Table of Contents Observing the Solar System The Sun The Inner Planets The Outer Planets Comets, Asteroids, and Meteors Is There Life Beyond Earth?

3-1 Observing the Solar System Observer Approx. Date Accomplishment Greek Scientists   Ptolemy Copernicus Galileo Brahe Kepler

Geocentric Heliocentric

Geocentric System - Observing the Solar System In a geocentric system, Earth is at the center of the revolving planets and stars.

Heliocentric System - Observing the Solar System In a heliocentric system, Earth and the other planets revolve around the sun.

The Sun and Planets - Observing the Solar System Shown below are the average distances of each planet from the sun.

Solar System Activity - Observing the Solar System Click the Active Art button to open a browser window and access Active Art about the solar system.

Planet Speed Versus Distance - Observing the Solar System Planet Speed Versus Distance Johannes Kepler discovered a relationship between the speed of a planet and its distance from the sun. Use the graph to discover what Kepler learned.

Planet Speed Versus Distance - Observing the Solar System Planet Speed Versus Distance Reading Graphs: According to the graph, what is Earth’s average speed? About 30 km/s

Planet Speed Versus Distance - Observing the Solar System Planet Speed Versus Distance Interpreting Data: Which is closer to the sun, Mercury or Mars? Which moves faster? Mercury; Mercury

Planet Speed Versus Distance - Observing the Solar System Planet Speed Versus Distance Drawing Conclusions: What is the general relationship between a planet’s speed and its average distance from the sun? Planets that are closer to the sun move faster.

Planet Speed Versus Distance - Observing the Solar System Planet Speed Versus Distance Predicting: The planet Uranus is about 2,900 million km from the sun. Predict whether its speed is greater or less than Jupiter's speed. Explain your answer. Uranus’s speed is less than that of Jupiter because Uranus is farther from the sun than Jupiter.

Previewing Visuals - Observing the Solar System Preview Figure 2 and Figure 3. Then write two questions you have about Earth’s history in a graphic organizer like the one below. As you read, answer your questions. Models of the Universe Q. What is a geocentric model? A. A model that shows Earth at the center of the revolving planets and stars Q. What is a heliocentric system? A. A model that shows Earth and the other planets revolving around the sun

End of Section: Observing the Solar System

The Layers of the Sun - The Sun The sun has an interior and an atmosphere, each of which consists of several layers.

- The Sun Outlining The Sun As you read, make an outline about the sun that you can use for review. Use the red headings for the main topics and the blue headings for the subtopics. The Sun’s Interior The Core The Radiation Zone The Convection Zone The Sun’s Atmosphere The Photosphere The Chromosphere The Corona Features on the Sun Sunspots Prominences Solar Flares Solar Wind

Click the Planet Diary button for an activity about the sun. More on the Sun Click the Planet Diary button for an activity about the sun.

End of Section: The Sun

Size of the Solar System Our Solar System is 2 light years wide.

The Inner Planets - The Inner Planets The inner planets take up only a small part of the solar system. Note that sizes and distances are not drawn to scale.

Mercury - The Inner Planets Mercury is the smallest terrestrial planet and the planet closest to the sun.

Mercury is dry, extremely hot, and almost airless. - The Inner Planets Mercury Mercury surface is covered by a thin layer of minerals called silicates Mercury is dry, extremely hot, and almost airless. Mercury does not have enough gases in its atmosphere to reduce the amount of heat and light it receives from the sun.

Venus - The Inner Planets Venus’s density and internal structure are similar to Earth’s. But, in other ways, Venus and Earth are very different.

Venus - The Inner Planets This figure combines images of Venus taken from space with a camera (left) and radar (right). The camera image shows Venus’s thick atmosphere. Radar is able to penetrate Venus’s clouds to reveal the surface. Both images are false color.

Thick clouds of sulfuric acid cover Venus. The surface of Venus is extremely hot and dry. There is no liquid water on the planet's surface because the high temperature would cause any liquid to boil away. Venus has a variety of surface features, plains, mountains, canyons, and valleys. The atmosphere consists primarily of carbon dioxide. Thick clouds of sulfuric acid cover Venus. Maat Mons, a mountain on Venus.

