1 interdisciplinary "space" studying the universe for ijso training course for ijso...
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Interdisciplinary "Space" Interdisciplinary "Space" Studying the UniverseStudying the UniverseInterdisciplinary "Space" Interdisciplinary "Space" Studying the UniverseStudying the Universe
for IJSO training coursefor IJSO training course
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Content
1. Solar system – an overview
2. Order of the planets
3. Key features of each planet
4. Asteroids, comets and meteoroids
5. Stars and their colors
6. Constellations
7. Galaxy
8. Space exploration
9. Scale model of planets
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1. Solar system
• Sun: its mass is about 300,000 times more massive
than the Earth. Its radius is 700,000 km, about 110
times that of the Earth.
• Energy source: thermonuclear reactions ( 熱核反應 )at
the core.
• Its atmosphere is divided into 3 layers:
• Photosphere (~ 500 km thick) ( 光球層 )
• Chromosphere ( 色球層 )
• Corona ( 日冕 )
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1. Core 2. Radiative zone 3. Convective zone 4. Photosphere 5. Chromosphere 6. Corona 7. Sunspot 8. Granules 9. Prominence
(Wikimedia Commons)
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• Sunspots ( 太陽黑子 ): cool, dark areas of the solar
surface, each consists of a darker, cooler (~ 4,000
K) region called umbra ( 本影 ), surrounded by a
less cool region called penumbra ( 半影 ).
A large group of sunspots in year 2004. The grey area around the spots can be seen very clearly, as well as the granulation of the sun's surface. (Wikimedia Commons)
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• Planets (行星 ): 8 planets and their
satellites
• lie close to a common plane.
• Planets move in nearly circular orbits around
the sun in counter-clockwise sense as seen
from “above”.
• The average distance between the sun and the
earth is about 1.5 1011 m, which is also called
1 AU (Astronomical unit).
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• Self-rotation is also in the counter-clockwise
sense as seen from “above”, except for Venus
and Uranus.
• Orbits of planets are not evenly spaced -
distances between successive planets increase
with their distances from the sun.
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• Earth: a grain of table salt (0.3 mm in diameter)
• Moon: A speck of pepper 1 cm away
• Sun: A plum 4 m away
• Mercury, Venus, Mars: grains of salt
• Jupiter: Apple seed 20 m from the sun
• Saturn: Smaller apple seed 36 m from the sun
• Uranus: lighter than salt grain
• Neptune: lighter than salt grain, 115 m from the
sun
Scale model of planets
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• Dwarf planets ( 矮行星 ): “Minor” planets.
The first three members are
• Ceres ( 穀神星 ) --- in the Asteroid Belt
• Pluto ( 冥王星 )
• Eris [formerly known as 2003 UB313 or Xena
( 齊娜 )]
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The orbit of Eris (blue) compared to those of Saturn, Uranus, Neptune, and Pluto (white/grey). The arcs below the ecliptic are plotted in darker colours, and the red dot is the Sun. The diagram on the left is a polar view while the diagrams on the right are different views from the ecliptic.
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• Small solar-system bodies: include
• Asteroids ( 小行星 ): Most can be found in
the Asteroid belt ( 小 行 星 帶 ) that lies
between the orbits of Mars and Jupiter.
• Comets (彗星 ): “Dirty snow balls” moving in
highly elliptical orbits around the sun
In the solar system, there are the sun, the planets, the dwarf planets and small solar-system bodies.
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Universal gravitation ( 萬有引力 )
• In hammer throw ( 投鏈球 ), the tension in the
chain keeps the ball
moving around a centre.
Without the tension, the
ball will fly straight away.
(Wikimedia Commons)
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• The gravitational force from the sun is just like the
tension in an invisible chain that keeps a planet in
its orbit around the sun.
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• Inverse square law: The attractive force (F)
between any two bodies is directly proportional to
the product of their masses (M1 and M2) and is
inversely proportional to the square of their
separation (r).
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r
MGMF G = 6.674 10-11 Nm2kg-2
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Circular motion ( 圓周運動 )
• An object is moving in a
circle of radius r. Its
speed is v.
• What is the
acceleration of the
object?
vr
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Time for the particle to travel from A to B is given by
v
r
vrt
1
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To find the acceleration, we have to know the change in velocity.
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To find the instantaneous acceleration at A, we
let tend to 0. We also note that sin(x) = x
when x is very small, hence
r
v
r
v
r
va
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2
2
2sin
2
r
va
2
Acceleration is
Direction: Perpendicular to the velocity and towards the centre, hence centripetal.
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Example 1
• It is given that the gravitational acceleration on
the Earth is 9.81 ms-2 and the radius of the
Earth is 6373 km.
