ASTRONOMY
LOOK UP. LOOK WAY, WAY UP.
WHAT DO YOU SEE?
SUN, MOON, STARS
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
WHAT DO YOU SEE?
WANDERING BODIES
SUN
RETROGRADE MOTION
MOON
MORNING STAR
EVENING STAR
OTHER MOVING BODIES
SOME FASTER THAN OTHERS
OCCASIONAL VISITORS: TAILED STARS
FALLING STARS
BRIGHT FLASHES
SEVEN WANDERERS
NAME
SPEED
BRIGHTNESS
(arc-sec/day) (Sirius=1.0
SUN
3550
15,000,000
MOON
48,100
30,000
MERCURY 14,900
0.9
VENUS
5,840
14
MARS
1,910
3.5
(moves the width of the moon in one day)
JUPITER
302
2.5
SATURN
102
0.4
They must be gods!
EARLY ASTROMOMICAL
OBSERVATION
CHINA:
BABYLONIANS
Records from 2000 BC
Halley’s comet 467 BC
Length of Year 365 1/4 days
Predicted eclipses
Star catalogs 1600 BC
Eclipse reported 1500 BC
continuous records 900 BC
LOOKING FOR PATTERNS
Pythagorus
Plato
Eudoxus
Aristole
Aristarchus
570-490 BC Cosmos model - spheres
428-348 BC Circular paths
400-347 BC First Mechanical model
384-322 BC Spherical Earth
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
ARISTARCHUS
MOON
Dm
Concluded Ds = 20x Dm
Actually it is 400:1
90o
a (ang separation
earth of sun and moon
on celestial sphere)
EARTH
SUN
Ds
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 Earth’s
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
Earth’s shadow on moon
larger than the moon, and
the sun is 7x larger than
Earth. Wrong, but clever.
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.
shadow
Syrene
Alexandria
6o
SUN
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 SyeneAlexandria distance to the Earth-Moon distance at 60 earth
radii and the moon 1/4 of the earth in size.
PTOLEMY: EPICYCLES WITHIN EPICYCLES
saturn
Field of stars
sol
mars
venus
jupiter
mercury
terra
luna
PTOLEMAIC GEO-CENTRIC MODEL
WITH EPICYCLES
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????
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
JOANNES KEPLER 1571-1627
Acquired Brahe’s records
Kept meticulous records of his own
KEPLER’S 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
KEPLER’S SECOND LAW
B
2b
F2
c
Sun
A
2a
Area A=B=C Planets (and comets)
move faster when they are closer to the sun
KEPLER’S THIRD LAW
r1
2b
Planet
r2
F2
F1
2a
r1 + r2 = 2a; p2 =k a3; (k= a constant)
p=period of rotation
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
THE PLANETS
NAME
PERIOD
(days)
MERCURY 88
VENUS
225
EARTH
365.25
MARS
686
JUPITER
11.86 yrs
SATURN
29.5 yrs
URANUS
84 yrs
(disc 1781)
NEPTUNE 164.8
(disc. 1846)
PLUTO-CHARON
ORBIT
(A.U.)
RADIUS
(km)
.4
2439
0.723
6057
1.0 (150MKm)6378
1.52
3393
5.2
71400
9.54
60330
19.19
25500
30.06
24750
~39.5
1900
BODE’S 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
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
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)
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
TELESCOPES
LIGHT BUCKETS
REFRACTORS: LARGEST 1 METRE DIAMETER
LENS
MIRROR LARGEST SINGLE 6 M
LARGEST MULTIPLE 10 M
DETECTION
ASTRONOMERS DO NOT LOOK
THROUGH THEIR TELESCOPES ANY
MORE.
THEY USE FILM, CCDs, OR SPECTRUM ANALYSERS
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
X-RAY , U-V & I-R
THE ATMOSPHERE IS OPAQUE TO
MANY WAVELENTHS.
SPACE TELESCOPES ARE NEEDED
FOR MUCH OF MODERN
ASTRONOMY
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.
STELLAR DISTANCES
PARALAX METHOD, CHANGE OF ANGLE
AGAINST BACKGROUND STARS
WHEN VIEWED SIX MONTHS APART,
THAT IS FROM OPOSITE SIDES OF
EARTH’S 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
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!!!
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
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
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
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