Chapter 25



Chapter 25

The Solar System

25.1 Exploring the Solar System

Planets – Greek word for wanderers

The planets earned that name because they appeared to “wander” among the stars.

The stars appeared to rotate around a fixed point- the North Star – Polaris.

Geocentric Model

Earth is stationary while objects move around it.

Accepted theory for 1400 years

Heliocentric Model

Greek Astronomer Aristarchus developed this model.

Earth and other planets revolve around the sun.

Planetary Orbits

Johannes Kepler discovered that orbits had an elliptical pattern instead of circular.

Newton explained the reason that the planets stay in orbit is because of his first law and the reason that they don’t go out into space is because of sun’s gravity.

Animation of the Geocentric Model

Components of a Solar System

Sun, planets, their moons and smaller objects that revolve in the same plane around the sun.

Distances are very large when measuring between components of the solar system so scientist use astronomical units (au) which is the average distance from Earth to the sun.

Exploring the Solar System

Started in 1940’s-50’s

Sputnik 1 was first satellite to space in 1957

April 12,1961, Soviet cosmonaut Yuri Gagarin was first human to orbit Earth.

May 5,1961, Alan Shepard first American in space

July 20, 1969, Neil Armstrong was the first person to set foot on the moon.

1972 was last mission to the moon on Apollo 17.

Recent Space Missions

Scientists today mostly rely on space probes and telescopes, like the Hubble Telescope, to gather new information about the solar system.

The space shuttles are reusable space vehicles that launch like a rocket but land like a airplane.

The International Space Station is used by 16 different countries.

Chapter 25.1

25.2 The Earth-Moon System

Earth’s Moon

The moon is Earth’s closest neighbor. If you traveled 55 mph it would take 6 months to get there.

The gravity is too weak to hold an atmosphere so the temperatures vary greatly.

Surface Features

Maria is Latin for “seas.” They are the flat parts of the moon. They are the darker parts of the moon and make up about 15% of the surface.

Highlands are the lighter areas that are rough mountain ranges.

Craters

Occur from impacts from meteoroids.

Show that erosion and plate movements are not occurring.

Formation of the Moon

Scientist theorized that the moon formed after a collision of a Mars-sized object caused debris to orbit the earth.

This ejected material orbited Earth until it came together to form the moon.

Phases of the Moon

Phases are caused by changes in the relative positions of the moon, sun, and Earth as the moon revolves around the Earth.

A lunar month is 29.5 days

Same side of the moon is always facing the Earth.

Animation of phases

Eclipses

Occurs when the shadow of one body in space falls on another.

Moon’s orbit is offset by 5 degrees from Earth’s orbit so they do not occur that often.

Solar Eclipse

During a new moon the moon is between the sun and Earth and Earth can pass through its shadow.

The darkest part of the shadow is the umbra and only a small part of the Earth will have this total eclipse. The penumbra is less dark and more people would see this partial eclipse.

Lunar Eclipse

A lunar eclipse occurs when the Earth between the moon and the sun when the moon is in the full moon stage. The shadow of Earth falls on the moon.

Lunar eclipses, unlike solar eclipses, can be seen from all over the Earth.

Tides on Earth

Cased by differences in the moon’s gravitational pull on Earth.

During spring tides, the Earth, moon, and sun are in a straight line so there is great differences between the high and low tides.

Neap tides occur when the moon is in the 1st and 3rd quarter and it is at right angles to the line of the sun and Earth. This causes the lowest changes in high and low tides.

View spring and neap tide video

25.3 The Inner Solar System

Mercury

Terrestrial Planets

Mercury, Venus, Earth, and Mars are called terrestrial planets because they have similar structure as Earth.

They have crust, mantle, and iron core.

They have rocky crusts. Mercury and Mars have more craters because Earth’s and Venus surface has eroded them.

They are warmer than the outer planets because they are closer to the sun.

Mercury

Smallest of terrestrial planets

Closest to the sun

Geologically dead – no mantle convection, very little erosion

Fastest moving – 88 days to orbit

Sunrise to sunset is 88 days

Very hot

No atmosphere

Visited by space probe- Mariner 10 in 1974-1975

Venus

Called evening star and morning star because it can only be seen in the west after sunset or east after sun rise.

Brightest object in Earth’s sky except for the moon.

