Earth and Space Ch 10

Structure of the Solar System

• Astronomy- study of the motions of the celestial bodies and the laws that govern them
• Solar system- a small part of the Milky Way galaxy that includes the sun and all natural objects that orbit it.
• Theories
• Earth-centered (Geocentric)
• Aristotle- geocentric theory that the universe in spherical layers in which all celestial bodies orbit the earth.
• Ptolemy- adopted an expanded geocentric theory that used detailed diagrams and mathematical data to explain the universe; assumed that planets traveled in small circles, called epicycles, set in a larger circle.
• Sun-centered (Heliocentric)
• Aristarchus- suggested that the earth orbits the sun, but at the time this was not accepted
• Copernicus- solved problems with the earth centered theories by proposing a heliocentric (sun centered) theory in which Earth is a planet and all the planets orbit the sun; assumed that al planets' orbits had to be perfect circles
• Galileo- built one of the first telescopes and used it to investigate space; observed 4 moons orbiting Jupiter( these were the first celestial objects ever observed that orbited something other than the earth or the sun.) Was a supporter of Copernicus' theory.
• Kepler and Brahe- helped prove Copernicus' heliocentric theory

Planetary Motions

• Elliptical paths
• Kepler discovered that the paths of the planets are not circles but are instead symmetrical ovals or ellipses
• Kepler's 3 laws-laws of planetary motion to help explain astronomy observations of the planets' paths.
• 1st law- states every planet orbits the sun in an ellipse, with the sun as one focus of the ellipse and an empty point in space as the other
• 2nd law - describes how a planet's speed changes as it orbits; as a planet moves closer to the sun, it travels faster and as it moves farther away, it slows down.
• Perihelion- earth's closest point to the sun
• Aphelion- earth's farthest point from the sun
• 3rd law- states the mathematical relationship between a planet's period( amount of time a planet takes to complete its orbit) and the planet's average distance from the sun; the farther a planet's average distance from the sun, the longer its period
• Measured in AU- astronomical units- one astronomical unit is approximately the distance between the earth and the sun (93 million miles)

Gravity and Interplanetary Space

• Sir Isaac Newton- greatest scientific achievement was gravity, the force of attraction that exists between two objects.
• Newton's Law of Universal Gravitation- states that the strength of the gravitational force between two objects depends on their masses and the distance between them.
• Objects with more mass will have a stronger gravitational force than objects with less mass.
• The force of gravity depends on the distance between the two objects
• Also suggests that if any object were completely free form influence of all outside forces, it would travel in a straight path through the universe without slowing down or changing direction.
• Gravity affects the planets by keeping them in their orbits, making them go faster when closer to the sun and slower when farther.
• Interplanetary space- the spacce between the planets, considered a vacuum(a space that doesn't contain any matter)
• Minuscule amount of matter in interplanetary space causes a pressure of almost zero
• Temperatures range from very hot to very cold.

Mercury

• Planets- celestial bodies that "wander" across the sky
• Closest planet to the sun
• Looks similar to our moon; rocky, barren, pitted with craters that formed when rocks from space collided with the planet
• Smallest of eight planets
• Speediest planet- has an 88 Earth-day orbit
• Orbit is unique in that the same 2 regions on opposite sides of the planet take turns enduring the high-noon sun at Mercury's perihelion. These are Mercury's hot spots.
• No atmosphere
• Experiences temperatures from 430°C to -170°C

Venus

• Brightest object in the night sky except the moon
• Typically seen around sunset or sunrise, earning the names of morning star and evening star
• Only planet that takes longer to rotate on its axis than it does to orbit the sun
• Retrograde- moving backward from east to west
• Takes 117 Earth days to go from sunrise to sunset
• "Earth's Twin"- resembles earth in density, mass, gravity and size
• Atmosphere is 94% CO2, clouds are made of sulfuric acid, has strong winds
• Venus is the hottest planet with temps at 460°C

Earth

• 5th largest planet
• Average distance from the sun is 93 million miles
• Earth's orbit is 365 days, 5 hours, and 48 minutes
• Earth is the only planet in the solar system that is suitable for life
• Moon- earth's only natrual satellite
• Gravity is weaker than the Earth's
• Lunar month- period it takes the moon to orbit the earth; 29 days , 12 hours, 44 min
• Earth only ever see one side of the moon known as the near side
• Maria- moon's dark patches were thought to be large bodies of water
• Moon's far side is more heavily cratered than the near side, but has fewer maria

