Day 1 6-10 pm

The Sky (what you see looking up) and Astronomy’s History

Observational AstronomyYour Backyard and up…

The Size of the Universe

• The scales of the universe• Powers of 10• In the text each frame is 100 X larger.• The increase in width is 10n larger.

• e.g. 3 jumps = 104 or 10,000 X wider

A square 52 feet acrosslight takes 0.000000578 seconds to cross this picture

100x = 1 mile wideit takes light takes .000003 seconds to cross this picture

100x more is 160km = 100 miles.0005 seconds

100X further and wider = 12,756km or about 8,000 mileswide It takes about .04 seconds for light to cross this distance.

100X further and wider takes us out to a distance of 1,600,000 km (2,600,000 miles or 2.6 X 106 miles) It takes 5 seconds for light to traverse this distance.

Another 100X further out = 2.6X108 miles wideLight takes 533 seconds =8.8 minutes to cross this distance.

Another 100X and we are at 2.6X1010 miles across

It takes 57,777 seconds = 16 hours for light to cross this frame

100X further! We now are looking at a square 2.6X1012 miles on a side or light takes 7,777,777 seconds = 668 days to cross it…

Yet another 100X out and wide:Now it is best to just use the light travel time - 17 years across this box, we say it is 17 light years wide. (This is 2.6X1010 miles across … etc.)

Still another 100X takes us to where Light takes 1700 years to cross this box … it is 1,700 light years wide.

Another 100X out and…We can now see 170,000 light years of space at once…and the Milky Way galaxy - our home galaxy. We have increased in size 100x 10 times. This means we have increased our view 1022 times!

Another 100X

we are now seeing 17,000,000 years at once.

And finally, another 100X further and we have 1,700,000,000 years = 1.7 billion years across the boxYou’d have to go 8X larger to be roughly the diameter of the observable universe. This is 1026 times larger than the roadway we started with, a 1 with 26 zeros after it!!!

• X10 more to gets us to the observable Universe SizeNumber of superclusters in the visible universe = 270 000

Number of galaxy groups in the visible universe = 500 million• Number of large galaxies in the visible universe = 10 billion• Number of dwarf galaxies in the visible universe = 100 billion• Number of stars in the visible universe = 2000 billion billion

Our place in time

• If the history of the universe is a calendar of one year, humans have only existed for the last 2 minutes, the pyramids were built 13 seconds to midnight New Years Eve, and we are in the last second before midnight.

The Universe in One Year was inspired by the late astronomer, Carl Sagan (1934-1996). Sagan was the first person to explain the history of the universe in one year—as a “Cosmic Calendar”—in his television series, Cosmos.

Constellations• Most civilizations created their own set.

– Ursa Major (The Big Bear)• The Big Dipper• The Plow• The Coffin and Bearers• The King and his Attendants• Tracks of the Running Deer

• Our present day constellations have origins in Mesopotamia over 5000 yrs ago

• Babylonians, Greeks, Egyptian added many – Myths and stories

Constellations• They are loose association in the sky• 88 Official modern (set in 1928 by the

International Astronomical Union). -They set definite boundaries-

• Asterisms– Ursa Major The Big Dipper– Sagittarius A Teapot– Cygnus The Northern Cross– Cassiopeia A “W”– etc.– You can make up your own! Whatever it looks

like to you!

Constellations

• Names of stars = Arabic• Brightness and the Greek Alphabet

– (Remind you of hurricane names?)

Key:

• Made of similar brightness's of stars (and the brighter stars in that area of the sky)

Constellations

Modern Constellations / boundaries

It’s all from our point of view

Astronomy as a Science • Astrology is it’s roots • Foretelling the future of nations, leaders, and

individuals, moment by moment or by birth etc. from positions of the sun, moon, & planets– Among the constellations ‘behind’ the path of the

sun, moon, and planets (more on this).– A pseudoscience – Force behind it?– Simple test… can a personality test predict sign?

Astronomy as a Science

• Astronomy = The scientific investigation of the Universe, it’s contents, structure, origin, and demise(?).

• Uses the Scientific Method

The Scientific Method • An Ideal that helps keep human bias

out of the discovery of reality– Observation– Hypothesis– Specific Observations/experiments– Theory– Law (eventually)

• Every Hypothesis, Observation, Theory and Law is subject to error and revision!

