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UNIT 3
Chapter 7: The Night Sky
Chapter 8: Exploring Our Stellar Neighbourhood
Chapter 9:The Mysterious Universe
The Study of the
Universe
CHAPTER 7 The Night Sky
In this chapter, you will:
• describe different views of the night sky, as well as reasons why
various cultures studied objects and events in the night sky
• explain the causes of: the seasons, the phases of the Moon, solar and
lunar eclipses, the tides, and comets
• describe the major and minor components of the solar system
• discuss some Canadian contributions to the study of the solar system
and the technology used to study space
Copyright © 2010 McGraw-Hill Ryerson Ltd.
(Page 268)
Copyright © 2010 McGraw-Hill Ryerson Ltd.
Constellations are star patterns that represent different people and
objects in the night sky. The stories about any particular constellation
vary, depending on the culture observing the star pattern.
Create Your Own Constellation
Why would different cultures come up with different stories about the
same constellation?
(Page 269)
Copyright © 2010 McGraw-Hill Ryerson Ltd.
Movement of objects through the night sky is very reliable. The rising
and setting of the Sun, the phases of the Moon, and the position of the
stars changing with the seasons are very consistent and measurable
events.
7.1 Ancient Astronomy
Early peoples developed
technologies based on
observations of the sky.
Structures that functioned as
calendars helped people to
mark the arrival and departure
of the seasons. This
information assisted people in
activities such as the planting
and harvesting of crops.Mayan pyramids functioned as calendars
(Page 271)
Copyright © 2010 McGraw-Hill Ryerson Ltd.
Calendars represent a way of showing days, organized into a schedule
of larger units of time such as weeks, months, seasons, or years. The
calendar information is usually shown as a table or chart.
Early Calendars and Sky Observations
Fishers, mariners, and
travellers used the fixed
patterns of the stars to
help them navigate on
land and water.
Calendars such as the pyramid on the left
allowed people to predict events such as the
seasons, spring rains, annual flooding of rivers
and lakes, and the location and migration of
birds, insects, and herds of animals.
(Page 272)
Copyright © 2010 McGraw-Hill Ryerson Ltd.
Early Calendars and Sky Observations
Early Aztec calendars
http://en.wikipedia.org/wiki/File:AztecCalendarMuseoAntropologia.JPGhttp://en.wikipedia.org/wiki/File:Aztec_calendar.svg
With the invention of the calendar, the first civilizations were
born. Calendars led to organized agriculture, which led to
more food; that in turn led to time and resources being freed
up to develop knowledge and skills in a variety of areas.
(Page 272)
Copyright © 2010 McGraw-Hill Ryerson Ltd.
Our earliest ancestors paid a great deal of attention to the sky, taking
care not to offend the deities (gods) they believed ruled the skies.
Changes in the heavens were thought to be signs that the gods might
be getting restless.
Early Astronomers
Celestial objects are objects that
exist in space, such as a planet,
star, or the Moon. Celestial
priests and priestesses studied
these objects and learned how to
predict seasons and eclipses.
(Page 272)
Copyright © 2010 McGraw-Hill Ryerson Ltd.
Astronomers are scientists who study astronomy, which is the study
of the night sky. The first astronomers were the Mesopotamians, who
kept detailed records of the sky as early as 6000 years ago.
Mesopotamian Astronomers, Years and Days
A rotation is the turning of an object around an imaginary
axis running through it.
Revolution is the time it
takes an object to orbit
another object.
Our year (365 days) is determined by
counting the number of days it takes the
Sun to return to exactly the same place in
the sky with respect to background stars.
This is the time it takes for Earth to make
one revolution around the Sun.
One day (24 hours) is the time it takes for
Earth to make one rotation.
(Page 273)
Copyright © 2010 McGraw-Hill Ryerson Ltd.
Early Clocks
Early clocks, such as the sundial shown below, tracked shadows to tell
the time of day. As Earth rotates, the position of the Sun in the sky
changes, and the sundial casts shadows in different directions. Time
was told by reading the position of the shadow on the sundial.
