SPACE PHYSICS
[BLOCK 6]
MST_CREATOR
FOLLOW ME ON:
Table of Contents
Note From Author .................................................................................................................................................. 2
Earth & The Solar System .................................................................................................................................... 3
Motion of The Earth .......................................................................................................................................... 3
Day & Night Cycle........................................................................................................................................... 3
Rising & Setting of The Sun ........................................................................................................................ 3
The Seasons..................................................................................................................................................... 3
Motion of The Moon ........................................................................................................................................... 5
Phases................................................................................................................................................................ 5
Rising & Setting .............................................................................................................................................. 5
Orbital Speed ...................................................................................................................................................... 6
The Solar System ............................................................................................................................................... 6
Asteroids .......................................................................................................................................................... 7
Comets .............................................................................................................................................................. 7
Elliptical Orbits .............................................................................................................................................. 7
Origin ..................................................................................................................................................................... 8
How They Formed .......................................................................................................................................... 8
Planet Gravitational Field Strength ............................................................................................................... 9
Travel Times ........................................................................................................................................................ 9
Planetary Data ................................................................................................................................................... 10
Stars & The Universe............................................................................................................................................ 11
The Sun as a Star .............................................................................................................................................. 11
Nuclear Reactions in Stars ......................................................................................................................... 11
Stars .................................................................................................................................................................... 12
Light Years ..................................................................................................................................................... 12
Galaxies........................................................................................................................................................... 12
The Life Cycle of a Star ............................................................................................................................. 13
The Universe ...................................................................................................................................................... 14
The Milky Way (Again) ................................................................................................................................ 14
The Expanding Universe ............................................................................................................................. 14
Microwave Background Radiation.............................................................................................................. 14
Hubble’s Law .................................................................................................................................................. 15
Notes By MST_Creator
Page 1
FOLLOW ME ON:
Note From Author
I would just like to tell you that my notes may be missing some things here and there or
may have some unneeded information every now and then, sorry about that.
It’s kind of hard to make notes with a book that has information embedded inside the
many paragraphs and having that as my only resource makes the process even more
troublesome.
Anyway, that’s all for this section, now you can start with the actual content!
Hope this helps!
Notes By MST_Creator
Page 2
FOLLOW ME ON:
Earth & The Solar System
Motion of The Earth
Day & Night Cycle
Day and night is caused by the constant rotation of Earth on its axis.
The earth makes a revolution every 24 hours, this means that in one half of the time (12
hours), it is daytime and in the other half, it is night-time.
Rising & Setting of The Sun
The rotation of the earth on its axis causes the sun to rise from east and set at west.
The Seasons
There are 2 factors that cause seasons, one being the fact that it takes the earth around
365 days to complete an orbit around the sun and the other is the tilt of the Earth on its
axis (23.5‫)ﹾ‬.
Notes By MST_Creator
Page 3
FOLLOW ME ON:
Figure 1
Part
Season
Day & Night Length
Hemisphere Tilt
BCD
Spring & Summer
Long Days
Short Nights
Northern hemisphere tilted away from
the sun
Autumn & Winter
Short Days
Long Nights
FGH
Southern hemisphere tilted away from
the sun
Part
Date
Northern Hemisphere Day &
Night Length
Southern Hemisphere Day &
Night Length
C
June 21st
Longest Day
Shortest Night
Shortest Day
Longest Night
G
December 21st
Shortest Day
Longest Night
Longest Day
Shortest Night
A & E
March 20th
And
September 23rd
Night & Day Have Same Length
(Equinox)
Night & Day Have Same Length
(Equinox)
Notes By MST_Creator
Page 4
FOLLOW ME ON:
Motion of The Moon
Phases
The moon completes an orbit around the sun in a month.
As the moon rotates around the earth, it appears differently to us, this means that the
moon has phases.
Figure 2
Image From timeanddate.com
The shaded parts are the parts which we don’t see as the sun light does not
go onto them.
Rising & Setting
The tilt of the Earth on its axis causes the moon to rise from the east and set at the
west.
