1. The Sun: The Sun is a G-type main-sequence star, which means it is a relatively stable, middle-aged star. It makes up about 99.86% of the Solar System's total mass. The Sun is composed mainly of hydrogen (about 74% by mass) and helium (about 24% by mass), with traces of other elements. It is the source of light and energy for the entire Solar System through nuclear fusion in its core. The Sun has a diameter of about 1.4 million kilometers (870,000 miles) and a mass approximately 333,000 times that of Earth. It has a surface temperature of around 5,500 degrees Celsius (9,932 degrees Fahrenheit) and is about 4.6 billion years old. The Sun's gravitational influence keeps the planets of the solar system in orbit around it, and its solar wind extends far beyond the orbit of Pluto, defining the heliosphere 2. Inner Planets (Terrestrial Planets) Outer Planets (Gas Giants) Dwarf Planets and Trans-Neptunian Objects (TNOs) Galaxies Galaxies are vast systems that consist of stars, stellar remnants, interstellar gas, dust, and dark matter, all bound together by gravity. They are the fundamental building blocks of the universe, and their study provides crucial insights into the structure, composition, and evolution of the cosmos. Types of Galaxies 1. Elliptical Galaxies: Elliptical, ranging from nearly spherical (E0) to highly elongated (E7). Comprised mainly of older stars, with little interstellar gas and dust. Generally, lack ongoing star formation and are often found in galaxy clusters. 2. Spiral Galaxies: Contain a mix of old and young stars, along with significant amounts of gas and dust. Ongoing star formation in the spiral arms, and they often have a rotating disk structure. 3. Irregular Galaxies: Lack a distinct regular structure. Varied mix of young and old stars, as well as gas and dust. Often the result of gravitational interactions or mergers between galaxies. Milky Way Galaxy: - The Milky Way is the barred spiral galaxy that includes our solar system. - It has a central bar-shaped structure with spiral arms extending outward. - The Milky Way is part of the Local Group, a collection of galaxies that also includes the Andromeda Galaxy and many smaller galaxies. Galaxy Clusters: - Galaxies are not randomly distributed; they often form groups and clusters. - Galaxy clusters are massive structures containing hundreds or thousands of galaxies bound together by gravity. - The Virgo Cluster is one of the closest galaxy clusters to the Milky Way. Galaxy Formation and Evolution: - Galaxies form through the gravitational collapse of gas and dark matter. - Interactions between galaxies, such as mergers, can significantly impact their structure and star formation. - Galaxies evolve over time, with factors like star formation, supernova explosions, and feedback from supermassive black holes playing key roles.

1. Solar System and Galaxies
D r . H a f i z K o s a r

2. Solar System and Galaxies
The Solar System is a vast and complex celestial
arrangement that consists of a central star, the Sun, and
a variety of celestial bodies, including planets, moons,
asteroids, comets, and other objects. Here's a detailed
description of the main components of the Solar System:

3. 1. The Sun
The Sun is a G-type main-sequence star, which means it is a relatively stable, middle-aged star. It makes up about
99.86% of the Solar System's total mass. The Sun is composed mainly of hydrogen (about 74% by mass) and helium
(about 24% by mass), with traces of other elements. It is the source of light and energy for the entire Solar System
through nuclear fusion in its core. The Sun has a diameter of about 1.4 million kilometers (870,000 miles) and a mass
approximately 333,000 times that of Earth. It has a surface temperature of around 5,500 degrees Celsius (9,932
degrees Fahrenheit) and is about 4.6 billion years old. The Sun's gravitational influence keeps the planets of the solar
system in orbit around it, and its solar wind extends far beyond the orbit of Pluto, defining the heliosphere

4. 2. Inner Planets (Terrestrial Planets)
2.1 Mercury
2.2 Venus
2.3 Earth
2.4 Mars

5. Mercury is a fascinating planet with unique characteristics. Mercury is the closest planet to the Sun in our solar system. It
orbits the Sun at an average distance of about 36 million miles (58 million kilometers). Mercury is one of the smallest
planets in our solar system, with a diameter of about 4,880 kilometers (3,032 miles).
Despite its small size, it is quite dense. This lack of atmosphere means that the planet doesn't have the protective layer to
retain heat, causing extreme temperature variations between its day and night sides. Slow rotation, taking about 59 Earth
days to complete one rotation, temperatures on Mercury can be extremely hot during the day, reaching up to 430 degrees
Celsius (800 degrees Fahrenheit), while at night, temperatures can drop drastically to around -180 degrees Celsius (-290
degrees Fahrenheit). However, its orbital period around the Sun is only about 88 Earth days.
2.1 Mercury

