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The Solar System

Chapter 19, 20, & 21

Please write down all the underlined items. Abbreviate to save time.

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What is Astronomy?

1. Astronomy is the study of the universe.– This includes planets, stars, galaxies, black

holes, moons, meteors, comets, asteroids and all of the matter that exists in space.

2. Astronomers are people who observe & study space.

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Modern Calendar1. Our modern calendar is based on the

observations of bodies in our solar system.

2. A year is the time it takes for the Earth to orbit the sun; year = revolution.

3. A month is the time it takes for the moon to orbit the Earth.

4. A day is the time it takes for the Earth to rotate once on its axis; day = rotation.

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The Size and Scale of our Universe

It is important to consider scale when we think about the universe.

Stars appear to be very small when viewed from Earth, but they are actually very large, some, like our sun, are bigger than Earth.

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The Scale of our Solar System

Earth

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Scale of the Universe

Mercury

SUN

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Our Galaxy and Scale• Our Milky Way galaxy is huge.

• Let's now pretend that our galaxy is a kid's sandbox, and our sun is a grain of sand in a sandbox.– The Earth is a dust speck near the grain of sand, too small

to be seen without a microscope.

– If our sun were a grain of sand in this sandbox representing the Milky Way galaxy, the sandbox would be somewhat oval and yet flat, and would be about 20 feet in diameter.

– The sand would be about 12 inches thick in the center, and thinner towards the edges.

•

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•Each swirling object you see is a galaxy in our universe.

1. We can estimate that there are about 100 billion stars in our galaxy.

2. Andromeda is the nearest major galaxy to our own Milky Way Galaxy.

3. Most scientists believe that Andromeda is about 2 million light years away from the Milky Way.

THE MILKY WAY GALAXY: our

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Milky Way Galaxy: home to our solar system

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Distance in Space1. Distance in space—mainly distance outside of

our solar system—is measured in light years.Example: distance to another star; which is a very,

very, large distance

2. A light year is the distance light travels in a year, 5.88 trillion miles. IT IS NOT TIME!!!

3. Light travels at 186,000 miles/sec or 300,000 km/s.

4. If it takes the light from a star 15 years to reach you, then how far away is the star?

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Distance from the Sun to Earth = An Astronomical Unit

• The distance from the Sun to the Earth is 93 million miles.

– 93 million miles = 1 astronomical unit– 1 astronomical unit = (150 million kilometers)

• this is the unit of measurement for distances b/w planets in our solar system

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Astronomical Unit (AU) for the planets

Planet Average Distance from the Sun(measured in AU)

Mercury 0.39

Venus 0.723

Earth 1.0

Mars 1.524

Jupiter 5.203

Saturn 9.539

Uranus 19.18

Neptune 30.06

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The Sun: The Center of Our Solar System

• Wider than 100 Earths

• 10,000 °F on surface & 27,000,000 °F in its core

• less bright & massive than the very largest stars

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Different Views of The Sun

3-D Image of the sun

UV Image of the sun

Normal Telescopic Image of the sun

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Just what is a planet anyway? Well, according to

The International Astronomical Union The IAU therefore resolves that planets and other bodies in

our Solar System, except satellites be defined into three distinct categories in the following way:

(1) A "planet“ 1 is a celestial body that (a) is in orbit around the Sun, (b) has sufficient mass for its self-gravity to overcome rigid body forces so that it assumes a hydrostatic equilibrium (nearly round) shape, and (c) has cleared the neighborhood around its orbit.

(2) A "dwarf planet" is a celestial body that (a) is in orbit around the Sun, (b) has sufficient mass for its self-gravity to overcome rigid body forces so that it assumes a hydrostatic equilibrium (nearly round) shape 2, (c) has not cleared the neighborhood around its orbit, and (d) is not a satellite.

http://www.iau.org/iau0602.423.0.html

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Just what is a planet anyway? Well, according to The International Astronomical Union

(3) All other objects, except satellites, orbiting the Sun shall be referred to collectively as "Small Solar System Bodies".

1. The eight planets are: Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, and Neptune.

2. An IAU process will be established to assign borderline objects into either dwarf planet and other categories.

3. These currently include most of the Solar System asteroids, most Trans-Neptunian Objects (TNOs), comets, and other small bodies.

http://www.iau.org/iau0602.423.0.html

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Distances of the Inner Planets from the Sun in Astronomical Units (150 million

km = 1 AU)

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The Inner Planets: the terrestrial planets; all are dense & rocky

• Mercury• Venus • Earth• Mars

• They are solids & close to the sun because the materials that make them can be a solid at high temperatures.

