Astronomy
Inner Planets
Colder Planets
Aspect
Dark Energy
CMB
Nature
Mysterious energy causing expansion
Microwave radiation from the early
universe
Origin
Unknown, potentially linked to
vacuum energy or fields
Thermal radiation from the Big Bang
Time of Relevance
Dominates in the current era (~5
billion years onward)
Dates back to ~380,000 years after
the Big Bang
Role
Drives accelerated expansion of the
universe
Provides a snapshot of early
conditions
Detectability
Indirectly, through its effects on
cosmic expansion
Directly observed as microwave
radiation
Composition
Represents ~68% of the universe's
energy density
Represents the leftover photons from
the Big Bang
• Aestroids
• Rocky objects that are too small and numerous to be considered
planets
• Most orbit between Mars and Jupiter (asteroid belt)
• One hit Earth 65
million years ago
• One could hit again
COMETS
• Comets Another kind of space rocks, shining lights in sky.(not shooting stars)
• They have icy middle (water + gases) mixed with bit of metals and rocks and
covered by black dust
• When a comet approaches the Sun, its ice vaporizes, creating a glowing coma (a cloud of gas
and dust) and often a tail that points away from the Sun.
• Short period comet – 200years to travel sun – haleys comet
• Long period comet Eneck’s comet
Meteors
• Meteoroid left over material when Sun and planets were created (chunk of rock or
dust in space) 100 miles long , some are just 2 ft.
• Meteor – a Aestroid that is burning up due to friction in air in
Earth’s atmosphere (shooting stars)
• Meteorite – a meteor that doesn’t
completely burn up and hits the
ground (found in antartica and deserts)
Types of Asteroid Collisions
1.Asteroid vs. Asteroid:
Collisions between asteroids occur primarily in the asteroid belt.
These impacts can:
1.Break large asteroids into smaller fragments.
2.Form asteroid families (groups with similar orbits).
3.Produce meteoroids, which are smaller fragments that may
eventually reach planets.
2.Asteroid vs. Planet (or Moon):
When asteroids collide with planets, it can lead to:
1.Formation of craters.
2.Significant ecological and climatic changes (on Earth).
Effects of an asteroid impact on the moon
• 1. Atmosphere
• Moon: The Moon has no atmosphere to burn up incoming
meteoroids, so even small objects reach its surface and create craters.
• Earth: Earth's thick atmosphere causes most meteoroids to burn up
before reaching the surface, forming "shooting stars" rather than
impact craters so we see less craters on Earth.
Effects of asteroid collisions
• Melting and exploding rocks thrown large distances from the point
of impact
• Major events like volcanoes , tsunamis and Earthquakes
• Clouds of dust and gas thrown into Earth’s atmosphere causing
Earth’s climate to change
• Causing mass extinction
• Debris and dust blocking sunlight for months or even years causing
permanent climate change.
Famous Asteroid Impacts
1.The Chicxulub Impact (66 million years ago):
1. Caused the mass extinction event that wiped out the dinosaurs.
2. An asteroid about 10 km- 80 km wide struck what is now the Yucatán Peninsula,
forming the Chicxulub Crater 150km wide
3. Effects:
1.Massive fireball and shockwaves.
2.Global wildfires.
3.A "nuclear winter" caused by dust and debris blocking sunlight.
Arizona Aestroid
• 50m wide diameter
• 1200 m wide crater
• Local fires and large explosion
• No mass extinction
• No long lasting climate change
• Minor shaking of crust.
1.Iridium Anomalies:
1. Iridium is a rare element on Earth's surface but abundant in asteroids.
2. A thin layer of iridium-enriched sediment, known as the K-Pg boundary, has been found
worldwide, consistent with a massive asteroid impact.
2.Shock-Metamorphic Features:
1. High-pressure and high-temperature effects, like shocked quartz and tektites (melted debris
ejected from the impact), are found only in impact events.
