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Regulatory Body1. The Earth in the Solar System (Universe and Earth)
What are Celestial Bodies
Celestial bodies are objects in space that astronomers study, including planets, stars, moons, asteroids, comets, nebulae, and galaxies. They are also known as astronomical objects, celestial objects, or heavenly bodies.
What are Stars ?
Stars are giant balls of hot gases that can produce their own light. Stars give out energy by converting Hydrogen gas into Helium in their cores. Stars are gigantic in size and have an immense gravitational attraction
New Moon
A new moon is when the moon is not visible from Earth, this happens when Moon is directly between us and the sun, the part facing us does not receive sunlight, and we cannot see the moon.
Full moon
A Full moon is when the entire face of the moon is illuminated by the sun, this happens when moon is halfway through the moon's phase cycle as the Earth is directly between the sun and the moon
Phases of the Moon
Different Moon Phases. The moon phase cycle begins with a new moon. The moon goes through eight phases in a cycle that repeats every 29.5 days.
What are Constellations ?
A constellation is an imaginary outline or pattern formed by a group of stars on the celestial sphere, typically representing an animal, mythological person or creature, god, or inanimate object. Let us look at some other Constellations not mentioned in NCERT !
Orion (The Hunter): This constellation is also known as hunter. The Indian name is Mriga. It consists of seven or eight bright stars. The orientation of stars in Orion is similar to the figure of hunter. This constellation is visible in the sky during the winter season in the late evening. One of the brightest stars in the sky at night is the Sinus, which is very close to the Orion constellation.
What is Ursa Major and Saptarishi
Ursa Major also known as Great Bear or Saptarishi consists of seven bright stars, which appear in the shape of a bear. It is visible during the summer season in the early part of the night and can be seen clearly during the month of April in the northern part of the sky. It also helps us to locate the position of the pole star in the sky. At night it appears to move from east to west as the pole star remains fixed in its position.
What are Planets ?
A planet is a celestial body that orbits a star. The word planet comes from the Greek word "Planetai", which means "wanderers".
According to the International Astronomical Union (IAU), a celestial body is considered a planet if it meets the following three criteria:
1.It is in orbit around the Sun.
2.It has sufficient mass to assume hydrostatic equilibrium (a nearly round shape).
3.It has “cleared the neighborhood” around its orbit.
Moon a Satellite
A satellite is an object that orbits a larger object, and the moon is a natural satellite of the Earth.
Pointer Stars
Locate the quadrilateral at the end of the constellation and select the two stars on the far side of the quadrilateral. Imagine a line connecting the two stars . Extend the line towards the top of the ladle or in the north direction. The faint star that meets the line is the Pole Star
North Star / Pole Star
Venus
Venus is similar in structure and size to Earth, and is sometimes called Earth's evil twin. Its thick atmosphere traps heat in a runaway greenhouse effect, making it the hottest planet in our solar system with surface temperatures hot enough to melt lead. Its the 2nd Planet from the Sun
Notable Features
⇒ Venus appears bright white from space because of its thick clouds that reflect sunlight. However, if you were standing on Venus, everything would look orange because of the thick atmosphere that filters sunlight.
⇒ Venus is the second brightest natural object in the night sky after the Moon. Venus is the first celestial body to become visible in the sky at evening and is the last one to disappear from the sky at sunrise. Venus is called the Evening Star when it appears in the western sky after sunset. It's called the Morning Star when it appears in the eastern sky before sunrise
⇒ The surface of Venus is covered in volcanic plains, valleys, mountains, and impact craters.
⇒ Venus's atmosphere is 96% carbon dioxide and 3% nitrogen. It has 90 times the atmospheric pressure of Earth
Mercury
Mercury, the smallest planet in our solar system, it looks similar to Earth's moon, with a surface covered in impact craters.
Notable Features:
⇒ Mercury's surface is mostly greyish-brown, with bright streaks called "crater rays". These rays are formed when asteroids or comets hit the surface, throwing crushed rock that falls back to the surface.
⇒ Mercury has gigantic cliffs, or scarps, that climb thousands of feet above the terrain. These features are the result of the planet's crust shrinking after it cooled
⇒ Atmosphere: Mercury has almost no atmosphere
Earth
We already Know about our Planet don't We?
Mars
Mars, also known as the Red Planet, appears as a bright red dot in the night sky. Its the Fourth Planet from the Sun
Notable Features
⇒ Color: Mars appears red because of the iron oxide (rust) in its soil, dust, and regolith.
⇒ The surface of Mars is rocky and covered in craters, volcanoes, dry lake beds, and canyons.