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The Inner Planets’ Orbits

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Mercury• 1/3 wide as Earth

• No moons; resembles our moon because of all of its craters

• Big, grey rock made of iron

• 2nd hottest planet & smallest

• Revolves around the sun in 88 days; Rotates on its axis every 58 days– 1.5 days on Mercury = 88 days on Earth

• Temperature varies -173°C to 427°C since it lacks a protective atmosphere.

• Temperature variations on Mercury are the most extreme in the solar system.

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Mercury

In Roman mythology Mercury is the god of commerce, travel and thievery, the Roman counterpart of the Greek god Hermes, the messenger of the Gods. The planet probably received this name because it moves so quickly across the sky.

Mercury has been known since at least the time of the Sumerians (3rd millennium BC). It was given two names by the Greeks: Apollo for its apparition as a morning star and Hermes as an evening star. Greek astronomers knew, however, that the two names referred to the same body. Heraclitus even believed that Mercury and Venus orbit the Sun, not the Earth.

http://www.nineplanets.org/mercury.html

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Venus• Earth’s twin—its size is almost as big as Earth

• No moons; thick yellow clouds of acid

• Dense nickel & iron planet w/a molten core; covered by many shield volcanoes (largest one is Sif Mons)

• Hottest planet in solar system at 464°C due to its thick atmosphere—exerts 90% times more pressure than the Earth’s atmosphere (would be like being 1km deep in the ocean to stand on Venus)

• Atmosphere made of carbon dioxide (90%) & sulfuric acid, which creates a monstrous greenhouse effect.

• Had water @ one point but it all boiled away.

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Venus

Venus (Greek: Aphrodite; Babylonian: Ishtar) is the goddess of love and beauty. The planet is so named probably because it is the brightest of the planets known to the ancients. (With a few exceptions, the surface features on Venus are named

for female figures.) Venus has been known since prehistoric times. It is the brightest object in the sky except for the Sun and the Moon. Like Mercury, it was popularly thought to be two separate bodies: Eosphorus as the morning star and Hesperus as the evening star, but the Greek astronomers knew better. (Venus's apparition as the morning

star is also sometimes called Lucifer.)

http://www.nineplanets.org/venus.html

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Earth

• “Third rock from the sun,” made completely of rock; core made of iron & nickel; has magnetic field lines

• 1 moon—Luna

• Temperatures range from -13°C to 37°C

• Densest planet in our solar system; has water in all 3 states of matter (solid, liquid,& gas)

• 5th largest planet in solar system

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Earth

Earth is the only planet whose English name does not derive from Greek/Roman mythology. The name derives from Old English and Germanic.

In Roman Mythology, the goddess of the Earth was Tellus - the fertile soil (Greek: Gaia, terra mater - Mother Earth).

It was not until the time of Copernicus (the sixteenth century) that it was understood that the Earth is just another planet.

http://www.nineplanets.org/earth.html

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Aurora Borealis: Earth’s atmosphere interacts with its magnetic field lines

creating a spectacular light show

http://earth.jsc.nasa.gov/sseop/efs/query.pl

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Earth’s Moon: Luna (384,400 km from Earth)

Called Luna by the Romans, Selene and Artemis by the Greeks, and many other names in other mythologies.

The Moon, of course, has been known since prehistoric times. It is the second brightest object in the sky after the Sun. As the Moon orbits around the Earth once per month, the angle between the Earth, the Moon and the Sun changes; we see this as the cycle of the Moon's phases. The time between successive new moons

is 29.5 days (709 hours).

http://www.nineplanets.org/luna.html

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Mars• The red planet—red from rust, meaning that it had water on it at one

time

• Once had water on it; has polar ice caps that have both frozen water & carbon dioxide in them

• Many scientists believe that most of Mars’ water lies frozen beneath Mars’ soil

• Has 2 volcanoes—Tharsis (8,000 km wide) & Olympus Mons—an extinct shield volcano; it is the largest volcano in the solar system

• Temperature ranges: -123°C to 37°C

• Revolution: 1 yr, 322 days

• 2 moons: Phobos & Deimos (mean fear & panic)

• Spirit & Endeavor

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Phobos

Phobos ("FOH bus") is the larger and innermost of Mars' two moons. Phobos is Greek for “fear.”Phobos is closer to its primary than any other moon in the solar system, less than 6000 km above the surface of Mars. It is also one of the smallest moons in the solar system.

http://www.nineplanets.org/phobos.html

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Deimos

Deimos ("DEE mos") is the smaller and outermost of Mars' two moons. It is one of the smallest known moons in the solar system.