6. Venus is the second planet from the Sun in our solar system. It has a nearly circular orbit, taking about 225 Earth days to
complete one orbit around the Sun. Venus has an extremely slow rotation on its axis, taking about 243 Earth days to
complete one rotation. Interestingly, Venus rotates in the opposite direction to most other planets, including Earth, leading
to a retrograde rotation. The atmospheric pressure on Venus is about 92 times that of Earth, making it inhospitable for
human exploration.
Venus has an extremely hot surface, with temperatures reaching up to 900 degrees Fahrenheit (475 degrees Celsius),
making it the hottest planet in our solar system. Venus does not have any natural satellites (moons).
2.2 Venus

7. Earth is the third planet our solar system, located between Venus and Mars. It has a relatively moderate climate and is the
only known celestial body to support life. Earth's surface is about 71% water and 29% land.
The land is divided into continents, with from the Sun in major ones being Asia, Africa, North America, South America,
Antarctica, Europe, and Australia. The Earth has five major oceans—Atlantic, Pacific, Indian, Southern (or Antarctic), and
Arctic.
The Pacific Ocean is the largest, covering more area than all the landmasses combined. Earth's atmosphere is primarily
composed of nitrogen (about 78%) and oxygen (about 21%), with trace amounts of other gases. It plays a crucial role in
supporting life by providing oxygen, trapping the sun's warmth, and protecting against harmful solar radiation.
Earth rotates on its axis, completing one full rotation approximately every 24 hours, causing day and night. It also orbits
the Sun, completing one revolution roughly every 365.25 days, resulting in a year. Earth has a natural satellite, the Moon,
which is about 1/6th the size of Earth. The gravitational interaction between Earth and the Moon causes tides. Scientists
estimate the age of the Earth to be around 4.54 billion years, determined through radiometric dating of rocks and minerals
2.3 Earth

8. Mars is the fourth planet from the Sun in our solar system. It is often referred to as the "Red Planet"
because of its reddish appearance, which is caused by iron oxide (rust) on its surface. Mars is a
terrestrial planet with a thin atmosphere, and it has surface features reminiscent of both the Earth
and the Moon. Mars has a diameter of about 6,779 kilometers (4,212 miles), which is roughly half the
size of Earth. It has a rocky surface with various types of terrain, including plains, valleys, and large
extinct volcanoes. Mars has a thin atmosphere composed mostly of carbon dioxide (95.3%), nitrogen
(2.7%), and argon (1.6%), with trace amounts of water vapor and other gases. The thin atmosphere
contributes to significant temperature variations on the planet. Mars has two small moons, Phobos
and Deimos. They are irregularly shaped and are thought to be captured asteroids. Mars has been a
focus of astrobiology research due to the possibility that it may have hosted microbial life in the past.
Scientists continue to study the planet's surface and subsurface to understand its history and assess
its potential for habitability.
2.4 Mars

9. 3. Asteroid Belt:
Located between the orbits of Mars and Jupiter. Contains numerous small celestial bodies, mostly asteroids, but also some
dwarf planets.

10. 4. Outer Planets (Gas Giants)
4.1 Jupiter
4.2 Saturn
4.3 Uranus
4.4 Neptune

11. Jupiter is the largest planet in our solar system. It has a diameter of about 86,881 miles (139,822 kilometers). It is more
than 11 times wider than Earth. Jupiter's mass is approximately 318 times that of Earth. Jupiter has a prominent
feature known as the Great Red Spot, a giant storm that has been raging for at least 350 years. Jupiter has at least 79
known moons. Jupiter orbits the Sun at an average distance of about 484 million miles (778 million kilometers). It takes
about 12 Earth years to complete one orbit.
4.1 Jupiter

12. Saturn is a gas giant, meaning it primarily consists of hydrogen and helium. It is the second-largest planet in our solar
system, with a diameter of about 74,900 miles (120,500 kilometers). Saturn is known for its rapid rotation, completing a full
rotation on its axis in just over 10 hours. Saturn orbits the Sun at an average distance of about 886 million miles (1.4 billion
kilometers) and takes approximately 29.5 Earth years to complete one orbit.
4.2 Saturn