• Phases
• New moon- when the moon is dark
• Waxing crescent- grows larger
• First quarter moon- half the moon is visible
• Waxing gibbous- more than half
• Full moon- entire face is illuminated
• Waning gibbous- goes back to more than half being light
• Third quarter moon- half the moon is visible
• Waning crescent- only a sliver is light
• Eclipses
• Solar eclipse- when the moon moves between the earth and the sun
• Lunar eclipse- when the earth moves between the moon and the sun

Mars

• The last of the four inner planets and half the size of Earth
• "Red planet" due to its iron-rich soil
• Unique orbit of 687 Earth days to orbit the sun
• Rotation period though is similar to Earth's being 24 hours and 37 min
• Temperatures range from -125°F to 23°F
• Has two tiny irregular moons: Phobos and Deimos
• Atmosphere is very thin and composed of 95% CO2
• Has global winds, rocky deserts of reddish dust, and mountains
• Olympus Mon- a shield volcano located in the largest mountain range in the solar system

Jupiter

• Gas giants- planets that are made primarily of gases and are much larger than earth
• Largest planet in the solar system.
• Second brightest planet
• Has an orbit of 4331 days
• Has the fastest rotation- 9 hrs and 56 min
• Causes a bulge in the middle
• Made primarily of hydrogen, helium, and minor gases, but has a solid core the size of Earth
• Great Red Spot- biggest storm seen in the solar system which has a diameter as large as 3 Earth's placed in a row.
• Faint rings are around the center
• 4 largest moons: Ganymede( largest moon in the solar system), Callisto, Europa, and Io( most volcanic celestial body in the solar system)

Saturn

• Second largest planet
• 29 1/2 year orbit around the sun
• Rotation is the second fastest, taking 10 hrs and 39 min.
• Has a visibly flattened appearance
• Mainly composed of hydrogen and helium with a rocky core
• Considered the least dense planet
• Most distinguishing feature is the system of rings composed of mainly water ice and rock debris
• Between rings A and B is a large space known as the Casini Division and a smaller space is located on the outer edge of ring A known as the Encke Gap
• Saturn has 60 moons the largest being Titan
• Only moon in the solar system with a thick atmosphere (95% Nitrogen)

Uranus

• First new planet discovered.
• Third largest planet
• Long orbit of 84 Earth years and a rotation on its axis of 17 hr and 14 min
• Gas giant composed mainly of hydrogen and helium, but it also has a methan layer on the outer atmosphere giving it a light blue color
• Has a ring system of dust
• Unique feature is its axis is tilted at a 98° angle making the planet on its side.
• Has at least 27 natural satellites

Neptune

• Only planet discovered mathematically before it was seen.
• Cannot be viewed by the naked eye.
• Has an orbit of 164 Earth years and a rotation of 16 hr and 7 min
• Made of large amounts of hydrogen and helium also similar to Uranus with a layer of methane, yet its color is a much deeper blue
• Has the Great Dark Spot that disappeared by 1994. A similar one developed a few years later.
• 13 satellites, the largest one being Triton which has the coldest temperature in the solar system at -235°C
• Triton has volcanoes that eject liquid nitrogen that freezes instantly

Asteroids

• Asteroids- a stony or metallic object that is smaller than the planets and orbits the sun
• Ceres- was first classified as a tiny planet, later was determined an asteriod, but not is considered a dwarf planet
• Come in a variety of shapes and sizes
• Orbits
• Asteroid belt-a large ring of asteriods located between the orbits of Mars and Jupiter
• Trojan asteroids- two groups of asteroids not in the asteroid belt; travel in the same orbit as Jupiter one group 60° behind Jupiter and one group 60° in front of Jupiter
• NEA- near earth asteroids; located in the inner solar system and some cross paths with the Earth

Comets

• Comet- asteroid-size object that is made of rock and frozen materials forms in a bright tail
• History
• Tycho Brahe observed a comet in 1577 and established it wasn't an invader of the
• Sir Isaac Newton, based on Brahe's discovery, concluded that comets are subject to the same orbital laws of motion as the planets
• Edmond Halley proved Newton's conclusion by correctly calculating the orbit of a comet seen in 1682 that matches exactly to a comet seen in 1531 and 1607. Halley unfortunatley died before his prediction was proven true
• In honor of Halley, this comet he studied that takes about 76 years to orbit around the sun, is named Halley's comet.