• Find the mass of the Earth.
Solution:
2R
GmMW
Let m be an object on the Earth, M the mass of
the Earth, R the radius of the Earth, the weight
of the object is
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Example 2
• It is given that the mean radius R of the Earth’s
orbit is 149600000 km. Mass of the sun M is
1.98911030 kg. Find the period of revolution of
the Earth around the sun.
Solution:
The centripetal acceleration of the Earth is caused
by the gravitational attraction from the sun.
2
2
R
GM
m
F
R
v v: speed of the Earth
m: mass of the Earth
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R
GMv
The period T is therefore
days 365.26
s 1016.3
s 109891.110674.6
)001496000000(2
22
7
3011
3
3
GM
R
v
RT
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2. Order of the planets
Radius Mass/Earth Rotation Period
Orbital Radius Revolution Period
No. of Satellites
Mercury 2439 km 0.055 59 days 57.9 106 km 88 days 0
Venus 6052 km 0.815 244 days 108.2 106km 224.7 days 0
Earth 6378 km 1 1 day 149.6 106km 365.2 days 1
Mars 3397 km 0.107 24.7 hours 227.9 106km 1.88 yrs 2
Jupiter 71492 km 317.8 9.9 hours 778.6 106km 11.8 yrs 63
Saturn 60268 km 95.2 10.7 hours 1433.5 106km
29.4 yrs 56
Uranus 25559 km 14.5 17.2 hours 2872.5 106km
83.8 yrs 27
Neptune 24764 km 17.2 16.1 hours 4495.1 106km
164 yrs 13
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Two kinds of planets: Terrestrial ( 類地行星 )
• Mercury, Venus, Earth, Mars, all lie in the inner solar
system
• Relatively dense (~3-5 g cm-3), with cores of iron and
nickel surrounded by a mantle of dense rocks.
• Small in size and mass
weak gravity
have a few satellites (e.g., one for Earth, two for
Mars) and thin atmospheres, no ring systems
• Their surfaces are scarred with craters.
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Two kinds of planets: Jovian ( 類木行星 )
Jupiter, Saturn, Uranus, Neptune, all lie in the
outer solar system
Gaseous-like, mainly made up of hydrogen and
helium, low-density (1 g cm-3)
They do not have solid surfaces, but have thick
liquid layers inside, possibly with small rocky core
of Earth’s size.
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Large in size and mass
strong gravity
all have ring systems ( 光環系統 ), many
satellites and thick atmospheres of hydrogen,
high atmospheric pressure and a lot of
weather activities.
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3. Key features of each planet
A. Mercury ( 水星 )
• Too hot and gravity too weak to
hold a thick atmosphere.
• Results:
– retains a lot of craters
– No thick atmosphere to retain
heat, large temperature
difference between day and
night (-173oC – 430oC)
(NASA)
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• Mercury in fact has a thin
layer of atmosphere, which
is mainly made up of
sodium and a little helium.
The atmospheric pressure
is almost zero. The
presence of gaseous
sodium means the
temperature is high enough
to allow sodium in rock be
released. This is expected
as Mercury is so near the
Sun. (NASA)
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• Secondly, the axis of
rotation is almost
perpendicular to the
orbital plane. (For the
Earth, the rotational
axis tilts 23.5o.) As a
result, there is no
seasonal change on
Venus.
(NASA)
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The atmosphere of Venus
• Venus has a thick atmosphere. The pressure
is 90 times that of the Earth. The atmosphere
consists of 90% of CO2 , 3% of N2 , and
some SO2 . The whole planet is completely
covered by clouds made up of sulphuric acid
(H2SO4). As a result, the rain on Venus is
acidic.
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• Much carbon dioxide
Greenhouse effect (溫室效應 ) : CO2
traps the heat of solar radiation
very hot surface (470C); the atmosphere
is full of vapour of chemical compounds.
A schematic representation of the exchanges of energy between outer space, the Earth's atmosphere, and the Earth surface. The ability of the atmosphere to capture and recycle energy emitted by the Earth surface is the defining characteristic of the greenhouse effect. (Wikimedia Commons)
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C. Mars ( 火星 )
• Like Earth, the axis of
rotation tilts 24o.
Hence, there are
seasonal changes on
Mars.
• Mars looks red
because its soil
contains minerals of
iron (like rust).
(NASA)
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• Mars has a mass less than 11% of Earth’s, its
gravity is weak• the atmosphere was much denser billions of years ago,
but volatile gases escaped, leaving a thin atmosphere (1%
of Earth’s). The chemical composition is mainly carbon
dioxide (95%) and nitrogen (3%).
