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ASTROPHYSICS
Stellar quantities
From physicsstackexchange.com
List the objects in the universe
List the objects in the universe
 Galaxies Cluster
 Solar systems Constellations
 Stars Planets
 Comets Asteroids
 Sa...
Objects in the universe…
www.englishbaby.com
The Solar System
Commons.wikipediea.org
You need to know the names of the planets
Planets orbit in ellipses
An ellipse is a “flattened circle” with two foci
about which the planet orbits.
Moons orbit the ...
The Sun
Commons.Wikipedia.org
Mass: 1.99 x 1030 kg
Radius:6.96 x 108 m
Surface temperature:
5800 K
Planets Data
Planet Picture Distance to the Sun
(km)
Diameter(km) Orbital period
around its
axis
Orbital
period
Surface da...
Use the table to compare
 The diameter of the Earth and
 A) Mars
 B) Saturn
 The distance to the Sun of Jupiter and
 ...
Mercury and Venus
Commons.Wikipedia.org
Earth and Moon
www.flickr.com
Messenger
Mars
Image of Mars from the
Hubble Space Telescope
from sci.esa.int
Mars
Commons.Wikipedia.org
Asteroid Belt
Wikipedia commons
Ceres (480km):
it was the first
asteroid to be
seen. Now it’s
a dwarf planet.
Mathilde
(52...
Where is the asteroid belt?
It is 2 – 3.5 AU
An AU is the astronomical unit, the mean
distance from the Earth to the Sun
D...
Jupiter
Flickr,com
(randyfmacdonald)
Pixabay.com
Jupiter and its moons: Io,
Europa, Ganymede and
Callisto
Approximate size...
Saturn
Commons wikipedia
www.eas.ee
A rough comparison of the sizes
of Saturn and Earth
Uranus
Commons wikipedia
Size comparison
of Earth and
Uranus
Neptune
Size comparison of Neptune and
Earth.
Planets & Stars
 Scale of Planets & Stars
Stellar cluster
A number of stars that are held together
in a group by a gravitational attraction.
They were created at ab...
Constellations
A group of stars in a recognizable pattern that
appear to be near each other in space.
Orion
Polaris
Nebulae
Nebula is an interstellar cloud of dust, hydrogen gas and
plasma. It is the first stage of a star's cycle but it c...
Nebulae
Eagle Nebula and the Cone nebula:
star-forming regions
Cat’s Eye Nebula
Planetary nebulae are nebulae that form from the gaseous
shells that are ejected from low-mass giant star...
Eskimo nebula
Supernovas
Eta Carinae Crab Nebula
Galaxies
A galaxy is a collection of a very large number of stars
mutually attracting each other through the gravitational...
Spiral Galaxies
Spiral galaxies consist of a rotating disk of stars and
interstellar medium, along with a central bulge of...
Spiral Galaxies
Andromeda
Spiral Galaxies
Sombrero Galaxy
Elliptical Galaxies
M49
Elliptical cross-section and no spiral arms.
They range in shape from nearly spherical to highly f...
Irregular Galaxies
• Irregular galaxies have no specific structure. The
Large and Small Magellanic Clouds, the nearest
gal...
Comets
 COMETS are frozen balls of ice and dust that
can resemble a “dirty snowball”.
 They orbit the Sun is highly elli...
Planet Orbits
 Solar System Simulation
 TOK
 Why were ancient civilisations so
interested in the motion of the planets?...
Comet’s orbit
Sun
Comet
Earth’s
Orbit
Stars
 Stars are formed by interstellar dust coming
together through mutual gravitational
attraction.
 The loss of poten...
Nuclear fusion
Very high
temperatures
are needed in
order to begin
the fusion
process:
usually 107 K.
Fusion Applet
1
2
H + 1
2
H 2
4
He + 25 MeV
Must overcome the coulomb (electrostatic) repulsion
between the nuclei so that they can fus...
A star is a big ball of gas, with
fusion going on at its center,
held together by gravity!
There are variations between st...
How big is the universe?
Astronomical distances
The SI unit for length, the metre, is a very small unit
to measure astronomical distances. There un...
Astronomical distances
The light year (ly) – this is the distance travelled by the
light in one year.
1 ly = 9.46x1015 m
...
Lightyear
 The distance across our galaxy, The
Milky Way is 80 000 light years.