- The Inner Planets Earth’s Layers Earth has three main layers—a crust, a mantle, and a core.

Mars - The Inner Planets Mars is called the “red planet.” When you see it in the sky, it has a slightly reddish tinge. This reddish color is due to the breakdown of iron-rich rocks, which creates a rusty dust that covers Mars’s surface.

- The Inner Planets Mars

Mars - The Inner Planets Mars has ice caps at both poles. Scientists think that a large amount of liquid water flowed on Mars's surface in the distant past.

- The Inner Planets Mars’ Atmosphere

Using Prior Knowledge - The Inner Planets Look at the section headings and visuals to see what this section is about. Then write what you know about the inner planets in a graphic organizer like the one below. As you read, write what you learn. What You Know Most of Earth is covered with water. Mercury is closest to the sun. Venus is very hot. Mars is called the “red planet.” What You Learned Earth is unique in our solar system for having liquid water at its surface. Mercury has a greater temperature range than any of the other planets. A day on Venus is longer than its year. The reddish tinge on Mars is caused by the breakdown of iron-rich rocks.

Click the SciLinks button for links on the planets. - The Inner Planets Links on the Planets Click the SciLinks button for links on the planets.

End of Section: The Inner Planets

Gas Giants and Pluto - The Outer Planets The four outer planets–Jupiter, Saturn, Uranus, and Neptune–are much larger and more massive than Earth, and they do not have solid surfaces. Pluto is small and rocky.

Jupiter Compared to Earth - The Outer Planets Jupiter Compared to Earth

Jupiter’s Structure - The Outer Planets Jupiter is composed mainly of the elements hydrogen and helium.

Jupiter’s Structure - The Outer Planets Jupiter is a giant ball of gas and liquid with little, if any, solid surface. Atmosphere—86 % Hydrogen and 14% Helium Chemicals have formed colorful layers of clouds at different heights. The highest white clouds in the zones are made of crystals of frozen ammonia. Darker, lower clouds of other chemicals occur in the belts The planet Jupiter's Great Red Spot is a huge mass of swirling gas. At its widest, it is about three times the diameter of the Earth. Image credit: NASA

Only 16 are wider than 6 miles across! - The Outer Planets Jupiter’s Moons 63 Moons Total! Only 16 are wider than 6 miles across! Galileo discovered Jupiter’s four largest moons. They are named Io, Europa, Ganymede, and Callisto.

Jupiter’s Random, But Totally Cool Fact - The Outer Planets Jupiter’s Random, But Totally Cool Fact 49 Number of named moons - also known as natural satellites - orbiting Jupiter. 6 Years it took the Galileo spacecraft to reach Jupiter. 1,321 Number of Earths that could fit inside Jupiter. 59 Minutes NASA's Galileo probe survived before it was crushed by the intense pressure of Jupiter's atmosphere. 3 The number of rings around Jupiter.

- The Outer Planets Saturn

- The Outer Planets Saturn Saturn is made mostly of hydrogen and helium. The surface and merges into its atmosphere. The seven rings make up Saturn. They are made up of billions of pieces of ice. These pieces range from ice particles that are the size of dust to chunks of ice that measure more than 10 feet in diameter. The dark side of Saturn's rings was photographed by Voyager 1 as it flew by the side opposite the sun. The dense B-ring -- the reddish-brown band -- appears dark because it blocks much of the sunlight. It is the brightest ring when viewed from earth. Image credit: JPL

Saturn’s Random, But Totally Cool Fact - The Outer Planets Saturn’s Random, But Totally Cool Fact 70,700 mph Speed of the Cassini spacecraft as it traveled to Saturn. 5,600 Number of years it would take to travel the same distance as Cassini at 60 mph. 1 Percentage of time Cassini's engines will burn during the mission. The other 99% is all cruising. 52 Number of named  moons orbiting Saturn. 1,100 mph Wind speeds at Saturn's equator. About 1,800 kph. Earth's most violent tornadoes hit 200 mph.

Uranus - The Outer Planets Although the gas giant Uranus is about four times the diameter of Earth, it is still much smaller than Jupiter and Saturn.

