Lesson 1, The Earth-Sun System Chapter 8, Astronomy Lesson 1, The Earth-Sun System

Objectives Model some of the ways in which scientists observe the planets. Relate evidence that Earth rotates and define revolution.

Main Idea Scientists use many tools to observe and study the universe.

Vocabulary astronomy universe telescope rotation standard time zone International Date Line revolution

What is astronomy? Astronomy is the study of the universe. The universe is everything that exists, including Earth, the planets, the stars, and all of space.

An astronomer is a scientist who studies the universe. They use the unaided eye to find the positions of the Sun and Moon. They also observe planets and stars with telescopes. Telescopes collect light and magnify images to make objects from far away appear close.

When you think of a telescope, you probably picture one that uses visible light to magnify images. Visible light is light you can detect with your eyes.

There are two types of telescopes that use visible light. Refracting telescopes use lenses to gather light from a faraway object and magnify its image. Reflecting telescopes use two or more mirrors, which amplify the image before it reaches the lenses in the eyepiece. Most large telescopes are reflecting telescopes.

Invisible light is any light frequency in the electromagnetic spectrum that people cannot see. Certain telescopes detect waves such as radio waves, radar, infrared, ultraviolet light, or x-rays to gather information that cannot be observed using visible light. Example: An infrared telescope collects data by the heat being produced by a planet or star.

Quick Check Draw Conclusion What kind of telescope would you expect to find in most observatories? The telescope you would find in most observatories is a reflecting telescope. It is easier to build larger mirrors than it is to build larger lenses to gather light.

Critical Thinking Why might an astronomer study objects in space with an infrared telescope? An astronomer would study objects in space with an infrared telescope to collect data not obtainable with visible light, such as the heat being produced by a sun or planet.

How can we prove that Earth rotates? Earth spins on an axis, which runs from the North Pole to the South Pole. One complete spin on the axis is called a rotation. Earth makes one rotation every 24 hours. During each rotation all locations on Earth receives a certain amount of sunlight and a certain amount of darkness, depending on the time of year.

The Sun seems to move because we are viewing it from a spinning Earth. The Sun appears to rise in the east and travel west, this is called the apparent path. You can follow this path by observing the changing shadows of objects at different times.

Evidence for Earth’s rotation comes from Jean Foucault, who hung a ball by a rope and placed sand underneath the hanging ball and observed the simple pendulum, swinging back and forth. Today scientists have the ability to use satellites to observe Earth’s rotation from space.

Standard Time Zones When the Sun is highest over your town it is midday; however, it is not midday everywhere else at the same time.

Earth rotates eastward at a rate of about 360° every 24 hours or 15 degrees per hour. Because of that, we separate Earth into 24 zones known as standard time zones, a vertical belt about 15° wide in longitude, in which all locations have the same time.

There is an hour difference between adjacent time zones. If you go east, you would have to set your clock an hour ahead. Going east through 24 time zones your watch would be one calendar day ahead. To prevent this, the International Date Line was created at the longitude of 180°.

Quick Check Draw Conclusions If it is 8:00P.M. Mountain Standard Time, what time is it in Honolulu, Hawaii? If it is 8:00P.M. Mountain Standard Time, then it is 5:00P.M. in Honolulu, Hawaii.

Critical Thinking What would happen if you traveled west across the International Date Line? If you crossed the International Date Line traveling west, you would add or go ahead one day.

What makes a year? During the year, the seasons change in a cycle. You may notice this as average temperatures rise and fall, as plants bloom, or as animals migrate. It is not due to the distance between the Earth and Sun; in fact the distance is the shortest during our winters.

Our seasons are due to the tilt of Earth’s axis. The axis is tilted 23.5°. The northern axis points towards Polaris, the North Star.

Earth takes 365.24 days to orbit the Sun. One complete trip around the Sun is called a revolution. During the summer in the Northern Hemisphere, that hemisphere is tilted toward the Sun. Six months later, when the Southern Hemisphere is tilted toward the Sun, sunlight strikes in the Northern Hemisphere at a lower angle, providing less energy.

Halfway between summer and winter, the Sun’s rays reach Earth at angles between those two seasons. This is when we have spring or autumn.

Changes in Sunlight The angle at which the Sun’s rays strike Earth causes the seasons. The angle is greatest in Summer and least in winter. This means the Sun is higher in the sky at noon in summer than at noon in winter.

Changes in the angle of the Sun’s rays affect the way objects cast shadows. In summer, when the sun is higher at midday, objects cast shorter shadows. In winter, when the sun is lower in the sky at midday, objects cast longer shadows.

Quick Check Draw Conclusions How do seasons in the Southern Hemisphere and Northern Hemisphere compare? The seasons are inverted. When the north has summer, the south has winter. When the north has autumn, the south has spring.

Critical Thinking You are an explorer who has just arrived on a planet in our solar system. You notice the Sun rising in the west and setting in the east. Based on these observations, what might you conclude about the planet’s rotation? The planet is rotating in a clockwise direction, opposite Earth’s.

How can we explore space? The atmosphere limits our view of space. Scientists launch artificial satellites to study Earth and transmit that data back to Earth. They also launch space probes to study objects various objects throughout the solar system using onboard instruments.

Space shuttles, reusable spacecraft, are sometimes used to launch satellites. The Hubble Space Telescope was placed in orbit this way. The Hubble Space Telescope has given us detailed views of distant planets and stars.

Surviving in Space Astronauts need oxygen, water, and food. With soil, plants can be grown to provide food, remove carbon dioxide, and produce oxygen. Experiments using plants are being done on the International Space Station.

Quick Check Draw Conclusions What type of data do you think an artificial satellite in orbit above Earth might gather? Satellites might collect and transmit data about Earth’s atmosphere and surface, such as pictures, weather conditions, and topographical information.

Critical Thinking What is the difference between planetary images taken from Earth and those taken from space? The sharpness and detail of the images would increase, from ground-based to satellite to probe, because there is no air in space.