⇒ Dust storms: Mars has some of the largest dust storms in the solar system, which can cover the entire planet.
⇒ Atmosphere: Mars has a thin atmosphere that's mostly carbon dioxide and contains very little oxygen.
Jupitar
Jupitar the biggest planet in our solar system but being a gas giant lacks a surface . It is the fifth planet from the Sun. Jupiter's thick clouds create the appearance of stripes. The planet's fast rotation creates strong jet streams that separate the clouds into dark belts and bright zones.
Notable Features
Saturn
Saturn is a giant gas planet with a yellowish-brown color and a ring system. Saturn is yellowish-brown due to its atmosphere, which is made up of hydrogen, helium, ammonia, phosphine, water vapor, and hydrocarbons
Notable Features
⇒ Rings: Saturn's rings are made of chunks of ice and rock, and are made up of many tiny ringlets
⇒ Shadow: The shadow of Saturn on its rings adds to the 3D appearance of the planet
⇒ Spokes: The rings can have spokes that are made of tiny ice particles that are lifted by an electrostatic charge
Uranus
Uranus looks blue-green with faint rings. Its blue-green color comes from methane gas in its atmosphere. It's the seventh planet from the Sun and the third largest planet in our solar system.
Notable Features
⇒ Rings: Uranus has 13 known rings, with the inner rings being narrow and dark and the outer rings being brightly colored and easier to see.
⇒ Atmosphere: Uranus's atmosphere is mostly hydrogen and helium, but it also has methane. The atmosphere looks quite calm, with very few clouds.
⇒ Rotation: Uranus rotates on its side, at a nearly 90-degree angle from the plane of its orbit. It also rotates in the opposite direction as most other planets.
Neptune
Neptune is an ice giant planet that appears blue and has a smooth surface because it's made of gas. Neptune is the eighth and most distant major planet from the Sun
Notable Features
⇒ Rings: Neptune has six rings, but they're very hard to see. A 2022 image taken by the Webb's Near-Infrared Camera (NIRCam) brought the planet's rings into focus for the first time in over 30 years.
⇒ Atmosphere: Neptune's atmosphere is made of hydrogen, helium, and methane.
⇒ Other features: Neptune has the Great Dark Spot, Scooter, and the Small Dark Spot
Asteroid Belt
The asteroid belt is a torus-shaped region in our solar system that contains millions of asteroids orbiting the sun between the orbits of Mars and Jupiter.
Comparision of Inner Planets
| Parameters | Definition as a Whole | Mercury | Venus | Earth | Mars |
| Surface Density (gm/cm3) | Inner or Terrestrial planets: Smaller and rockier. Have relatively high densities. | 5.4 | 5.2 | 5.5 (Highest) | 3.9 |
| Mass (Kg) | How massive a planet is has more to do with its composition and density.The four outer planets, called the gas giants, collectively make up 99% of the mass known to orbit the Sun. | 3.3×1023 kg | 4.8685 x 10^24 kg | 5.9736 x 10^24 kg | 6.4185 x 10^23 kg |
| Size (Radius) | A planet's size is not necessarily proportional to its mass. The size of a planet is determined by its composition and rotation speed. while Jupiter is 318 times as massive as Earth, its composition and density mean that it is only 11.21 times Earth's size. | 2,440 km | 6,052 | 6,371 | 3,390 km |
| Surface Gravity | Gravitational force a planet exerts upon an object at the planet's surface is proportional to its mass and to the inverse of the planet's radius squared. | 3.7 M/sec^2 | 8.9 M/sec ^2 | 9.81 m/s2 | 3.7 M/sec ^2 |
| Atmosphere | Generally inner planets have thin or very Little atmosphere with the exception of Venus | Thinnest | Thickest | Thicker to Mars | Thiiner to Earth |
| Temperature | Inner planets are hotter because of their closeness to the sun | +427 | +480(Highest) | +22 | -23 |
| Moons and Rings | Inner plaets have no or few moons.They do not have Rings | 0 | 0 | 1 | 2 |
| Brightness | Inner planets are Brighter | ||||
| Distance | Distance from Sun in (AU) | 0.4 | 0.7 | 1 | 1.5 |
| Type of Rotation and Period | Inner Planets Slower and Rotate Anti Clock Wise except Venus | 58 days | 243 days | 23:56 hrs | 1.025 days |
| Period of Revolution | Inner planets have Smaller orbits and move faster around the Sun | 87 days | 224 days | 365 days | 687 days (Highest) |
Comparision for Outer Planets
| Parameters | Definition as a Whole | Jupitar | Saturn | Uranus | Neptune |
