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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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(Wikimedia Commons)

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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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2

sin2

vvc

Magnitude of acceleration a is then

2sin

22 r

v

t

va c

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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

222

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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kg 105.97

kg 10674.6

)6373000(81.9

24

11

2

2

2

G

gRM

R

GM

m

WgHence

From table: 5.97 1024 kg

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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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Rotation of Venus• Firstly, its self-rotation is in the clockwise sense.

B. Venus ( 金星 )

(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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Volcano Eista

Crator Cunitz:

diameter ~ 48.5 km

(NASA)

(NASA)

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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

37(NASA)

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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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Large bodies of liquid water may have existed on Mars

(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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Deimos

Its two satellites

Phobos (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 I: Dark belts and light zones

(NASA)

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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)

47(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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• Jupiter has 63

satellites, the four

largest ones were

discovered by

Galileo.

Satellites

(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)

51(NASA)

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Erupting volcano

(NASA)

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A volcano spewing out gas.

(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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Callisto ( 木衛四 )

• A heavily cratered, dark surface.(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)

Shepherd satellites for inner F ring

Pandora (pan-DOR-uh)

Prometheus (pra-MEE-thee-us)

(NASA)59

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Mimas

Rhea

DioneTethys

(NASA)

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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)

63(NASA)

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Shepherd satellites

(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 )

66(NASA)

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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)

68(NASA)

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Changing

(NASA)

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(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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Gaspra ：19 12 11 kmSpins once every 7 hours

(NASA)

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Ida and its satellite Dactyl

(NASA)

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Comet Hale-Bopp

Comets ( 彗星 )

Comet Hyakutake(Wikimedia Commons)

(Wikimedia Commons)

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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)

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• 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.

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• 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