Download 03/13/15 Astronomy

CP Space Science
Unit
(Textbook reference Chapters 12, 13, 14, 15 and 16)
1
Key Ideas
• Galaxies: clusters of stars; different shapes
• Stars: Sun; differ in size, temperature and
color; source for all bright objects
• Gravity: planets, stars, solar system
• Know the appearance, composition,
position and size, and motion of objects in
our solar system
• Astronomical units for measuring
2
What is astronomy?
What is a Meteor?
What is a Star?
?
?
?
What is an Open Cluster?
What is a Nebula?
What is a Comet?
?
?
?
What is a Quasar?
What is a Black Hole?
M33, The Pinwheel Galaxy in Triangulum
by George Greaney
What is astronomy?
M33, The Pinwheel Galaxy in Triangulum
by George Greaney
Basically, if its off this planet its a study
of some realm of astronomy.
As one might imagine that covers an awful lot
of subjects, even more than we know right
now.
•NGC 253, galaxy in Sculptor
What is astronomy?
Astronomy is a science that attempts
to understand the make-up and the
M83 in Hydra
history of the universe.Galaxy
by George Greaney
•Stars
•Nebula
•Planets
•The Sun
•The Great Andromeda Galaxy
by George Greaney
•Star clusters
•Galaxies
•Galaxy clusters
•Dark matter
•Black holes
What is an
astronomer
?
Galileo Galilei (1564-1642)
A night watchman with a college education?
An astronomer is a
scientist, skilled in
mathematics,
physics, and
astronomy.
Most professional
astronomers work
for universities or
government
agencies.
Galileo Observatory in Italy
Source: The Berkeley Cosmology Group
Few astronomers spend
much time looking through a
telescope. Most operate
telescopes from a control
room or even from their
computer at home via the
Internet.
Typical astronomers only
spend one or two weeks each
year observing, and the rest
of their research time
analyzing their data.
Source: Applied Theoretical and Computational Physics Division
Los Alamos National Laboratory
Astronomer Serena Kim at work
At Cerro Tololo in Chili
What is an amateur
astronomer?
Amateurs and
their tools
What is an amateur
astronomer?
Although the term has
different meanings for
different people, a basic
definition would include
anyone who looks into
the sky, and wants to
see or learn more.
What is
astronomy
?
Reflection nebula IC4606
by George Greaney
The Expanding Universe 15-5
Theories on How the Universe Formed
• The Big Bang Theory
• Steady-State Theory and Plasma Theory
Hubble’s Law
Age of the Universe
15
What is space like?
• No air
• No gravity-when you’re
not very close to a planet,
sun, or moon
• No wind
• No friction
• No real “up” or “down”
• No pressure
What is a “galaxy”?
(15.4 Textbook reference)
• A large group of stars outside of our own Milky Way
• Made of billions to trillions of stars
– Also may have gas and dust
• Spiral, or elliptical, or irregular shaped
Image at http://hubblesite.org/newscenter/archive/releases/galaxy/spiral/2007/41/results/50/
Spiral galaxy--Andromeda
NOAO/AURA/NSF Images at http://www.noao.edu/image_gallery/html/im0606.html and
http://www.noao.edu/image_gallery/html/im0685.html
Elliptical Galaxies
Images at http://hubblesite.org/newscenter/archive/releases/galaxy/elliptical/2007/08/image/a/format/large_web/results/50/
and http://hubblesite.org/newscenter/archive/releases/galaxy/elliptical/1995/07/results/50/
Irregular Galaxies
NASA and NOAO/AURA/NSF Images at
http://hubblesite.org/newscenter/archive/releases/galaxy/irregular/2005/09/results/50/ ,
http://www.noao.edu/image_gallery/html/im0560.html , and http://www.noao.edu/image_gallery/html/im0993.html
Our Galaxy: the Milky Way
• has about 200 billion stars, and lots of gas
and dust
• is a barred-spiral (we think)
• about 100,000 light-years wide
• our Sun is halfway to the edge, revolving at
half a million miles per hour around the
center of the Galaxy
• takes our Solar System about 200 million
years to revolve once around our galaxy
The Milky Way
Image at http://news.nationalgeographic.com/news/bigphotos/1945371.html
Mapping the Milky Way
How do we know what our galaxy looks like?