(Page 273)
Copyright © 2010 McGraw-Hill Ryerson Ltd.
Reviewing Rotation and Revolution
Click the “Start” button to review the revolution and rotation of Earth.
Copyright © 2010 McGraw-Hill Ryerson Ltd.
Most early peoples thought that Earth was flat. Two ancient Greek
philosophers, Eratosthenes and Aristarchus (310-230 BCE)
hypothesized that Earth was spherical. They based their hypothesis on
three pieces of evidence.
Inferring Earth’s Spherical Shape
2. The appearance of the sky
changed as travellers journeyed
farther north or south.
1. The hull and
then the masts of
ships appeared to
descend below
the horizon as
ships sailed
away.
3. During a
lunar eclipse,
the shadow of
Earth on the
moon was
curved.
(Pages 274-5)
Copyright © 2010 McGraw-Hill Ryerson Ltd.
Section 7.1 Review
Concepts to be reviewed:
• How did early sky watchers develop the first calendars? What
were calendars used for?
• Why were the calendars developed by early peoples so useful?
• What is the difference between a revolution and a rotation?
• What evidence was used by ancient Greeks to infer the spherical
shape of Earth?
(Page 276)
Copyright © 2010 McGraw-Hill Ryerson Ltd.
Most cultures imagined that the patterns formed by the stars in the
night sky represented different people, animals, and objects.
Constellations are groups of stars that seem to form a distinctive
pattern in the sky.
7.2 The Constellations
Because they lie in the same line of sight, the stars in a constellation
appear to be close to each other and at exactly the same distance from
Earth. They may in fact be light-years apart.
A light-year is the distance that
light travels in one year, about
9.5 x 1012km.
(Page 277)
Copyright © 2010 McGraw-Hill Ryerson Ltd.
Star maps such as the one
shown to the right show
constellations and
individual stars. The larger
the dot, the brighter the star.
A star’s apparent
magnitude is its brightness
as seen from Earth.
Random Stars in Space
Stars that appear as a
constellation when viewed
from Earth may appear to
be unrelated when viewed
from space.
Stellar magnitude scales compare the brightness of stars.
(Page 278)
Copyright © 2010 McGraw-Hill Ryerson Ltd.
Reviewing Star Rise and Star Set
Click the “Start” button to review how the rotation of Earth
affects star rise and star set.
Copyright © 2010 McGraw-Hill Ryerson Ltd.
The International Astronomical Union (IAU) is the group that names
and classifies celestial objects, including the 88 official constellations.
Names of Constellations
The star pattern in the Big Dipper was recognized by many cultures,
and a variety of stories attempt to explain its existence and motion.
The Big Dipper is considered to be an asterism, a pattern within a
constellation, Ursa Major.
Many of the constellation
names, particularly in the
northern hemisphere, are
from ancient Greek or Latin.
Orion
Ursa Major
Libra
(Page 279)
Copyright © 2010 McGraw-Hill Ryerson Ltd.
The Big Dipper’s two end stars are called pointer stars because they
point towards Polaris, the North Star.
Polaris and the Pointer Stars
During the night, the stars seem to revolve counterclockwise around
Polaris. In the northern hemisphere, Polaris seems to stay stationary in
the north sky, making it useful for navigation.
The distance from the pointer stars to
Polaris is about five times the distance
between the two pointer stars.
(Page 280)
Copyright © 2010 McGraw-Hill Ryerson Ltd.
Due to Earth’s revolution
around the Sun, you see
different constellations in the
evening sky at different times
of the year.
Viewing Different Constellations
The constellations you see also depends on where you are in relation
to the equator (the latitude where you’re making your observations).
view from Ottawa view from Miami
(Page 281)
Copyright © 2010 McGraw-Hill Ryerson Ltd.
Viewing Different Constellations
Click the “Start” button to review how the revolution of Earth
around the Sun affects the constellations observed.