• Long ago water was dissociated by the solar
radiation (unlike the earth, Mars has no ozone layer
to shield the solar ultraviolet radiation)• no liquid water on surface, a little water combined with
minerals in soil; polar caps ( 極冠 ) contain layers of frozen
CO2 (dry ice) with frozen water beneath.
The atmosphere of Mars
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• Although the atmosphere consists mainly of
carbon dioxide, it is too thin to trap heat. So,
the surface temperature varies enormously,
from -100oC to -10oC. Moreover, owing to the
long distance from the Sun, the temperature is
quite low on average.
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• Mars is a cratered world having gigantic volcanoes (e.g.
Olympus Mons 奧林匹斯山 ), deep canyons (e.g. Valles
Marineris 水手谷 ), dry channels, and vast dust storm.
Features on the surface
25 km above the surface and is 600 km in diameter
5000 km long, 200 km wide and 7 km deep (NASA)(NASA)
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Evidence of old channels and signs of erosion,
seemingly carved by running liquid
billions of years ago Mars was much warmer
(with a thicker atmosphere)
Large bodies of liquid water may have existed (NASA)
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D. Jupiter ( 木星 )
• The largest and most
massive planet in our solar
system. The mass of
Jupiter is about 300 times
that of the Earth, however
its density is low. In fact,
these are general features
of Jovian planets.
• Almost completely made
up of gases.(NASA)
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• The rotational period of Jupiter is about 10 hours,
and such a high velocity flattens Jupiter at the two
poles.
• Mainly made up of hydrogen, helium, and a small
amount of methane and ammonia.
• The atmospheric pressure is extremely high, over
1000 times than that of the Earth. Because of the
great pressure, the core of Jupiter is made up of
metallic hydrogen. The rapid rotation of such
metallic core explains the strong magnetic field of
Jupiter.
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Feature II: Great Red Spot
• A great cyclone lasting for at least 300 years.
• 3 times the size of the Earth.
• Red: presence of sulphuric compounds.
(NASA)
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Feature III: Ring system
• The dark and thin ring of Jupiter. It is composed of
small particles.
(NASA)
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Io ( 木衛一 )
• Famous for its active volcanic activity that emits sulphuric
compounds, and has a geologically young surface.
(NASA)
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Europa ( 木衛二 )
• A rocky world with an icy crust.
• There may be a lake under the icy surface.
(NASA)
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Ganymede ( 木衛三 )
• The largest
satellite in the
solar system, its
surface is old and
is heavily
cratered, crossed
with grooved ( 有溝槽 ) terrain.
(NASA)
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• The second largest planet. It has 47 satellites.• Atmospheric condition is similar to Jupiter, but the
belts and zones seem less distinct.• Average density is lower than water (0.7 g cm-3).
E. Saturn ( 土星 )
(NASA)
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Ring system
• Three concentric
rings (A, B and C) can
be easily observed on
Earth.
• Thickness ~ I km
• Made of dust and ice.
• The most obvious gap
is Cassini’s division.
(Wikimedia Commons)
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Titan ( 土衛六 )
• The most famous
satellite.
• It is cold enough to
hold an atmosphere
of nitrogen ( 氮 )
and methane ( 甲烷 ).
(NASA)
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Discovered in 1781 by William Herschel.
Uranus appears blue because of the methane in its
atmosphere. It has much less distinct atmospheric
circulation than Jupiter.
F. Uranus ( 天王星 )
(NASA)
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Astronomers in 19th century found that Uranus’
orbit deviated from a perfect ellipse, it was under
the gravitational pull of an unknown outer planet.
Newtonian mechanics predicted the mass and
orbit of this planet.
discovery of Neptune in 1846.
G. Neptune ( 海王星 )
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It is similar to Uranus in size, mass, and
atmospheric condition.
Cyclone patterns have been discovered (e.g.
Great Dark Spot 大黑斑 ).
(NASA)
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4. Asteroids, comets and meteoroids
Small rocky debris that revolve around the sun.
Most orbits lie in the asteroid belt ( 小行星帶 )
between those of Mars and Jupiter.
Only two dozens or so are larger than 200 km, most
as small as 0.1 km, irregular in shape.
Asteroids are either fragments of a planet broken up
long ago, or primal rocks never managed to
accumulate into a planet. Researchers favour the
latter view.
Asteroids ( 小 行 星 )
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• They are dirty “snow balls”.
• Nucleus ( 彗核 ): is very small (a few km), it is
the main solid body of a comet. Only this frozen
part exists when a comet is far from the sun.
• Coma (彗髮 ): Dust and evaporated gas
surrounding the nucleus. Its maximum size could
be as large as Jupiter.
• Tail (彗尾 ): Vapourized materials directed away
from the sun by solar wind (particles from the
sun) and pressure of the sunlight.
