ASTRONOMY

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ASTRONOMY
LOOK UP. LOOK WAY, WAY UP.
WHAT DO YOU SEE?
SUN, MOON, STARS
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WHAT DO YOU SEE UP THERE?
Sun crosses the sky at different levels Length of
days change (8-16 hrs in Ottawa) Different at
different latitude Seasons change Star patterns
rotate about pole star Sun and Moon travel
through zodiac Moon has phases
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WHAT DO YOU SEE?
WANDERING BODIES
RETROGRADE MOTION
SUN
MOON
EVENING STAR
MORNING STAR
OTHER MOVING BODIES SOME FASTER THAN OTHERS
OCCASIONAL VISITORS TAILED STARS FALLING
STARS BRIGHT FLASHES
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SEVEN WANDERERS
NAME SPEED BRIGHTNESS (arc-sec/day) (Sirius1.0
SUN 3550 15,000,000 MOON 48,100 30,000 MERCURY
14,900 0.9 VENUS 5,840 14 MARS 1,910 3.5 (move
s the width of the moon in one day) JUPITER 302 2
.5 SATURN 102 0.4
They must be gods!
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EARLY ASTROMOMICAL OBSERVATION
CHINA Records from 2000 BC Halleys comet
467 BC Length of Year 365 1/4 days Predicted
eclipses
BABYLONIANS Star catalogs 1600 BC Eclipse
reported 1500 BC continuous records 900 BC
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LOOKING FOR PATTERNS
Pythagorus 570-490 BC Cosmos model -
spheres Plato 428-348 BC Circular
paths Eudoxus 400-347 BC First Mechanical
model Aristole 384-322 BC Spherical
Earth Aristarchus 310-230 BC Sun/Moon dist
size heliocentric model Eratosthenes 275-194
BC Radius of the Earth Hipparchus 160-127 BC
Earth-Moon distance Ptolemy 85-165 AD Almegest
(120) Geocentric model
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ARISTARCHUS
MOON
Concluded Ds 20x Dm Actually it is 4001
Dm
90o
SUN
a (ang separation of sun and moon on celestial
sphere)
earth
Ds
EARTH
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ARISTARCHUS (2)
If sun and moon look the same size, and the sun
is 20x further away, the sun must be 20x larger
than the moon.
From the size of the Earths shadow on the moon
during a lunar eclipse, and with his values of
the distance from the sun to Earth, he calculated
the earth is 3x larger than the moon, and the sun
is 7x larger than Earth. Wrong, but clever.
Earths shadow on moon
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ERATOSTHENES
Eratosthenes measured the circumference of the
Earth by noting that the Sun was at an angle of
6 south of the vertical at Alexandria at the
same time that, at Syrene, 800 km south of
Alexandria, the sun was observed to be exactly
overhead. Based on these data, the circumference
of the Earth in kilometers was measured to be
37,200 km or 23,250 miles, very close to the
modern value of 40,000 kilometres.

6o
shadow
SUN
Syrene
Alexandria
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HIPPARCHUS 190-120 BC
Hipparchus measured the distance from the Earth
to the Moon during a solar eclipse that was a
total eclipse at Syene and a partial eclipse at
Alexandria. At the same time that an observer at
Syene saw the entire Sun blocked by the Moon, one
at Alexandria saw 1/5th of the Sun's disk, that
is 1/5th of 30 arcminutes of the Sun's disk was
visible (The Sun's angular diameter is 30
arcminutes or 1/2 degree). The angular size of
the visible Sun seen at Alexandria therefore is
1/10th of a degree (0.1 degree) and this angle,
expressed in radians and applying the small angle
approximation gives the ratio of the
Syene-Alexandria distance to the Earth-Moon
distance at 60 earth radii and the moon 1/4 of
the earth in size.