13. Scientists call it an "ice giant" because it's mostly made of things like hydrogen, helium, and methane. The methane in its
air gives Uranus a bluish-green color. Uranus also has 13 faint rings around it, and scientists found them in 1977 using a
special technique with telescopes. The planet has 27 moons. One really interesting thing about Uranus is that it tilts a lot
– about 98 degrees! This means its poles are almost lying down as it goes around the Sun. This tilt causes Uranus to have
really different seasons. It's one of the coldest planets with temperatures dropping as low as -224 degrees Celsius (-371
degrees Fahrenheit).
4.3 Uranus

14. Neptune, discovered in 1846 by Johann Galle, is an ice giant with a gas giant atmosphere primarily composed of
hydrogen and helium. It has a dynamic atmosphere, high-speed winds, storm systems, a faint ring system, a strong
magnetic field, 14 known moons, and a cold average temperature of -353 degrees Fahrenheit.
4.4 Neptune

15. The Kuiper Belt is a vast region of the solar system, located beyond Neptune. It is primarily composed of small
icy bodies and the Kuiper Belt is thought to be home to hundreds of thousands of objects with diameters
exceeding 100 kilometers. Pluto, once considered the ninth planet, is one of the largest known Kuiper Belt
objects. The discovery of the Kuiper Belt was first theorized by astronomers in the mid-20th century.
5. Kuiper Belt

16. Pluto, Eris, Haumea, Makemake, and Ceres are examples of dwarf planets.
Many TNOs exist in the Kuiper Belt and the scattered disk.
6. Dwarf Planets and Trans-Neptunian Objects (TNOs)

17. 6. Dwarf Planets and Trans-Neptunian Objects (TNOs)

18. A theoretical region far beyond the Kuiper Belt. Contains icy bodies and comets.
7.Oort Cloud

19. Each planet, including the dwarf planets, can have one or more moons. Earth's moon is one example, and Jupiter's Ganymede is
the largest moon in the Solar System.
8.Moons (Natural Satellites)

20. Icy bodies that originate from the outer regions of the Solar System. When a comet approaches the Sun, it develops a bright
coma and a tail due to solar radiation.
9. Comets
The Solar System is a dynamic and fascinating system, with each component playing a crucial role in the overall structure and
function of our cosmic neighborhood.

21. Galaxies
Galaxies are vast systems that consist of stars, stellar remnants, interstellar gas, dust, and dark matter, all bound together by
gravity. They are the fundamental building blocks of the universe, and their study provides crucial insights into the structure,
composition, and evolution of the cosmos.

22. Types of Galaxies
1. Elliptical Galaxies
2. Spiral Galaxies
3. Irregular Galaxies

23. Contain a mix of old and young stars, along with significant amounts of gas and dust. Ongoing star formation in the spiral
arms, and they often have a rotating disk structure.
Lack a distinct regular structure. Varied mix of young and old stars, as well as gas and dust. Often the result of gravitational
interactions or mergers between galaxies.
Types of Galaxies...
1. Elliptical Galaxies:
Elliptical, ranging from nearly spherical (E0) to highly elongated (E7). Comprised mainly of older stars, with little
interstellar gas and dust. Generally, lack ongoing star formation and are often found in galaxy clusters.
2. Spiral Galaxies
3. Irregular Galaxies

24. Milky Way Galaxy:
The Milky Way is the barred spiral galaxy that includes our solar system.
- It has a central bar-shaped structure with spiral arms extending outward.
- The Milky Way is part of the Local Group, a collection of galaxies that also includes the Andromeda Galaxy and many
smaller galaxies.
Galaxy Clusters:
- Galaxies are not randomly distributed; they often form groups and clusters.
- Galaxy clusters are massive structures containing hundreds or thousands of galaxies bound together by gravity.
- The Virgo Cluster is one of the closest galaxy clusters to the Milky Way.
Active Galactic Nuclei (AGN):
Some galaxies have an active galactic nucleus, which is a highly energetic region at the galaxy's
center.
- AGN can emit large amounts of radiation across the electromagnetic spectrum.
- Theories suggest that supermassive black holes at the galactic center power AGN.
Galaxies...

25. Dark Matter:
- Observations of galaxy dynamics indicate the presence of dark matter.
- Dark matter is an elusive form of matter that does not emit, absorb, or reflect light, making it challenging to detect
directly.
- It contributes significantly to the mass of galaxies and the overall structure of the universe.
Galaxy Formation and Evolution:
- Galaxies form through the gravitational collapse of gas and dark matter.
- Interactions between galaxies, such as mergers, can significantly impact their structure and star formation.
- Galaxies evolve over time, with factors like star formation, supernova explosions, and feedback from supermassive black
holes playing key roles.
Galaxies...

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