Astronomy and experiments

• Most of what we do is with light(much more on this in Week 3) – Other forms of scientific research can touch their

subject…lab experiments. – Not as easy in astronomy (but DOES happen)

Astronomy and experiments

• It uses MANY other branches of physics– Optics, Radio technology, Microwave technology

and even X-ray and Gamma Ray technology– Atomic Physics/Quantum Mechanics– Newtonian/Relativistic Physics– Electricity and Magnetism– Fluid Flows, Engineering– And the most advanced mathematics

discovered/createdBasically a bit of EVERYTHING!

More Astronomy basics:

• Looking up at night…

Stellar Magnitudes

• Hipparchus (~100BC) – Greek Astronomer – 6 classifications of stellar brightness– Brightest – 1st class, dimmest = 6th class– Magnitudo = Latin ; magnitude (size

brightness)

Stellar Magnitudes

• Some Examples:• Sun –23.5, Full Moon –12, Venus(max) – 4.5,

Sirius -1.4, Polaris 2.8, Low end for eyes 6 to 7, 8” telescope 15, Mt. Palomar 22, Hubble 26

Stellar Magnitudes Continued• Greek = alphabet; alpha,beta,gamma,delta

etc… • Each 5 magnitudes = 100X brighter

(or dimmer)• One magnitude is 2.512X greater (or lesser)

intensity

Observing the Sky• Naked Eye you can see:

– Constellations– Planets– Sun/Moon– Meteors– Comets

• Binoculars– Planets, Comets, Star Clusters, a couple of Galaxies– The Milky Way (in the city)

• Telescopes allow you to see details on:– The Moon, (more) Planets, Galaxies, Nebula, Star

Clusters, Comets, asteroids (minor planets)

Your modern enemy:

• Civilization

• Outdoor Lighting!!!

Light Pollution

Light Pollution - Close-up

BAD FIXTURES

Flood LightIf used as in the picture. 30-50% light goes upward Pointed down Zero light loss.photo © BGE

Decorative~70% upwardphoto © BGE

Sidewalk Light~30% upward photo © BGE

Cobra HeadThe most used design for street lights Unchanged since 1960s ~30% upward photo © BGE

http://www.pha.jhu.edu/~atolea/second/page1.html

GOOD FIXTURES

Box Design Best design ever. Can have round, cylindrical or other shape head. Receded bulb Flat lens 100% downwardphoto © BGE

Good decorative.In campus at JHU. Receded bulb only ~ 5% upward photo © BGE

http://www.starrynightlights.com/Outdoor_Lighting/

Once you get to a dark sky…

• You can get lost.

• How to find your way around:

Measuring your way around the sky• Coordinate Systems

• Altitude- Azimuth• Right Ascension (Longitude) – Declination (Latitude)• Others…

• Assumption:A celestial Sphere• No observable

parallax to the eye

• Measurementsare fixed to this ‘sphere’

Movement in the Sky• Just like a

globe spinningon an axis, thesky spins on theline through theNorth Pole andSouth Pole

• Things rise inthe east, and climb to the pointabove south, thendrop into the west

• EVERYTHING!

Measuring your way around the sky• Circumpolar Stars

(and anti-circumpolar)• Everything in the northern sky ‘wheels’ around the

North Star = Polaris• Counter-Clockwisesee next page

• Latitude and Polaris• If you end up on a reality show, this can help

pinpoint where you are on the planet.

Polaris and Circumpolar Stars

Landmarks in the sky• Alt/Az or Altitude and Azimuth System

– Horizon (0° Altitude)– Zenith (90° Altitude)– Cardinal Points (N, S, E, W)– Meridian (Halfway line in the sky – Connect S to

Zenith to N)

Landmarks in the sky• Equatorial System

Right Ascension and Declination– Equator (line in the sky halfway between North &

South Poles = 0°)– North Celestial Pole (South Celestial Pole = 90°)– Meridian (same as before, divides the sky in half; S to

Zenith to N)

Getting around…• Angles in the Sky

– 360 degrees (A full circle- all the way around the sky)

– Hand estimations –pinky nail=1°, three fingers = 5°, fist =10°, longhorn=18-20°

Motions of the sky• The Position of the North Celestial Pole

– Latitude and the NCP– Daily Motion– Circumpolar Stars– Anti-Circumpolar Stars (south circumpolar stars)

Less important motions

• Precession(messes up the Zodiac/Astrology) 26,000 year wobble (more in the planetarium show) – Shouldn’t keep you up at night– Need New Star Charts every 50

years– Computers simplify this A LOT!