Copyright © 2010 McGraw-Hill Ryerson Ltd.
Section 7.2 Review
Concepts to be reviewed:
• What are constellations? How are the positions of stars within
them related in space?
• What is a star’s apparent magnitude?
• What is the significance of the Big Dipper? Why is it considered
to be an asterism?
• How can Polaris be found in the night sky? Why is it useful for
navigation?
• Why do different cultures have different interpretations of the
night sky.
• What is a light-year?
(Page 282)
Copyright © 2010 McGraw-Hill Ryerson Ltd.
The study of the movement of Earth and Moon are important to
understanding seasons, the cause of tides, the observed phases of the
Moon, and eclipses.
7.3 Movements of Earth and the Moon
Earth’s orbit around
the Sun is not a perfect
circle. It is an ellipse
(an oval or egg-like
shape).
The Sun is found at one of the ellipse’s two
focal points.
(Page 283)
Copyright © 2010 McGraw-Hill Ryerson Ltd.
Earth rotates with its axis tilted 23.5o from its flat orbital plane.
Why Do We Experience Seasons?
In the summer, the northern
hemisphere is tilted towards the
Sun, while in winter it is tilted
away. It is this difference in tilt
that causes the seasons.
As a result of these tilts, Earth
receives sunlight at a larger angle
for longer periods of time during the
summer, and at a smaller angle for
shorter periods of time in the winter.
Summer
Winter
(Page 284)
Copyright © 2010 McGraw-Hill Ryerson Ltd.
Why Do We Experience Seasons?
The approximate height of the Sun in the sky around the start of each
season is shown in the diagram below.
The length of the day and how high the Sun rises in the sky is directly
related to the tilt of Earth.
(Page 284)
Copyright © 2010 McGraw-Hill Ryerson Ltd.
Why Do We Experience Seasons?
Click the “Start” button to review how the movement of Earth
and its tilt affect the seasons.
(Page 284)
Copyright © 2010 McGraw-Hill Ryerson Ltd.
The Moon makes a complete orbit around Earth in about 29.5 days.
As the Moon completes one orbit, it rotates only once on its axis. As a
result, you always see the same side of the Moon.
The Moon’s Motion
The phases of the
Moon, which are the
monthly progression of
changes in the Moon’s
appearance, results
from different portions
of the Moon’s sunlit
side being visible from
Earth.
The “dark side of the moon” was not observed by humans until 1959,
when a Russian spacecraft passed behind the Moon and took photos.
(Page 286)
Copyright © 2010 McGraw-Hill Ryerson Ltd.
Phases of The Moon
Click the “Start” button to review the cause of the Moon’s phases.
Copyright © 2010 McGraw-Hill Ryerson Ltd.
An eclipse is a phenomenon in which one celestial object moves
directly in front of another celestial object.
Lunar Eclipses
In a total lunar eclipse.
the full Moon passes in
Earth’s shadow.
On average, lunar eclipses only
occur about twice a year
because the Moon’s orbit is
tilted about 5o to Earth’s orbit.
If the Moon passes through only the penumbra
or part of the umbra, a partial eclipse results.
(Page 287)
Copyright © 2010 McGraw-Hill Ryerson Ltd.
Solar Eclipses
Solar eclipses also happen about twice a year, but only people living
in a very small area can observe the phenomena.
In a solar eclipse, the shadow of the Moon falls on Earth.
(Page 288)
Copyright © 2010 McGraw-Hill Ryerson Ltd.
Reviewing Lunar and Solar Eclipses
Click the “Start” button to review lunar and solar eclipses.
Copyright © 2010 McGraw-Hill Ryerson Ltd.
The Moon’s motion is responsible for the tides. The gravitational
force (a force of attraction between all masses in the universe) exerted
by the Moon and Earth pulling on each other causes tides.
Tides
The difference between the force of gravity on the side of Earth
nearest the Moon and the force of gravity on the side of Earth farthest
from the Moon results in a stretching effect called the tidal force.