 Our nearest neighbouring galaxy, The
An...
 The furthest galaxies that can be
detected with the Hubble Telescope are
over 10 billion light years away!!!
 This mark...
Astronomical distances
The parsec (pc) – this is the
distance at which 1 AU subtends an
angle of 1 arcsecond.
1 pc = 3.08...
1 parsec = 3.086 X 1016 metres
 Nearest Star
1.3 pc
(206 000 times
further than
the Earth is
from the Sun)
Parallax
Angle star/ball
appears to
shift
“Baseline”
Distance to
star/ball
Where star/ball
appears relative
to background
...
Parallax
Parallax, more accurately
motion parallax, is the change of
angular position of two
observations of a single obje...
Parallax
Baseline – R
(Earth’s orbit)
Distanceto
Star-d
Parallax - p
(Angle)
We know how big the Earth’s orbit is, we meas...
Parallax
(Distance)d
(Baseline)R
(Parallax)tan p
For very small angles tan p ≈ p
d
R
p
In conventional units it means th...
Parallax
arcsecond)(p
1
(parsec)d 
m10x3.986m
3600
1
360
2
10x1.5
pc1 16
11















d
R
p 
p
R
d 
Angular sizes
 360 degrees (360o)
in a circle
 60 arcminutes (60’)
in a degree
 60 arcseconds
(60”) in an
arcminute
Parallax has its limits
The farther away
an object gets,
the smaller its
shift.
Eventually, the shift
is too small to see.
Questions
 The parallax angle for Barnards star
from the Earth is 0.545 arc secs. What
is its distances in ly, parsecs an...
Solutions
 Using d = 1/p to find parsec
 1.83 pc, 376000AU, 5.96ly
 3pc, 9.78ly
What is the most important
thing about a star?
MASS!
The mass of a normal star almost
completely determines its
LUMINOSITY...
The LUMINOSITY of a star is
the TOTAL ENERGY emitted per
time from the surface of the star:
The energy the Sun emits is ge...
What does luminosity have to do
with mass?
The mass of a star determines
the pressure in its core:
Pressure
Gravity pulls ...
The core pressure determines
the rate of fusion…
MASS PRESSURE &
TEMPERATURE
RATE OF
FUSION
…which in turn determines
the ...
Luminosity is an intrinsic property…
it doesn’t depend on distance!
This light bulb has a luminosity
of 60 Watts…
…no matt...
Luminosity
The Luminosity of a star is the energy that it releases
per second. Our Sun has a luminosity of 3.90x1026 W
(of...
TOK
 The ancient Greeks classified stars by
their brightness using the naked eye.
They were quite good at it. Have we
los...
Apparent brightness
 When the light from the Sun reaches the Earth it will
be spread out over a sphere of radius d. The e...
Apparent brightness
 The apparent brightness is directly
proportional to the star’s luminosity and
varies as the inverse ...
Luminosity
Question
The Sun is a distance d=1.5 x 1011 m from the Earth.
Estimate how much energy falls on a surface of 1m...
At a distance of d=1.5 x 1011 m, the energy is “distributed”
along the surface of a sphere of radius 1.5 x 1011 m
d
The sp...
Distance
measurement
by parallax
d = 1 / p
Luminosity
L = 4πd2 b
apparent
brightness
spectrum
Wien’s Law
(surface
temperat...
Apparent
brightness
Distance (d)
b = L / 4πd2
Luminosity
class
spectrum
Surface temperature (T)
Wien’s Law
Chemical
compos...
