Interdisciplinary "Space" Studying the Universe

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Interdisciplinary "Space" Studying the Universe

• for 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 (????)at
  the core.
• Its atmosphere is divided into 3 layers
• Photosphere ( 500 km thick) (???)
• Chromosphere (???)
• Corona (??)

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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 (????) cool, dark areas of the solar
  surface, each consists of a darker, cooler (
  4,000 K) region called umbra (??), surrounded by
  a less cool region called penumbra (??).

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 (??) 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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Scale model of planets

• 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

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• Dwarf planets (???) Minor planets. The first
  three members are
• Ceres (???) --- in the Asteroid Belt
• Pluto (???)
• Eris formerly known as 2003 UB313 or Xena (??)

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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 (???) Most can be found in the
  Asteroid belt (????) that lies between the orbits
  of Mars and Jupiter.
• Comets (??) 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 (????)

• In hammer throw (???), 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).

G 6.674 ? 10-11 Nm2kg-2
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Circular motion (????)

• An object is moving in a circle of radius r. Its
  speed is v.
• What is the acceleration of the object?

r
v
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Time for the particle to travel from A to B is
given by
To find the acceleration, we have to know the
change in velocity.
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Magnitude of acceleration a is then
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To find the instantaneous acceleration at A, we
let Dq tend to 0. We also note that sin(x) x
when x is very small, hence
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
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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Hence
From table 5.97 ? 1024 kg
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Example 2

• It is given that the mean radius R of the Earths
  orbit is 149600000 km. Mass of the sun M is
  1.9891?1030 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.
v speed of the Earth
m mass of the Earth
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The period T is therefore
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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 (????)

• 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 (????)

• 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 Earths size.

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• Large in size and mass
• strong gravity
• all have ring systems (????), 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 (??)

• 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
B. Venus (?? )
(NASA)

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

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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 (????) CO2 traps the heat of
  solar radiation
• very hot surface (470?C) 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
(NASA)
Crator Cunitz diameter 48.5 km
(NASA)
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C. Mars (??)

• 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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The atmosphere of Mars

• Mars has a mass less than 11 of Earths, its
  gravity is weak
• the atmosphere was much denser billions of years
  ago, but volatile gases escaped, leaving a thin
  atmosphere (1 of Earths). 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 (??)
  contain layers of frozen CO2 (dry ice) with
  frozen water beneath.

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(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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Features on the surface

• Mars is a cratered world having gigantic
  volcanoes (e.g. Olympus Mons ?????), deep canyons
  (e.g. Valles Marineris ???), dry channels, and
  vast dust storm.

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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Its two satellites
(NASA)
Deimos
Phobos
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D. Jupiter (??)

• 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
(NASA)

• A great cyclone lasting for at least 300 years.
• 3 times the size of the Earth.
• Red presence of sulphuric compounds.

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(NASA)
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Feature III Ring system
(NASA)

• The dark and thin ring of Jupiter. It is composed
  of small particles.

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Satellites

• Jupiter has 63 satellites, the four largest ones
  were discovered by Galileo.

(NASA)
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Io (???)
(NASA)

• Famous for its active volcanic activity that
  emits sulphuric compounds, and has a geologically
  young surface.

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(NASA)
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Erupting volcano
(NASA)
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A volcano spewing out gas.
(NASA)
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Europa (???)
(NASA)

• A rocky world with an icy crust.
• There may be a lake under the icy surface.

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Ganymede (???)

• The largest satellite in the solar system, its
  surface is old and is heavily cratered, crossed
  with grooved (???) terrain.

(NASA)
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Callisto (???)
(NASA)

• A heavily cratered, dark surface.

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E. Saturn (??)

• 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).

(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 Cassinis division.

(Wikimedia Commons)
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Pandora (pan-DOR-uh)
Shepherd satellites for inner F ring
Prometheus (pra-MEE-thee-us)
(NASA)
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Mimas
Rhea
(NASA)
Dione
Tethys
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Titan (???)

• The most famous satellite.
• It is cold enough to hold an atmosphere of
  nitrogen (?) and methane (??).

(NASA)
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F. Uranus (???)

• 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.

(NASA)
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(NASA)
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Shepherd satellites
(NASA)
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G. Neptune (???)

• 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.

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(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 ???).

(NASA)
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(NASA)
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Changing
(NASA)
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(NASA)
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4. Asteroids, comets and meteoroids
Asteroids (? ? ?)

• Small rocky debris that revolve around the sun.
• Most orbits lie in the asteroid belt (????)
  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.

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Gaspra 19 ? 12 ? 11 km Spins once every 7 hours
(NASA)
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Ida and its satellite Dactyl
(NASA)
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Comets (??)
Comet Hyakutake
Comet Hale-Bopp
(Wikimedia Commons)
(Wikimedia Commons)
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• They are dirty snow balls.
• Nucleus (??) 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 (??) Dust and evaporated gas surrounding
  the nucleus. Its maximum size could be as large
  as Jupiter.
• Tail (??) 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 tailsCyan for gas tail (controlled
by the solar magnetic field), grey for dust tail
(bends due to the comets motion). (Wikimedia
Commons)
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Meteoroids (??)

• Meteoroids are interplanetary debris hitting
  Earth, heated up by friction in Earths
  atmosphere.
• appear as bright streaks of shooting stars
  called meteors (??).
• Most meteoroids are destroyed in the atmosphere
  any parts that reach the ground are called
  meteorites (??).

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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 500p.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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6. Constellations (??)

• Visual groupings of stars.
• There are totally 88 constellations today, some
  added in modern days (e.g., Telescopium ? ? ? ?).
• Usually no real correlation among the stars in
  the same constellations they could be very far
  away from one another.

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7. Galaxy (??)

• 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 (??) 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 (??) Thin scattering of old, lower mass
  stars, globular star clusters almost no gas and
  dust.
• Nuclear bulge (??) 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 (????)

• 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 (????)

• 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 (?????)

• 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 11 First 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)
1990 Hubble Space Telescope
1996 Mars Pathfinder First Mars Rover
1997 Cassini-Huygens First Saturn Orbiter
1998 International Space Station (date of first section)
2003 Shenzhou 5 First Chinese Manned Earth orbiter