Chapter 9Planets and

Other Objects in Space

On a clear night away from city lights, about 3,000 stars are

visible. Why can we see these objects only at night? What other objects can be seen in the night

sky?

Page 304

Page 306 Lesson 1:How Do Earth and Its Moon Move?

Sun, Moon, and Myths: To the ancient Romans, Diana was the

goddess of the moon. They honored Apollo as the sun god. The ancient Romans

believed that their gods caused day and night and brought about changes in

weather and seasons.

Page 308 Earth’s Tilt and the Seasons• Night follows day. Spring follows winter. The changes of night and

day, as well as the seasons, occur because of the ways Earth moves.

• Earth moves in two ways:• Earth rotates, or spins, on its axis. An axis is an imaginary line

through both poles. It takes 24 hours for Earth to completely rotate on its axis.

• The second way Earth moves is by orbiting, or revolving around, the sun.

• The path of one object in space around another object is its orbit.• As Earth orbits the sun, part of it is tilted toward the sun. That part

of Earth takes in more energy from the sun. This energy is in the form of heat.

• During June, July, and August, the Northern Hemisphere of Earth is tilted toward the sun (causing summer) and the Southern Hemisphere is tilted away (causing winter). The cycle continues as Earth orbits the sun.

Page 309 1. The summer solstice, about June 21 in the Northern Hemisphere, is the day of the year that has the most hours of daylight. 3. The winter solstice, about December 21, is the day that has the most hours of darkness. 2. On the autumn equinox, about September 21, and the 4. spring equinox, about March 21, the hours of daylight and darkness are the same. These dates mark the beginning of autumn and of spring.

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Page 310 Moon Phases The moon is a small planet like body that orbits Earth, rather than the

sun. The moon appears to shine, but the light you observe, is actually

reflected light from the sun. As the moon orbits Earth, different amounts of its lit surface can be seen. That’s why the moon seems to have different shapes, or phases.

The phases of the moon follow the same pattern about every 29.5 days. On one of those days, all of the lit side of the moon can be seen from Earth (full moon). Then, as the moon orbits one day we see none of the lit side at all (new moon).

Page 311 New Moon To Full Moon

• When the moon’s orbit brings it between Earth and the sun, its lit side can’t be seen from Earth. This phase is called the new moon. Later in the month, when Earth is between the moon and the sun, we see the sun’s light reflected from one whole side of the moon. When this happens, we see a full moon.

BrainPOP Moon Phases

Page 312 Calendars We use calendars to divide time into days,

months, and years. All of these units of time are based on the movements of Earth.

A solar year is 365 days, 5 hours, 48 minutes, and 45.5 seconds long. This is based on the amount of time it takes Earth to make one complete orbit around the sun. Today’s calendars have 365 days in a year. So every four years, an extra day is added in February to make up for the extra hours and minutes in a solar year. Years with an extra day are called leap years.

Some ancient people based months on the movements of the moon. They knew that the moon completes a cycle of phases in about 29.5 days. Each cycle was almost a month, so a lunar year is 11.5 days shorter than a solar year. Some cultures that use lunar calendars add a month to their calendar every few years to make up for the shorter lunar year.

Lesson 1 Review Match the vocabulary terms.

phases

orbits

axis

moon

When Earth moves around the sun, it _________ the sun.

The moon has __________ that follow a pattern, repeating about every 29.5 days.

The _______ is the imaginary line from one pole of Earth to the other.

orbits

phases

axis