Notes By MST_Creator
Page 5
FOLLOW ME ON:
Orbital Speed
To calculate the average orbital speed, we use the formula:
𝑣=
2𝜋𝑟
𝑇
𝐴𝑣𝑒𝑟𝑎𝑔𝑒 𝑂𝑟𝑏𝑖𝑡𝑎𝑙 𝑆𝑝𝑒𝑒𝑑 =
𝑂𝑟𝑏𝑖𝑡 𝐶𝑖𝑟𝑐𝑢𝑚𝑓𝑒𝑟𝑒𝑛𝑐𝑒
𝑂𝑟𝑏𝑖𝑡𝑎𝑙 𝑃𝑒𝑟𝑖𝑜𝑑
Orbital Period is the time taken to complete 1 orbit
Average orbital speed is the speed of an object that is orbits around a body.
The Solar System
The solar system is made of:
Name
The sun
Eight Planets
Asteroid Belt
Moons
Minor Planets
Smaller Bodies
Notes By MST_Creator
Description
This is a start that is in the middle and is the heart of the Solar
System.
Inner Planets:
Outer Planets:
1. Mercury
1. Jupiter
2. Venus
2. Saturn
3. Earth
3. Uranus
4. Mars
4. Neptune
They are smaller, solid, rocky,
They are large, colder, have
have a layered structure, and
low densities, and are mainly
have high densities.
made up of gases.
This is a belt of asteroids going around the sun, it can be found
between Mars & Jupiter.
These are the moons that orbit the planets in the solar system.
(Like IO, Europa, Phobos, etc)
These are dwarf planets (like Pluto or Ceres) and certain asteroids
from the asteroid belt.
Like comets (i.e., Halley’s Comet) & other small bodies.
Page 6
FOLLOW ME ON:
Asteroids
An asteroid is any object that orbits a star and does not have a large enough mass for
gravitational attraction to pull it into spherical shape.
Asteroids are classified as minor planets.
Comets
Comets are objects that consist of a nucleus of ice and dust.
When comets are near the sun, they develop a bright head and long tail that points away
from the sun.
Elliptical Orbits
Elliptical orbit basically refers to the path an object orbits around another object:
Figure 3
Figure 4
Image Source: NSO
Elliptical orbit of a comet
This is the elliptical orbit of a planet around the sun
As you saw in both figures, the sun was inside the elliptical orbit, but not in the middle,
the reason for this is that the sun is never in the middle of an elliptical orbit unless the
orbit is perfectly circular.
In Figure 4, we can see that the elliptical orbit of a comet is in an oval shape, it shows us
that the speed of the comet increases as it approaches the sun and decreases as it moves
away, energy is conserved as the kinetic energy the comet had when near the sun is
converted to potential energy.
Notes By MST_Creator
Page 7
FOLLOW ME ON:
Origin
How They Formed
Formation
Sun
Formed when gravitational attraction pulled clouds of Hydrogen gas and dust.
Planets
First, the matter that was left after creating the sun formed an accretion disk,
gravitation attraction eventually pulled the matter together to form planets.
Planet Formation
Planets Group
Position
Properties
Inner
Between Sun & Asteroid Belt
Dense
Small
Rocky
Layered Structure
As the sun grew, it became hotter.
This meant that the area of the inner
planets would also be very hot, this
caused light molecules to be in gaseous
or liquid form.
Property
Reasoning
This meant that the inner planets would
be made of matter with high melting
points which also meant that they would
be dense, these included metals and
silicates.
Since there was a low number of heavy
elements, this resulted with the inner
planets being small, rocky, and solid.
Outer
After Asteroid Belt
Low Density
Large
Mainly Made of Gases
Cold
Since these planets were in the
colder region, far from the sun.
This meant that the light molecules
were able to exist as solids.
This meant that they would be made
of the lighter molecules which had
low melting points and were less
dense, these included Hydrogen,
Methane, Water, etc.
Since most of the leftover matter
was the light elements, this resulted
with the outer planets being large and
gaseous.
Some Things to Know About the Sun
The sun makes up most of the mass of the Solar System (more than 99%).
Another thing is that the force that causes the objects (like planets) to keep orbiting the
sun is the gravitational attraction of the sun.
Notes By MST_Creator
Page 8
FOLLOW ME ON:
Planet Gravitational Field Strength
Gravitational field strength of a planet depends on the mass of the planet.
Planet Mass
Gravitational Field Strength
Increase
Increase
Decrease
Decrease
𝑃𝑙𝑎𝑛𝑒𝑡 𝑀𝑎𝑠𝑠 ∝ 𝐺𝑟𝑎𝑣𝑖𝑡𝑎𝑖𝑜𝑛𝑎𝑙 𝐹𝑖𝑒𝑙𝑑 𝑆𝑡𝑟𝑒𝑛𝑔𝑡ℎ
Gravitational Field Strength acting on an object decreases as the distance between the
object and the planet increases.