2. These are absent in volcanic eruptions.
3.Crater Evidence:
1. The Chicxulub Crater off the coast of Mexico is direct evidence of a massive asteroid impact.
2. It dates precisely to the time of the K-Pg extinction (~66 million years ago).
4.Global Distribution of Ejecta:
1. A fine layer of debris from the impact is found globally, indicating a single catastrophic event.
5.Timing and Suddenness:
1. The asteroid impact explains the abrupt nature of the extinction event. While volcanic activity
can also cause extinctions, it usually operates over a longer timescale.
(Asteroid impact hypothesis)ALVAREZ HYPOTHESIS
• Likely explaination for mass extinction is called Alvarez hypothesis.
• An asteroid collided with Earth about 66 million years ago and gas,
dust and rock fragments would have been thrown high into the
atmosphere. The amounts produced would have caused Earth’s
climate to change significantly.
Evidence for Alvarez hypothesis
• Large amount of Iridium in rock layers from around 66 million years ago.
Iridium is rare on Earth but found in abundance within meteorites.
• Large impact crater (about 150km diameter) centred on Chicxulub, near the
coast of Mexico , Rock samples near it show evidence of formation 66 million
years ago.
• At North Dakota in US, fossils contained large numbers of glassy rock formed when rocks
were melted and cooled.
• volcanic eruptions played a major role in the mass extinction event, it is still
debated whether the eruptions alone could have caused the extinction or
whether they acted in combination with other factors, such as the asteroid
impact. The most widely accepted view today is that both volcanic activity and
the asteroid impact were likely contributing factors to the mass extinction.
Moon FORMATION
• Capture hypothesis : Idea that moon is large asteroid that has been
pulled into orbit around Earth dur to gravitational force if the Earth.
• Co-formation Hypothesis: The moon formed at about the same time
as Earth, from dust and gas of the solar Nebula and was pulled by
gravity into the orbit around the Earth.
• Collision hypothesis: A large object same size and mass as that of
planet Mars, formed same time as Earth , crashed into early Earth and
split mass of the rock into two objects- the Earth & the Moon.
M. Giant Impact Theory
1. The Moon formed about 4.6 billion years ago when a
Mars-sized object collided with Earth.
2. The violent collision melted and vaporized some of
Earth’s crust and mantle and hurled it into space.
3. Some material fell back to Earth, some escaped into
interplanetary space, and some orbited Earth as a ring of
hot gas and debris.
4. Solid particles eventually condensed from the
cooling gas and the Moon began to form.
Giant – Impact
Early Earth collided with Mars size object
Violent collision melted and vapourized some of the Earth’s
crust and mantle and hurled them in space.
Some fell on Earth, some escaped in space, while some
orbited around Earth as gas and debris
Moon formed from ejecta of lighter crust and mantele of
Earth.
• Moon rocks contain material that forms quickly at high temperatures.
• Moon rock contains less Iron than Earth rock ( as collision blew away
crust and mantle in debris)
• Moon rock has less water than Earth rock ( collision evaporated all of
the water
• Moon rock and Earth rock have similar chemical composition.
• Moon rock has low density compared to Earth. (Similar composition
as Earth but depleted in heavy elements)
Evidence against collision theory
• More than 60% of the moon should be made up of same material
that came from colliding object.
1. What are the three challenges humans will
face to live on Moon.
• Oxygen
• No atmosphere
• Lack of water and other volatile elements
• Less of heavy metals
Stars
Stars A star is a massive, luminous
ball of gas that is held together
by gravity.
The Sun is a typical star that
consists of about 75%
Hydrogen, 24% Helium and 1%
other elements such as carbon
and oxygen.
The Pleiades Star Cluster
Nuclear Fusion is always
occuring producing huge
amounts of energy
There are about 2 billion stars
in our galaxy.
Stars colours
The colour of a star depends on
its surface temperature.
The Sun is an average
temperature yellow star.
