1) Stars originate from nebulae of dust and gas. They spend most of their life fusing hydrogen into helium through nuclear fusion in their cores as main sequence stars. 2) When stars have exhausted their hydrogen, their cores collapse and outer layers expand, forming red giants. More massive stars explode as supernovae, leaving behind neutron stars or black holes. 3) The sun is classified as a yellow dwarf star. Its atmosphere consists of the photosphere, chromosphere, and corona. Nuclear fusion in its core provides its energy.

1. Chapter 24

2. The Big Bang
Most acceptable theory
because of its accuracy and
comprehensiveness in
terms of the evidences and
presented facts and
explanations.
Georges Lemaître, first
proposed the theory in
primeval atom, underlies
the basic tenets of Eintein’s
conceptions.
In 1949 radio broadcast, Fred
Hoyle is credited with
coining the term Big Bang.

3. The star’s Life Cycle
All stars originate from clouds of dusts and gases which are
commonly referred to as nebulae.
It is The process of Nuclear fusion that powers a star for most of
its life.
Star first attain the red giant phase, its core collapses into a dense
white dwarf that will soon expel planetary nebula in its outer
layers.
Larger stars can explode in a supernova as their cores collapse
forming an extremely dense neutron star or the commonly
known black hole.
Stars have varying luminosity based on the surface temperature.

4. The Sun
The atmosphere of the sun consists
of three parts .
These includes the photosphere,
chromosphere, and corona.
An extremely hot outermost layer
extending outward from the
chromosphere several million
miles, all of the major features of
the sun can be explained by the
nuclear reactions that make its
energy, the magnetic fields that
are caused by the movements of
the gas, the immense gravity.

5. Stars: The main Sequence
A hot ball gas made up of
entirely gas with hydrogen
fusing into helium, found in
its core.
After fusion, the star send out
energy in space, and there is
a slow contraction
happening to compensate for
the lost energy. This phase is
referred to as the main
sequence.

6. The Life and Death of a star
Most important factor in categorizing a star is its mass. The
star that weighs less than 3 solar masses spends most of its
life being into the main sequence, 90% of all stars are like
this.
If the star is above 3 solar masses, lesser time is required to
be spent in being a main sequence.

7. Energy Making during
normal life
Two protons join together to form
a deuterium nucleus,
commonly known as heavy
water where a positron and a
neutrino are released as by-
products.
The deuterium nucleus is
bombarded by another proton
that gives to a helium-3
nucleus.

8. Main Sequence Star Death
It is only after Ten billion years that a
main sequence star can be converted
approximately 10% of its hydrogen to
helium. Because of the great pressure
at the core of stars fusion occur- in a
fixed volume, increased pressure leads
to increased heat.
The helium core begins to contract,
outer layers expand and cool, glowing
redder. The Star is now called a red
giant. At this point, the Red giant is
made up of mostly carbon. The next
process would be to fuse the carbon
into iron. Great pressure is needed to
undertake this process.

9. Supergiant Star Death
Dies more quickly than a main sequence star because of the
greater mass that pulls the gravity inward in its core
creating tremendous pressure and results to a much faster
fusion rate.
Has pressure needed to fuse carbon into iron, this process
takes energy. When the energy is lost, the star no longer
possesses the balance between outward pressure and gravity
pushing which can result in its violent explosion known as
Supernova.

10. Dwarf Death
Sun is considered a main sequence star, but it is more
classified to as a yellow dwarf.
Red dwarfs are the only active dwarf and its mass ranges
from 1/3 up to 1/12 compared to the mass of the sun.

11. Neutron Stars, Pulsars,
and Black Holes
Black holes. Death of a giant
star results in the formation
of a black hole where the
mass is contained in a single
point, the point at the center
is referred to as Singularity
with a distance having a very
strong gravitational pull that
not even light can pass
through. The distance is
known as Event horizon.

12. Neutron stars and Pulsars
are very dense and spin very
fast, are only 10-15 km in
radius. Form from burnt-out
stars, they do not glow.
Some of it emit radio waves
that pulse on and off. These
stars are called Pulsars.

13. Galaxies
contains the stars, interstellar
media clouds of dust and gases
and remnants.
The Milky Way
most popular one because this is
where the solar syatem is found.
Edwin Hubble and Galileo Galilei
who first made observations in
Milky Way Galaxy in early 16th
and 19th centuries.
Milky Way is a barred spiral galaxy
which is 100,000-120,000 light-
years in diameter. Contains
approximately 200-400 billion
stars. It is estimated to be moving
at a speed of 552 to 630 km per
second. It is estimated to be 13.2
billion years old.

14. Quasars
the term quasar is a short
term from a quasi-stellar
radio source.
It is considered to be a very
high energy containing
distant active nucleus, it
makes it very luminous and
identified as a redshift
source of electromagnetic
energy, radio waves, and
visible light.
Are describe to be composed
of a compact region in the
center of a massive galaxy
surrounding its very massive
collapsed star.

15. Dark Matter
described to be a body that neither emits nor scatters the
light. Existence of dark matter was first postulated by Fritz
Zwicky in 1933 to account for evidence of “missing mass” in
the orbital velocities of galaxies in clusters.