| Surface Density (gm/cm3) | Outer planets: Larger and and are made up of gas. composed of low-boiling-point materials | 1.3 | 0.7 | 1.3 | 1.6 |
| Mass (Kg) | How massive a planet is has more to do with its composition and density.The four outer planets, called the gas giants, collectively make up 99% of the mass known to orbit the Sun. | 1.899 x 10^27 kg (Highest) | 5.685 x 10^26 kg | 8.682 x 10^25 kg | 1.024 x 10^26 kg |
| Size (Radius) | A planet's size is not necessarily proportional to its mass. The size of a planet is determined by its composition and rotation speed. while Jupiter is 318 times as massive as Earth, its composition and density mean that it is only 11.21 times Earth's size. | 69,911 km | 58,232 km | 25,362 km | 24,622 km |
| Surface Gravity | Gravitational force a planet exerts upon an object at the planet's surface is proportional to its mass and to the inverse of the planet's radius squared. | 24.9 M/sec^2 (Highest) | 10.4 M/sec ^2 | 8.8 m/s2 | 11.1 M/sec ^2 |
| Atmosphere | Generally outer planets have a very thick atmosphere | Thicker to Saturn | Thicker to Uranus | Thicker to Neptune | Less Thicker to Uranus |
| Temperature | Outer planets are colder because of they are further away from Sun | -150 | -180 | -214 | -220 |
| Moons and Rings | Outer Planets have Numerous moons . Their moons are, however, solid. They have extensive Ring Systems | 79 | 82 | 27 | 14 |
| Brightness | Outer planets are Less bright as sun’s light barely reach them | ||||
| Distance | Distance from Sun in (AU) | 5.2 | 9.6 | 19.2 | 30 |
| Type of Rotation and Period | Outer Planets Rotate Faster Anti Clock Wise except Uranus | 9.9 hrs (Fastest) | 10.7 hrs | 17 hrs | 16 hrs |
| Period of Revolution | Outer planets have Longer orbits and thus tae more time to move around the Sun | 11.9 years | 29 years | 84 years | 164 years |
Orbits
An orbit in the solar system is the curved/elliptical path that an object takes around another object due to gravity. The object in orbit is called a satellite, which can be natural or human-made. Orbits in the solar system are not visible
Here are some examples of orbits in our solar system:
⇒ Earth's orbit: Earth orbits the sun, taking about one year to complete a full orbit.
⇒ Moon's orbit: The moon orbits Earth, taking about one month to complete a full orbit.
Sun's Location, Composition and Pulling Force ?
While the Sun is Located in the Centre of the Solar System but when we talk about its location in the Milky way Galaxy The Sun (and, of course, the rest of our solar system) is located near the Orion arm, between two major arms (Perseus and Sagittarius)
The sun Composition by mass :
⇒ Hydrogen: About 71% of the sun's mass
⇒ Helium: About 27% of the sun's mass
⇒ Other elements: About 2% of the sun's mass
The Sun accounts for 99.85% of all the matter of the solar system
Suns Pulling Force
The sun's gravitational force is 274 meters per second squared (m/s²), which is 28 times stronger than Earth's gravity. The sun's gravitational field extends out to a distance of up to two light years.
Sun's Distance from Earth ?
The distance from Earth to the Sun is 93 million miles (149 million kilometers). In terms of light-years, it can be quantified to 1.58 × 10-5 light-years. This is actually the mean distance of the centre of the Sun to the centre of the earth.
⭕Additional iNFO: Light Year?⭕
A light year is a unit of distance. It is the distance light travels in one Earth year. A light-year is used to represent astronomical distances. One Light Year = 9.4607×1012 kilometres
Pluto Why not a Full-Sized Planet? What are Dwarf Planets?
So, the three criteria of the IAU for a full-sized planet are:
1. It is in orbit around the Sun.
2. It has sufficient mass to assume hydrostatic equilibrium (a nearly round shape).
3. It has “cleared the neighborhood” around its orbit.
⭕Additional iNFO: Dwarf Planets, Kuiper Belt⭕
Pluto meets only two of these criteria, losing out on the third. It has not cleared the neighborhood around its orbit, Pluto is considered a dwarf planet It orbits in a disc-like zone beyond the orbit of Neptune called the Kuiper belt, a distant region populated with frozen bodies left over from the solar system's formation.
⇒ So Pluto is a Dwarf Planet and by definition Dwarf planets are celestial bodies that orbit the sun and have enough mass to be nearly round, but have not cleared their orbit of debris.