• Components
• Nucleus- heart of the comet composed of 2/3 ice and 1/3 dust
• Coma- cloud made of dust and gas around the nucleus
• Tail-highly reflective streamer emitted from the comet
• A comet's course
• Have more elongated orbits
• Short- period comet- has a period shorter than 200 years
• Ex: Encke's comet has a period of 3yrs and 4 months
• Long-peirod comet- has a period longer than 200 years
• Ex: Hale-Bopp has a period of 4000 years
• Comet belt
• Kuiper belt- similar to an asteroid belt that contains Pluto, Eris, and other known dwarf planets; located past Neptune

Meteoroids

• Meteoroids- small chunks of rock or metal in space; range in size from microscopic dust to giant boulders
• Meteroids are smaller than asteriods
• Shooting stars
• Meteor- when a meteoroid enters the earth's atmosphere
• As a meteor heats up, it begins to burn, creating a brilliant flash
• Meteor shower- orbiting comet leaves a trail of meteoroid debris; as the earth passes through a meteroid stream, meteors fall much faster than normal
• Three biggest and easiest to see
• Jan 3-4
• Aug 12-13
• Dec 13-14
• Meteorites- meteors that don't completely burn up

The Celestial Sphere

• Celestial Sphere- an imaginary, giant, hollow sphere with the earth at the center and the sun, moon, stars, and other planets on its inner surface
• Horizon- the line that separates the visible portion of the celestial sphere from the part that we cannot see
• Distances on the sphere- the distance between objects on the celestial sphere is measured as an angle
• Rotation of the sphere
• Celestial pole- the points on the celestial sphere that are directly overhead at the earth's poles
• Polaris- north celestial pole; North Star or Polar star
• There is no star at the south celestial pole
• Celestial equator- halfway between the celestial poles; directly above the Earth's equator
• Circumpolar- stars always above the horizon; any star that is the same distance away from the visible celestial pole as the observer's latitude north or south of the equator is circumpolar; any star that distance away from the other celestial pole will never rise at all

• At the Earth's North Pole all star's within 90 of the visible (north) celestial pole are circumpolar; these are all the stars visible from the North Pole
• Zodiac- imaginary band, extending for about 8 on either side of the ecliptic, in which the sun, moon, and planets appear
• Constellations- 88 zones that astronomers divide the celestial sphere into
• Asterisms- a small group of stars that are used to form a picture or represent an object
• Not all constellations are visible from all latitudes

Seasonal Constellations

• Stargazers divide constellations based on the seasons
• Spring
• Ursa Major- the great bear
• Contains the Big Dipper
• Ursa Minor- the little bear
• Contains Polaris at the end of the long tail
• Also contains the Little Dipper
• Leo- the lion; best seen during the spring and summer months
• Contains the star Regulus and the asterism Sickle
• Bootes- the heardsmen; constellation lines look like a knife
• Virgo-the virgin
• Summer
• Draco- the dragon; curves around Usra Minor
• Lyra- the lyre; small constellation with one bright star Vega( the brightest summer star)

• Cygnus- the swan; at the tail is Denneb which also starts the Northern Cross
• Summer Triangle- a prominent asterism
• Scorpius- the scorpion; near the southern horizon during the summer in the most of the Northern Hemisphere; brightest star is Antares marks the heart of the scorpion
• Sagittarius- the archer; includes an asterism called the Teapot or Milk Dipper
• Autumn constellations
• Cassiopeia- names after a mythical queen of Ethiopia; has 5 bright stars resembeling a distorted M or W.
• Cepheus- five-sided constellation named after Cassiopeia's husband
• Great Square- a bright asterism formed by Andromeda galaxy and neighboring constellation Pegasus
• Pegasus- front half appears in the night sky
• Winter constellations
• Perseus- located directly above
• Orion- located south on a winter night; the brightest of all constellations
• Gemini- the twins; shaped like a U
• Taurs- the bull; V shaped

Southern Constellations

• Centaurus- the centaur; to the naked eye only seems to be a single star
• Crux- between the legs of the centaurus; four brightest stars form an asterism called the Southern Cross.

The Sun

• Temperatures ranging from 11,000 F to 27,000,000 F(in the core)
• Core- scientist believe that hydrogen atoms are constantly fusing to from helium atoms and releasing atomic energy in the process.
• Photosphere- visible part of the sun; extremely bright and can harm your eyes.
• Appears to be covered with bubbles called granules( each being 600 miles across)
• Supergranules-convection cells that last from 12 to 24 hours and may be 22,000 miles across.
• Sunspots- dark patches mixed among the thousands of supergranules that make up the photosphere; appear darker than the rest of the sun because they are cooler than the granules that surround them
• Chromosphere- outside the photosphere; lowest layer of the sun's atmosphere
• Spicules- flamelike columns of gas that continually erupt from the chromosphere; they last 5-10 min and are 600 mi across and 6000miles high
• Solar flares- tremendous bursts of energy that follow spicules; believed to be caused by magnetic stress within the sun.