We can see
– stars
– star clusters
– nebulae
– galaxies
Reviewing Galaxies
• Groups of stars,
planets, and space
debris
• Irregular, Elliptical,
Spiral
• Milky Way is our
galaxy
24
15.3 Lives of Stars
25
What
Is a
Star?
Image of the Sun from Goddard Space Flight Center
What is a Star?
Our Sun is the closest star.
At the simplest, a star is just a ball of gas
that has condensed out of interstellar
material.
The largest part of its lifetime is spent as a
main sequence star during which hydrogen
is being converted to helium balancing
gravitational contraction so that the radius
and energy output remain almost constant.
Source: The British Astronomical Association
Stars (Textbook reference 15-2 and 15-3)
• Bodies of gases that
give off tremendous
amounts of radiant and
heat energy
• Constellations are
groups of stars used for
navigation, storytelling,
honoring heroes
Life Cycle of a
Star Video
28
Nearby Stars:
Name
Distance from Earth
Sun
93 million miles (8 light minutes)
Proxima Centauri
4.22 Light Years
Alpha Centuri A,B
4.39 Light Years
Barnards Star
5.94 Light Years
Wolf 359
7.8 Light Years
Lalande 21185
8.3 Light Years
Sirius A,B
8.6 Light Years
Image courtesy of Dave Dockery
Astronomical Society of Las Cruces
Source: The British Astronomical Association
Evolution of Stars
30
How do Black Holes form?
31
Black Holes
• Remains of a neutron star
that has collapsed due to
intense gravity
• Event horizon = surface of a
black hole from which light
cannot escape
32
15.2 Characteristics of Stars
• Star sizes
– White dwarf, Medium, Large, Giant Star
• Spectrograph
– Device that breaks light into colors and produces a light
emmissions spectrum.
• ROYGBIV – Low energy to High energy
– Red, Orange, Yellow, Green, Blue, Indigo, Violet
• Light Year
– Light travels at 300,000 km/second
– Distance light travels in one year (9.5 million million km.
33
Hertzsprung-Russell Diagram
Video on the
Hertzsprung-Russell
Diagram
The Doppler Effect:
Spectroscopy Video
Red Shift – stars moving away from Earth
Blue Shift – stars moving toward Earth
34
Hertzsprung-Russell Diagram
Images from
http://www.nasa.gov/centers/goddard/news/topstory/2007/spectrum_plants.html and
http://sunearthday.gsfc.nasa.gov/2009/TTT/65_surfacetemp.php
Using a Star’s Spectrum
• We can use a star’s spectrum to classify it.
NOAO/AURA/NSF image at
http://antwrp.gsfc.nasa.gov/apod/ap010530.html
Time to Create a Stellar Graph
• Everyone will receive several “stars”
• Place them on the large paper, according to
their color and their brightness
• This is a version of the Hertzsprung-Russell
diagram.
Measuring Distances
• Parallax – apparent change in position of an object when you look at it
from a different position.
• (let’s model it)
– As Earth orbits the Sun, we see nearby stars move relative to more distant
stars
– How many degrees did the plate move, relative to the background?
– Can you calculate the distance to the plate?
– The angles involved for stellar observations are very small and difficult to
measure. Proxima Centauri, has a parallax of 0.77 arcsec. This angle is
approximately the angle subtended by an object about 2 centimeters in
diameter located about 5.3 kilometers away.
The Sun (Textbook reference 14-2
• The sun is an ordinary star.
• The sun is the biggest,
brightest, and hottest object in
the solar system.
• Its energy is the result of the
fusion of hydrogen nuclei into
helium nuclei.
• The sun is made of about 70%
hydrogen and 28% helium.
