Download Friday Feb 25th, 2000

Day 1 6-10 pm
The Sky (what you see looking up)
and Astronomy’s History
Observational Astronomy
Your Backyard and up…
The Size of the Universe
•
pages 2-3
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 across
light takes 0.000000578 seconds to cross this picture
100x = 1 mile wide
it 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 miles
wide 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 wide
Light 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 box
You’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 Size
Number of superclusters in the visible universe = 270 000
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•
•
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
• See page 26 in your textbook (and next
slide
• 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
•
page 40-49
Most civilizations created their own set.
–
Ursa Major (The Big Bear)
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•
•
•
•
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
•
•
•
page 40-49
They are loose association in the sky
88 Official modern (set in 1928 by the
International Astronomical Union).
-They set definite boundariesAsterisms
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–
–
–
–
–
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
•
•
page 40-49
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
pg 103-106
pg 106-108
– 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
pg 103-106
• 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/created
Basically a bit of EVERYTHING!
More Astronomy basics:
• Looking up at night…
Stellar Magnitudes
page 475-476
• Hipparchus (~100BC) – Greek Astronomer
– 6 classifications of stellar brightness
– Brightest – 1st class, dimmest = 6th class
– Magnitudo = Latin ; magnitude (size 
brightness)
Stellar Magnitudes
page 475-476
• 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:
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–
–
–
–
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 Light
If used as in the picture.
30-50% light goes
upward
Pointed down
Zero light loss.
photo © BGE
Decorative
~70%
upward
photo © BGE
Sidewalk
Light
~30% upward
photo © BGE
Cobra Head
The 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% downward
Good decorative.
In campus at JHU.
Receded bulb only ~ 5% upward
photo © BGE
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
pg 41-44
• Altitude- Azimuth
• Right Ascension (Longitude) – Declination (Latitude)
• Others…
• Assumption:
A celestial Sphere
• No observable
parallax to the eye
• Measurements
are fixed to
this ‘sphere’
• Just like a
globe spinning
on an axis, the
sky spins on the
line through the
North Pole and
South Pole
• Things rise in
the east, and
climb to the point
above south, then
drop into the west
• EVERYTHING!
Movement in the Sky
Measuring your way around the sky
• Circumpolar Stars pg46-7
(and anti-circumpolar)
• Everything in the northern sky ‘wheels’ around the
North Star = Polaris
• Counter-Clockwise
see 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 pg 44-45
– 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
pg 45-47
• The Position of the North Celestial Pole
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–
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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
pg 45-47
• Nutation 18.6yrs. 9.2 arcseconds – tiny
wobble
– Shouldn’t keep you up at night either.
Seasons
•
pg 48-50
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:
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–
–
–
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
pg 48-50
• 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
pg 48-50
• 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 for
the season
• THE TILT
ONLY !!!!!!!!!!
– 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
pg48
• 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 sky
pg48
Precession Again (and astrology) – about 1.5
constellations off now
The 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
pg48
• 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
pg 50-53
• 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
pg 53-58
• 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
pg 53-58
• 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
pg 142-145
• Gravitational pull of Moon AND Sun
– Moon is stronger
– 1 foot to 40 feet based on location on the earth
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•
•
•
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 pg 127-8
• 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
pg 92-100
– 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.)
pg 100-102
• 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.
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•
•
•
•
•
pg 101-103
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 pg 58-62
This model lasted for 1500 years
History Continued
• Copernicus 1473-1593
See timeline next frame…
pg 103-104, 133-134
– 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
pg 134
– Tycho Brahe 1543-1601
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•
•
•
•
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)
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–
–
–
pg 105, 135
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
pg 136-139
– 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)
pg137
– 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
pg139-140
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=ma
3. 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) pg 115-117,384,409 etc.
– 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 nullresult 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
pg 567-579
• 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
pg 444,530
Next …
• A tour of the Solar System
• All the stuff that goes around OUR star,
the Sun.