• Solar prominences- streams of dense gas erupting off the chromosphere and returning in a loop-like fashion; linked to the sun's magnetosphere.
• Transition regions- thin layer located outside the chromosphere; releases uv radiation
• Can only be studied using space based solar observatories
• Corona- solar crown; outermost layer of the sun's atmosphere composed of a blanket of gas that extends hundreds/thousands of miles from the transition region.
• Coronal holes- punctures in the corona which expand and shrink according to changes in solar magnetism
• Solar wind- sources is coronal holes; high-speed stream of charged particles ejected from the sun.
• Shapes the Earth's magnetosphere
• Extends to the edge of the solar system.

Stellar Measurements

• Light-year- the distance light travels in one year
• Approximately 300,000 km/s(180,000 mi/s)
• About 5.9 trillion miles every year
• To large to measure the solar system with
• Parallax and parsecs
• Parallax- the apparent change in the position of an object caused by the actual change in the position of the observer.
• Test
• Stellar Parallax- half the angle that hte star appears to move on the celestial sphere when viewed from opposite sides of the Earth's orbit
• The larger the stellar parallax the closer the start is to the Earth
• Parsec- to express the distance to starts; unit based upon the measurement of a stellar parallax; defined as the distance of an object with a stellar parallax of 1 second of arc.

Star Magnitude

• Apparent magnitude- the brightness of a star as it appears to an observer on the earth; measured with a system developed by the Greek astronomer and mathematician Hipparchus
• The lower the apparent magnitude number, the brighter the object.
• Brightest star in the night sky is Sirius
• The apparent magnitude of a star depends not only on its actual brightness but also on its distance from the earth
• Absolute magnitude- the apparent magnitude that star would have to an observer located 10 parsecs from the star.
• Ex: Sirius vs Betelgeuse

Star Categories

• Temperature and Color-a star's color depends primarily on its surface temperature
• Cool stars glow a deep red
• Warmer stars like our sun glow a bright yellow
• Hot stars glow white
• Hottest stars glow blue-white
• Temperature and magnitude- a star's absolute magnitude depends on its surface temperature and its size.
• H-R diagrams- Hertzsprung-Russell diagram; dimensional graph taht compares stars by their temperature and by the amount of light they produce.
• Temperature is plotted horizontally with the highest temperatures to the left
• Brightness is plotted vertically either as the brightness compared to the sun or as the absolute mangitude.
• 3 groups
• Giants/Supergiants- bright, cool stars are in the upper right corner of the diagram; their brightness is due to their large size.

• Main sequence stars- stretching from the top left to the bottom right of the H-R diagram; considered average stars because their brightness depends primarily on their temperature.
• Ranges from bright hot blue stars to small red dwarfs.
• Our sun us a yellow star near the middle of the main sequence.
• White dwarfs- found in the lower left corner of an H-R diagram; small, dim stars outside the main sequence.
• Stars in groups
• Binary star- a system in which two stars are bound together by gravity, these two stars circle each other in the same way that the moon revolves around the earth.
• Sirius B orbits Sirius A
• Optical double- a pair of stars that are close on the celestial sphere but are far apart in space
• Open clusters- loose, asymmetrical clumps containing tens to hundreds and occasionally thousands or millions of stars
• Global clusters-tightly clumped spherical groups of stars, travel outside the boundaries of the Milky Way in unusual orbits around the galaxy's center

Stellar Explosions

• Nova- occasionally a star will suddenly flare up to many times its original brightness; star will be very bright for a time then return to its original magnitude
• Supernova- the explosion of a star; this leads to a nebula(a cloud of interstellar gas and dust
• Neutron stars- hot core of a star left over after a supernova
• Pulsar- a rapidly rotating neutron star that emits directional beams of radio waves.

Galaxies, Quasars, Nebulae

• Galaxy- a massive star system containing millions to billions of stars, as well as gas and dust.
• Milky Way- our galaxy; contains over 400 billion stars, including our own sun.
• Groups of galaxies
• Clusters-smallest of the orderly complex structures
• Local Group- contains the Milky Way galaxy
• Andromeda galaxy- largest galaxy in the Local Group; locvated in the constellation Andromeda
• Superclusters- clusters grouped into larger clusters.
• Galaxy shapes
• Spiral galaxies- look like giant pinwheels spinning through space; Ex are the Milky Way and Andromeda
• Have a nucleus and arms
• Barred spirals- the spiral arms attach to a straight bar that runs through the nucleus of the galaxy

• Black hole- an object so massive and dense that not even light can escape its gravity
• Elliptical galaxies- resemble eggs or footballs.
• Lenticular galaxy- flat with a bulging nucleus; has a solid disk instead of spiral arms
• Irregular galaxies- composed of stars clumped together in no definite shape.
• Quasars- extremely bright object that emits both visible light and radio waves; some of the brightest known objects in the universe
• Nebulae- large clouds of gas and dust floating in space