Characteristics of the Sun
• Interior: Core, Radiation Zone, Convection
Zone
• Exterior: Photosphere, Chromosphere, Corona
• Features: Sunspots, Prominences, Solar
Flares
• Central star in our solar system around which
planets revolve
• Composed of gases (H2 and He) burning at
15,000,000 o C
40
The Sun: Seasons
(Textbook Reference 12-1)
Seasons:
Solstices
sun directly overhead
two times a year (June 21 and December 21)
June=longest day, December=shortest day
Equinoxes
halfway between solstices
neither hemisphere is tilted toward the sun
daylight and darkness=equal
41
What causes the seasons?
1. 23.5° tilt of Earth’s axis
2. Direct vs. indirect sun
rays
3. Length of daylight
42
Fall
Summer
Sun
Winter
Spring
43
The Sun: Solar Energy (14-2)
Energy in the Atmosphere:
Energy reaches earth’s atmosphere
Reflected back or absorbed
clouds, dust and gases
surface
Energy is transferred within the troposphere
radiation: heats land and water
reflected back into atmosphere
convection: moves heat through the troposphere
warm air is replaced by denser, cool air
conduction: transfers heat from land and water directly
into the air nearest Earth’s surface
44
Our Sun is a star that has already spent
about 5 billion years on the main sequence.
Scientist believe our Sun is roughly halfway
through it's life.
Source: The British Astronomical Association
Stars are the source of light for
all objects in outer space
Earth’s Moon
Phases of the Moon
(Textbook reference 12-3)
waxing = increasing waning = decreasing
gibbous = > ½
crescent = < ½
47
Lunar Phases
• New Moon
• Waxing Crescent
• First Quarter
• Waxing Gibbous
• Full Moon
New
Waxing
FirstFull
Quarter
Gibbous
Waxing
Crescent
48
Lunar Phases
• Full Moon
• Waning Gibbous
• Last Quarter
• Waning Crescent
• New Moon
Waning
Last Full
Quarter
Gibbous
Crescent
New
49
Rotate vs. Revolve
• Rotation – spin of an object on its axis
• Revolution – orbit of an object around
another object
50
Why does one side of the
moon always face us?
• Moon rotates once every 27.3 days
• Moon revolves once every 29.5 days
• Moon’s rotation approximately equal
to its revolution
51
Moon’s Orbit and Phases
52
Eclipses, 12.3
1. Lunar Eclipse
2. Solar Eclipse
3. Total Eclipse
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54
55
A total eclipse of the sun
occurs during the day!
Only the corona is visible.
56
Tides
•Effect of gravity between
the moon and the sun
57
Spring Tides
• When the sun,
the moon, and
the Earth are all
o
aligned in a 180
angle
58
Neap Tide
• When the sun,
the moon, and
the Earth form
a 90° angle
59
Stars are the source of light for
all objects in outer space
• Complete the standards-based reading
handed out in class to address this
concept
• Answer the assessment questions that
accompany the handout
60
SOLAR SYSTEM
• The Sun
• Eight Planets and Pluto
• Sixty-one satellites of the planets
• Many Comets and asteroids
Formation of the Solar System
(Textbook reference 15-5)
A collapsing interstellar cloud
• Stars and planets form from interstellar clouds
– They appear dark because of dust blocking out the
light
– The light can cause it to glow, or even become
heated
– Stars and solar systems are “born” this way
• Collapse accelerates
– The collapse of this cloud is slow, but it accelerates
and becomes denser at the center
– This collapse and spin results in a flattening at the
equatorial plane
• Matter condenses
– Our solar system may have formed this way when
temperature and pressure caused hydrogen to fuse
into helium
– The temperature differential allowed for different
elements to concentrate in different areas around
the sun
• This is why the inner planets are rocky and have a
higher melting point
• Outer ones are less dense and made of ice and gas
Planetesimals
• The planetesimals
combined to get larger and
in many cases to become
the known planets.