• Coma and tail are most pronounced when the
comet is closest to the sun.
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Comets have highly elliptical orbits. Note the two distinct tails:Cyan for gas tail (controlled by the solar magnetic field), grey for dust tail (bends due to the comet’s motion). (Wikimedia Commons)
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• Meteoroids are interplanetary debris hitting
Earth, heated up by friction in Earth’s
atmosphere.
• appear as bright streaks of “shooting stars”
called meteors (流星 ).
• Most meteoroids are destroyed in the
atmosphere; any parts that reach the ground
are called meteorites (隕石 ).
Meteoroids ( 隕星 )
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Some are fragments dislodged from
comets, spreading along the comets’
orbits.
Marília Meteorite, a chondrite H4, which fell in Marília, São Paulo state, Brazil, on October 5, 1971, at 5:00p.m. (Wikimedia Commons)
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5. Stars and their colors
• When we heat something up, it will radiate
electromagnetic waves. When the object is not very
hot, it will be red. If it is hotter, it will be yellow, then
white and finally blue. The color of a star depends
only on its surface temperature, and nothing else.
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• Visual groupings of stars.
• There are totally 88 constellations today,
some added in modern days (e.g.,
Telescopium 望 遠 鏡 座 ).
• Usually no real correlation among the stars in
the same constellations; they could be very
far away from one another.
6. Constellations ( 星座 )
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7. Galaxy ( 星系 )
• Almost all the stars visible by naked eyes are
in our galaxy, the Milky Way Galaxy.
• A galaxy is a collection of hundred billions of
stars.
• Galaxies are categorized into three basic
classes according to their shapes: Elliptical
galaxies, spiral galaxies and irregular
galaxies.
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Milky Way Galaxy• About 200 billion stars whirling in a great wheel-like
system; the sun is 8.5 kpc (1 pc 3.3 light years) from
the galactic centre.
Artist's conception of the spiral structure of the Milky Way with two major, stellar arms and a bar. (Wikimedia Commons)
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• Disk component
contains almost all of the
gas and dust in the
galactic plane.– Spiral arms (旋臂 ): Long
spiral patterns of bright
stars, star clusters, gas
and dust.
Observed and extrapolated structure of the spiral arms (Wikimedia Commons)
84
• Spherical component– Halo (銀暈 ): Thin scattering of
old, lower mass stars, globular
star clusters; almost no gas and
dust.
– Nuclear bulge (核心 ): The
most crowded part of spherical
component around the galactic
core; about 20000 light years in
diameter; the center is obscured
at visual wavelengths and
requires radio or infrared
observations.
85
• The universe contains 100 billion galaxies.
• Along the plane of Milky Way, dust clouds block
our view of distant galaxies.
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Elliptical galaxies ( 橢圓星系 )
• Spherical or elliptical in
shape, lacking in gas and
dust, they contain
relatively old, low-mass
stars.– Disk component is not
obvious or missing
The giant elliptical galaxy ESO 325-G004. (Wikimedia Commons)
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Spiral galaxies ( 旋渦星系 )
• contain gas, dust, and hot
bright stars outlining spiral
arms, having a mixture of
star types.
• Obvious disk component.
• They are very luminous
and therefore easy to find. 2/3 of all known galaxies
are spiral, but they may
make up only a small
fraction of all galaxies
An example of a spiral galaxy, the Pinwheel Galaxy (also known as Messier 101 or NGC 5457) (Wikimedia Commons)
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Irregular galaxies ( 不規則星系 )
• Irregular in shape, clouds of gas and dust mixed
with both young and old stars.– e.g., the Large Magellanic Cloud and Small Magellanic
Cloud are neighbors of the Milky Way Galaxy.
NGC 1427A, an example of an irregular galaxy about 52 Mly distant. (NASA)
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Hubble classification of galaxies
Types of galaxies according to the Hubble classification scheme. An E indicates a type of elliptical galaxy; an S is a spiral; and SB is a barred-spiral galaxy. (Wikimedia Commons)
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8. Space exploration
1957 Sputnik First Earth orbiter
1969 Apollo 11First Manned Lunar Landing (Total six manned lunar landings, Apollo 17 shown below)
1972 Pioneer 10 First Jupiter Flyby
1977 Voyager 1 and 2 Multiple Planet Flybys (still active)
1989 Galileo First Asteroid Flyby (on trip to Jupiter)
1990Hubble Space Telescope
1996 Mars Pathfinder First Mars Rover
1997 Cassini-Huygens First Saturn Orbiter
1998International Space Station
(date of first section)
2003 Shenzhou 5 First Chinese Manned Earth orbiter
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