Distance Between Object & Planet
Gravitational Field Strength
Increase
Decrease
Decrease
Increase
𝐷𝑖𝑠𝑡𝑎𝑛𝑐𝑒 𝐵𝑒𝑡𝑤𝑒𝑒𝑛 𝑂𝑏𝑗𝑒𝑐𝑡 & 𝑃𝑙𝑎𝑛𝑒𝑡 ∝
1
𝐺𝑟𝑎𝑣𝑖𝑡𝑎𝑖𝑜𝑛𝑎𝑙 𝐹𝑖𝑒𝑙𝑑 𝑆𝑡𝑟𝑒𝑛𝑔𝑡ℎ
Travel Times
To calculate the amount of time light takes to travel through space, we can use:
𝑆𝑝𝑒𝑒𝑑 =
𝐷𝑖𝑠𝑡𝑎𝑛𝑐𝑒
𝑇𝑖𝑚𝑒
We can then rearrange the formula to give time:
𝑇𝑖𝑚𝑒 =
𝐷𝑖𝑠𝑡𝑎𝑛𝑐𝑒
𝑆𝑝𝑒𝑒𝑑
Note:
Speed refers to the speed of light (3 x 108)
The value for distance is given in the question.
Notes By MST_Creator
Page 9
FOLLOW ME ON:
Planetary Data
One of the requirements in the 2023 syllabus is to analyse and interpret planetary data
for various things.
We get this table for reference:
Figure 5
Table With Data for Each Planet
Here is the reasoning for the required things:
Value
How It Changes
Orbital
Distance
Increases as distance from the sun
increases.
Orbital
Speed
Decreases as distance from the sun
increases.
Orbit
Duration
Increases as distance from the sun
increases.
Surface
Temperature
Density
Decreases as distance from sun
increases (except Venus which has
high surface temperature due to its
carbon clouds which traps heat).
Decrease as distance from sun
increases (except Uranus & Saturn,
they are ice giants, so they have more
density than gas giants)
Surface
Gravity
Notes By MST_Creator
Reasoning
This happens because the elliptical orbit
grows larger because the distance from
the sun increases.
As the distance from the sun increases
the gravitational field decreases which
means that the centripetal force is
weaker, this decreases the orbital speed
and increases the orbital duration.
Sun emits infrared radiation; the
intensity of this radiation decreases as
we go farther from the sun.
Discussed in planet formation
Discussed in Planet Gravitational Field Strength
Page 10
FOLLOW ME ON:
Stars & The Universe
The Sun as a Star
Star Size
Medium
Elements
Hydrogen & Helium
Energy Emitted
Infrared rays, Visible Light, and UV rays
Nuclear Reactions in Stars
Stars are powered by nuclear reactions.
These reactions are fusion reactions of Hydrogen & Helium.
Remember that these reactions can only occur in stars that are stable and have a hot and
dense enough core to carry out the fusion reactions.
Why The High Temperature?
The high temperature in the core is needed to sustain the nuclear reactions and is
maintained large amount of energy release in the fusion process.
How It Glows
Some of the energy that is generated at the core is transferred to the outer layers of
the star.
The outer layers are cooler and not as dense as the core but still allow the Hydrogen gas
to glow and emit EM radiation into space.
Notes By MST_Creator
Page 11
FOLLOW ME ON:
Stars
Light Years
One light year is the distance travelled by light in a vacuum in one year.
1 light year = 9.5 x 1012 km
Galaxies
A galaxy is a large collection of stars.
Galaxies also consist of clouds of gas (mostly Hydrogen & dust) and they many rotate in
spiral disks
The Milky Way
The sun is a star that is in a galaxy called the milky way.
The solar system is also located in the milky way.
Unlike the sun, other stars are located light years away from the Earth.
Notes By MST_Creator
Page 12
FOLLOW ME ON:
The Life Cycle of a Star
Stage
1
2
3
4
What Happens
Interstellar clouds of dust & gas including Hydrogen
collapse under the gravitational attraction and forms a
protostar.
As the protostar’s mass increases, so does its
temperature. The protostar contracts under the internal
gravitation forces and
when the core is hot enough, the fusion reaction starts
where Hydrogen turns to Helium.
