1

Honors Space Science Unit

(Textbook reference Chapters 12, 24, 25 and 26)

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 Comet?

What is a Star?

What is a Nebula?

What is an Open Cluster?

What is a Black Hole?

What is a Quasar?

?

??

? ??

M33, The Pinwheel Galaxy in Triangulumby 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

by George Greaney

What is astronomy?

Astronomy is a science that attemptsto understand the make-up and the history of the universe.

Galaxy M83 in Hydraby George Greaney

•Stars •Nebula •Planets

•The Sun

•The Great Andromeda Galaxy by George Greaney

•Star clusters •Galaxies

•Galaxy clusters

•Dark matter •Black holes

Galileo Galilei (1564-1642)

What is an astronomer?

A night watchman with a college education?

Galileo Observatory in Italy

An astronomer is a scientist, skilled in mathematics, physics, and astronomy.

Most professional astronomers work for universities or government agencies.

Source: The Berkeley Cosmology Group

Astronomer Serena Kim at work At Cerro Tololo in Chili

Few astronomers spend much time looking through a telescope. Most operate telescopes from a control room or even from their computer at home via theInternet.

Typical astronomers only spend one or two weeks eachyear observing, and the rest of their research time analyzing their data.

Source: Applied Theoretical and Computational Physics DivisionLos Alamos National Laboratory

Amateurs and their tools

What is an amateur astronomer?

What is an amateurastronomer?

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

15

The Expanding Universe 26-5

Hubble’s Law

How Did We Get Here?The Big Bang TheorySteady-State Theory

Plasma Theory

Continued Expansion

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”? (Textbook reference 26-4)

• 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 shapedImage 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

We can see

– stars

– star clusters

– nebulae

– galaxies

How do we know what our galaxy looks like?How do we know what our galaxy looks like?

24

Reviewing Galaxies

• Groups of stars, planets, and space debris

• Irregular, Elliptical, Spiral

• Milky Way is our galaxy

WhatIs aStar?

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 gasthat 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

27

Stars (Textbook reference 26-2 and 26-3)

• 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

Image courtesy of Dave DockeryAstronomical Society of Las Cruces Source: The British Astronomical Association

Nearby Stars:

Name Distance from Earth

Sun 93 million miles (8 light minutes) Proxima Centauri 4.22 Light YearsAlpha Centuri A,B 4.39 Light YearsBarnards Star 5.94 Light YearsWolf 359 7.8 Light YearsLalande 21185 8.3 Light YearsSirius A,B 8.6 Light Years

29

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

Hertzsprung-Russell Diagram

The Doppler Effect:

Red Shift – stars moving away from EarthBlue Shift – stars moving toward Earth

Video on the Hertzsprung-Russell Diagram

Spectroscopy Video

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 (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 26-1, 24-2 and 24-3)

• 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.

38

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

39

The Sun: Seasons

Seasons: Solstices

sun directly overheadtwo times a year (June 21 and December 21)June=longest day, December=shortest day

Equinoxeshalfway between solsticesneither hemisphere is tilted toward the sundaylight and darkness=equal

40

What causes the seasons?

1. 23.5° tilt of Earth’s axis

2. Direct vs. indirect sun rays

3. Length of daylight

41

Winter

Fall

Summer

Spring

Sun

42

Energy in the Atmosphere:Energy reaches earth’s atmosphere

Reflected back or absorbedclouds, dust and gasessurface

Energy is transferred within the troposphereradiation: heats land and water

reflected back into atmosphereconvection: moves heat through the troposphere

warm air is replaced by denser, cool airconduction: transfers heat from land and water directly

into the air nearest Earth’s surface

The Sun: Solar Energy

43

The Sun: WindsWinds:

Caused by differences in air pressureLarger differences in pressure=stronger winds

Local Winds:Where land meets large bodies of water Sea Breeze Land Breeze

Global Winds: Trade windsWesterliesPolar easterlies

Source: The British Astronomical Association

Our Sun is a star that has already spentabout 5 billion years on the main sequence.

Scientist believe our Sun is roughly halfwaythrough it's life.

Stars are the source of light for all objects in outer space

Earth’s Moon

46

Phases of the Moon (Textbook reference 25-2)

waxing = increasing waning = decreasing

gibbous = > ½ crescent = < ½

47

Lunar Phases

• New Moon

New

Waxing CrescentFirst QuarterWaxing GibbousFull

• Waxing Crescent

• First Quarter

• Waxing Gibbous

• Full Moon

48

Lunar Phases

• Full Moon

• Waning Gibbous

• Last Quarter

• Waning Crescent

• New Moon FullWaning GibbousLast QuarterWaning CrescentNew

49

Rotate vs. Revolve

• Rotation – spin of an object on its axis

• Revolution – orbit of an object around another object

50

Moon’s Orbit and Phases

51

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

52

Eclipses (Textbook reference 25-2)

1. Lunar Eclipse

2. Solar Eclipse

3. Total Eclipse

53

54

55

A total eclipse of the sunoccurs during the day!

