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Extra Credit by HInVl2Y



    Jacob Emery

   We live in a solar system in the vast Milky
    Way Galaxy. The Sun is our central star,
    orbited by nine planets, and containing
    more than 100 moons, millions of rocky
    asteroids, and billions of icy comets and

   Scientists believe that the number of
    galaxies in the universe could be as few as
    10 billion or as many as 100 billion.

   Astronomers categorize galaxies primarily
    by their shapes -- elliptical, spiral, and
                                NGC 4242
   NGC 4242 is a very low
    surface brightness
    spiral galaxy in the
    constellation of Canes

   It is estimated to be 27
    million light years away!
                            NGC 5792
   NGC 5792 is a spiral
    galaxy, the most
    common type.

   Images of this galaxy
    were taken at the
    Lowell Observatory.
                               NGC 6946
   NGC 6946 is more than
    15 million light-years

   NGC 6946 is a big spiral
    galaxy that looks a lot
    like our own galaxy, the
    Milky Way.

   Over the last century,
    astronomers have
    recorded six supernovae
    in the galaxy.
                             NGC 3516
   NGC 3516 is one of
    Astronomers favorites. They
    keep turning their
    telescopes toward it
    because it is interesting and
    easy to study.

   NGC 3516 is near the Big

   It's a spiral galaxy
    containing hundreds of
    billions of stars.

   It's about a hundred million
    light-years away -- close as
    galaxies go.
                              NGC 4731
   This very dim galaxy
    appears a bit bent out of
    shape due to the
    gravitational effect of its

   NGC 4731 is an
    estimated distance of 65
    million light years away.

   The background is
    mottled with galaxies
    perhaps hundreds of
    times more distant.
   There are nine planets including Earth that orbit
    the Sun.
   Is our Solar System alone? Astronomers have
    discovered planets orbiting several other stars,
    but we have not found any Earth-like planets.
   The inner planets are made up of mostly rock
    and metal and the outer planets are mostly
    made of ice and gas.
   Saturn is the second
    largest planet.
   Saturn's rings are
    made of ice and rock.
   It spins so fast that it
    bulges at the equator,
    and stretches its clouds
    into bands that encircle
    the globe.
   Saturn has more than
    three dozen moons,
    and it's encircled by
    bright rings.
   This view was taken by
    the Hubble Telescope.
   Mercury is the planet closest
    to the Sun.

   It is slightly larger than
    Earth's Moon, and looks very
    much like the Moon, with
    craters scarring its rocky

   Mercury flies along in its
    orbit at an average speed of
    29 miles per second – faster
    than any other planet!
   Venus is the second planet
    from the Sun.

   It is the hottest world in
    the solar system.

   It has a thick atmosphere
    that heats its surface to
    almost 900 degrees
    Fahrenheit (480 C).
   Jupiter is the largest planet
    in the solar system.

   In fact, it is more massive
    than all the other planets
    and moons in our solar
    system combined.

   Its core may be as hot as
    54,000 degrees Fahrenheit
    (30,000 C).
   Mars is the fourth planet.
   Although Mars is smaller
    and colder than Earth, it is
    still quite similar to our
   It has a thin atmosphere
    and polar ice caps, and dry
    riverbeds across its
   Frozen or even liquid
    water may exist beneath
    the red Martian soil --
    perhaps providing a home
    for living organisms.
   This was taken by the
    Hubble Space Telescope.
           Stars and Nebulas

   On a really dark night, you can see about
    1000 to 1500 stars.
   Stars form deep inside vast clouds of
    interstellar gas and dust called nebulae.
   The nearest star to Earth is the one we
    see every day – the Sun. It is 93 million
    miles away.
                 Red Rectangle Nebula
   A dying star lights up
    clouds of dust around it in
    this nebula.
   This old star began
    blowing its outer layers
    into space, one by one,
    about 14,000 years ago.
   Dust grains reflect light
    from the star, creating the
    nebula's layered look.
   Eventually, the star will
    lose all of its outer layers,
    exposing its hot core,
    which will cause vast
    clouds of gas around the
    star to glow like a neon
   Image from the Hubble
    Space Telescope.
   This infrared image
    from the Spitzer Space
    Telescope hints that
    one or more planets
    may orbit Fomalhaut, a
    nearby bright star

   One side of the disk (at
    the bottom of the
    picture) is brighter than
    the other. This could
    indicate that a planet is
    hidden inside this
    portion of the disk, and
    its gravity is causing
    more of the dust grains
    to congregate around
                    Supernova 1987A
   Supernova 1987A is a
    massive star in a nearby
    galaxy that blasted itself to

   The ring around the
    exploded star spans about
    one light-year. It formed
    when the star expelled a
    shell of gas about 20,000
    years before it exploded.

   Image from Hubble Space
                         M17 Nebula
   Clouds of hydrogen gas
    mix with small amounts of
    oxygen, sulfur, and other
    elements of a region of
    M17, a nebula that is
    giving birth to new stars.
   The nebula is about 5,500
    light-years away.
   The energy of hot, young
    stars in the nebula causes
    the gas to glow.
   The different colors
    represent different
   Image from Hubble Space
                     M22 Star Cluster
   The globular cluster M22
    is just one of several
    bright star clusters
    visible in the
    constellation Sagittarius.

   M22 contains several
    hundred thousand stars
    packed into a region of
    space just a few dozen
    light-years in diameter.