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PTOLEMY EPICYCLES WITHIN EPICYCLES
saturn
Field of stars
sol
jupiter
venus
mars
mercury
terra
luna
PTOLEMAIC GEO-CENTRIC MODEL WITH EPICYCLES
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COPERNICUS 1473-1543
THE COPERNICAN REVOLUTION WE ARE NOT SPECIAL
IN ANY WAY NOT THE CENTRE NOT THE FIRST NOT THE
BIGGEST NOT THE SMALLEST WHAT IS THE WORLD COMING
TO????
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TYCHO BRAHE 1546-1601
Ruler of island of Hveen off the caost of
Denmark Built first observatory in Europe (no
telescopes) Collected massive amounts of precise
measurments
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JOANNES KEPLER 1571-1627
Acquired Brahes records Kept meticulous records
of his own
KEPLERS THREE LAWS
1. Planets move in ellipses, sun at one focus
2. A vector drawn from the sun to the planet
will sweep out equal areas in equal times
3. P2 / a3 a constant
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KEPLERS SECOND LAW
B
2b
F2
c
Sun
A
2a
Area ABC Planets (and comets) move faster
when they are closer to the sun
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KEPLERS THIRD LAW
Planet
r2
r1
F2
2b
F1
2a
r1 r2 2a p2 k a3 (k a
constant) pperiod of rotation
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GALILEO 1564-1642
Developed the telescope first to see Multiple
stars (1609) Sunspots (rotation of sun, sun
imperfect) Phases of Venus (sphere, reflected
light) Moons around Jupiter (1610) (other
centres) Mountains on moon (heavenly bodies
are imperfect) Rings (handles) of Saturn (did not
understand them) Recorded Uranus (in 1617 - but
did not know it) Verified Coperican Model
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THE PLANETS
NAME PERIOD ORBIT RADIUS (days)
(A.U.) (km)
MERCURY 88 .4 2439 VENUS 225 0.723 6057 EARTH
365.25 1.0 (150MKm)6378 MARS 686 1.52 3393 JUP
ITER 11.86 yrs 5.2 71400 SATURN 29.5
yrs 9.54 60330 URANUS 84 yrs 19.19 25500 (dis
c 1781) NEPTUNE 164.8 30.06 24750 (disc.
1846) PLUTO-CHARON 39.5 1900
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BODES LAW
To find the mean distances of the planets,
beginning with the following simple sequence of
numbers 0 3 6 12 24
48 96 192 384 With the
exception of the first two, the others are simply
twice the value of the preceding number. Add 4 to
each number 4 7 10 16 28
52 100 196 388 Then
divide by 10 0.4 0.7 1.0 1.6 2.8
5.2 10.0 19.6 38.8 the
result is very close to the distribution of mean
distances of the planets from the Sun 0.4 0.72
1.0 1.52 2.8 5.2 9.54 19.2
30.1 39.5 M V E M
asteroids J S U
N P-C
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PLANETS
Mercury like the moon, no tectonics, 450 to
-270 oC
Venus 500oC, Atm CO2 H2SO4, 100x earth pressure
Mars 30 to -150oC, atm CO2, 0.01 earth p., ice
cap
Asteroids more than 10,000, various sizes
Jupiter largest gas giant, 600kph winds, storms,
rings, moons
Saturn gas giant, least dense, prominent rings,
large moons
Uranus, mid size gas giant, blue/green methane atm
Neptune mid sized gas giant, winds and storms
Pluto-Charon odd orbit, out of plane, eccentric,
small
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SCALE OF THE SOLAR SYSTEM
If the earth-sun distance is set as one
metre Mercury is 30 cm away from the sun Neptune
is 30 meters away (four light-hours) and the
entire solar system fits inside a 60 metre circle
Alpha Centauri, the nearest star, is 271 km
away! (4.3 light-years)
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THE SUN
99.8 OF THE TOTAL MASS OF THE SOLAR
SYSTEM MOSTLY HYDROGEN, SOME HELIUM 2 X 1030
Kg SURFACE TEMP 5800K. FUSION OF HYDROGEN INTO
HELIUM POWERS THE SUN AT T 107 K IT HAS ENOUGH
FUEL FOR 1011 YEARS
SUN AND PLANETS FORMED OUT OF A ROTATING CLOUD
OF INTERSTELLAR GAS. MOST WENT INTO THE
SUN, PLANETS ARE JUST SCRAPS LEFT OVER
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TELESCOPESLIGHT BUCKETS
REFRACTORS LARGEST 1 METRE DIAMETER
LENS
MIRROR LARGEST SINGLE 6 M LARGEST MULTIPLE 10 M
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DETECTION
ASTRONOMERS DO NOT LOOK THROUGH THEIR TELESCOPES
ANY MORE.