• Gas giants form
– Jupiter was the first to form
• Icy planetesimals combined
to form it
• Its mass (gravity) caused it to
collect much of the debris
– The others formed the same
way, but Jupiter took most
of the extraneous material
• Terrestrial planets form
– the merging of planetesimals in the inner portion of the disk
– Made of materials that resist vaporization
– Most of the gaseous material and “smaller stuff” consumed
by the sun, hence fewer satellites.
• Debris
–
–
–
–
All of the “junk” left over
Some became comets
Some ejected from solar system or destroyed in collisions
The asteroid belt between mars and Jupiter is the rest
Planets…Wandering Stars?
The Greeks called the five points
of light that seemed to move
among the stars ______, meaning
“______”.
• planets
• wanderers
The ancient Romans later
called these planets:
•
•
•
•
•
Mercury
Venus
Mars
Jupiter
Saturn
Greek Ideas: Earth at the Center
(Textbook reference 14-1)
Initially the geocentric
theory stated that everything
moved around the earth.
 Retrograde motion (apparent
westward movement) led
astronomers to find a different
explanation
Describe the ancient Greek
beliefs of the solar system.
• The ancient Greeks thought Earth
was a stationary object and the sun,
moon, and planets were on a rotating
celestial sphere
Checkpoint: What is a geocentric system?
• A geocentric system is one in which
Earth is at the center of a system of
revolving planets.
Figure 2: Interpreting Diagrams
Where is Earth located in this illustration?
• The Earth is in the
middle of the solar
system
• The sun, moon, and
a planet are
orbiting Earth on a
large circle, while
moving on a smaller
cirlce
How is Ptolemy’s model of the solar system
differ from the Greeks before him?
• The Greeks before Ptolemy thought the
universe was unchanging and the sun, moon,
and planets moved together on a celestial
sphere (like a carousel). Earth was
stationary
• Ptolemy introduced the idea of the sun,
moon and planets rotating on little circles
which rotate on bigger circles
Copernicus’s Idea: Sun at the Center
The heliocentric model
(Copernicus) put the sun at
the center and planets in
orbit around it.
Proximity to the sun caused
planets to move at different
speeds
This explained retrograde
Heliocentric
• A description of
the solar system
which all planets
revolve around the
sun
Guide For Reading: How do the heliocentric
and geocentric descriptions of the solar
system differ?
• In a geocentric system, Earth is at the
center of the revolving planets.
• In a heliocentric system, Earth and the
other planets revolve around the sun.
What two discoveries made by Galileo
supported the heliocentric description
of the solar system?
• Jupiter’s four moons revolve
around the planet.
• Venus goes through phases
similar to those of Earth’s moon.
Brahe and Kepler
Brahe, a ______ ______, made much
more accurate observations by
carefully observing the positions of the
planets for almost _____ years.
• Danish astronomer
• 20
What did Kepler discover about the
orbits of the planets?
• Kepler had discovered that the orbit of
each planet is an ellipse.
• Ellipse: an elongated circle or oval
shape.
The Space Program
(textbook reference 13-2)
• Space Race began in 1957 with the
launch of the Soviet satellite Sputnik I
– Satellite – an object revolving around another object
• Humans in Space
– Soviets launched the first human in 1961
• The Moon Landing
– 1969, Apollo 11, and Neil Armstrong and Buzz
Aldrin
80
Exploring the Solar System
(textbook reference 14-1 continued)
Ellipse
• An elongated
circle, or oval
shape; the shape
of the planets’
orbit
• Kepler’s Laws
– 1st law in general, the planets orbit the sun in an ellipse
The eccentricity of the orbit is how “squashed” the orbit is
– 2nd law a line drawn from the sun to any planet, sweeps out equal areas in
equal times (although the orbital distance may be different)
– 3rd law he defined the size of the ellipse and the orbital period (year)
Which planet’s orbit did Kepler calculate to
discover that a planet’s orbit is not a circle?
• Mars
Inertia and Gravity
(textbook reference 12-2)
86
Inertia
• Inertia: tendency of a moving object
to continue in a straight line or a
stationary object to remain in place.
The more _____ an object has, the
more ______ it has.