Motions of the sky

• Nutation 18.6yrs. 9.2 arcseconds – tiny wobble– Shouldn’t keep you up at night either.

Seasons• Terms: Rotation vs. Revolution

– Rotation= Something spinning on its own axis Days– Revolution= Something orbiting something Years

• Forget everything you know… start fresh right now!• Seasonal features:

– The days grow longer and shorter– The weather in the N. Hemisphere gets hot then cold– The weather in the S. Hemisphere gets cold then hot– Different stars are out at night (Orion?)

• So what causes the seasons?

Seasons• The Earth is closer to the sun at one time of the

year, and further six months later.• Does that Matter? (hold that thought)

And then…?• Another important fact:

– The earth’s axis is tilted compared to the rest of the flat solar system (planets roll around in their orbits like BB’s on a plate)

– So the motion of the sun (and everything else in the solar system) is along a tilted line or path = ecliptic

– That tilted path runs through some constellations… how could it not?

Interesting aside… all planets have a bit of tilt…

The plane of the Solar System:NOT to scale!

Zodiac constellations (aside Astrology vs. Astronomy)

The word Zodiac = “circle of animals”

Seasons

• The sun seems to travel 360deg in 365.256 days

• The Earth’s axis tilt = 23.5deg– Gives an celestial equator to ecliptic tilt of 23.5deg

• SOOO the celestial equator and ecliptic cross in two special places = the equinoxes– The vernal equinox (~March 21) and the autumnal equinox

(~ Sept 22)– The solstice = maximum angles up = Summer Solstice

(~June 21) maximum angle down = Winter Solstice (~Dec 22).

• Precession Again (and astrology – age of Aquarius, Age of Pisces – abt. 2600AD) …

Seasons continued…• The Earth is closest to

the Sun (Perihelion)~January 4th ; The Earth is furthest (Aphelion) ~ July 3rd

• The reason forthe season

• THE TILTONLY !!!!!!!!!!

– Longer days in summer;higher sun angle

– Shorter days in winter;lower sun angle

The earth on opposite sides of the sun (six months apart).

Season Recap

• The tilt of the Earth’s axis ALONE makes the seasons.

• Light coming in from overhead heats a lot! Light from a shallow angle does not heat well.

• The distance between the Earth and Sun is OPPOSITE of what we would expect.

Locations of the planets in the sky• Almost all are found on the Ecliptic

(or very close to it= Zodiac again)• Remember- the Ecliptic is only the plane of the

Solar System

Locations of the planets in the skyPrecession Again (and astrology) – about 1.5

constellations off nowThe inner planets (Mercury & Venus) are always

near the sun• Mercury = 27deg 50min• Venus = 47 deg

– Venus = Morning Star/Evening Star

Locations of the planets in the sky

• The outer planets (Mars,Jupiter,Saturn, etc.) can be anywhere along the ecliptic at any time.

More on planets.• Retrograde motion (more on this later) = loops

in the sky (over weeks of time)

• Bright…Colorful(sometimes)…Non-Twinkling

What’s the brightest thing at night?

• Luna.

Lunar Phases

• The Moon’s orbital period = 27.322 days (sidereal period = against the stars) ~ month– Similar to a woman’s cycle – Luna always a female association in all cultures

• The Moon travels 13deg a day (26X its apparent diameter!!)