Only the corona is visible.

56

Tides (Textbook reference 25-2)

•Effect of gravity between the moon and the sun

57

Spring Tides

• When the sun, the moon, and the Earth are all aligned in a 180o angle

58

Neap Tide

• When the sun, the moon, and the Earth form a 90° angle

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

59

SOLAR SYSTEM

• The Sun

• Eight Planets and Pluto

• Sixty-one satellites of the planets

• Many Comets and asteroids

The Origin of the Solar System(Textbook reference 25-5)

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

The Greeks called the five points of light that seemed to move among the stars ______, meaning “______”. • planets• wanderers

Planets…Wandering Stars?

The ancient Romans later called these planets:

• Mercury• Venus• Mars• Jupiter• Saturn

Greek Ideas: Earth at the Center(Textbook reference 25-1)

Initially the geocentric theory stated that

everything moved around the earth.

Retrograde motion 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 DiagramsWhere 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

speedsThis 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, a ______ ______, made much more accurate observations by carefully observing the positions of

the planets for almost _____ years.

• Danish astronomer• 20

Brahe and Kepler

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.

79

Exploring the Solar System

• Travel to the Moon

–Escape Velocity – speed needed to escape Earth’s atmosphere

• Recent Space Missions

–Have led to technology used in daily life

Exploring the Solar System (textbook reference 25-1 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 ellipseThe 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 12-4)

85

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

• Newton’s explanation of gravity supported Kepler’s laws of planetary motion.

Dark Matter helps Gravitational Pull

94

Solar System Characteristics (Textbook reference 25-3)

• Inner Planets

–Mercury, Venus, Earth, Mars• Terrestrial planets with atmosphere and crust

95

The Inner Planets

• 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

97

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%

98

• 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 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 sunA thin atmosphere that contains

mostly carbon dioxideAppears as bright reddish color

in the night skySurface features volcanoes and

huge dust stormsHas 2 moons: Phobos and

Deimos

Moons of Mars

Phobos

Deimos

104

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)• Pluto is neither terrestrial or Jovian

The Outer Planets

• The Gas Giants

• These planets include: Jupiter, Saturn, Uranus and Neptune

• All larger than Earth by 15-300 times

105

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

106

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 sizeThe is because of it composition (H and He in gas or

liquid form.

RotationShortest day in the solar system about 10hrs

This fast spin distorts the shapeThis also contributes to its banded appearance

Belts are low lying dark-colored cloudsZones are high light-colored clouds

MoonsMore than 60, but some are very smallMostly composed of ice and rock

Gravity assist 108

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 twenty-three 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

117

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

• AtmosphereBluish appearance cause by methane gasClouds are similar in appearance to the

surfaceLiquid surface with a small solid core

• RotationAlmost a top to bottom rotationPoles vacillate between 42 years of darkness

and light

119

Uranus

Norm Herr (sample file)

URANUS

• Uranus has more moons (15) than any other planet except Jupiter (16) and Saturn (23)!

0

5

10

15

20

25

Number of Moons

MercuryEarthMarsJupiterSaturnUranusNeptunePluto

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.

Neptune• Atmosphere

– 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

122

123

Note the apparent storms

The blue coloration of Neptune is probably due to the presence of methane

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.

124

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.

125

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 DockeryAstronomical Society of Las Cruces

Comet Ikeya Zhang

What Are Comets, Asteroids and Meteors?(textbook reference 25-3 and 25-4)

Space Debris

CometsA comet is basically a ball of ice and dust in space. The typical comet is less than 10 kilometers across. Most of their time is spent frozen solid in the outer reachesof our solar system.

Image by Harvard-Smithsonian Center for Astrophysics

Comet Hale Bopp

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

Image by Harvard-Smithsonian Center for Astrophysics

Source:NASA

Comet Hale Bopp

Reviewing Comets

• Small icy bodies

• Travel past the Sun

• Give off gas and dust as they pass by

• Tail of gasses called a coma

138

Asteroids

• Asteroid – rocks orbiting in space

• Asteroid belt – 100,000 asteroids located between Mars and Jupiter

–separates inner and outer planets

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

140

141

Meteors

• Meteor – meteoroid striking Earth’s atmosphere

• Meteorite – meteor that hits Earth’s surface

Solar System Writing Activity• Write an informational essay on our solar system.

Include an introductory paragraph, 5 detail paragraphs, and a concluding paragraph.

• The five detail paragraphs should discuss the following topics:

• Stars

• Orbits (inertia and gravity)

• Planets

• Planetary satellites (moons)

• Comets and asteroids

Solar SystemActivities

• Order the Planets 

• Fun with Planets

• Constellations of the Northern Sky

• Planets

• Solar System 

144

Units of Time from Space

• Year – 1 revolution of Earth

• Day – 1 rotation of Earth

• Month – 1 revolution and/or rotation of Moon

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.

146

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

147

Are We Alone in the Universe?

• SETI http://www.seti.org/seti-institute/about-seti/scientists

vs Pseudoscience 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