• mass
• inertia
Gravity
• Gravity: The
attractive force
between two
objects; its
magnitude
depends on their
masses and the
distance between
them.
The strength of gravity depends on the ______ of
the objects and the ______ between them.
• mass
• distance
Figure 5: Interpreting Diagrams -What
would happen if a planet had no inertia?
• The planet
would be
pulled into
the sun
Figure 5: Interpreting Diagrams -What would
happen if a planet had no gravity?
• The planet
would continue
to travel
straight off
into space
Guide For Reading:
What two factors keep the planets in their orbits?
• Newton concluded that two factors –
inertia and gravity – combine to keep
the planets in orbit.
• Inertia keeps the planets the moving
• Gravity from the sun keeps the planets
from traveling off in space
Reviewing Gravity
• Gravity is the attractive force between 2
objects
– It is affected by mass and distance
• Gravity is what determines the orbit planets
follow
Dark Matter helps
Gravitational Pull
• Newton’s explanation of gravity supported
Kepler’s laws of planetary motion.
Solar System Characteristics
(Textbook reference 14-3)
• Inner Planets
–Mercury, Venus, Earth, Mars
• Terrestrial planets with atmosphere and crust
95
The Inner Planets
•
•
•
•
96
Terrestrial Planets
4 inner planets
Similar densities to Earth
Solid rocky surfaces
Mercury
• closest to the sun
• 1/3 Earth’s size(or the
size of Earth’s moon)
• no moons
• solid and covered with
craters
• almost no atmosphere
• the eighth largest
planet(second smallest
planet)
• Surface
– covered with craters and plains
– the plains formed much like the maria on the moon
– the craters are smaller with less ejecta
• Interior
– the density suggests a dense core similar to the
Earth
– the magnetic field suggests its partially molten
98
Venus
•
• Sixth largest planet
• Sister planet to Earth
• About three-fourths the
size of Earth
•
• Has no moons or rings
• The brightest object in our
sky besides the sun and
moon because of proximity •
and albedo 75%
Surface is rocky and
very hot (covered in
craters, volcanoes and
mountains)
Atmosphere completely
hides the surface and
traps the heat.
Probes and satellites
have provided radar
images of 98% of the
99
surface
Earth
• Third planet from the sun
• Fifth largest planet
• Liquid covers 71 percent of the Earth’s
surface.
• The Earth has one moon.
• Only planet known to have life and liquid
water
• Atmosphere composed of composed of
Nitrogen (78%), Oxygen (21%), and
other gases (1%).
Earth, from 6,100,000,000 km (3,700,000,000 miles) away – can you find it?
Mars
Fourth planet from the sun
A thin atmosphere that
contains mostly carbon dioxide
Appears as bright reddish
color in the night sky
Surface features volcanoes and
huge dust storms
Has 2 moons: Phobos and
Deimos
Moons of Mars
Phobos
Deimos
Solar System Characteristics
(Textbook reference 25-4)
• Outer Planets
–Jupiter, Saturn, Uranus, Neptune, Pluto
• Jovian planets have ring systems and gas atmospheres
(J, S, U, N)
105
• Pluto is neither terrestrial or Jovian
The Outer Planets
(Textbook reference 14-4)
• The Gas Giants
• These planets include: Jupiter, Saturn,
Uranus and Neptune
• All larger than Earth by 15-300 times
106
Jupiter
• The largest planet (1/10 of the sun
and 11X Earth’s)
• Better than 70% of the planetary
mass of the solar system
• 52% albedo
• Has a banded appearance
107
Jupiter
• Rings have 3 parts: Halo
Ring, Main Ring,
Gossamer Ring
• Brightest planet in sky
• Strong magnetic field
• 60+ moons, 5 visible from
Earth
Density is relatively low for its size
 The is because of it composition (H and He in gas or
liquid form.