Takes 243 days to rotate around its axis

Rotates in the opposite direction that it revolves

Venus

This atmosphere composed of carbon dioxide

Very hot – 460 degrees Celsius

High sulfur content in atmosphere indicates volcanoes

Earth

Unique because water can exist as a liquid

Gravity can hold gas molecules

The carbon dioxide in the air has been dissolved by Earth’s oceans.

Mars

Most like Earth of all of the planets

“red planet” because of high iron content on its surface

Last volcanic activity about 100 million years ago

Olympus Mon is largest volcano in solar system. If on Earth, its base would cover the space between Cleveland and Washington D.C.

Mars

Very thin atmosphere -95% carbon dioxide – similar to Venus

Once has an ocean. Water is now frozen in poles, underground, or escaped into space.

Seasons marked by huge dust storms

There have not been found any signs of life.

Asteroids

Asteroids are small rocky objects that orbit the sun.

The asteroid belt is beyond Mars.

Scientists hypothesis that the asteroids are remnants of the early solar system that never came together to form a planet.

Relative size of inner planets

25.4 The Outer Solar System

Gas Giants

They are larger than the terrestrial planets

Composed of hydrogen and helium

They are so large that the pressure is so great that the hydrogen and helium is in the liquid form.

Jupiter

Largest Planet – can hold 1300 Earths

One day is equal to 10 hours

Brown bands are colder and move faster than the white bands

Storms occur at the borders of these bands. The Great Red Spot is a storm that was first seen in 1664.

Jupiter

Has at least 50 moons

Two of them are the size of Mercury

Two of them are about the size of Earth’s moon

Ganymede

About the size of Mercury

Metal core rocky mantle

Covered with ice

Callisto

Close to same size as Mercury

Cover in ice

Europa

About the size of the moon

Has metal core and rocky mantle

Covered with ice

Icy crust appears to rest on top of a liquid salt-water ocean

Hypothesized that it is most likely place in the solar system to support like

Io

About the size of the moon

Metal core and rocky mantle

Has active volcanoes

Saturn

Second largest planet

Has rings – made of particles of ice and ice-coated rock

Least dense of all of the planets

Helium and Hydrogen comprise the atmosphere

Scientist hypothesis that helium condenses, falls, gains potential energy and generates heat

It releases more energy than Jupiter

Saturn’s Moon – Titan

Has at least 30 moons

Titan is the largest

Titan is bigger than Mercury

Only moon with an atmosphere

Covered by rivers and lakes of liquid hydrocarbons

Uranus

Very cold – farthest from the sun

Atmosphere hydrogen and helium with methane which gives it the blue-green appearance

Uranus

Probably has a rocky core

Mantle is liquid water an ammonia

Liquid hydrogen and helium surrounds the mantle

Axis of Uranus’s rotation is tilted more than 90°

Neptune

One revolution takes 165 Earth years

Same composition and size of Uranus

Has clouds of methane gives it the bluish color

Has 8 moons – Triton is the largest and has a thin atmosphere and icy surface

Has rings similar to those like Uranus

Pluto

Small so some scientists don’t consider it to be a planet

Smaller and denser than the other outer planets

About the size of the gas giant’s moons

Rotates like Uranus 90° axis

Charon

Pluto’s only moon

Has a diameter about half the size of Pluto

Comets

Are dusty pieces of ice and rock that partially vaporize when they pass near the sun

Meteoroids

Pieces of rock that travel through the solar system

Oldest remnants of the early solar system

Scientists have radioactive dating to determine that the solar system is about 4.6 billion years.

Kuiper belt

Wide belt that extends from Pluto’s Orbit to about 100 AU

Oort cloud

Lies beyond the Kuiper belt

Great reservoir of comets

Occasionally objects from the Oort loud enter the inner solar system as a comet

25.5 The Origin of the Solar System

Nebular Theory

Material expelled by previous stars

Makes think cloud of dust and gas – solar nebula

Rotating cloud of dust and gas formed the solar system.

Protoplanetary Disk

As the nebula rotated faster it flattened out

Density increases at the center until fusion reactions with hydrogen occur

Planetesimals

Asteroid-like bodies that grew by adding mass as they collided - accretion

All plants are revolving the same direction as the protoplanetary disk

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