1

The Solar System

Astronomy Unit

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Motion of the Earth

Rotation is the spinning of the earth on its axis. This movement

determines the length of a day, 24 hours.

Revolution is the movement of one object around another object. This movement

determines the length of a year, 365.25 days.

Every four years is a leap year.

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Seasons

Seasons are caused by the tilt of the earth’s axis as the earth revolves around the sun.

Vernal equinox is the beginning of Spring.

Summer solstice is the beginning of Summer.

Autumnal equinox is the beginning of Autumn.

Winter Solstice is the beginning of Winter.

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What causes Earth to experience different seasons?

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1. It rotates on its axis while it revolves around the sun.

2. It revolves on its axis while it rotates around the sun.

3. It is tilted while it rotates around the sun.

4. It is tilted while it revolves around the sun.

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5

During which season is the axis of the Earth pointed towards the sun?

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Sum

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1. Autumn

2. Spring

3. Summer

4. Winter

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How does the length of day compare to the length of night during the Vernal Equinox?

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1. Day is longer than night.

2. Night is longer than day.

3. The day and night are equal in length.

4. The day and night are not equal in length.

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Phases of the Moon

The moon is illuminated by the sun.

The moon reflects sunlight to the earth.

The different phases of the moon is affected by the moon revolving around the earth as the earth revolves around the sun.

The complete cycle of phases takes 29.5 days, this is known as a synodic month.

Each phase takes about 3.5 days.

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Phases of moon

New Moon Waxing Crescent First Quarter Waxing Gibbous Full Moon Waning Gibbous Last Quarter Waning Crescent

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Our Moon

Orbits the earth. Has 1/6 the gravity as

earth. Causes the tides on

Earth. High tides are 12.5

hours apart Spring tide is the

highest high tide (Full & New moon).

Neap tide is the lowest high tide (First & Last Quarter moon).

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Other Facts About Our Moon

The length of rotation is the same as the length of revolution, 27.3 days.

We only ever see one side of the moon.

The side facing away from the earth is more heavily cratered.

The Apollo mission sent seven manned missions to land on the moon.

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Which phase occurs when the moon is in between the Earth and the sun?

Full

moo

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New

moon

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Quar

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28

A. Full moon

B. New moon

C. 1st Quarter moon

D. 3rd quarter moon

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Solar Eclipses

In a solar eclipse, the moon is in between the sun and the earth.

The complete shadow is the umbra.

The partial shadow is the penumbra.

Only occur during a new moon.

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Lunar Eclipse

In a lunar eclipse, the earth is between the sun and the moon.

Only occur during a full moon.

Eclipses don’t happen every month because there is a tilt in the orbit of the moon around the earth and the moon, sun & earth don’t line up in a straight line.

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When studying a solar eclipse, which is the proper method for viewing the sun?

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Use

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27

2

A. Wear sunglasses

B. Use a refracting telescope

C. Use a pinhole camera

D. Use a magnifying glass

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Forces that Hold Earth in Orbit around the Sun

Gravity is the attraction between any two objects.

Inertia is the tendency of an object to resist change in motion.

The balance between gravity and inertia keeps earth in orbit around the sun.

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Members of the Solar system

Sun (closest star to earth)

Planets Moons Asteroids Meteoroids Comets

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Inner Planets: Mercury

0.4 AU from the sun. Rotational period 59 Earth

days. Revolution period of 88 Earth

days. No moon. Average temperature range

is 670 K to 103 K. Almost no atmosphere and

no water.

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Inner Planets: Venus

0.7 AU from the sun. Retrograde rotational period

243 Earth days. Revolution period of 225

Earth days. The day on Venus is longer

than a year. No moon. Average temperature range

is 700 K. Atmospheric pressure 90

times that of Earth. Atmosphere of sulfuric acid. Large amount of CO2 causing

the Greenhouse Effect.

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Inner Planets: Earth

1.0 AU from the sun. Rotational period 24

hours. Revolution period of

365.25 days. One moon. Atmosphere 78%

nitrogen, 21% oxygen & 1 % carbon dioxide.

71 % of Earth’s surface is covered by water.

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Inner Planets: Mars

1.5 AU from the sun. Rotational period 23.9 Earth

hours. Revolution period of 687

Earth days. Two moons: Phobos &

Deimos. Average temperature range

is 144 K to 300 K. Thin atmosphere of carbon

dioxide and some water. Largest volcano is Olympus

Mons. Polar caps of dry ice.

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Asteroid Belt

Found between the orbits of Mars & Jupiter.

Trojan refers to asteroids or moons that share the same orbit as a larger planet or moon, but does not collide because it orbits.

