Download apparent magnitude

Look and Learn
•Describe how color indicates the temperature of a
star.
•Explain how a scientist can identify a star’s
composition.
•Describe how scientists classify stars.
•Compare absolute magnitude with apparent
magnitude.
•Identify how astronomers measure distances from
Earth to stars.
•Describe the difference between the apparent
motion and the actual motion of stars.
Vocabulary
• Spectrum the band of colors produced when
white light passes through a prism
• apparent magnitude
the brightness of a star as seen from Earth
• absolute magnitude
the brightness that a star would have at a
distance of 32.6 light-years from Earth
• light-year
the distance that light travels in one year; about
9.46 trillion kilometers
PG 585 TEXTBOOK
• North Star as 431 light-years than as
4,080,000,000,000,000 km.
VOCABULARY
• Apparent Motion Stars appear to move
across the sky due to the Earth's rotation.
http://my.hrw.com/sh2/sh07_10/student/flash/visual_concepts/80354.htm
• Absolute Motion
• The color of a star depends on its temperature.
Hot stars are blue. Cool stars are red.
• The spectrum of a star shows the composition of
a star.
• Scientists classify stars by temperature and
brightness.
• Apparent magnitude is the brightness of a star
as seen from Earth. Absolute magnitude is the
measured brightness of a star at a distance of
32.6 light-years.
• Astronomers use parallax and trigonometry to
measure distances from Earth to stars.
• Stars appear to move because of Earth’s
rotation. However, the actual motion of stars is
very hard to see because stars are so distant.
• Types of Stars A star is a large celestial body
that is composed of gas and that emits light.
Stars are classified by how hot they are and are
arranged in order of temperature. Temperature
differences result in color differences that you
can see.
Pg 590 textbook
- red giant
a large, reddish star late in its life
cycle
- white dwarf
a small, hot, dim star that is the
leftover center of an old star
- H-R diagram
- main sequence
- supernova
- neutron star
- pulsar
- black hole
A red giant large, reddish star late in its life cycle
A white dwarf
is what stars
like the Sun
become after
they have
exhausted
their nuclear
fuel.
When Stars Get Old
Average stars, such as the sun, become
red giants and then white dwarfs.
Stars that are more massive than the sun
may explode with such intensity that they
become a variety of strange objects such
as supernovas, neutron stars, pulsars, and
black holes.
neutron star
a star that has collapsed
under gravity to the point
that the electrons and
protons have smashed
together to form neutrons
black hole
an object so
massive and dense
that even light
cannot escape its
gravity
Supernova a gigantic explosion in
which a massive star collapses and
throws its outer layers into space
Galaxy
a collection of stars,
dust, and gas bound
together by gravity
Pg 596
Pg 598 textbook
Section Summary
• Edwin Hubble classified galaxies
according to their shape including spiral,
elliptical, and irregular galaxies.
• Some galaxies consist of nebulas and star
clusters.
• Nebulas are large clouds of gas and dust.
Globular clusters are tightly grouped stars.
Open clusters are closely grouped stars.
• Scientists look at distant galaxies to learn
what early galaxies looked like.
cosmology.
• the study of the origin, properties,
processes, and evolution of the
universe
Describe the big bang theory.
Explain evidence used to support the big bang theory.
Describe the structure of the universe.
Describe two ways scientists calculate the age of the universe.
Explain what will happen if the universe expands forever
big bang theory
the theory that all matter and energy in the universe was
compressed into an extremely small volume that 13 billion to 15
billion years ago exploded and began expanding in all directions
Every object in the
universe is part of a larger
system.
Earth is part of our solar
system, which is in turn
part of the Milky Way
galaxy.
Pg 602
• Observations show that the universe is
expanding.
• The big bang theory states that the universe
began with an explosion about 13.7 billion years
ago.
• Cosmic background radiation helps support the
big bang theory.
• Scientists use different ways to calculate the age
of the universe.
• Scientists think that the universe may expand
forever
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Holes Where Stars Once Were
An invisible phantom lurks in space, ready to
swallow everything that comes near it. Once
trapped in its grasp, matter is stretched, torn,
and crushed into oblivion. Does this tale sound
like a horror story? Guess again! Scientists call
this phantom a black hole. As a star runs out of
fuel, it cools and eventually collapses under the
force of its own gravity. If the collapsing star is
massive enough, it may shrink to become a
black hole. The resulting gravitational attraction
is so strong that even light cannot escape! Many
astronomers think that black holes lie at the
heart of many galaxies. Some scientists suggest
that there is a giant black hole at the center of
our own Milky Way.