In Greek mythology, Deimos is one of the sons of Ares (Mars) and Aphrodite (Venus); "deimos" is Greek for "panic".

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Mars

Mars (Greek: Ares) is the god of War. The planet probably got this name due to its red color; Mars is sometimes referred to as the Red Planet. (An interesting side note: the Roman god Mars was a god of agriculture before becoming associated with the Greek Ares; those in favor of colonizing and terraforming Mars may prefer this symbolism.) The name of the month March derives from Mars.

http://www.nineplanets.org/mars.html

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Mars—Home to the largest volcano in the solar system

Olympus Mons is the largest volcano on Mars. This shield volcano, similar to volcanoes in Hawaii, measures 624 km (374 mi) in diameter by 25 km (16 mi) high. It is 100 times larger than Mauna Loa on Earth. Located on the Tharsis Plateau near the equator, Olympus Mons is bordered by an escarpment. The caldera in the center is 80 km (50 mi) wide and contains multiple circular, overlapping collapse craters created by different volcanic events. The radial features on the slopes of the volcano were formed by overflowing lava and debris.

http://www.nineplanets.org/mars.html

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The Asteroid Belt• Small, rocky bodies that revolve around the sun

– Made of leftovers from the formation of the universe

• Range in size from a few meters to greater than 900 km in diameter

• Irregular shapes, but larger ones are spherical

• Most orbit the sun in the asteroid belt—a region of space b/w Mars & Jupiter

• Asteroids vary in color depending on their location in the asteroid belt– Outermost region = reddish brown to black (organic

composition)– Innermost region = gray (carbon); light gray = stony/metallic

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Famous AsteroidsHektor

Ida and Dactyl

http://neo.jpl.nasa.gov/images/ida.html

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Ceres: the largest of the asteroids

Observations of 1 Ceres, the largest known asteroid, have revealed that the object may be a "mini planet," and may contain large amounts of pure water ice beneath its surface.

http://www.spaceflightnow.com/news/n0509/07ceres/

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Meteoroids: “cousins” to asteroids; shooting stars

• Much smaller than asteroids

but very similar

• Meteoroids are small, rocky bodies that revolve around the sun.– Once it enters Earth’s atmosphere it becomes

a meteor & stays a meteor if it burns up in the atmosphere.

– If it strikes the ground it is a meteorite.

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Meteoroids continued

• 3 types:

– Stony(Rocky)—rocky material

– Metallic—iron & nickel

– Stony-iron—rocky, iron & nickel

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Stony (Rocky) Meteorites: most primitive; contain water

http://meteorites.asu.edu/images/new-concord-big.jpg

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Metallic Meteorites

http://www.astro.virginia.edu/class/oconnell/astr121/im/iron-meteorite.jpg

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Stony-iron Meteorites

http://www.gpc.edu/~pgore/myphotos/rocks/stonyironmeteor.jpg

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Meteorite Crater

In Canyon Diablo in Arizona, USA, you can visit the best preserved meteorite crater on earth. It was formed about 22,000 years ago by the impact of a giant metallic nickel-iron meteorite, which arrived from space at a speed of about 50,000 kilometers per hour, and weighed many hundreds of tons. Friction with the atmosphere does not really slow such a mighty mass, which smashed into the solid earth, punching away 300 million tons of rock in a mighty blast which left a crater which even today is still 1.5 kilometers in diameter and 170 meters deep. (http://www.rocksonfire.com/About-Meteorites.htm)

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Stars Fell On Alabama, November 12, 1833, Leonid Meteor Shower

• New car license plate introduced in January, 2002, commemorating this.

• The new slogan on these plates is "Stars Fell on Alabama," in reference to the 1934 song written by Mitchell Parish and Frank Perkins and made famous by Ella Fitzgerald and Louis Armstrong, Frank Sinatra, and other artists over the years.

• The top of the plate contains a field of stars and musical notes around the slogan.

http://www.15q.net/al.html

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The Outer Planets: The Gas Giants or Jovian Planets

• Jupiter, Saturn, Uranus, & Neptune

• All are made of gas. They are not solids like the inner planets. – They get denser with increasing depth.

• All have rings. Some are barely visible unlike Saturn’s rings.

• Since their masses are so much larger, they have more moons than the inner planets.– Which planet should have the largest number of moons?

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Distances of the Outer Planets from the Sun in Astronomical Units

(150 million km = 1 AU)

Jupiter 5.203 AU

Saturn 9.539 AU

Uranus 19.18 AU

Neptune 30.06 AU

Pluto 39 AU

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Jupiter• The largest planet in our solar system (318 times as large as Earth)

– Its mass holds the asteroid belt in place & protects Earth from asteroid assault.