THEY USE FILM, CCDs, OR SPECTRUM ANALYSERS
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RADIO ASTRONOMY
THE ELECTROMAGNETIC SPECTRUM EXTENDS WELL BEYOND
THE VISIBLE IN BOTH DIRECTIONS. RADIO TELESCOPES
DETECT RADIO TRASNMISSIONS FROM THE STARS. LARGE
DISH ANTENNAE OR MULTIPLE ARRAYS OF ANTENNAE
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X-RAY , U-V I-R
THE ATMOSPHERE IS OPAQUE TO MANY
WAVELENTHS. SPACE TELESCOPES ARE NEEDED FOR MUCH
OF MODERN ASTRONOMY
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STARS
VISIBLE STARS RANGE FROM BRIGHT TO TOO DIM TO
SEE THEY VARY IN ABSOLUTE BRIGHTNESS BY UP TO
100,000 MORE THAN OUR SUN.
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STELLAR DISTANCES
PARALAX METHOD, CHANGE OF ANGLE AGAINST
BACKGROUND STARS WHEN VIEWED SIX MONTHS
APART, THAT IS FROM OPOSITE SIDES OF EARTHS ORBIT
STARS OF DIFFERENT CLASSES HAVE
DIFFERENT TEMPERATURES, COLOURS, SPECTRAL
LINES THEIR BRIGHTNESS GIVES THEIR DISTANCE
LIFE-CYCLE OF STARS IS PRETTY WELL WORKED OUT
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SUPERNOVAS
WHEN CERTAIN STARS BURN OUT, THEY EXPLODE ALL
ATOMS LARGER THAN HELIUM COME FROM THE ASHES OF
EXPLODED STARS. YOU ARE MADE OF STARDUST!!!
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MASS OF THE UNIVERSE
HEAVIER ATOMS MAKE UP 0.01 OF THE MASS
NEUTRINOS ARE 0.03 OF THE MASS
STARS (75 H, 25 He) ARE 0.5 OF THE MASS
COLD.DARK MATTER IS 25-35
Dark Energy is 60-70 OF ALL MASS
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GALAXIES
MILKY WAY GALAXY 100 BILLION STARS MASS IS 1012
SOLAR MASSES
A LARGE DISC WITH SPIRAL ARMS SUN 2/3 OF THE WAY
FROM THE CENTRE
ONE BILLION OTHER GALAXIES SPIRALS AND
ELLIPTICALS EACH HAS FROM ONE BILLION TO ONE
TRILLION SOLAR MASSES
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THE HUBBLE CONSTANT
DISTANT GALAXIES ARE MOVING AWAY FROM EACH OTHER
(AND US) AT A SPEED PROPORTIONATE TO THEIR
DISTANCE
THIS OBSERVATION, AND A MEASURE OF THAT SPEED,
LED TO THE BIG BANG THEORY AGE OF THE UNIVERSE
IS 10-20 BILLION YEARS
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OTHER PLANETS?
SO FAR 100 EXTRA-SOLAR SYSTEM PLANETS HAVE BEEN
FOUND, MOSTLY LARGE AND CLOSE TO THEIR STARS,
REVOLVING RAPIDLY
THESE ARE DETECTED BY MEASURING CHANGES IN THE
OUTPUT OF THE STARS CHANGES IN BRIGHTNESS,
WOBBLE, GRAVITATIONAL LENSING