The Orion Nebula, a vast cloud of dust and gas that
is 35 trillion miles wide, is part of the familiar Orion
constellation. Here, swirling clouds of dust and gas
give birth to systems like our own solar system.
• Explain the relationship between gravity
and pressure in a nebula.
•Describe how the solar system formed.
The Horsehead Nebula is a cold, dark cloud
of gas and dust. But observations suggest
that it is also a site where stars form.
Gravity Pulls Matter Together
• The gas and dust that make up nebulas
are made of matter. The matter of a
nebula is held together by the force of
gravity. In most nebulas, there is a lot of
space between the particles. In fact,
nebulas are less dense than air! Thus, the
gravitational attraction between the
particles in a nebula is very weak. The
force is just enough to keep the nebula
from drifting apart.
solar nebula
• a rotating cloud of gas and dust from
which the sun and planets formed
How the Solar System Formed
• The solar system formed out of a vast
cloud of gas and dust called the nebula.
• Gravity and pressure were balanced until
something upset the balance. Then, the
nebula began to collapse.
• Collapse of the solar nebula caused
heating at the center, while planetesimals
formed in surrounding space.
• The central mass of the nebula became
the sun. Planets formed from the
surrounding materials.
• Describe the basic structure and
composition of the sun.
•Explain how the sun generates energy.
•Describe the surface activity of the sun, and
identify how this activity affects Earth.
Fusion in the Sun
During fusion, under normal
conditions, the nuclei of hydrogen
atoms never get close enough to
combine. The reason is that they
are positively charged. Like
charges repel each other.
In the center of the sun, however,
the temperature and pressure are
very high. As a result, the hydrogen
nuclei have enough energy to
overcome the repulsive force, and
hydrogen fuses into helium.
•List the planets in the order in which they
orbit the sun.
•Explain how scientists measure distances
in space.
•Describe how the planets in our solar
system were discovered.
•Describe three ways in which the inner
planets and outer planets differ.
A Combination of Systems
Our solar system, includes the sun, the planets, and many smaller
objects. In some cases, these bodies may be organized into smaller
systems of their own. For example, the Saturn system is made of the
planet Saturn and the several moons that orbit Saturn. In this way, our
solar system is a combination of many smaller systems.
One astronomical unit (AU) is the average
distance between the sun and Earth, or
approximately 150,000,000 km.
Another way to measure distances in space
is by using the speed of light. Light travels
at about 300,000 km/s in space. This
means that in 1 s, light travels 300,000
km.
One astronomical unit equals about 8.3 light-minutes.
The Inner Planets
The planets of the inner
solar system are more
closely spaced than the
planets of the outer
solar system.
The inner planets are
also known as the
terrestrial planets
because their surfaces
are dense and rocky.
However, each of the
inner planets is unique.
The Outer Planets
The planets of the
outer solar system
include Jupiter,
Saturn, Uranus, and
Neptune.
The outer planets
are very different
from the inner
planets.
• In the order in which they orbit the sun, the
eight planets are Mercury, Venus, Earth,
Mars, Jupiter, Saturn, Uranus, and
Neptune.
• Two ways in which scientists measure
distances in space are to use astronomical
units and to use light-years.
• The inner planets are spaced more closely
together, are smaller, and are rockier than
the outer planets.
• Explain the difference between a
planet’s period of rotation and period
of revolution.
• Describe the difference between
prograde and retrograde rotation.
• Describe the individual characteristics
of Mercury, Venus, Earth, and Mars.
• Identify the characteristics that make
Earth suitable for life.
The inner
planets
The inner planets are also called
terrestrial planets because, like
Earth, they are very dense and
rocky.
The inner planets are smaller,
denser, and rockier than the outer
planets.
A Year on Mercury
A curious thing about Mercury is that its year is only 88 Earth
days long.
As you know, a year is the time that a planet takes to go
around the sun once.
The motion of a body orbiting another body in space is called
revolution.
The time an object takes to revolve around the sun once is
called its period of revolution.
Venus is more like Earth than any
other planet.
Venus is only slightly smaller, less massive, and
less dense than Earth.
