Space Physics

The Earth:

Our home planet is the third planet from the Sun, and the only place
we know of so far that’s inhabited by living things.

While Earth is only the fifth largest planet in the solar system, it is the
only world in our solar system with liquid water on the surface. Just
slightly larger than nearby Venus, Earth is the biggest of the four
planets closest to the Sun, all of which are made of rock and metal.

1.Earth's orbital speed averages 29.78 km/s (107,208 km/h; 66,616

mph), which is fast enough to cover the planet's diameter in 7 minutes
2.The Earth's orbit takes about 365 days, this is also called a year. This
means that in 365 days the Earth has gone around the Sun.

3.The seasonal changes on Earth are because of the 23.44° axial tilt of
its rotation and slightly elliptical path around the Sun.
4.The earth rotates once every 23 hours, 56 minutes and 4.09053
seconds
(24 hrs) called the sidereal period, and its circumference is roughly
40,075 km.

5.The Moon takes about one month to orbit Earth (27.3 days to complete
a revolution). As the Moon completes each 27.3-day orbit around Earth,
both Earth and the Moon are moving around the Sun.

6.It takes sunlight an average of 8 minutes and 20 seconds to travel

from the Sun to the Earth. Sunlight travels at the speed of light.
Orbital Speed:
The orbital speed of the body which is generally a planet or a natural
satellite is the speed at which it orbits around the center of the
system. This system is usually around a massive body. The orbital
speed of the earth around the sun is 108,000 km per hour.
Average Orbital Speed Equation:
V= 2πr / T
r=it is the average radius of the orbit
T= orbital speed
The Sun

 The SUN as a Star

 Our Sun is a 4.5 billion-year-old star – a hot glowing ball of
hydrogen and helium at the center of our solar system.

 The Sun is the largest object in our solar system. The Sun’s
volume would need 1.3 million Earths to fill it. Its gravity holds
the solar system together, keeping everything from the biggest
planets to the smallest bits of debris in orbit around it. The
hottest part of the Sun is its core, where temperatures top
 27 F (15 million degrees Celsius). The Sun’s activity, from its
powerful eruptions to the steady stream of charged particles it
sends out, influences the nature of space throughout the solar
system.

Nuclear Fusion
Nuclear Fusion reactions power the Sun and other stars. In a
fusion reaction, two light nuclei merge to form a single heavier
nucleus. The process releases energy because the total mass of
the resulting single nucleus is less than the mass of the two
original nuclei.
The Sun is a main-sequence star, generates its energy by nuclear fusion
of hydrogen nuclei into helium. in the fusion of two hydrogen nuclei to
form helium, 0.645% of the mass is carried away in the form of kinetic
energy of an alpha particle or other forms of energy, such as
electromagnetic radiation.
Mostly Infrared, visible and ultraviolet regions of the
electromagnetic spectrum
1.Gravity is the force that pulls us to the surface of the Earth, keeps the planets in
orbit around the Sun and causes the formation of planets, stars and galaxies.
2.The strength of the Sun’s gravitational field decreases and that the orbital speeds
of the planets decrease as the distance from the Sun increases

The Solar System

 The Solar System consists of:
1. The Sun
2. Eight planets
3. Natural and artificial satellites
4. Dwarf planets
5. Asteroids and comets

The Sun & the Planets

 The Sun lies at the centre of the Solar System

o The Sun is a star that makes up over 99% of the mass of the solar
system

 There are eight planets and an unknown number of dwarf

planets which orbit the Sun
o The gravitational field around planets is strong enough to have
pulled in all nearby objects with the exception of natural satellites
o The gravitational field around a dwarf planet is not strong
enough to have pulled in nearby objects
  The 8 planets in our Solar System in ascending order of the distance from
the Sun are:
o Mercury
o Venus
o Earth
o Mars
o Jupiter
o Saturn
o Uranus
o Neptune

Satellites

 There are two types of satellite:

o Natural
o Artificial

 Some planets have moons which orbit them

o Moons are an example of natural satellites

 Artificial satellites are man-made and can orbit any object in space
o The International Space Station (ISS) orbits the Earth and is an
example of an artificial satellite

Asteroids & Comets

 Asteroids and comets also orbit the sun

 An asteroid is a small rocky object which orbits the Sun
o The asteroid belt lies between Mars and Jupiter

 Comets are made of dust and ice and orbit the Sun in a different orbit
to those of planets
o The ice melts when the comet approaches the Sun and forms the
comet’s tail
Accretion Model of the Solar System

 There are 4 rocky and small planets: Mercury, Venus, Earth and Mars
o These are the nearest to the Sun
 There are 4 gaseous and large planets: Jupiter, Saturn, Uranus and
Neptune
o There are the furthest from the sun

 The Sun was thought to have formed when gravitational attraction

of pulled together clouds of hydrogen dust and gas (called nebulae)
 As the Sun grew in size it became hotter
 Where the inner planets were forming near the Sun, the temperature was
too high for molecules such as Hydrogen, Helium, water and Methane to
exist in a solid state
o Therefore, the inner planets are made of materials with high
melting temperatures such as metals (e.g. iron)
o Only 1% of the original nebula is composed of heavy elements, so
the inner, rocky planets could not grow much and stayed as a small
size, solid and rocky
 The cooler regions were further away from the Sun, and temperature was
low enough for the light molecules to exist in a solid state
o The outer planets therefore could grow to a large size up and
include even the lightest element, Hydrogen

 Seven Main Stages of a Star

 Stars come in a variety of masses and the mass determines how radiantly the star will
shine and how it dies. Massive stars transform into supernovae, neutron stars and black
holes while average stars like the sun, end life as a white dwarf surrounded by a
disappearing planetary nebula. All stars, irrespective of their size, follow the same 7
stage cycle, they start as a gas cloud and end as a star remnant.