RED = 3000°C
ORANGE = 5000°C
YELLOW = 6000°C
WHITE = 8000°C
BLUE = 10000°C and
above
Sirius, the brightest star in the
night sky is a blue-white star
Nebula
Stars usually form inside a
nebula.
This is a cloud of mostly
hydrogen along with
smaller amounts of other
elements ‘dust’.
Many young stars are found inside the
Orion nebula
Protostar
Due to gravitational
attraction, the gas and dust
clumps together.
Gravitational potential
energy is converted into heat
energy.
The gas starts to glow forming
a protostar.
Artist's conception of the birth of a
star within a nebula
Nuclear fusion
When the temperature rises
above about 10 million°C
hydrogen nuclei join together to
form Helium by the process of
nuclear fusion.
Energy is released.
The star becomes stable when the
radiation produced causes an
outward pressure that prevents
further gravitational collapse of
the star.
Nuclear fusion from hydrogen
isotopes deuterium (H2) and
tritium (H3)
The birth
theofsolar
system
About of
99.9%
the original
gas and dust formed the
Sun. The remaining 0.1% formed the planets and other
bodies of the solar system.
The future of the Sun - Main sequence
The Sun is about half way through a
10 billion year period in its life cycle
called ‘main sequence’
During this time hydrogen in the core
of the Sun is converted into Helium
by the process of nuclear fusion.
The Sun will gradually become hotter
over time so that in about two billion
years time life will no longer be
possible on Earth.
Red InGiant
about 5 billion years time the hydrogen
in the Sun’s core will run out.
Without outward radiation pressure the
core will collapse under gravity and become
even hotter.
Eventually the temperature will be high
enough to cause the fusion of helium into
heavier elements such as carbon and
oxygen.
The now greater outward radiation
pressure will cause the Sun to expand into a
Red Giant.
When the Sun becomes a Red Giant it
will be nearly as big as the Earth’s orbit
about the Sun.
Planetary Nebula and White Dwarf
After only a few million years the Helium
will also run out in the Sun’s core.
A final collapse of the core occurs to form a
very hot dense object about the size of the
Earth called a white dwarf.
The rest of the Sun is blown away to form a
planetary nebula (from which a new star
might form).
The Ring Nebula
The white dwarf will gradually cool over
billions of years to form a black dwarf.
The NOTE:
life cycle of the Sun
Due to its relatively low mass the Sun will not become a red
supergiant, supernova, neutron star or black hole.
Star evolution summary
protostar
main
sequence
star
MASS
>4ʘ
ʘ = Sun
CORE MASS
red supergiant
< 1.4 ʘ
> 1.4 ʘ
supernova
MASS
0.23 to 4 ʘ
MASS
> 0.05 ʘ
red giant
nebula
MASS
< 0.05 ʘ
MASS
< 0.23 ʘ
CORE MASS
planetary
nebula
brown dwarf
(failed star)
white
dwarf
<3ʘ
>3ʘ
neutron
star
black
hole
LowThemass
stars
Sun is an average star.
There are many cooler stars of
lower mass called red dwarfs.
These are very faint and can only
be seen through telescopes.
The nearest star to the Sun is a
red dwarf called Proxima Centauri.
It is just over 4 light years away.
High mass stars
Most of the stars we can see in the sky are
more massive than the Sun.
Compared with the Sun they:
- are larger
- are brighter
- are bluer when main
sequence
- pass through their life cycles
more quickly
- sometimes end their lives
differently
All the main stars in the
constellation of Orion are more
massive than the Sun.
Red supergiants
Higher mass stars form larger red
giants.
The star Betelgeuse (top left in Orion)
is larger than the orbit of Mars about
the Sun.
Supergiants will also cause elements
such as carbon and oxygen to
undergo nuclear fusion to form even
heavier elements such as silicon and
iron.
The internal ‘onion’ structure of a
red supergiant star
Supernovae
When a red supergiant star causes
iron in its core to undergo nuclear
fusion energy is absorbed causing a
great implosion.