The highest tides are on the
side of Earth that faces the
Moon.
High Tide Low Tide
(Page 289)
Copyright © 2010 McGraw-Hill Ryerson Ltd.
Reviewing Tides
Click the “Start” button to review tidal forces.
Copyright © 2010 McGraw-Hill Ryerson Ltd.
Section 7.3 Review
Concepts to be reviewed:
Describe and explain the following by referencing the relative
motion and position of Earth, Moon, and the Sun.
• Earth’s seasons
• the phases of the Moon
• lunar and solar eclipses
• tides
(Page 290)
Copyright © 2010 McGraw-Hill Ryerson Ltd.
A solar system is a group of planets that circle one or more stars.
7.4 Meet Your Solar System
The current heliocentric (Sun-centered) model of the solar system was
first introduced in the 1500s by Polish astronomer Nicolaus
Copernicus. Previous models of the solar system were geocentric
(Earth-centered), originating with the Greek astronomer Ptolemy.
A planet is an object that orbits one or more stars (and is not a star
itself), is spherical, and does not share its orbit with another object.
(Page 291)
Copyright © 2010 McGraw-Hill Ryerson Ltd.
When we observe planets in the night sky, Venus and Mercury stay
near the Sun and can thus only be seen in the early evening or
morning. Mars, Jupiter, and Saturn usually appear to move westward
as Earth rotates but at times seem to “wander” westward in a slow
looping motion. This unusual movement from east to west is called
retrograde motion.
Planetary Motion
Retrograde motion is
caused by Earth catching up
to and then passing an outer
planet in its orbit. Earth is
on an inside track and thus
moves faster than the outer
planets.
(Page 292)
Copyright © 2010 McGraw-Hill Ryerson Ltd.
Reviewing Retrograde Motion
Click the “Start” button to review retrograde motion.
Copyright © 2010 McGraw-Hill Ryerson Ltd.
Distances Between Planets
The distances between planets are so large that units such as
kilometres cannot represent them in a meaningful way. For this reason,
astronomers created a unit for measuring distances in the solar system:
the astronomical unit (AU). One AU is approximately equal to the
distance between Earth and the Sun, about 150 million kilometres.
Earth is 1 AU from the Sun.
The average distance between the
Sun and an object orbiting the
Sun is called the object’s orbital
radius. The orbital radius is
expressed in astronomical units.
(Page 293)
Copyright © 2010 McGraw-Hill Ryerson Ltd.
Mercury,
Venus, Earth,
and Mars are
called the
inner planets.
These planets
are also called
the terrestrial
(Earth-like)
planets. They
are relatively
small and
have solid
cores and
rocky crusts.
Classification of the Planets
Saturn, Jupiter,
Uranus, and
Neptune are
called the outer
planets or the gas
giants. These
planets were
formed from large
clumps of gas,
ice, and dust.
They are also
known for their
large gaseous
bands and cold
temperatures.
Mercury
Venus
Earth
Mars
Uranus
Saturn
Jupiter
Neptune
(Pages 294-5)
Copyright © 2010 McGraw-Hill Ryerson Ltd.
Solar System Data
Inner Planet Data
Outer Planet Data
(Pages 294-5)
Copyright © 2010 McGraw-Hill Ryerson Ltd.
Reviewing The Planets of the Solar System
Click the “Start” button to review characteristics of the planets
of the solar system.
Copyright © 2010 McGraw-Hill Ryerson Ltd.
Section 7.4 Review
Concepts to be reviewed:
• How does the geocentric model of the solar system compare to
the heliocentric model?
• What are the basic differences and similarities between the
planets of the solar system?
• How do the inner and outer planets differ from each other?
• What units are used to measure distances within the solar
system?
(Page 296)
Copyright © 2010 McGraw-Hill Ryerson Ltd.
In addition to the Moon and planets, other important objects in the
solar system include comets, meteoroids, and asteroids.