Stellar quantities 2015
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Stellar quantities 2015

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Stellar quantities 2015

  1. 1. ASTROPHYSICS Stellar quantities From physicsstackexchange.com
  2. 2. List the objects in the universe
  3. 3. List the objects in the universe  Galaxies Cluster  Solar systems Constellations  Stars Planets  Comets Asteroids  Satellites Black holes  Pulsars Quasars
  4. 4. Objects in the universe… www.englishbaby.com
  5. 5. The Solar System Commons.wikipediea.org You need to know the names of the planets
  6. 6. Planets orbit in ellipses An ellipse is a “flattened circle” with two foci about which the planet orbits. Moons orbit the planets in much the same way. SUN Planet X Foci
  7. 7. The Sun Commons.Wikipedia.org Mass: 1.99 x 1030 kg Radius:6.96 x 108 m Surface temperature: 5800 K
  8. 8. Planets Data Planet Picture Distance to the Sun (km) Diameter(km) Orbital period around its axis Orbital period Surface day temp (ºC) Density (water=1) Satellites Mercury 58 million 4 878 km 59 days 88 days 167 5,43 0 Venus 108 million 12 104 km -243 days 225 days 464 5,24 0 Earth 149,6 million 12 756 km 23, 93 h 365,2 days 15 5,52 1 Mars 228 million 6 794 km 24h 37min 687 days -65 3,04 2 Jupiter 778 million 142 800 km 9h 50min 30s 12 years -110 1,32 +63 Saturn 1 427 million 120 000 km 10h 14min 29,5 years -140 0,69 +56 Uranus 2 870 million 51 800 km 16h 18min 84 years -195 1,27 27 Neptune 4 497 million 49 500 km 15h 48min 164 years -200 1,77 13 Dwarf- Pluto 5 900 million 2 400 km 6 days 248 years -225 2 1 More info at http://nssdc.gsfc.nasa.gov/planetary/factsheet/
  9. 9. Use the table to compare  The diameter of the Earth and  A) Mars  B) Saturn  The distance to the Sun of Jupiter and  A) Venus  B) Uranus  Another quantity of your choosing for 2 other planets.
  10. 10. Mercury and Venus Commons.Wikipedia.org
  11. 11. Earth and Moon www.flickr.com Messenger
  12. 12. Mars Image of Mars from the Hubble Space Telescope from sci.esa.int
  13. 13. Mars Commons.Wikipedia.org
  14. 14. Asteroid Belt Wikipedia commons Ceres (480km): it was the first asteroid to be seen. Now it’s a dwarf planet. Mathilde (52km) Eros (13x13x33km)
  15. 15. Where is the asteroid belt? It is 2 – 3.5 AU An AU is the astronomical unit, the mean distance from the Earth to the Sun Distance = 2 * 1.496 x 108 km = 293200000000 m from the sun
  16. 16. Jupiter Flickr,com (randyfmacdonald) Pixabay.com Jupiter and its moons: Io, Europa, Ganymede and Callisto Approximate size comparison of Earth and Jupiter
  17. 17. Saturn Commons wikipedia www.eas.ee A rough comparison of the sizes of Saturn and Earth
  18. 18. Uranus Commons wikipedia Size comparison of Earth and Uranus
  19. 19. Neptune Size comparison of Neptune and Earth.
  20. 20. Planets & Stars  Scale of Planets & Stars
  21. 21. Stellar cluster A number of stars that are held together in a group by a gravitational attraction. They were created at about the same time. There may be many thousands of stars in a group.
  22. 22. Constellations A group of stars in a recognizable pattern that appear to be near each other in space. Orion
  23. 23. Polaris
  24. 24. Nebulae Nebula is an interstellar cloud of dust, hydrogen gas and plasma. It is the first stage of a star's cycle but it can also refer to the remains of a dying star (planetary nebula). Originally nebula was a general name for any extended astronomical object, including galaxies beyond the Milky Way (some examples of the older usage survive; for example, the Andromeda Galaxy was referred to as the Andromeda Nebula before galaxies were discovered by Edwin Hubble). Nebulae often form star-forming regions, such as in the Eagle Nebula.
  25. 25. Nebulae Eagle Nebula and the Cone nebula: star-forming regions
  26. 26. Cat’s Eye Nebula Planetary nebulae are nebulae that form from the gaseous shells that are ejected from low-mass giant stars when they transform into white dwarfs.
  27. 27. Eskimo nebula
  28. 28. Supernovas Eta Carinae Crab Nebula
  29. 29. Galaxies A galaxy is a collection of a very large number of stars mutually attracting each other through the gravitational force and staying together. The number of stars varies between a few million and hundreds of billions. There approximately 100 billion galaxies in the observable universe. There are three types of galaxies: - Spiral (Milky Way) - Elliptical (M49) - Irregular (Magellanic Clouds)
  30. 30. Spiral Galaxies Spiral galaxies consist of a rotating disk of stars and interstellar medium, along with a central bulge of generally older stars. Extending outward from the bulge are relatively bright arms. Milky Way
  31. 31. Spiral Galaxies Andromeda
  32. 32. Spiral Galaxies Sombrero Galaxy
  33. 33. Elliptical Galaxies M49 Elliptical cross-section and no spiral arms. They range in shape from nearly spherical to highly flattened ellipsoids and in size from hundreds of millions to over one trillion stars. In the outer regions, many stars are grouped into globular clusters. ESO 325-G004
  34. 34. Irregular Galaxies • Irregular galaxies have no specific structure. The Large and Small Magellanic Clouds, the nearest galaxies, are an example of irregular galaxies. Small Magellanic Cloud Hoag's Object, a ring galaxy.