Buttttttttt~~~~~
On Venus, the sun rises in the west and sets in
the east.
The reason is that Venus and Earth rotate in opposite directions.
Earth is said to have prograde rotation because it
appears to spin in a counterclockwise direction
when it is viewed from above its North Pole.
If a planet spins in a clockwise direction, the planet
is said to have retrograde rotation.
The Atmosphere of Venus
Of the terrestrial planets, Venus has the densest
atmosphere.
Venus’s atmosphere has 90 times the pressure of
Earth’s atmosphere!
The air on Venus is mostly carbon dioxide, but the
air is also made of some of the most destructive
acids known.
The carbon dioxide traps thermal energy from
sunlight in a process called the greenhouse
effect. The greenhouse effect causes Venus’s
surface temperature to be very high. At 464°C,
Venus has the hottest surface of any planet in
the solar system.
The Atmosphere of Mars
• Because of its thinner atmosphere and greater
distance from the sun, Mars is a cold planet.
• Midsummer temperatures recorded by the Mars
Pathfinder range from –13°C to –77°C.
• Martian air is so thin that the air pressure on the
surface of Mars is about the same as it is 30 km
above Earth’s surface.
• The air pressure is so low that any liquid water
would quickly boil away.
• The only water found on the surface of Mars is
in the form of ice.
Water on Mars
Even though liquid water cannot exist on
Mars’s surface today, there is strong
evidence that it existed there in the past.
Next is an area on Mars with features that
might have resulted from deposition of
sediment in a lake. This finding means that
in the past Mars might have been a
warmer place and had a thicker
atmosphere.
The origin of the features shown in this image is unknown. The
features might have resulted from deposition of sediment in a lake.
Where Is the Water Now?
Mars has two polar icecaps made of both frozen
water and frozen carbon dioxide. But the polar
icecaps do not have enough water to create a
thick atmosphere or rivers.
Looking closely at the walls of some Martian
craters, scientists have found that the debris
around the craters looks as if it were made by
the flow of mud rather than by dry soil.
In this case, where might some of the “lost”
Martian water have gone? Many scientists think
that it is frozen beneath the Martian soil.
Martian Volcanoes
Mars has a rich volcanic history.
Unlike Earth, where volcanoes exist in many places, Mars
has only two large volcanic systems.
The largest, the Tharsis region, stretches 8,000 km across
the planet. The largest mountain in the solar system,
Olympus Mons, is an extinct shield volcano similar to
Mauna Kea on the island of Hawaii.
Mars not only is smaller and cooler than Earth but also has
a slightly different chemical makeup. This makeup may
have kept the Martian crust from moving around as
Earth’s crust does. As a result, the volcanoes kept
building up in the same spots on Mars.
The Sojourner rover, part of the Mars Pathfinder
mission, is shown here creeping up to a rock named
Yogi to measure its composition. The solar panel on
the rover’s back collected the solar energy used to
power the rover’s motor.
• A period of rotation is the length of time that an
object takes to rotate once on its axis.
• A period of revolution is the length of time that
an object takes to revolve around the sun.
• Mercury is the planet closest to the sun.
• Of all the terrestrial planets, Venus has the
densest atmosphere.
• Earth is the only planet known to support life.
• Mars has a rich volcanic history and shows
evidence of once having had water.
The Outer
Planets
• Explain how gas giants are different from
terrestrial planets.
• Describe the individual characteristics of
Jupiter, Saturn, Uranus, Neptune, and
Pluto.
• Because they are so much larger than the
inner planets, the outer planets are called
gas giants. Gas giants are planets that
have deep, massive atmospheres rather
than hard and rocky surfaces like those of
the inner planets.
Jupiter: A Giant Among Giants
• Jupiter is the largest planet in our solar
system.
• Like the sun, Jupiter is made mostly of
hydrogen and helium.
• The outer part of Jupiter’s atmosphere is
made of layered clouds of water, methane,
and ammonia.
• The beautiful colors you see in are
probably due to small amounts of organic
compounds.
• At a depth of about 10,000 km into Jupiter’s
atmosphere, the pressure is high enough to
change hydrogen gas into a liquid.
• Deeper still, the pressure changes the liquid
hydrogen into a liquid, metallic state.
• Unlike most planets, Jupiter radiates much more
energy into space than it receives from the sun.
The reason is that Jupiter’s interior is very hot.