• Is only ½° in diameter• ½ your pinky nail in width

Lunar Phases• Inclined (tilted) orbit to the ecliptic >5deg• Shines by reflected sunlight only and phase is related to where

the sun is– 1st quarter always ¼ around the sky east of the sun (in the

evening sky)– Full moon always opposite the sun and rises at sunset– 3rd quarter moon always 3/4ths the way around the sky and is high

in the sky at dawn– New moon always near the sun (and invisible) next screen

• Gibbous is > ½ lit , Crescent is < ½ lit• Waxing is increasing phase, waning is decreasing phase

• All this summarized on the next frame:

Eclipses• Two kinds- Solar and Lunar

• Solar is at New Moon ONLY– The moon blocks the sun from our point of

view (we see the sun covered)

• Lunar is at Full Moon ONLY– The Earth blocks the sun from the Moon’s

point of view (we see the moon go dark)

Eclipses• Why we don’t we see an eclipse EVERY

Full and New Moon????

• The Moon’s orbit is tilted a tiny amount from the flat Solar System Plane

• The tilt is 5 degrees.• This keeps eclipses from happening all

the time.

Anatomy of an Eclipse • Parts of an eclipse

– Penumbra (less than total darkness- sun only partly covered by moon on earth or by earth on moon)

– Umbra (total coverage of moon over sun or earth over sun) darkest part of eclipse

Lunar Eclipses • Moon is Full and the Earth casts its shadow

on the Moon darkening it see next screens• Umbra = cone behind earth that is about 2X

the moons diameter in space at the Moon’s mean distance

• Penumbra is much larger.• Red color on Moon comes from the red light

refracted from all the sunsets on the earth at once visible to the Moon.

• Can be seen by an entire hemisphere- lasts around an hour and a half+ (in Umbra for longest eclipses).

Solar Eclipses• Moon is New and casts shadow on the Earth• Umbra is very small on the Earth’s surface

(168 miles at maximum (7.5 minutes) down to zero!).

• Normal totality lasts 2-3 minutes

During the Eclipse• Total eclipses allow us to see the Sun’s outer

atmosphere (Chromosphere) and an effect called the diamond ring effect (sunlight peaking through canyons on the Moon’s rim

Different Sizes?• If Moon is closer to Earth (perigee) = bigger

shadow and longer eclipse; total eclipse • If Moon is further from Earth (apogee) =

umbra does not reach earth surface = annular eclipse

Eclipses of the Future…

• See next frames• The eclipses only occur when the Moon is on the

ecliptic = nodes• The Moon’s orbit precesses (like the Earth’s axis)

every 18.61 years• Eclipse cycles begin earlier each year by 3 weeks• So the same eclipses happen again and again every

18 years 11.3 days BUT shifted 1/3rd the way around the world Westward = The Saros Cycle.

Tides

• Gravitational pull of Moon AND Sun– Moon is stronger– 1 foot to 40 feet based on location on the earth

• Land and Sea affected (Water more!)• At 1st and 3rd quarter, mild tides (Neap tides)• At Full and New, stronger tides (Spring tides)• Not exactly lined up (Friction) because the

Earth rotates faster than the Moon revolves (so tide is ahead of moon – transfers momentum to the Moon) next screen

Side note… things in orbit• The moon, or satellites, or the space shuttle

are in orbit around the Earth.• There is no weight to objects in orbit of other

objects because they are falling around the body they are circling.

• There IS gravity, it is constantly pulling the object downward, but the satellite is traveling sideways at the same speed it is falling.

Computers (the included CD’s) and the Internet

(see links at www.bikerjohn.com)

and the History of Astronomy

The History of Astronomy• Pre-Copernican Astronomy

– Astrology/Astronomical Observations• Babylonians, Chinese, Arabia Region

– Aristotle 384 to 322 B.C.in Greece• His work persisted for

almost 2000 years• Created a Philosophy

not science• Assumptions

– The Earth was changeable and imperfect, the heavens were perfect and unchangeable

– Crystalline spheres – No parallax

» Bowl shaped sky

History Continued– Eratosthenes (?273-192B.C.) – Determined the size of the earth using sticks at the Summer

Solstice • Was accurate to within 1%

– Some other famous Greek astronomers were Anaxagoras, who figured out what caused eclipses, Aristarchus, who figured out that the earth went around the sun, and Thales, who figured out that the earth was round.