Rotation
 Shortest day in the solar system about 10hrs
This fast spin distorts the shape
This also contributes to its banded appearance
 Belts are low lying dark-colored clouds
 Zones are high light-colored clouds
Moons
 More than 60, but some are very small
 Mostly composed of ice and rock
Gravity assist
109
Jupiter’s Red Spot
• “the great spot” is a
storm of swirling gas
that has lasted for better
than 300 years
• Jupiter does not have a
solid surface. The planet
is a ball of liquid
surrounded by gas.
Moons of Jupiter
Jupiter has four large Galilean moons,
twelve smaller named moons and twentythree more recently discovered but not
named moons.
We’ll take a look at the four large Galilean
moons which were first observed by Galileo
in 1610.
Io
– Io is the fifth moon of
Jupiter. It’s the third
largest of Jupiter’s
moons.
– Io has hundreds of
volcanic calderas. Some
of the volcanoes are
active.
Europa
• Europa is the sixth of
Jupiter’s moons and is the
fourth largest.
• It is slightly smaller than the
Earth’s moon.
• The surface strongly
resembles images of sea ice
on Earth. There may be a
liquid water sea under the
crust.
• Europa is one of the five
known moons in the solar
system to have an
atmosphere.
Ganymede
• Ganymede is the
seventh and largest of
Jupiter’s known
satellites.
• Ganymede has
extensive cratering and
an icy crust.
Callisto
• Callisto is the eighth of Jupiter’s known satellites and
the second largest.
• Callisto has the oldest, most cratered surface of any
body yet observed in the solar system.
Saturn
•
•
•
•
•
•
Second largest planet
Sixth from the sun.
Slightly smaller than Jupiter
Easily visible in the night sky
Voyager explored Saturn and its rings.
Made of materials that are lighter than water. (If you
could fit Saturn in a lake, it would float!)
Rings of Saturn
•
•
•
•
7 major rings made up of ringlets
Gravity keeps the rings in place
rings are not solid
composed of small countless
particles
• rings are very thin.
• Though they’re 250,000 km or
more in diameter, they’re less
than one kilometer thick
• Moons
• 55 moons
• 31 moons
– Largest moon, Titan,
• Titan, the largest is bigger than Mercury
• Odd among moons because of content with dense
atmosphere and methane’s existence in 3 states
118
Uranus
•
•
•
•
•
7th planet from sun
Has a faint ring system (they are dark and hard to observe)
27 known moons
Covered with clouds
Uranus sits on its side with the north and south poles
sticking out the sides.
• 4x larger and 15Xmass of the Earth
Uranus
• Atmosphere
 Bluish appearance cause by methane gas
 Clouds are similar in appearance to the
surface
 Liquid surface with a small solid core
• Rotation
 Almost a top to bottom rotation
 Poles vacillate between 42 years of darkness
and light
120
URANUS
• Uranus has more moons (15) than any other
planet except Jupiter (16) and Saturn (23)!
25
Mercury
Earth
Mars
Jupiter
Saturn
Uranus
Neptune
Pluto
20
15
10
5
0
Number
of Moons
Norm
Herr (sample
file)
Neptune
• 4th largest planet
• 8th planet from sun
– Because of the orbits, from 1979 to 1999, Neptune
was the ninth planet.
• Discovered through math
• 7 known moons
• Great Dark Spot thought to be a hole, similar to
the hole in the ozone layer on Earth
• Like Uranus, the methane gives Neptune its
color.
• Atmosphere
Neptune
– Smaller and denser than Uranus but 4XEarth
– Similar in color to Uranus (twins??) but does have
some color variation on surface
– Belts and zones give it texture
• Moons and Rings
– 13 moons Triton being the largest
• Triton has retrograde orbit
• Also has nitrogen geysers when heated by the sun
• Rings are invisible from Earth but exist
123
The blue coloration of Neptune is probably
due to the presence of methane
Note the apparent storms
124
Pluto…a planet?
• Today, Pluto is called a "dwarf planet.“
• A dwarf planet orbits the sun just like other
planets, but it is smaller.
• A dwarf planet is so small it cannot clear
other objects out of its path.
125
Per NASA.gov.
