A friend of mine is a teacher in CSS preperation academy in Sargodha. He is preparing notes for the General Science and shared some with me, he is just in the start and had prepared the first 3 or 4 topics. Can anyone of you please review the notes and share your view with me, so I can tell him how he is doing.

General Science &
Ability
Physical Sciences
(Constituents and Structure)
Universe:-
Universe: The totality of everything that exists all the matter and energy, stars, planets and contents of the intergalactic space.
Astronomy: The branch of science which investigates all the matter and energy in the Universe; its distribution, composition, physical states, movements and evolution. People who study Astronomy are called Astronomers.
Cosmology: The branch of science that deals with the scientific study of the origins and evolution of the Universe and the nature of Universe on its larger scale.
Astrology: The study of movements and relative-positions of celestial bodies interpreted as having an influence on human affairs and natural world is called Astrology.
Evolution of Cosmological Theories:
Humans have been wondering about the sky for many millennia. As scientific discoveries have been made, ideas about the origin of the Universe have changed and are still changing.
Geocentric Theory:
Ptolemy, an Alexandrian astronomer proposed a theory that the planets, sun and moon moved in small circles around much larger cricles in which the earth is at the center. The Ptolemic view helds that the earth is stationary and is at the center of the Universe. Ptolem is considered as the father of Geocentric Theory,
Heliocentric Theory: Polish astronomer Sir Nicolaus Copernicus believed that the earth revolved around the sun, upsetting the long-accepted view that the earth is stationary and is at the center of the Universe. Fearing his theory would be judge heretical by the Roman Catholic Church, he delayed its publication shortly before his death in 1543. Sir Nicolaus Copernicus is considered as the father of modern Astronomy.
Origins of the Universe:
In 1959, a group of scientists conducted a survey across America concerning their understandings of the physical sciences. One particular question was asked, what is your concept about the age of the Universe? More than 2/3 of scientists responded that the Universe had no origin. They believed that the Universe was eternal.
However, after 5 years in 1964, two radio astronomers Arno Penzios and Robert Wilson discovered a microwave signal buried in their data. They attempted to filter out the data signal assuming that it was a merely unwanted noise. However, they soon realized that they had unknowingly discovered the CMB (Cosmic Microwave Background). Effectively, the CMB is the afterglow of the Big-Bang, the event that set our Universe in motion. This discovery was the first evidence that the Universe had a beginning!
The Big-Bang:
Once it was understood that the Universe had a beginning, scientists begin to ask how it came into existence and what existed before it?
Most scientists now believe that answer to the first part of the question is that the Universe sprang into existence from a singularity (A term physicists used to describe
the regions of space that defies the law of physics). We know very little about singularities, but we believe that others probably exist in the cores of Blackhole.
The second part of the question what existed before the Big-Bang had bewildered many scientists. By definition, nothing existed prior to the beginning, but the fact creates more questions than answers. For instance if nothing existed prior to the Big-Bang, what caused the singularity to be created in the first place.
Once the singularity is created (However it is), it began to expand through a process called inflation. The Universe went from very small, very dense and very hot to the cool expanse that we see today. This theory is referred to as the Big-Bang, a term first coined by Sir Fred Hoyle in 1950.
Interestingly there wasn’t any sort of bang or explosion as the name suggests. But rather it was rapid expansion of space and time. It is like blowing up a balloon, as we blow air in, the exterior of the balloon expands outward.
Moments after the Big-Bang:
Scientists believe that the Universe was initially so hot and dense that even elementary particles like protons and neutrons could not exist. Instead, different types of matter called matter and anti-matter, collided together creating pure energy. But as the Universe began to cool, during the first few minutes,
protons and neutrons began to form. Then slowly over time, these protons, neutrons and electrons came together to form hydrogen and small amounts of helium. During the billions of years that followed stars, planets and galaxies formed to create the Universe as we see it today.
In 1927, George Lemaitre proposed the Big-Bang theory of the Universe.
Future of the Universe:
Astronomers recognizes four models of possible futures for the Universe.
Closed Model: According to the closed model theory, many billions of years from now, expansion will slow, stop and the Universe will contract back in upon itself.
Flat Model: In the flat model, the Universe will not collapse upon itself, but expansion will slow and the immense will approach a stable size.
Open Model: According to the open model, the Universe will continue expanding forever.
Cyclic Model: Cyclic model states that Universe will collapse, then there will be a Big-Bang again, it will expand first and will collapse again. This cycle will go on.
Galaxy:-
Galaxy: A massive aggregate of hundreds of millions of stars, all gravitationally interacting and orbiting about a common center. Astronomers estimates that there are about 125 billion galaxies in the Universe. Milky-Way and Andromeda are the examples of galaxies.
