The energy falling on a 1 m^2 surface on Earth in a year is:
Lsun x π x 1 x (1 year) = 3.90x1026 W x π x 1 x (3600 s/hr x 24 hr/day x 365.25 day/year) = 1.36x1017 J
Where Lsun is the luminosity of the Sun (3.90x1026 W) and 1 year is converted to seconds.
3. List the objects in the universe
Galaxies Cluster
Solar systems Constellations
Stars Planets
Comets Asteroids
Satellites Black holes
Pulsars Quasars
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
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. 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.
19. 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
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. Constellations
A group of stars in a recognizable pattern that
appear to be near each other in space.
Orion
Sketch 2 in your
booklet
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.
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.
29. Supernovae
As the name suggests, are much brighter
than “nova”.
Occur at an average rate of 3 every 100
years they often outshine a whole galaxy.
They’re caused by stars exploding, in one
of two main ways.
30. 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)
31. 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
34. 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
35. 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.
36. 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 75 years).
38. 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?
39.
40. 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.
42. 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.
43. 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
45. 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
46. 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
47. 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.
48. 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!
49. 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
50. 1 parsec = 3.086 X 1016 metres
Nearest Star
1.3 pc
(206 000 times
further than
the Earth is
from the Sun)
52. 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
53. 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…
56. Angular sizes
360 degrees (360o)
in a circle
60 arcminutes (60’)
in a degree
60 arcseconds
(60”) in an
arcminute
57. Parallax has its limits
The farther away
an object gets,
the smaller its
shift.
Eventually, the shift
is too small to see.
58. 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
59. Solutions
Using d = 1/p to find parsec
1.83 pc, 376000AU, 5.96ly
3pc, 9.78ly
60. 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”).
61. 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
62. 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!
63. The core pressure determines
the rate of fusion…
MASS PRESSURE &
TEMPERATURE
RATE OF
FUSION
…which in turn determines
the star’s
luminosity!
64. 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.
65. 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.
66. 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?
67. 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
68. Apparent brightness
The apparent brightness is directly
proportional to the star’s luminosity and
varies as the inverse square of the stars
distance.
69. 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
70. 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
71. 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:
72. 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