– Ptolemy 140 A.D. – Mathematical model of the universe

• Geocentric universe• Uniform circular motion (assumption)• BUT planetary speeds varied! RETROGRADE MOTION

see next frame• Solution: Epicycles. Also on next frame • This model lasted for 1500 years

History Continued See timeline next frame…

• Copernicus 1473-1593 • Long church affiliation

• Uncle was an important bishop in Poland• Lived in quarters adjoining the cathedral in Frauenburg

– Heliocentric model (sun central model)– De Revolutionibus Finished in 1530

• Explained planetary motions without epicycles• BUT didn’t predict the motions well – still

– “Perfection” still expected– Circular orbits modeled, real orbits ellipses– He had to add small epicycles to fix it

History continued

Post-Copernican Astronomy Tycho Brahe 1543-1601

• Measured positions of planets in the sky• 1572 a “new star” appeared (Tycho’s supernova)• Measured the parallax of the nova- no parallax!• Broke the ‘perfect universe’ assumption• He saw no parallax in the stars – concluded Copernican

model poor• Without telescope measured 777 star positions• Planetary positions daily for 20 years• Hired Mathematicians to work out the orbit = Kepler

History continued• Johannes Kepler (1571-1630) • Poor beginning

– Mystical Almanac (five solids = six planets)– Illegally kept Tycho’s books– 1609 the book Astronomia Nova (New Astronomy)

• Planets move faster when nearer the sun• Laws of planetary motion• Very close to stating the law of mutual gravitation

(Newton later)

History continued

• Kepler’s Three Laws– Ellipse solved the motion problems LAW 1

• Foci• Semimajor axis, a• Eccentricity, e (foci dist/longest diameter)• Equal Area in Equal Time LAW 2• P2(years)=a3(AU) LAW 3

– BUT he didn’t know why the planets moved

History Continued• Galileo Galilei (1564-1642) • False ‘Facts’

• He did not invent the telescope• He was not condemned by the Inquisition for believing the Earth

went around the sun– He did solidify the scientific method– The telescope was invented by lens makers in Holland around

1608– He was not the first person to look up into the sky either, but he

was first for systematic observations.– First 3 major discoveries

• The moon is not perfect (philosophy crumbles) – Calculated sizes for mountains– The moon was another world like ours

• The Milky Way was made up of more tiny dim stars• Jupiter had 4 new ‘planets’ circling

History continued• Galileo

– The Moons of Jupiter • Small things go around larger things• Critics had said the Earth can’t go around the Sun; the moon would be left behind.

But not at Jupiter…– More discoveries

• Sunspots on the sun (the sun was not perfect)• The sun rotated• Venus had phases proved planets go around the sun (and Venus was closer than

the Earth)– Galileo was embraced by church leaders in Rome but was outspoken, forceful

and sometimes tactless.– Controversy flared- opponents fought and debated him– He was asked by Pope Paul V to cease debate and his books were banned or

revised. – Later Pope (his friend) encouraged him to continue to work– Wrote the controversial “Dialogue Concerning Two Chief World Systems”– Put under house arrest for life for not following orders by the Inquisitors.

History marches on

• Isaac Newton (1642-1727) • Discoveries

• Studied optics• Developed the Three Laws of Motion• Expressed the Nature of Gravity• Invented Differential Calculus

History schmistory• Newton’s Three Laws

1. A body (mass) continues at rest or in uniform motion unless acted upon by an outside force

2. A body’s change of motion is proportional to the force acting on it and is in the direction of the force

F=ma3. When one body exerts a force on a second

body, the second body exerts an equal and opposite force back on it.

History…• Newton’s Law of Gravity

• Greater speed results in eventual orbit; orbital speed = speed needed to move sideways fast enough to fall around the body rather than into it.

Recent History

• Albert Einstein (1879-1955)– Assumption from Newton: Absolute rest in the universe – As a teenager wondered what light would look like if you

tried to catch up with it– Michaelson-Morley Experiment (most important null-

result in science)– Mass-Energy Relationship– Only used simple geometry and algebra! – Special Relativity– General Relativity (more on this later)

Don’t know much about…

– Edwin Hubble• Observed red shift of galaxies (more on that later) and showed

the universe is expanding• Einstein had to revise General Relativity to put back the

expansion term

– Modern Names• John Wheeler• Kip Thorne• Alan Guth• Steven Hawking• Michio Kaku

Next …

• A tour of the Solar System

• All the stuff that goes around OUR star, the Sun.