Types of Galaxies:
Spiral Galaxy: A spiral galaxy is shaped like a disk, usually with a bulge in the center and with arms that spiral outwards as the galaxy rotates. Spiral galaxies tend to contain more middle aged stars along with clouds of gas and dust.
Elliptical Galaxy: A type of galaxy that tends to contain older stars and very little gas and dust.
Irregular Galaxy: A type of galaxy that has an undefined shape and has lots of young stars, dust and gas.
Milky-Way:
Milky-Way is a large, disk-shaped galaxy that includes our solar system, In addition to the sun, Milky-Way contains about 200-400 billion other stars. Most of the star that we see in the sky are in the Milky-Way galaxy. The main plane of the milky was
galaxy looks like a faint band of white in the night sky. Main features of the Milky-Way galaxy are the following:
1. It is a spiral galaxy.
2. This spiral galaxy is formed about 14 billion years ago.
3. It is about 100,000 light years in diameter.
4. Sun takes roughly 250 million years to orbit around the Milky-Way.
5. Our solat system is about 30,000 light years away from the center of the Milky-Way galaxy.
6. The major arms of the Milky-Way galaxy are Persues Arm, Sagitarious Arm, Centaurus Arm and Cygnus Arm.
7. The region in the space occupied by Milkyway is called galactic plane.
8. Nearest galaxy to the Milky-Way is Andromeda.
9. Our Milky-Way is the part of cluster of 3 dozens of galaxies called Local Group.
10. Our solar system is in a minor arm called the orion arm.
Light Year:-
Light year is the distance light can travel in vacuum in one year’s time. A light-year is how astronomers measure distance in space. It’s defined by how far a beam of light travels in one year. This distance is equivalent to roughly 9,461,000,000,000 km or 5,878,000,000,000 miles. 9.4605284 × 1015 meters.
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Solar System:-
Solar System: Our solar system consists of the sun, planets, dwarf planets, moons, an asteroid belt, comets, meteors and other objects. The sun is the centre of our solar system and all other objects in the solar system orbits the sun. Our solar system is elliptical in shape, which means that it is shaped like an egg. Astronomers believe that our solar system is about 4.5 billion years old.
Sun:-
Sun: The sun is the biggest object in our solar system and contains more than 99% of the solar system mass. It is our closest star and is a yellow dwarf star, which means it’s a Interesting Information The main reason for using light years, however, is because the distances we deal with in space are immense. If we stick to miles or kilometers we quickly run into unwieldy numbers just measuring the distance to the nearest star. Traveling at that speed, you would encircle the globe of Earth almost eight times in one second.
medium star size. It is about 4.5 billion years old. The scientists predict that it will die after 4.5 billion years.
Structure of Sun:
The Core: The sun’s core has tremendously high temperature and pressure. The temperature is roughly 15 million centrigrade. At this temperature nucluer fusion occurs, turning hydrogen nuclei into helium nucleus plus a lot of energy is released.
The Photosphere: It is the lower atmosphere of the usn and the part that we see. This layer is about 300 miles thick. The temperature is about 55,00 centrigrade. It lies between the chromosphere and central core.
The Chromosphere: This reddish layer is the area of rising temperature. This is a layer outside the photosphere. The temperature ranges from 6000 to 50,000 centrigrade. It appears red because hydrogen atoms are in an excited state and emit radiation near the red part of the visible spectrum. The chromosphere is visible during solar eclipse when the moon blocks the photosphere.
The Corona: The corona is the outer layer of the sun’s atmosphere. It extends for millions of miles from surface of the sun and the temperature is tremendous, reaching one million centrigrade.
Solar Wind: The stream of charged particles known as the solar wind flow out from the sun. These particles are emitted from the sun as the sun rotates, the solar wind blows in a pin-wheel pattern thorugh the solar system it takes the solar wind about 5 days to reach earth. It has a velocity of 800km/sec. Solar winds are generated due to the presence of plasma.
Sunspots: Sunspots are cool, dark patches on the surface of the sun. they are caused by the disturbance in the sun’s magnetic field which makes them cooler than the surrounding area. The large sunspots can be wider than the earth.
Solarflares & Coronal Mass Ejection: Solarflares and coronal mass ejections are the explosions in the corona. Solarflares releases energy from the magnetic loops in the corona, heating the gases of the corona and sending particles and radiation out in the solar system. A coronal mass ejection occurs when an explosion in the corona pushes millions or billions of metric tonnes of material out in the space.
Features of Sun:
1. Diameter of sun is 1,391,684 km.
2. Mass of sun is 1.989E30 kg.
3. Density of sun is 1.41 g/cm^3.
4. Sun is composed of 74% H2, 24% he and 2% of heavy metals.
5. Age of sun is 4.5 billion years.
6. Temperature at the core of sun is 15 million C.
7. Temperature at the surface of sun is 55,00 C.
8. Mean distance from sun is about 150 million km.
9. It has a very large and active magnetic field.
10. Sun rotates around its axis in 25-35 days ( 25 days at equators and 35 days at poles).
11. Sun is moving around the center of galaxy at velocity of 220 km/s.
12. It revolves around milky-way galaxy in about 250 million years. The time it takes to complete one revolution is called cosmic year.
13. Sun rays reach earth surface in 8 minutes and 20 seconds.

Good going. Carry on.

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