 1. Giant Gas Cloud

 A star originates from a large cloud of gas. The temperature in the cloud is low
enough for the synthesis of molecules. The Orion cloud complex in the Orion system
is an example of a star in this stage of life.
 2. Protostar
 When the gas particles in the molecular cloud run into each other, heat energy is
produced. This results in the formation of a warm clump of molecules referred to as
the Protostar. The creation of Protostars can be seen through infrared vision as the
Protostars are warmer than other materials in the molecular cloud. Several Protostars
can be formed in one cloud, depending on the size of the molecular cloud.
 3. T-Tauri Phase
 A T-Tauri star begins when materials stop falling into the Protostar and release
tremendous amounts of energy. The mean temperature of the Tauri star isn’t enough
to support nuclear fusion at its core. The T-Tauri star lasts for about 100 million
years, following which it enters the most extended phase of development – the Main
sequence phase.
 4. Main Sequence
 The main sequence phase is the stage in development where the core temperature
reaches the point for the fusion to commence. In this process, the protons of hydrogen
are converted into atoms of helium. This reaction is exothermic; it gives off more heat
than it requires and so the core of a main-sequence star releases a tremendous amount
of energy.
 5. Red Giant
 A star converts hydrogen atoms into helium over its course of life at its core.
Eventually, the hydrogen fuel runs out, and the internal reaction stops. Without the
reactions occurring at the core, a star contracts inward through gravity causing it to
expand. As it expands, the star first becomes a subgiant star and then a red giant. Red
 giants have cooler surfaces than the main-sequence star, and because of this, they
appear red than yellow.
 6. The Fusion of Heavier Elements
 Helium molecules fuse at the core, as the star expands. The energy of this reaction
prevents the core from collapsing. The core shrinks and begins fusing carbon, once
the helium fusion ends. This process repeats until iron appears at the core. The iron
fusion reaction absorbs energy, which causes the core to collapse. This implosion
transforms massive stars into a supernova while smaller stars like the sun contract into
white dwarfs.

 7. Supernovae and Planetary Nebulae

 Most of the star material is blasted away into space, but the core implodes into a neutron
star or a singularity known as the black hole. Less massive stars don’t explode, their
cores contract instead into a tiny, hot star known as the white dwarf while the outer
material drifts away. Stars tinier than the sun, don’t have enough mass to burn with
anything but a red glow during their main sequence. These red dwarves are difficult to
spot. But, these may be the most common stars that can burn for trillions of years.
 The above were the seven main stages of the life cycle of a star. Whether big or small,
young or old, stars are one of the most beautiful and lyrical objects in all of creation. Next
time you look up at the stars, remember, this is how they were created and how they will
die.


Life Cycles of different sizes of stars :

The Universe:
Milky Way Galaxy:

Our Milky Way galaxy is one of billions in the universe.

The Milky Way is approximately 100,000 light-years across. We do not

know its exact age, but we assume it came into being in the very early
universe along with most other galaxies: within perhaps a billion years
after the Big Bang.

Although most stars in the Galaxy exist either as single stars like
the Sun or as double stars, there are many conspicuous groups
and clusters of stars that contain tens to thousands of members.
These objects can be subdivided into three types: globular
clusters, open clusters, and stellar associations. They differ
primarily in age and in the number of member stars.

Just as Earth orbits the sun, the solar system orbits the center of the
Milky Way.

our solar system takes approximately 250 million years to complete a

single revolution

Astronomical distances are measured in light years.

Unit of astronomical distance= Light Year

Light Year: The distance that light travels in one year

Light year = 9.46 trillion km

MILKY WAY QUICK FACTS:

– Galaxy type: Barred spiral
– Age: 13.6 billion years (and counting)
– Size: 100,000 light-years across
– Number of stars: about 200 billion
– Rotation time: 250 million years

Red Shift:
There are a few theories that explore how our universe
came into existence. These theories are based on
observations that astronomers have made and on looking
at concepts such as red

-shift and dark energy. As part of the red-shift topic, we'll

also explore and explain the big bang theory.

 Red-shift is the phenomenon of light we observe from

distant galaxies being 'redder' when it reaches Earth
than when it was originally emitted by a galaxy. The
light's wavelength is shifted towards the red end of
the visible spectrum. One source of red-shift is the
expansion of the universe. The expansion of space
causes galaxies that are further away from us to
recede from us faster. The light waves emitted by
further and relatively faster-moving galaxies are red-
shifted more than closer slower galaxies. The redder-
more shifted the light from a galaxy is, the faster the
galaxy is moving away from us.
 The fact that we can observe red-shift is evidence
supporting the big bang theory. The big bang theory
suggests that the universe began as a very small
region that was extremely hot and densely packed.
This theory is further backed up by the fact that the
universe seems to be expanding, and we have
observed this expansion thanks to red-shift.
 There is still more about the universe that we do not
know. Two such examples are dark energy and dark
matter.

The Doppler red-shift of light observed from distant stars and galaxies gives
evidence that the universe is expanding (moving away from a central point).
This allows for Big Bang Theory, because after a “bang” occurs all of the matter
moves away from the point of origin.