This rebounds and causes a massive
explosion that can for a few days
outshine a whole galaxy. This is
called a supernova.
Supernovae are very rare. They can
be seen in the daylight sky. The last
observed supernovae in our galaxy
took place in 1604.
The Crab Nebula was formed
after a supernova observed in
1054
Neutron stars
The core left over from a
supergiant star can be so massive
that gravity causes electrons and
protons to combine to form
neutrons. This is a neutron star.
A neutron star is only about 10km
in diameter and is extremely
dense. A teaspoon full of neutron
star has a mass of about two billion
tonnes.
Some neutron stars, called pulsars,
emit regular radio signals.
X-ray image of the neutron star
inside the Crab Nebula
Black holes
The most massive stars collapse to
form black holes.
The gravity caused by black holes is so
strong that nothing can escape,
including light.
Black holes can only be observed from
the affect they have on surrounding
objects such as a companion star.
Star formation and Solar system formation
Both Begin from a Nebula (Gas and Dust Cloud)
Stars and solar systems both form from a nebula, a massive cloud of gas and dust in space.
•Star Formation: Gravity causes the nebula to collapse, forming a dense core that becomes a
protostar.
•Solar System Formation: After a star forms, the remaining gas and dust create a protoplanetary
disk, from which planets, moons, and other objects form.
2. Gravity and Accretion Play a Major Role
•Gravity is the key force driving both processes.
•In Star Formation: Gravity pulls gas and dust together, increasing pressure and temperature until
nuclear fusion starts, forming a new star.
•In Solar System Formation: Gravity causes small particles in the disk to collide and stick together,
forming larger bodies like asteroids, planets, and moons through a process called accretion.
We see light from a nebula because of the following reasons:
 . Reflection of Starlight (Reflection Nebulae)
•Some nebulae reflect light from nearby stars.
•The dust particles in the nebula scatter and reflect the light, making the nebula
visible.
•Example: The Pleiades Nebula (blue glow due to scattered starlight).
 Emission of Light (Emission Nebulae)
•Some nebulae glow because their gas is excited by nearby stars (usually hot, young
stars).
•The ultraviolet (UV) radiation from the stars energizes the hydrogen gas, causing it
to emit its own light. (pink hue)
•glowing cloud of ionized gas that is excited by ultraviolet radiation absorbed from hot nearby stars. Such a star
must be hotter than 25,000 K to emit enough UV radiation to ionize the gas. When a gas is ionized, it's excited
and produces an emission spectrum with a distinct pink color.
Example: The Orion Nebula (bright glowing gas due to hydrogen emission).
 Absorption of Light (Dark Nebulae - Indirect Visibility)
•Some nebulae block light from stars behind them, appearing as dark silhouettes.
•These nebulae are visible because they create a contrast against a bright
•Stars Create Heavy Elements – In their cores, stars fuse lighter elements
•(like hydrogen and helium) into heavier ones through nuclear fusion.
For example:
•Carbon and oxygen are formed in medium-sized stars.
•Iron and other heavier elements are formed in massive stars.
•Supernova Explosions – When massive stars explode in supernovae,
they scatter these elements into space.
•Formation of New Planets and Life – The gas and dust from old,
exploded stars mix together, forming new stars, planets, and eventually, life.
•The Earth (and everything on it, including us) is made from these recycled star
materials.
Choose appropriate words to fill in the gaps below:
hydrogen
Stars are made mostly from __________
and generate their
energy by nuclear _________.
Stars are formed in nebulae
fusion
when ________
causes gas and dust to clump together.
gravity
expand
Towards the end of its life, the Sun will _________
to form a
red giant after which most of its material will be blown away
nebula leaving behind a small white _____
dwarf star.
as a planetary ______
massive
More ________
stars than the Sun may undergo a supernova
neutron
explosion and become _________
stars or black holes.
WORD SELECTION:
expand
neutron
gravity
fusion
massive
nebula
hydrogen
dwarf