- The Outer Planets Uranus The surface of Uranus consists of blue-green clouds made up of tiny crystals of methane. Far below the visible clouds are probably thicker cloud layers made up of liquid water and crystals of ammonia ice.

Uranus - The Outer Planets Uranus’s axis of rotation is tilted at an angle of about 90 degrees from the vertical.

- The Outer Planets Neptune is the only planet that cannot be seen without a telescope

Neptune Neptune’s bluish color is caused by small amounts of methane gas in its atmosphere. The planet has 13 moons and a very narrow, faint ring system.

Neptune Neptune’s bluish color is caused by small amounts of methane gas in its atmosphere. The atmosphere is mostly hydrogen, helium and water. The planet has 13 moons and a very narrow, faint ring system.

Neptune Neptune may be the windiest planet in the solar system. Winds tear through the clouds at more than 1,200 mph  Scientists think there might be an ocean of super hot water under Neptune's cold clouds. It does not boil away because of the incredible pressure. 

- The Outer Planets Pluto Pluto has a solid surface and is much smaller and denser than the other outer planets. 3!

From Pluto, our Sun would look like a very bright star. - The Outer Planets Pluto From Pluto, our Sun would look like a very bright star.

Pluto The surface of Pluto is made of two parts An icy part made of nitrogen and a non-icy part. The air is made mostly of nitrogen. Pluto may in the group of icy objects just beyond Neptune called the Kuiper Belt. The Kuiper Belt is made up of millions of icy and rocky objects.

Identifying Main Ideas - The Outer Planets Identifying Main Ideas As you read the section “Gas Giants and Pluto,” write the main idea–the biggest or most important idea–in a graphic organizer like the one below. Then write supporting details that further explain the main idea. Main Idea The four gas giants are similar in… Detail Detail Detail Detail Structure– they do not have a solid surface. Atmosphere– thick and made up mainly of hydrogen and helium. Rings– each is surrounded by a set of rings. Size and mass– each is very large and massive.

Click the PHSchool.com button for an activity about the planets. - The Outer Planets More on the Planets Click the PHSchool.com button for an activity about the planets.

End of Section: The Outer Planets

Structure of a Comet - Comets, Asteroids, and Meteors The main parts of a comet are the nucleus, the coma, and the tail. Most comets have two tails—a bluish gas tail and a white dust tail.

Comet Orbits - Comets, Asteroids, and Meteors Most comets revolve around the sun in very long, narrow orbits. Gas and dust tails form as the comet approaches the sun.

The Asteroid Belt - Comets, Asteroids, and Meteors Most asteroids revolve around the sun between the orbits of Mars and Jupiter. This region is called the asteroid belt.

Comparing and Contrasting - Comets, Asteroids, and Meteors Comparing and Contrasting As you read, compare and contrast comets, asteroids, and meteoroids by completing a table like the one below. Comets, Asteroids, and Meteoroids Feature Comets Asteroids Meteoroids Kuiper belt and Oort cloud Between the orbits of Mars and Jupiter Origin Comets or asteroids Excluding the tail, about the size of a mountain Typically less than 1 km; some are more than 300 km in diameter Smaller than comets or asteroids Size Ice, dust, small rocky particles Composition Rock Rock or dust

Links on Comets, Asteroids, and Meteors Click the SciLinks button for links on comets, asteroids, and meteors.

End of Section: Comets, Asteroids, and Meteors

Asking Questions - Is There Life Beyond Earth? Before you read, preview the red headings. In a graphic organizer like the one below, ask a question for each heading. As you read, write answers to your questions. Question Answer What are the “Goldilocks”conditions? The favorable conditions on Earth that allow life to exist Is there life on Mars? Scientists have not yet found evidence for life on Mars. Why do scientists think Europa might have life? Europa has an ice crust that could have a liquid water ocean underneath.

Links on Extraterrestrial Life - Is There Life Beyond Earth? Links on Extraterrestrial Life Click the SciLinks button for links on extraterrestrial life.

End of Section: Is There Life Beyond Earth?

Graphic Organizer Feature Geocentric System Heliocentric System Object at center Earth Sun Objects that move around center Planets and sun Planets Proposed by Early Greek astronomers Copernicus Supporters Ptolemy Brahe, Kepler, Galileo

End of Section: Graphic Organizer