   Its stars are some of the
    oldest in the galaxy, at
    more than 10 billion
   Comets are a ball of frozen water and gases mixed with
    solid chunks of rock.
   There is a vast shell of comets that surrounds the solar
   Something disturbs the comet's orbit -- like the gravity of
    a passing star -- starting it on a long fall toward the Sun.
   As a comet approaches the Sun, some of its ice
    vaporizes, freeing particles of rock as well. This material
    forms a bright cloud around the comet. And some of the
    material is pushed into a long, glowing tail.
                  Comet C/2001 Q4
   Comet C/2001 Q4 (NEAT)
    streaks around the Sun in
    this recent image.

   The comet passed closest
    to Earth in early May.

   Image from the WIYN
    telescope at Kitt Peak
    National Observatory in
                            Comet Wild 2
   Comet Wild 2 appears to
    glow in this image from the
    Stardust spacecraft, which
    flew past the comet in

   The dark part of the picture
    shows craters, pits, and
    bright spots on the surface.

   The bright rays around the
    comet show where gas and
    dust is blowing into space
    from "jets" on the comet's

   It has a tail several million
    miles long.
                 Comet Ikaya-Zhang
   Comet Ikeya-Zhang, was
    in its peak brightness this
    past February.

   This false-color image
    shows the comet's nucleus
    in white and blue, and a
    tail of electrically charged
    water molecules in red.
                        Comet Borrelly
   Comet Borrelly slowly
    tumbles through space in
    this image.

   The comet's nucleus, which
    is a chunk of ice mixed with
    rock, measures about five
    miles long.

   Ice is vaporizing from the
    bright patch near the
    center of the nucleus,
    spraying a "jet" of gas and
    dust into space.

   Image from Deep Space 1.
                       Comet Encke
   Since its discovery in
    1786, Comet Encke has
    circled the Sun more than
    60 times!

   Encke orbits the Sun once
    every 3.3 years -- more
    often than any other
    comet yet discovered.
   Most of the planets in our solar system
    have moons — planet-like bodies that
    orbit a bigger body.
   Earth has only one moon, but some
    planets have many: Jupiter, for example,
    has 63 known moons.
   A planet and its moons actually revolve
    about each other.
                           Titan Moon
   Titan is the largest
    moon of Saturn.

   Astronomers cannot see
    Titan's surface directly
    because a cold, hazy
    atmosphere envelopes
    the big moon.

   Image by the European
    Southern Observatory's
    Very Large Telescope in
                            S/2001 U1
   S/2001 U1 is the 21st
    known moon of the planet

   It is a small chunk of rock
    that follows an irregular
    orbit around the giant
   Warm ice bubbling to
    the surface creates
    reddish patches on the
    icy surface of Jupiter's
    moon Europa.

   A deep ocean of liquid
    water may exist beneath
    Europa's ice crust,
    perhaps providing a
    home for living

   NASA released the
    image, which combines
    two pictures from the
    Galileo spacecraft.
   American astronomer
    Asaph Hall discovered
    the moons of Mars 125
    years ago.

   Phobos, shown in this
    image from Mars
    Global Surveyor, is the
    larger moon.

   Its surface is covered
    with impact craters.
    The largest crater, at
    top left, is about six
    miles across and is
    named Stickney.
                          Earth’s Moon
   The Moon probably formed
    very early in the history of
    the solar system when a
    large object -- perhaps
    several times the mass of
    Mars -- slammed into

   Unlike Earth, the Moon has
    no atmosphere, and no

   The lunar surface is
    covered with craters, the
    scars from countless
    boulders -- some much
    bigger than mountains --
    that struck it over billions
    of years ago.

   The name "asteroid" comes from a Greek
    word that means "starlike." When seen
    through a telescope, an asteroid looks like
    a faint star.
   Asteroids are made up mostly of rock,
    often rich in iron and other metals, and
    perhaps some ice.

   A close picture of
    Mathilde revealed the
    asteroid’s heavily crater

   One of only 4 asteroids
    photographed up close.

   First scanned in 1997.
   The surface of Gaspra,
    shown in a Galileo
    image, has been pitted
    by asteroid collisions.
    Grooves in its surface
    may have been caused
    by an impact that split
    Gaspra from a larger
   Galileo found that
    Gaspra is about 22 by
    14 by 12 miles.
   It's covered with
    impact craters, which
    means it's taken a
    pounding as smaller
    asteroids slammed into
                                 433 Eros
   Images show the asteroid
    433 Eros to have a 21-
    mile-long solid body and a
    face pockmarked with

   Observations show that
    Eros is left over from the
    formation of our solar
    system four and a half
    billion years ago.

   It hasn't been heated very
    much, so it's still the
    same jumbled up mixture
    of rock and metal as
    when it formed.
   Ceres was the first
    asteroid discovered back in
   Ceres is only about a
    quarter of the size of our
    own Moon.
   The surface of Ceres
    consists of dark, carbon-
    rich rock mixed with a fair
    amount of water.
   The picture at right is a
    circular scar -- known as
    the Manicouagan crater –
    left when an asteroid
    rammed into present-day
    Quebec about 200 million
    years ago.
   As first, Astrnomers thought
    Pallas was a planet, when it
    was discovered on March
    28th, 1802.
   At right, This microscopic
    sample of zircon is one bit of
    evidence that a giant asteroid
    slammed into Earth about 3.5
    billion years ago, triggering
    massive changes in the
   Although there is no remaining
    impact crater, a team has
    found microscopic remains of
    the collision in Australia and

The more scientists
discover, the more
complicated our world
seems. Earth is a
warm, wet planet with
an oxygen-rich
atmosphere – the
perfect place for life, but
who knows what is yet
to be discovered?

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