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Earth’s Place in Space
• Earth rotates and revolves around the Sun,
even though it appears as though the Sun is
moving!
• Rotation – spinning of Earth on its axis, which
occurs once every 24 hours
• Earth moves around the Sun in a regular, curved
path called an orbit
• It takes one year for Earth’s revolution around the
Sun
• SEASONS occur due to Earth’s tilted axis and its
revolution around the Sun
Our Solar System
• Earth orbits the Sun as the solar system
revolves within the Milky Way, which is
among billions of galaxies that make up
the universe
• Introduction to the Solar System –
VIDEO CLIP
The Seasons
• Change of seasons is a result of the tilt of the
Earth’s rotation axis with respect to the plane
of the ecliptic
• Sun, moon, planets run along the ecliptic
Motion of the Moon
• Moon shines not by its own light but by reflected light
of Sun
• Moon revolves around the Earth
• Moon’s period of rotation = 27.3 days
• Period of revolution =also 27.3 days
• The Moon’s changing shapes are known as phases
Phases of the Moon (THE LUNAR CYCLE) – caused by the
position of the Earth, the Moon, and the Sun; new to full = waxing;
full to new = waning
Phases of the Moon – caused by the position of the Earth, the
Moon, and the Sun; new to full = waxing; full to new = waning
…and the phases…with oreos!
Eclipses
• One celestial object hidden by other or in the
shadow of another
• Solar eclipse: sun hidden by the Moon, as
Moon is between the Sun and Earth and the
Moon’s shadow falls on Earth
• Lunar eclipse: Earth is between the Moon
and the Sun and Earth’s shadow falls on the
Moon
• Also: eclipses of Jupiter’s moons, etc.
• Most spectacular because moon and sun
appear to be the same size from earth
Solar Eclipses
• Umbra – region of total shadow
• Penumbra – region of partial shadow
• Totality lasts only a few minutes!
Solar Corona
Lunar Eclipses
Moon moves
into earth’s
shadow…
Free powerpoints at http://www.worldofteaching.com
OUR SOLAR SYSTEM
THE MILKY WAY
Our Solar System is filled with
eight major planets, the Sun, and
other objects that orbit the Sun
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Mercury
Venus
Earth
Mars
Jupiter
Saturn
Uranus
Neptune
Pluto (not classified as a
planet any longer!)
Measuring Space
• Distances in space are so vast they
require different units of measurement
than are used to measure things on
Earth.
• An astronomical unit (AU) is about 150
million km (93,000,000 miles), the mean
distance from Earth to the Sun
THE SUN
The Sun
• The Sun is one of one-hundred billion stars in
our galaxy.
• It is the brightest object in the sky.
• Its diameter is 1,390,000 km.
• The suns mass is 1.989e30 kg.
• The temperature is 5800 k on the surface and
15,600,000 k at the core.
• The sun is by far the largest object in our
solar system.
Inner Planets
• Solid, with minerals similar to those on
Earth
• Include Mercury, Venus, Earth, and
Mars
MERCURY
Mercury
• Mercury is the closest planet to the sun and
is the smallest planet now that Pluto is
deemed a “dwarf planet”
• It orbits 57,910,000 km from the sun.
• Mercury’s diameter is 4,880 km
• The mass of this planet is 3.30e23 kg
• Little atmosphere, resulting in extremes of
temperature; can reach 430 degrees Celsius
during the day and drop to –180 degrees
Celsius at night!
Mercury Facts
VENUS
Venus
• Venus is the third brightest object in the sky.
• It is the second closest planet from the sun and is the
sixth largest.
• It orbits 108,200,000 km from the sun.
• Its diameter is 12,103.6 km.
• Venus’ mass is 4.869e24 kg.
• Heavy cloud layer; clouds trap solar energy, making
the planet extremely hot ~ 470 degrees Celsiu!
Venus Facts
EARTH
Earth
• Earth is the third planet from the sun and is
the fifth largest.
• It orbits 149,600,000 km from the sun.
• Its diameter is12,756.3 km.
• Earth’s mass is 5.972e24 kg.
• This planet is the densest major body in our
solar system.
• Atmosphere allows life to flourish; water
exists as a solid, liquid, and gas
Earth Facts
MARS
Mars
• Mars is the fourth planet from the sun and is
the seventh largest.
• It orbits 227,940,000 km from the sun.
• Its diameter is 6,794 km.
• Its mass is 6.4219e23.
• The first space craft to visit Mars was the
Mariner 4 in 1965.
• Has seasons and polar ice caps; may have
water shaping its surface
• Red due to rocks containing iron oxide
• Two small moons – Phobos and Deimos
Exploring Mars
Asteroid Belt
• Separates the inner (rocky) and outer (gas
giants with lots of moons and rings) planets
• Pieces of rock made of minerals similar to
those that formed the rocky planets and
moon
• Jupiter’s huge gravitational force might have
prevented a small planet from forming in the
area of the asteroid belt
JUPITER
Jupiter
• Jupiter is the fifth planet from the sun and is
by far the largest planet.
• It orbits 778,330,000 km from the sun.
• Its diameter is 142,984 km.
• Its mass is 1.900e27 kg.
• Jupiter is the fourth brightest object in the sky.
• 28 moons; Giant Red Spot is a giant storm on
the planet’s surface
Jupiter Facts
SATURN
Saturn
• Saturn is the sixth planet from the sun and is
the second largest.
• It orbits 1,429,400,000 km from the sun.
• Its diameter is 120,536 km.
• The mass of Saturn is 3.68e26 kg.
• Saturn is the least dense of all the planets
• Has 30 moons; several broad rings of ice and
dust.