• In 2003, an astronomer saw a new object beyond Pluto. The
astronomer thought he had found a new planet. The object he saw was
larger than Pluto. He named the object Eris (EER-is).
Finding Eris caused other astronomers to talk about what makes a
planet a "planet." There is a group of astronomers that names objects in
space. This group decided that Pluto was not really a planet because of
its size and location in space. So Pluto and objects like it are now
called dwarf planets.
Pluto is also called a plutoid. A plutoid is a dwarf planet that is farther
out in space than the planet Neptune. The three known plutoids are
Pluto, Eris and Makemake (MAH-kee-MAH-kee). Astronomers use
telescopes to discover new objects like plutoids.
126
Dwarf Planet Pluto
• Pluto, is one of three plutoids.
• It is a small (smaller than
Earth’s moon), solid and icy
• It is so far from the sun that it
has never been visited by
spacecraft.
• It orbits the sun very slowly.
Sample Quiz Questions
Question: Which of the planets are rocky?
Answer: The inner planets: Mercury, Venus, Earth and Mars
Sample Question 2
• Which of the planets has the most satellites?
Saturn!
Image by Dave Dockery
Astronomical Society of Las Cruces
What Are Comets,
Asteroids and
Meteors?
(textbook reference 14-5)
Comet Ikeya Zhang
Space Debris
Comets
A comet is basically
a ball of ice and
dust
in space. The
typical comet is
less than
10 kilometers
across. Most of
their time
Comet Hale Bopp
is spent frozen solid
in the outer
Image by Harvard-Smithsonian Center for Astrophysics
A comet orbits around the sun, in a
wide, elliptical path. When a comet
gets within a few million miles of the
sun, it begins to melt, leaving a tail of
gas and dust that is blown by solar
winds
Source:
NASA
Comet Hale Bopp
Image by Harvard-Smithsonian Center for Astrophysics
Reviewing Comets
• Small icy bodies
• Travel past the Sun
• Give off gas and dust as
they pass by
• Tail of gasses called a
coma
Asteroids
• Asteroid – rocks orbiting in
space
• Asteroid belt – 100,000
asteroids located between Mars
and Jupiter
–separates inner and outer planets 139
Asteroids
• Small bodies
• Believed to be left over from the
beginning of the solar system billions of
years ago
• Largest asteroids have been given
names
Meteoroids
• Meteoroid – smallest asteroids or
comets
– Come from asteroids colliding in space
– Come from a comet breaking up and creating a
cloud of dust continuing to move through the
solar system
141
Meteors
• Meteor – meteoroid striking
Earth’s atmosphere
• Meteorite – meteor that hits
Earth’s surface
142
Solar System
Activities
•
•
•
•
•
Order the Planets
Fun with Planets
Constellations of the Northern Sky
Planets
Solar System
Units of Time from Space
• Year – 1 revolution of Earth
• Day – 1 rotation of Earth
• Month – 1 revolution and/or
rotation of Moon
144
Measuring Distances
• What is a Light Year?
– A light year is the distance light travels in a year. Light moves at a
velocity of about 300,000 kilometers (km) each second; how far
would it move in a year?
– About 10 trillion km (or about 6 trillion miles).
• Why do we use light years?
– Show me how far 5 centimeters is.
– Now show me 50 centimeters.
– Now tell me (without thinking about it, or calculating it in meters) how far
500 centemeters is. 2000? 20,000?
– We need numbers that make sense to us in relationship to objects; we
scale up and use meters and kilometers for large numbers.
Measurements in Space
• Light year – distance light
travels in one Earth year
• Astronomical Unit –
distance from Earth to Sun
http://www.youtube.com/watch?v=
3bmb0YE9VGM
146
Are We Alone in the Universe?
(textbook reference 14-6)
• SETI
Pseudoscience
http://www.seti.org/seti-institute/about-seti/scientists
vs
http://www.chem1.com/acad/sci/pseudosci.html
• “If it is just us, it seems like an awful
waste of space.”
– Ellie Arroway in Carl Sagan’s Contact
147