• Another striking feature of Jupiter is the Great
Red Spot, a storm system that is more than 400
years old and is about 3 times the diameter of
Earth!
The Rings of Saturn
• Although all of the gas giants have rings,
Saturn’s rings are the largest.
• Saturn’s rings have a total diameter of
272,000 km.
• Saturn’s rings are only a few hundred meters
thick.
• The rings are made of icy particles that range
in size from a few centimeters to several
meters wide.
Uranus (YOOR uh nuhs)
•Uranus (YOOR uh nuhs) was discovered by the
English amateur astronomer William Herschel in 1781.
•The atmosphere of Uranus is mainly hydrogen and
methane.
•Because these gases absorb the red part of sunlight
very strongly, Uranus appears blue-green in color.
•Uranus and Neptune have much less mass than
Jupiter, but their densities are similar.
•This suggests that their compositions are different
from Jupiter’s.
•They may have lower percentages of light elements
and a greater percentage of water.
Unlike most other planets, Uranus is tipped over
on its side. So, its axis of rotation is tilted by
almost 90° and lies almost in the plane of its
orbit.
For part of a Uranus year, one pole points toward
the sun while the other pole is in darkness. At
the other end of Uranus’s orbit, the poles are
reversed. Some scientists think that early in its
history, Uranus may have been hit by a massive
object that tipped the planet over.
The Atmosphere of Neptune
Although the composition of Neptune’s atmosphere is
similar to that of Uranus’s atmosphere, Neptune’s
atmosphere has belts of clouds that are much more
visible.
At the time of Voyager 2’s visit, Neptune had a Great Dark
Spot like the Great Red Spot on Jupiter. And like the
interiors of Jupiter and Saturn, Neptune’s interior
releases thermal energy to its outer layers.
This release of energy helps the warm gases rise and the
cool gases sink, which sets up the wind patterns in the
atmosphere that create the belts of clouds.
Voyager 2 images also revealed that Neptune has a set of
very narrow rings.
• Jupiter is the largest planet in our solar
system. Energy from the interior of Jupiter
is transferred to its exterior
• Saturn is the second-largest planet and, in
some ways, is still forming as a planet.
• Uranus’s axis of rotation is tilted by almost
90°.
• Neptune has a faint ring, and its
atmosphere contains belts of clouds.
• Pluto is a dwarf planet, and its moon,
Charon, is more than half its size.
• Describe the current theory of the origin of
Earth’s moon.•Explain what causes the
phases of Earth’s moon.•Describe the
difference between a solar eclipse and a
lunar eclipse.•Describe the individual
characteristics of the moons of other
planets.
Natural or artificial bodies that revolve around larger
bodies such as planets are called satellites. Except for
Mercury and Venus, all of the planets have natural
satellites called moons.
Phases the change in the sunlit area of one celestial body as seen from
another celestial body
eclipse
an event in which the shadow of one celestial
body falls on another
On the left is a diagram of the positions of
the Earth and the moon during a solar
eclipse. On the right is a picture of the
sun’s outer atmosphere, or corona, which
is visible only when the entire disk of the
sun is blocked by the moon.
The view during a lunar eclipse is spectacular.
Earth’s atmosphere acts like a lens and bends
some of the sunlight into the Earth’s shadow.
When sunlight hits the particles in the
atmosphere, blue light is filtered out. As a result,
most of the remaining light that lights the moon is
red.
The Tilted Orbit of the Moon
You may be wondering why you don’t see
solar and lunar eclipses every month. The
reason is that the moon’s orbit around
Earth is tilted—by about 5°—relative to the
orbit of Earth around the sun. This tilt is
enough to place the moon out of Earth’s
shadow for most full moons and Earth out
of the moon’s shadow for most new
moons.
The Moons of Other Planets
The moons of the other planets range in size from
very small to as large as terrestrial planets.
All of the gas giants have multiple moons, and
scientists are still discovering new moons. Some
moons have very elongated, or elliptical, orbits,
and some moons even orbit their planet
backward!
Many of the very small moons may be captured
asteroids. As scientists are learning from recent
space missions, moons may be some of the
most bizarre and interesting places in the solar
system!
• Scientists reason that the moon formed from the
debris that was created after a large body
collided with Earth.
• As the moon revolves around Earth, the amount
of sunlight on the side of the moon changes.