7.5 Other Objects in the Solar System
Comets are composed
of rocky material, ice,
and gas that originate in
the Kuiper Belt and the
Oort Cloud.
The Kuiper Belt is a disc-shaped group of millions of small objects
orbiting the Sun beyond the orbit of Neptune (trans-Neptunian objects)
(Page 297)
Copyright © 2010 McGraw-Hill Ryerson Ltd.
Visualizing the Kuiper Belt (Page 298)
Copyright © 2010 McGraw-Hill Ryerson Ltd.
In 2006, the IAU demoted Pluto to dwarf planet status because its orbit
sometimes crosses Neptune’s orbit.
The Plight of Pluto
Other Kuiper Belt objects, such as the dwarf planet Eris, are actually
larger than Pluto.
(Page 299)
Copyright © 2010 McGraw-Hill Ryerson Ltd.
The Oort Cloud
The Oort Cloud is a spherical
cloud of icy fragments of
debris 50 000 to 100 000 AU
from the Sun. This region is
thought to be home to many
comets. It marks the outer
boundary of the Sun’s
gravitational influence.
Wikipedia/AZcolvin 429
(Page 299)
Copyright © 2010 McGraw-Hill Ryerson Ltd.
Most comets originate in the Kuiper Belt and the Oort Cloud.
Occasionally Jupiter’s gravitational influence will nudge a comet to
change its orbit and enter the inner solar system.
Comets
While some
comets visit the
Sun just once,
periodic comets
orbit the Sun.
When a comet comes too close to
the Sun, the radiation from the
Sun causes it to release gases and
particles, forming a tail that
always points away from the Sun.
Periodic Comets
(Pages 299-300)
Copyright © 2010 McGraw-Hill Ryerson Ltd.
Asteroids
Asteroids are small, non-spherical objects that range in size from a
tiny speck, like a grain of sand, to 500 km wide. Most asteroids
originate in the asteroid belt between Mars and Jupiter. They are
believed to be composed of debris left over from the formation of the
solar system.
Asteroids can have their own moons, as shown in the image above.
Asteroid Ida
Moon Dactyl
(Page 300)
Copyright © 2010 McGraw-Hill Ryerson Ltd.
Meteoroids, Meteors, and Meteorites
The most famous meteor
shower is the Perseid
meteor shower, which
occurs around August 12
every year. It results from
Earth passing through
debris left along the path
of Comet Swift Tuttle.
A meteoroid is a piece of rock moving through space, while a meteor
is a meteoroid that hits Earth’s atmosphere and burns up. Meteorites
are meteoroids that are large enough to pass through Earth’s
atmosphere and reach the ground without being totally burned up.
(Page 301)
Copyright © 2010 McGraw-Hill Ryerson Ltd.
Asteroid and Meteor Impacts
An asteroid the size of a mountain hit Earth 65 million years ago.
Many scientists believe that this impact led to climate changes that
resulted in the global mass extinctions of thousands of species.
Impact craters in Nunavut (A)
and in Arizona (B) are evidence
of impacts many years ago.
(Page 302)
Copyright © 2010 McGraw-Hill Ryerson Ltd.
Tunguska Devastation
A more recent impact occurred on June 30, 1908, in Tunguska, Siberia,
when an object entered Earth’s atmosphere and destroyed an area of
more than 2000 km2. The object (thought to be about 50 m in
diameter) flattened nearly 100 million trees and killed thousands of
forest animals.
Many astronomers around the world
are currently working to discover and
map the courses of any Near Earth
Objects (NEOs) that could pose an
impact risk to Earth.
In 2010, Canada will launch
NEOSSat to help find NEOs.
(Page 303)
Copyright © 2010 McGraw-Hill Ryerson Ltd.
Section 7.5 Review
Concepts to be reviewed:
• In addition to planets, what other objects are found in the solar
system? What distinguishing characteristics do these objects have?
• Why do scientists think that an asteroid or large meteor will hit
Earth in the future?
• What measures could be taken to protect Earth from future
impacts?
(Page 306)