The protostar becomes stable when the gravitation
attraction force pulling inwards is balanced out by the
force of expansion due to the high temperature.
When the star starts to run out of Hydrogen as fuel for
the nuclear reactions, it becomes unstable because the
balance between the forces pulling inward and the forces
pulling outward has been disturbed. When this happens,
the core becomes extremely hot, and the remaining
hydrogen is burned up fast and the surface is cooled
down.
Low Mass Stars
High Mass Stars
When the red giant
runs out of helium, the
red giant collapses
under its own gravity
and releases enough
energy to expel some of
its outer layers.
This means that the
core becomes a white
dwarf at the center of
a glowing shell of
ionised gas called
planetary nebula.
When the red supergiant runs
out of helium, the core
collapses further into gravity
and hot enough for nuclear
fusion of Carbon into Oxygen,
Nitrogen, and Iron to occur.
Nuclear fusion then stops and
is released in a supernova
explosion.
In supernova explosions, star’s
brightness increases, and the
core is hot enough for fusion
of many elements heavier than
iron and becomes available for
the formation of new stars and
planetary systems.
The center of the supernova
collapses to a dense neutron
star and if the center is very
dense, black hole is formed
Notes By MST_Creator
What Forms
Protostar
Large Mass:
Blue
or
White
Star
Smaller Mass:
Red dwarf
or
Yellow dwarf
Red giant but it can also be a
red supergiant if the star if
the star is very massive.
Low Mass
Star
White dwarf
with glowing
ionised gas
around it.
(The white
dwarf
eventually
becomes a
black dwarf)
High Mass
Stars
A Neutron star
forms which
acts as pulsar
and sends out
radio wave
pulses.
A Black hole
forms when the
center is
extremely
dense, a Black
hole sucks
anything into
it, from solids
to gases.
Page 13
FOLLOW ME ON:
The Universe
The Milky Way (Again)
The milky way galaxy is one of the many galaxies in the universe.
The diameter of the milky way is 100,000 light years and is made up of more than 800
billion stars.
The Expanding Universe
Redshift
Redshift is when the light emitted from stars in distant galaxies is shifted to the red end
of the spectrum, this means that it increases the wavelength.
Another thing to note is that the greater the distance between the observer and the star,
the more the redshift.
Redshift supports the fact that the universe is expanding & the big bang theory.
The Big Bang Theory
The theory suggests that all the matter of the universe was packed in a dense state, it
tells us that an explosion took place (the big bang) around 14 billion years ago.
The expansion of the universe continues to this day.
(Extremely short summary of the idea, hope it helps)
Microwave Background Radiation
The big bang produced radiation energy which exists in the universe as Cosmic Microwave
Background Radiation (CMBR) of a certain frequency.
CMBR fills the whole universe with similar intensities.
As the universe has expanded over the years, this caused the CMBR to redshift into the
microwave region of the EM spectrum.
Notes By MST_Creator
Page 14
FOLLOW ME ON:
Hubble’s Law
This law states that:
“The velocity of the galaxy which is also known as the redshift is directly
proportional to its distance.” (Source: Byjus)
Formula:
𝑣 = 𝐻0 × 𝑑
Quantity
Description
How To Find It
v
Speed at which the galaxy is moving away
from the Earth.
Found from the change in wavelength
of the galaxy’s starlight due to
redshift.
H0
Ratio of the speed at which a galaxy is
moving away from the earth and the
distance between the galaxy and the Earth.
𝑣
(𝑑 )
It’s a ratio, you must calculate it using
the other 2 quantities.
d
Distance between the galaxy and the earth.
Calculated using the brightness of a
supernova in that galaxy.
Current Estimate of H0
The current estimate for H0 is 2.2 x 10-18 per second.
Calculating The Age of The Universe
We can rearrange the formula of Hubble’s law to get the age of the universe:
𝑑
1
=
𝑣
𝐻0
𝑑
𝑣
refers to the age of the universe so we can say:
𝑎𝑔𝑒 =
1
𝐻0
This means that the age would be around 4.5 x 1017 seconds.
We can simplify this value into years by dividing by 31,536,000 giving us:
1.4 x 1010 which is 14 billion years!
(It’s a rough estimate as I reduced the values to 1 d.p)
Notes By MST_Creator
Page 15
FOLLOW ME ON:
Thanks For Reading!
If this helped you in any way…
I am happy for you
Notes By MST_Creator
Page 16