  35. 35. Comets  COMETS are frozen balls of ice and dust that can resemble a “dirty snowball”.  They orbit the Sun is highly elliptical orbits.  Their orbital periods can range from a few years to several thousand years.  Halley's Comet is famous due to the fact that everyone has a chance to see it in their lifetime (Orbital Period of 77 years).
  36. 36. Planet Orbits  Solar System Simulation  TOK  Why were ancient civilisations so interested in the motion of the planets?  Is imagination the best way of knowing for gaining knowledge about the universe?
  37. 37. Comet’s orbit Sun Comet Earth’s Orbit
  38. 38. Stars  Stars are formed by interstellar dust coming together through mutual gravitational attraction.  The loss of potential energy is responsible for the initial high temperature necessary for fusion.  The fusion process releases so much energy that the pressure created prevents the star from collapsing due to gravitational pressure.
  39. 39. Nuclear fusion Very high temperatures are needed in order to begin the fusion process: usually 107 K. Fusion Applet
  40. 40. 1 2 H + 1 2 H 2 4 He + 25 MeV Must overcome the coulomb (electrostatic) repulsion between the nuclei so that they can fuse together. In Stable Stars there is an equilibrium between the gravitational attraction of all of the gas and dust particles and… … the outward pressure exerted by the nuclear fusion process. This keeps a stable star from collapsing or exploding.
  41. 41. A star is a big ball of gas, with fusion going on at its center, held together by gravity! There are variations between stars, but by and large they’re really pretty simple things. Massive Star Sun-like Star Low-mass Star
  42. 42. How big is the universe?
  43. 43. Astronomical distances The SI unit for length, the metre, is a very small unit to measure astronomical distances. There units usually used is astronomy: The Astronomical Unit (AU) – this is the average distance between the Earth and the Sun. This unit is more used within the Solar System. 1 AU = 150 000 000 km or 1 AU = 1.5x1011m
  44. 44. Astronomical distances The light year (ly) – this is the distance travelled by the light in one year. 1 ly = 9.46x1015 m c = 3x108 m/s t = 1 year = 365.25 x 24 x 60 x 60= 3.16 x 107 s Speed =Distance / Time Distance = Speed x Time = 3x108 x 3.16 x 107 = 9.46 x 1015 m
  45. 45. Lightyear  The distance across our galaxy, The Milky Way is 80 000 light years.  Our nearest neighbouring galaxy, The Andromeda galaxy, is 2.2 million light years away.
  46. 46.  The furthest galaxies that can be detected with the Hubble Telescope are over 10 billion light years away!!!  This marks the edge of the detectable Universe.  It is a big place!
  47. 47. Astronomical distances The parsec (pc) – this is the distance at which 1 AU subtends an angle of 1 arcsecond. 1 pc = 3.086x1016 m or 1 pc = 3.26 ly “Parsec” is short for parallax arcsecond
  48. 48. 1 parsec = 3.086 X 1016 metres  Nearest Star 1.3 pc (206 000 times further than the Earth is from the Sun)
  49. 49. Parallax Angle star/ball appears to shift “Baseline” Distance to star/ball Where star/ball appears relative to background Bjork’s Eyes Space
  50. 50. Parallax Parallax, more accurately motion parallax, is the change of angular position of two observations of a single object relative to each other as seen by an observer, caused by the motion of the observer. Simply put, it is the apparent shift of an object against the background that is caused by a change in the observer's position. Parallax Applet
  51. 51. Parallax Baseline – R (Earth’s orbit) Distanceto Star-d Parallax - p (Angle) We know how big the Earth’s orbit is, we measure the shift (parallax), and then we get the distance…
  52. 52. Parallax (Distance)d (Baseline)R (Parallax)tan p For very small angles tan p ≈ p d R p In conventional units it means that m10x3.086m 3600 1 360 2 10x1.5 pc1 16 11               
  53. 53. Parallax arcsecond)(p 1 (parsec)d  m10x3.986m 3600 1 360 2 10x1.5 pc1 16 11                d R p  p R d 
  54. 54. Angular sizes  360 degrees (360o) in a circle  60 arcminutes (60’) in a degree  60 arcseconds (60”) in an arcminute
  55. 55. Parallax has its limits The farther away an object gets, the smaller its shift. Eventually, the shift is too small to see.