Because the amount of sunlight on the side of
the moon changes, the moon’s appearance from
Earth changes. These changes in appearance
are the phases of the moon.
• A solar eclipse happens when the shadow of the
moon falls on Earth.
• A lunar eclipse happens when the shadow of
Earth falls on the moon.
• Mars has 2 moons: Phobos and Deimos.
• Jupiter has dozens of moons. Ganymede,
Io, Callisto, and Europa are the largest.
• Saturn has dozens of moons. Titan is the
largest.
• Uranus has several moons.
• Neptune has several moons. Triton is the
largest.
• Pluto has 3 known moons.
Small Bodies in
the Solar System
• Explain why comets, asteroids, and
meteoroids are important to the study of
the formation of the solar system.
•Describe the similarities of and differences
between asteroids and meteoroids.
•Explain how cosmic impacts may affect life
on Earth.
A small body of ice, rock, and
cosmic dust loosely packed
together is called a comet.
Some scientists refer to
comets as “dirty snowballs”
because of their
composition. Comets
formed in the cold, outer
solar system..
Nothing much has happened to comets since the birth of the
solar system 4.6 billion years ago.
Comets are probably left over from the time when the planets
formed. As a result, each comet is a sample of the early solar
system. Scientists want to learn more about comets to piece
together the history of our solar system
Comets have very elongated orbits. When a comet
gets close to the sun, the comet can develop one or
two tails.
Comet Origins
Many scientists think that comets come from
the Oort (AWRT) cloud, a spherical region
that surrounds the solar system.
When the gravity of a passing planet or star
disturbs part of this cloud, comets can be
pulled toward the sun. Another recently
discovered region where comets exist is
the Kuiper (KIE puhr) belt, which is the
region outside the orbit of Neptune.
Asteroids
•
•
•
•
•
•
Small, rocky bodies that revolve around the sun
are called asteroids.
They range in size from a few meters to more
than 900 km in diameter.
Asteroids have irregular shapes, although
some of the larger ones are spherical.
Most asteroids orbit the sun in the asteroid belt.
The asteroid belt is a wide region between the
orbits of Mars and Jupiter.
Like comets, asteroids are thought to be
material left over from the formation of the solar
system.
The Asteroid Belt
Types of Asteroids
• The composition of asteroids varies depending
on where they are located within the asteroid
belt.
• In the outermost region of the asteroid belt,
asteroids have dark reddish brown to black
surfaces. This coloring may indicate that the
asteroids are rich in organic material.
• Asteroids that have dark gray surfaces are rich
in carbon.
• In the innermost part of the asteroid belt are light
gray asteroids that have either a stony or
metallic composition.
meteoroid
• A small, rocky body that revolves around the sun.
• Most meteoroids are probably pieces of asteroids.
• A meteoroid that enters Earth’s atmosphere and
strikes the ground is called a meteorite.
• As a meteoroid falls into Earth’s atmosphere, the
meteoroid moves so fast that its surface melts. As the
meteoroid burns up, it gives off an enormous amount of
light and thermal energy..
• A meteor is the bright streak of light caused by a
meteoroid or comet dust burning up in the atmosphere.
From the ground, you see a spectacular streak of light,
or a shooting star
Meteors are the streaks of light caused by
meteoroids as they burn up in Earth’s
atmosphere.
Types of Meteorites
• Like their asteroid relatives, meteorites
have different compositions.
• The three major types of meteorites—
stony, metallic, and stony-iron
• Many of the stony meteorites probably
come from carbon-rich asteroids.
• Stony meteorites may contain organic
materials and water. Scientists use
meteorites to study the early solar system.
• Like comets and asteroids, meteorites are
some of the building blocks of planets.
The Role of Impacts in the Solar System
An impact happens when an object in space
collides with another object in space. Often,
the result of such a collision is an impact
crater.
Many planets and moons have visible impact
craters. In fact, several planets and moons
have many more impact craters than Earth
does.
Planets and moons that do not have
atmospheres have more impact craters than
do planets and moons that have
atmospheres.
• Studying comets, asteroids, and
meteoroids can help scientists understand
more about the formation of the solar
system.
• Asteroids are small bodies that orbit the
sun.
• Meteoroids are similar to but smaller than
asteroids.
• Most meteoroids come from asteroids.
• Most objects that collide with Earth burn
up in the atmosphere.
• Large impacts, however, may cause a
global catastrophe.