Saturn Facts
URANUS
Uranus
• Uranus is the seventh planet from the sun
and the third largest.
• It orbits 2,870,990,000 km from the sun.
• Its diameter is 51,118 km.
• The mass is 8.683e25 kg.
• Uranus has only been visited one time, by the
Voyager 2 in 1986.
• Axis makes the planet spin nearly sideways;
has rings and 21 moons
Exploring Uranus
NEPTUNE
Neptune
• Neptune is the eighth planet from the sun and
is the fourth largest.
• It orbits 4,504,000,000 km from the sun.
• Its diameter is 49,532 km.
• Its mass is 1.0247e26 kg.
• Neptune has 8 moons.
• Atmosphere is composed of hydrogen,
helium, and methane (make planet blue)
Neptune Facts
PLUTO
Pluto
• Pluto is the farthest object from the sun
and is by far the smallest.
• It orbits 5,913,520,000 km from the sun.
• Its diameter is 2274 km.
• Its mass is 1.27e22 kg.
• Pluto is the only dwarf planet that has
not been visited by a space craft.
Exploring Pluto
All planets move in same plane
except Pluto
Pluto’s strange Orbit
• Very far out there: 40 A.U.
• Very eccentric orbit:
• Pluto’s year = 248 Earth
• Perihelion: 30 A.U.
years
(inside the Neptune orbit!)
• Orbit inclined 17° w.r.t. ecliptic • Aphelion: 50 A.U.
Is Pluto a planet?
• Orbit too
weird
• Too small
• Today Pluto
may not be
classified as
a planet.
Why do all planets move in
the same plane?
• Reason: Formation
process of the Solar
System
• Condenses from a rotating
cloud of gas and dust
• Conservation of angular
momentum flattens it
• Dust helps cool the nebula
and acts as seeds for the
clumping of matter
Formation of Planets
• Orbiting dust –
planitesimals
• Planitesimals collide
• Different elements form in
different regions due to
temperature
• Asteroids
• Remaining gas
What’s up in the night sky?
The Celestial
Sphere
• A Geocentric model
(Earth Centered Universe)
• Axis through Earth’s
north and south pole
goes through
celestial north and
south pole
• Earth’s equator
Celestial
equator
The Zodiac throughout the Year
(Heliocentric)
In Winter sun in Sagittarius, Gemini at night sky
In Summer sun in Gemini, Sagittarius at night sky
Constellations of Stars
• About 5000 stars visible with naked eye
• About 3500 of them from the northern hemisphere
• Stars that appear to be close are grouped together
into constellations since antiquity
• Officially 88 constellations
(with strict boundaries for classification of objects)
• Names range from
• mythological (Perseus, Cassiopeia)
• technical (Air Pump, Compass)
Constellations of Stars
Orion as seen at night
Orion as imagined by men
Constellation Orion Distances
Stars in a constellation are not connected
by relative distances.
Zodiacal signs vs.
Constellations
•“Constellation” is a modern,
well-defined term
- Some constellations are big, some
are small on the celestial sphere
•“Zodiacal sign” is the old
way of dividing the year and
the Sun’s path into 12 equal
parts
-
3600/12=300
0 degrees:
30 degrees:
60 degrees:
90 degrees:
Each zodiacal sign is exactly 30 degrees
Aries
Taurus
Gemini
Cancer
Comets
• Large body of frozen ice and rock that travels
toward the center of the solar system
• As a comet approaches the Sun, radiation
vaporizes some of the material; solar winds blow
vaporized gas and dust away from the comet,
forming what appears from Earth as a bright,
glowing tail
• Comets originate in the Oort Cloud beyond the
orbit of Pluto; some comets may come from
the Kuiper belt
Meteorites
• Fragments of space material that land
on Earth’s surface
• Pieces may be iron, rock, or both
• Age (4.5 billion years) provides a clue to
the Solar System’s age
Constellations
• Groups of stars that form a pattern in
the sky; named after animals, objects,
and people – real or imaginary
Lives of Stars
• A star has a life that depends on its size
• When a medium-sized star like the Sun uses
up some of the gases in its center, it expands
to become a giant star; Sun will become a
giant in about 5 billion years and will expand
to cover the orbits of Mercury, Venus, and
possibly Earth
• Sun will lose its outer shell, shrink to a hot
white dwarf, and eventually cool and become
a black dwarf
Lives of Stars, cont.
• Stars begin their lives as huge clouds of gas
and dust
• Force of gravity causes dust and gases to
move closer together
• Temperatures within the cloud begin to rise
• Star is formed when this cloud gets so dense
and hot that the atoms within it merge (fusion)
Supergiants
• When a large star begins to use up the fuel in
its core, it becomes a supergiant
• Over time, the core collapses
• Supernova occurs, in which the outer part of
the star explodes and becomes bright; core is
now a neutron star
• If neutron star is massive enough, it could
become a black hole
• Black holes are so dense that even light
cannot escape their gravity
Galaxies
• Group of stars, gas, and dust held together
by gravity
• Elliptical-shaped galaxies are most common
• Spiral galaxies look like a pinwheel
• Irregular galaxies are smaller and less
common than other galaxies
• Earth is in a spiral galaxy called the Milky Way
Speed of Light/Light-Years
• Light travels through space at 300,000
km/s – so fast it could go around Earth
seven times in one second
• Light-Year: distance light travels in one
year (9.5 trillion km)
• 100 billion galaxies might exist ~ all
these galaxies with all their stars make
up the UNIVERSE!
Here are some more great sites
for learning about Planets
The Nine Planets
Exploring the Planets
Welcome to the Planets