Distance light travels in 1 year◦Light travels about 5.8 million miles a

year◦Travels 186,000 miles per second

A. The Moon

◦Earth’s only natural satellite

◦May have formed when a body the size of Mars struck Earth and resulted in a part of Earth breaking off

Characteristics:

◦Rotates once on axis every 29 days◦Revolves once around Earth every 29

days – so only see 1 side of moon◦No atmosphere or water◦Many craters◦1/6 the gravity of Earth

Phases of the Moon – during its trip around Earth, the lighted area of the moon seems to change shape

◦Moon reflects the light of the Sun◦Starts with new moon Moon and sun are on the same side of

Earth Dark side faces the Earth – cannot see

moon

Eclipses:

◦Occur when 1 body passes through the shadow of another.

◦Types:

1. Lunar Eclipse – Earth is between moon and Sun

2. Solar Eclipse – Moon is between Earth and Sun

Can you see the small dot in the middle of the circle? That is the moon blocking out the SUN.

Notice that the MOON is being blocked out.

Tides: 

◦Rise and fall of the ocean that occurs twice a day

◦Cause of tides = gravitational pull from moon

◦Pulls on one side of Earth, then the other

1. Facts:

◦Contains planets, moons, stars, comets, asteroids, etc.

◦About 4.6 billion years old

◦Big Bang Theory – Theory that a huge explosion created the universe about 20 billion years ago

2. Within our Solar System:

A. Planets: 2 groups:

Inner Rocky (terrestrial) planets – mostly

rock with little gas (smaller) Mercury, Venus, Earth, Mars

Outer

Gas giants – large planets – small liquid/rock core surrounded by mostly gas

Jupiter, Saturn, Uranus, Neptune

Dwarf Planets

Too small to be an actual planet

Ceres – in asteroid belt

Pluto and Eris – orbit beyond Neptune

◦Surface temp on planet depends on its distance from the sun

Mars and Venus are the hottest

Venus is the hottest planet – has a very dense atmosphere with lot of carbon dioxide (greenhouse gas that traps sun’s heat)

 

Planets revolve around sun because sun’s gravity is so great

Planet Characteristics

Mercury 1. No moons2. Closest planet to the sun

Venus 1. No moons2. Hottest planet3. Brightest planet in our sky

Planet Characteristics

Earth 1. Has life because of liquid water, proper temp., and atmosphere with oxygen2. Has seasons3. 1 moon

Mars 1. Called ‘Red Planet’2. Has largest volcano in solar system

Planet Characteristics

Jupiter 1. Largest planet2. Most moons3. Has ‘Great Red Spot’

Saturn 1. Known for its rings2. 2nd largest

Planet Characteristics

Uranus 1. Rotates lying on its side2. Blue-green in color from methane gas

Neptune 1. Has ‘Great Dark Spot’ – hurricane-like storm2. Has strongest winds 3. Bright blue color due to methane gas

Seasons on Earth - due to Earth’s tilt at 23 ½ degrees

◦Earth is closest to the sun in the winter and farthest from the sun in the summer

◦The tilt is what determines how cold or hot it is

1. Equinoxes

When there is exactly 12 hours of daylight

Vernal (spring) equinox- – around 3/21 Autumnal equinox (fall) – around 9/22

2. Solstices – Depends on the length of the sun’s path through sky

Summer = longest day of year (greatest amount of daylight)

Winter = shortest day of year (shortest amount of daylight)

1. Asteroids

◦Irregularly shaped rocky and metallic objects

◦Orbit the sun - mostly found in asteroid belt between Mars and Jupiter

◦Range in size from a pebble to 600 miles across

◦Idea that 65 million years ago an asteroid struck Yucatan Peninsula in Mexico that led to mass extinction (dinosaurs)

2. Meteoroids

◦Asteroids that have entered Earth’s atmosphere

3. Meteors Small, solid particles from space – enter Earth’s atmosphere

Burn up due to friction = ‘shooting stars’

4. Meteorites

Meteors that hit the ground

The crater is 1.2 kilometers in diameter and 200 meters deep. It formed approximately 49,000 years ago when an iron meteorite that was roughly the size of a school bus struck the Arizona desert east of what is now Flagstaff.

5. Comets

Called ‘dirty snowballs’ Made of ice, frozen gas, dust Orbit the sun

◦ When they get close to the sun, they vaporize and a tail is produced

◦ Example – Halley’s Comet – orbits the sun once every 75 years- next appearance 2061

6. Satellites and probes

◦Example – US owned Hubble Space Telescope – orbits Earth – has made numerous discoveries

http://hubblesite.org/

C. Galaxies

◦Solar systems are found in galaxies

◦Define Galaxy - Huge body of stars and other matter in space

There are billions of stars in each galaxy

Types of Galaxies

◦1. Spiral galaxy – spiral shaped, has arms – made of old and young stars

2. Elliptical – most common shape, smaller than spiral, old stars, oval-shaped

Ex – Andromeda Galaxy

3. Irregular – least common, no definite shape, made of young stars

Draw the shape of each type of galaxy:

Spiral Elliptical Irregular

We live in the Milky Way Galaxy

◦ Early astronomers looked into sky – they observed a dim band of light across sky, so they called it the Milky Way for its faint white color

◦ About 100,000 light years wide

◦ Milky Way is a spiral galaxy - our solar system is in 1 arm

Local Group -

◦ Closest 30 galaxies to us

◦ Example – Andromodea – One of our closest neighbors It’s so far it takes light from there 2 million

years to reach us.

D. Stars

1. Large bodies of gas that create energy

2. Temperature

Can be estimated by the color they shine and their brightness Violet stars are very hot (short, fast

wavelength of light) Red stars are cooler (longer, slower

wavelength of light) Yellow stars (like the sun) are in between

Most common elements in stars are H and He

3. The Sun

Facts

Average-sized star that is the closest star to Earth

Core is 15 million degrees Celsius

◦Mass is 300,000 times Earth’s mass, so its huge gravity keeps planets in orbit around it

◦Produces energy through nuclear fusion – hydrogen is changed into helium

Features

◦ Sunspots

Dark spots on surface of sun Temporary storms that are cooler than rest of

surface

Movement of sunspots proves that the sun rotates

◦Solar flares

Brief explosions near sunspots Release tons of energy Can result in auroras

Called northern and southern lights Makes atmosphere glow beautiful

colors

4. Nebula

◦Areas of gas and dust – glow different colors

◦May be where stars are born

Crab Nebula Helix Nebula

5. Star evolution (how they change over time)

◦1. Birth – born in dark, cool clouds rich in gas and dust (nebula) maybe due to a shockwave

◦2. Protostar – large red object – not hot enough yet for nuclear fusion, so not yet a star

3. Main-sequence stage – main part of a star’s life – the sun is in this stage – lifespan of sun is about 10 billion yers – it’s about ½ way through life, so as about 5 billion more years to go

  4. Red Giant stage – all of the hydrogen is

gone in the core, so the star expands, the surface cools, and it turns red