Chapter 8,
Astronomy

Model some of the ways in which scientists
observe the planets.

Relate evidence that Earth rotates and
define revolution.
Scientists use many tools to observe and
study the universe.







astronomy
universe
telescope
rotation
standard time zone
International Date Line
revolution

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.
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.
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.

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°.
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.

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.

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.
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.

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.

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.
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.