• Made mainly of hydrogen & helium– Outer part is made of layered clouds of water, methane, &

ammonia

• Radiates more energy into space than it receives from the sun

• Cold planet; average temperature = -110°C

• Great Red Spot (1.5X the size of the Earth) is a storm system similar to a hurricane that is > 400 yrs old.

• Rotation = 9 hrs, 54 min; Revolution = 11 yrs, 313 days

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Jupiter continued• Has 63 moons as of Feb. 2004

• Jupiter probably has a core of rocky material amounting to something like 10 to 15 Earth-masses.

• Above the core lies the main bulk of the planet in the form of liquid metallic hydrogen.

• The environment near Jupiter contains high levels of energetic particles trapped by Jupiter's magnetic field. – This "radiation" is similar to, but much more intense than, that

found within Earth's Van Allen belts. It would be immediately fatal to an unprotected human being.

• Has rings like Saturn, but much fainter & smaller

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Jupiter: http://www.nineplanets.org/jupiter.html

Jupiter (a.k.a. Jove; Greek Zeus) was the King of the Gods, the ruler of Olympus and the patron of the Roman state. Zeus was the son of Cronus (Saturn). Jupiter is the fourth brightest object in the sky (after the Sun, the Moon and

Venus). It has been known since prehistoric times as a bright "wandering star". But in 1610 when Galileo first pointed a telescope at the sky he discovered

Jupiter's four large moons Io, Europa, Ganymede and Callisto (now known as the Galilean moons) and recorded their motions back and forth around Jupiter.

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Jupiter’s Rings

http://www2.jpl.nasa.gov/galileo/callisto/p48188.html

Unlike Saturn's, Jupiter's rings are dark. They're probably composed of very small grains of rocky material. Unlike Saturn's rings, they seem to contain no ice.

http://www.nineplanets.org/jupiter.html

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Saturn• 2nd largest planet in the solar system (95 X larger

than Earth)

• Composed mainly of hydrogen & helium w/a small rocky core– Methane, ammonia, & ethane are in upper

atmosphere

• Gives off more heat than it gets from the sun because of the helium falling from its atmosphere—Saturn seems to still be forming

• Average temperature = -140°C

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Saturn• Saturn’s rings are the largest of the gas giants.

– Made of icy particles that range from a few cm to a few m wide

• Gold, brown,& white; rings gold, brown, white, red, yellow, & green

• Revolution: 29 years, 155 days

• Rotation: 10 hrs, 42 min

• 31 moons

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Saturn

In Roman mythology, Saturn is the god of agriculture. The associated Greek god, Cronus, was the son of Uranus and Gaia and the father of Zeus (Jupiter). Saturn is the root of the English word "Saturday“.

http://www.nineplanets.org/saturn.html

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Saturn’s Rings

http://www.nineplanets.org/saturn.html

Saturn’s rings are 250,000 km or more in diameter & they're less than one kilometer thick .

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Uranus• Super cold -195°C

• 21 moons; 11 rings

• Revolution: 83 yrs, 273 days; Rotation: 17 hrs, 12 min

• 3rd largest planet

• Rotates on its side---planet was probably knocked on its side after a collision w/an asteroid– One side points toward the sun & the other in complete

darkness for part of the year

• Made of hydrogen & methane—2 gases that absorb red light, giving Uranus its distinct blue/green color

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Uranus

Uranus is the ancient Greek deity of the Heavens, the earliest supreme god. Uranus was the son and mate of Gaia the father of Cronus

(Saturn) and of the Cyclopes and Titans (predecessors of the Olympian gods).

Uranus, the first planet discovered in modern times, was discovered by William Herschel while systematically searching the sky with his

telescope on March 13, 1781.

http://www.nineplanets.org/uranus.html

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Uranus’ rings

http://hubblesite.org/newscenter/archive/releases/1996/15/image/a/format/web/

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Neptune: Big Blue World

• 11 moons

• Rotation: 16 hrs, 6 min.

• Revolution: 163 yrs, 263 days

• Temperature: -200 °C

• Has dark rings

• Neptune & Pluto’s orbits overlap causing Neptune to sometimes orbit beyond Pluto

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Neptune: Big Blue World

• Gets its blue color from being made of methane gas that absorbs red light, making Neptune appear blue

• Has belts of clouds & a great Dark Spot similar to Jupiter’s great Red Spot

• Tilted at a 30° angle so its poles are in light or dark for 40 yrs @ a time

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Neptune

In Roman mythology Neptune (Greek: Poseidon) was the god of the Sea.