  56. 56. Questions  The parallax angle for Barnards star from the Earth is 0.545 arc secs. What is its distances in ly, parsecs and AU  The parallax angle for 61 Cygni star from the Earth is 0.333 arc secs. What is its distances in parsecs and AU
  57. 57. Solutions  Using d = 1/p to find parsec  1.83 pc, 376000AU, 5.96ly  3pc, 9.78ly
  58. 58. What is the most important thing about a star? MASS! The mass of a normal star almost completely determines its LUMINOSITY and TEMPERATURE!  Note: “normal” star means a star that’s fusing Hydrogen into Helium in its centre (we say “hydrogen burning”).
  59. 59. The LUMINOSITY of a star is the TOTAL ENERGY emitted per time from the surface of the star: The energy the Sun emits is generated by the fusion in its core… This light bulb has a luminosity of 60 Watts
  60. 60. What does luminosity have to do with mass? The mass of a star determines the pressure in its core: Pressure Gravity pulls outer layers in, Gas Pressure pushes them out. The core supports the weight of the whole star! The more mass the star has, the higher the central pressure!
  61. 61. The core pressure determines the rate of fusion… MASS PRESSURE & TEMPERATURE RATE OF FUSION …which in turn determines the star’s luminosity!
  62. 62. Luminosity is an intrinsic property… it doesn’t depend on distance! This light bulb has a luminosity of 60 Watts… …no matter where it is, or where we view it from, it will always be a 60 Watt light bulb.
  63. 63. Luminosity The Luminosity of a star is the energy that it releases per second. Our Sun has a luminosity of 3.90x1026 W (often written as L): it emits 3.90x1026 joules per second in all directions. The energy that arrives at the Earth is only a very small amount when compared will the total energy released by the Sun.
  64. 64. TOK  The ancient Greeks classified stars by their brightness using the naked eye. They were quite good at it. Have we lost skills because of our reliance on technology? Is this a concern?
  65. 65. Apparent brightness  When the light from the Sun reaches the Earth it will be spread out over a sphere of radius d. The energy received per unit time per unit area is b, where: 2 4 d L b   d b is called the apparent brightness of the star
  66. 66. Apparent brightness  The apparent brightness is directly proportional to the star’s luminosity and varies as the inverse square of the stars distance.
  67. 67. Luminosity Question The Sun is a distance d=1.5 x 1011 m from the Earth. Estimate how much energy falls on a surface of 1m2 in a year. d L= 3.90x1026 W
  68. 68. At a distance of d=1.5 x 1011 m, the energy is “distributed” along the surface of a sphere of radius 1.5 x 1011 m d The sphere’s surface area is given by: A = 4πd2 = 4 π x (1.5 x 1011)2 = =2.83 x 1023 m2 The energy that falls on a surface area of 1m2 on Earth per second will be equal to: b = L/A = 3.90x1026 / 2.83 x 1023 = = 1378.1 W/m2 or 1378.1 J/s m2 In a year there are: 365.25days x 24h/day x 60min/h x 60s/min = 3.16 x 107 s So, the energy that falls in 1 m2 in 1 year will be: 1378.1 x 3.16 x 107 = 4.35 x 1010 joules
  69. 69. Distance measurement by parallax d = 1 / p Luminosity L = 4πd2 b apparent brightness spectrum Wien’s Law (surface temperature T) Chemical composition of corona L = 4πR2 σT4 Stefan-Boltzmann Radius Distance measured by parallax:
  70. 70. Apparent brightness Distance (d) b = L / 4πd2 Luminosity class spectrum Surface temperature (T) Wien’s Law Chemical composition Stefan-Boltzmann L = 4πR2 σT4 Radius Distance measured by spectroscopic parallax / Cepheid variables: H-R diagram Spectral type Luminosity (L) Period Cepheid variable

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