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Outer Planets: Jupiter

5.0 AU from the sun. Rotational period 9.9 hours. Revolution period of 11.9

earth years. 63 moons including Io,

Europa, Ganymede & Callisto.

Has rings. The Great Red Spot is a

major storm on the surface of the planet.

Average temperature of 163 K.

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Outer Planets: Saturn

9.6 AU from the sun. Rotational period 10.7 Earth

hours. Revolution period of 29 Earth

years. Has 47 moons including

Titan. Has a ring system. Density is less than water. Average temperature of

133 K.

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Outer Planets: Uranus

19 AU from the sun. Retrograde rotational period

17.2 Earth hours. Revolution period of 83.7

Earth years. 27 moons. Has rings. Discovered by William

Herschel in 1781. Average temperature is 78 K.

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Outer Planets: Neptune

30 AU from the sun. Rotational period 17 Earth

hours. Revolution period of 164

Earth years. 13 moons. Has rings. Discovered by John Galle in

1846. Average temperature is 73 K.

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Planet diameters

Mercury - 4879 km Venus – 12,104 km Earth – 12,756 km Mars – 6794 km Jupiter – 142,982 km Saturn – 120,536 km Uranus – 51,118 km Neptune – 49,528 km

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Oort Cloud

The Oort Cloud is the area surrounding the solar system where the comets are found.

Comets are dirty snow balls. Comets have a head

(nucleus & coma) and a tail. Halley’s comet appears every

76 years.

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Meteors

Meteoroids are pieces of rock from object such as asteroids that fly through space.

Meteors are meteoroids that are burning up in the earth’s atmosphere (shooting stars).

Meteorites are meteoroids that have landed on the earth’s surface.

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Models of the Solar System

Models of the solar system: Geocentric model placed the

earth in the center of the solar system (Aristotle & Ptolemy).

Heliocentric model placed the sun in the center of the solar system and that all the planets orbited the sun (Copernicus).

Newton stated that gravity kept the planets in orbit around the sun.

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Theories of the Formation of the Solar System

Nebular Theory states that the sun formed from a cloud of gas and dust and that collapsed because of the gravity. As the cloud collapsed, it

formed into a flat, rotating disk.

Planetesimals formed when small particles collide and stick together (accretion).

The radiation from the sun burned off most of the gases of the inner planets

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Formation of the Moon

Earth collided with a large body.

The debris began to clump together to form the moon.

The moon began to orbit the earth, being pulled in by the earth’s gravity.

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Kepler’s Laws of Planetary Motion

LAW 1: The orbit of a planet/comet about the Sun is an ellipse with the Sun's center of mass at one focus.

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Kepler’s Laws of Planetary Motion

LAW 2: A line joining a planet/comet and the Sun sweeps out equal areas in equal intervals of time.

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Kepler’s Laws of Planetary Motion

LAW 3: The squares of the periods of the planets are proportional to the cubes of their semi major axes.

This means, the longer the orbital period, the farther the distance from the sun.

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Chapter 19 Test – The Solar System

November 20th or 21st.

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Review Questions:

Which forces are responsible for keeping the planets in orbit around the sun?

(gravity & inertia)What causes the phases of the moon?(the relative positions of the Earth, moon

& sun)Which planet has the Great Red Spot?(Jupiter)

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Review Questions:

Which planet has a longer day than its year? (Venus) Which planet lies on its side as it rotates? (Uranus) What happens when the moon goes between

the sun and the earth, casting a shadow on the earth?

(solar eclipse)

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Review Questions:

Which planet is the largest in our solar system?

(Jupiter) Where do you find all of the comets in our

solar system? (Oort cloud) What is located between Mars and Jupiter? (Asteroid Belt)

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Review Questions:

What do you call a piece of rock that is burning up as it goes through the Earth’s atmosphere?

(meteor) Which planet has the most moons? (Jupiter) Which planet has the Greenhouse Effect? (Venus)

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Review Questions:

What is the shape of planetary orbits according to Kepler’s First Law of Motion?

(ellipse) What causes the seasons on Earth? (tilt of the Earth’s axis) Which theory explains the creation of the solar

system? (Nebular theory)

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Review Questions:

Why do we only ever see one side of the moon?

(the length of rotation & revolution are the same)

Nate Hoff weighs 240 pounds on Earth. What is his weight on the moon?

(40 pounds-1/6 the gravity)

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Review Questions:

Which model of the solar system states that the sun is in the center of the solar system and everything revolves around it?

(Heliocentric)What do we call the highest, high tide?(Spring Tide)