The Great Dark Spot

http://www.nineplanets.org/neptune.html

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Neptune’s Dark Rings

60http://starchild.gsfc.nasa.gov/docs/StarChild/solar_system_level2/pluto_image.html

In Roman mythology, Pluto (Greek: Hades) is the god of the underworld.

Pluto was discovered in 1930 by a fortunate accident. Calculations which later turned out to be in error had predicted a planet beyond Neptune, based on the motions of Uranus and Neptune.

Not knowing of the error, Clyde W. Tombaugh at Lowell Observatory in Arizona did a very careful sky survey which turned up Pluto anyway.

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Kupier Belt (pronounced kew p a)

• A region in space beyond Neptune where @ least 70,000 small, icy, slow-moving objects orbit the sun

• A region where the planet-building process stopped before any large objects where formed

• Pluto & is moon Charon (pronounced Sharon) are thought to be large members of it

• Short-lived comets like Haley’s comet are also thought to come from the Kupier Belt

• Discovered in 1992 by Dutch-American astronomer Gerard P. Kupier

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Pluto: the dwarf planet that rotates on its side• No longer a planet

– Now called a “dwarf planet”—reclassified in 8/2006

• Has 3 moons—Charon, Nix, & Hydra

• Rotation: 6 days, 10 hrs

• Revolution: 248 yrs, 4 days

• Temperature: -225°C

• Covered by frozen nitrogen

• Made of rock & ice

• Less than ½ the size ofMercury

• Will be visited in 2015

http://www.nineplanets.org/pluto.html

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Pluto’s largest moon Charon (which is more than ½ the size of Pluto)

Charon is named for the mythological figure who ferried the dead across the River Acheron into Hades (the underworld).

http://pluto.jhuapl.edu/science/everything_pluto/5_looks.php?selectedImage=image07.php

http://www.nineplanets.org/pluto.html

(Though officially named for the mythological figure, Charon's discoverer was also naming it in honor of his wife, Charlene. Thus, those in the know pronounce it with the first syllable sounding like 'shard' ("SHAHR en").

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Oort Cloud

• A large sphere that surrounds the solar system

• Where the bulk of comets originate

• Suggested by astronomer Jan Oort in 1950

• Both the Kupier Belt & the Oort Cloud are relatively pristine remnants of the nebula from which the entire solar system was formed.

• Could contain as many as a trillion comets

http://www.nineplanets.org/kboc.html

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http://www.astro.rug.nl/~onderwys/ACTUEELONDERZOEK/JAAR2000/oort/oort_cloud.gif

67http://www.fas.org/irp/imint/docs/rst/Sect19/H_oort-cloud_02,0.jpg

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Comets

http://www.nineplanets.org/comets.html

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Comets

• Comets are sometimes called dirty snowballs or "icy mud balls". They are a mixture of ices (both water and frozen gases) and dust that for some reason didn't get incorporated into planets when the solar system was formed. This makes them very interesting as samples of the early history of the solar system.

http://www.nineplanets.org/comets.html

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Comets: When they are near the Sun & active, comets have several distinct parts:

nucleus: relatively solid & stable, mostly ice & gas with a small amount of dust & other solids—the icy dirt core

coma: dense cloud of water & gases from the nucleus

hydrogen cloud: huge (millions of km in diameter) but very sparse envelope of hydrogen

dust tail: up to 10 million km long composed of smoke-sized dust particles driven off the nucleus by escaping gases; this is the most commonly seen part of the comet

ion tail: as much as several hundred million km long; composed of plasma & laced with rays and streamers caused by interactions with the solar wind

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Dust

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Label the parts of a comet: hydrogen envelope, ion tail, coma, nucleus, & dust tail

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Sedna

• Large planetoid or asteroid

• More than 2X as far from the sun as Pluto

• Huge ball of ice, w/reddish color

• Revolves around the sun once every 10,500 yrs

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Sedna—what we think it looks like

Sedna's physical composition is a bit of a mystery. You would expect it to be mostly ices but apparently that's not the case. About all that's known at this

time is that it is very red and that water and methane ices seem to be absent on the surface.

Sedna is definitely not the "Planet X" that many astronomers anticipated before the discovery of Pluto. Planet X was supposed to be a much larger

object. http://www.nineplanets.org/sedna.html

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Eris—the next “dwarf planet”

• Officially named in 9/2006

• Named for the goddess of chaos & strife

• 1 moon = Dysomia• Spirit of lawlessness

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Xena

• Another planetoid that will probably become another “dwarf planet” in the coming months