The first five recognised dwarf planets are Ceres, Pluto, Eris, Makemake and Haumea.
Earth Shape
Earth is a little flattened at the poles. We call this shape Geoid. It has an equatorial circumference of 40075 km, while that of Polar is 40008 km, thus a difference of 67 kilometers.
⭕Additional iNFO: Who gave the term Geoid?⭕
The term "geoid," which refers to the shape of the Earth, was coined by Sir George Biddell Airy, an English mathematician and astronomer. Airy served as the Astronomer Royal of England from 1835 to 1881
What is Sol ?
In Roman mythology, Sol is the sun god, or the personification of the sun. The family of the sun is, therefore, called the solar system.
⇒ In geography, a sol is a solar day on Mars, which is a unit of timekeeping on the planet.
Origin of Word Geography
The word geography comes from the Greek Origins,
Geo (Earth) and Graphia (Writing). Writing about Earth. Other Words and their Origins from Greek are also given.
Geo (Earth) + Logy (the study of) = Study of the Earth
Geo (Earth) + Metry (Process of measuring) = Measurement of the Earth
Geo (Earth) + Oid (Something resembling a (specified) object) = Resembling the Shape of Earth
⭕Additional iNFO: Who Coined the Term Geography⭕
The Greek scholar Eratosthenes (276–194 BC) was the first person to use the word geography. He is known as the "Father of Geography".
Who are Astronomers ?
Astronomers are scientists who study the universe and the objects in it, such as planets, stars, galaxies, and black holes. They use ground-based and space-based equipment to make observations and conduct experiments.
⭕Additional iNFO: Some Famous Indian Astronomers and their Contribution to Geography⭕
⇒ Aryabhata (476–550 CE): A mathematician and astronomer from ancient India who concluded theories of earth rotation on its axis. He also measured the distance between the earth and the moon to the nearest millimetre. He also explained that planets and the moon shine due to reflected sunlight. He also provided a theoretical explanation for solar and lunar eclipses. Famous books - Aryabhattiya. The final two parts of Aryabhattiya, also known as Khagol-shastra, are about astronomy.
⇒ Brahmagupta (598–668 CE): A mathematician and astronomer who proposed a mathematical model for planetary motion and contributed to the understanding of eclipses. Calculating the Earth's circumference and Also First to describing gravity as an attractive force. Famous books- Brahmasphutasiddhanta - which covered many topics related to astronomy and mathematics
⇒ Varahamihira (505-587 CE) He wrote about weather patterns, cloud formation, rainfall, and how to predict the weather using astronomical observations. Famous books - Pancha Siddhantika: An account of the five systems of Astronomy. Brahjataka: An astrological work
⇒ Bhaskara II (1114–1185 CE): His work documented his observations of planetary positions, eclipses, and cosmography. He also defined many astronomical quantities, such as the length of a sidereal year. Famous books -Goladhyaya, Siddhānta Shiromani are an astronomical treatise
What Conditions are Required for a Habitable Planet ?
Even if we assume any habitable planet must be Earth-like (and it may not be), chances are we're not alone. Astrobiologists estimate that the Milky Way has 500 habitable planets, which fit the following criteria:
⇒ They're a comfortable distance away from a star similar to our sun. That is, they're far enough away to be out of the heavy heat and radiation zone, but not so far that they're extremely cold. This just-right distance is called the "habitable zone or the Goldilocks zone".
⇒ They're made of rock. Jupiter, Saturn, and Uranus in our solar system are made of gases, so we don't expect life to be able to survive there.
⇒ They're big enough to have a molten core. Earth's core gives us a source of geothermal energy, it allows cycling of raw materials, and it sets up a magnetic field around the planet that protects us from radiation. Mars probably had a hot liquid core at one time, but because it's a smaller planet its heat dissipated more quickly.
⇒ A protective atmosphere. The atmosphere holds carbon dioxide and other gases that keep the planet warm and protect its surface from radiation.
Earth's Percentage of Water and Land
About 71% of Earth's surface is water, while the remaining 29% is land. Also most of the water on Earth is salt water in the oceans. Only about 3% of the water on the surface is fresh water
Moon's Size and Distance from Earth
⇒ Size: The moon is about one-fourth the size of Earth and has a diameter of about 3,474 kilometers.
⇒ Distance from Earth: The average distance between Earth and the Moon is 384,400 kilometers (238,855 miles). This is about 30 times the diameter of Earth.
⭕Additional iNFO: Other Facts about Moon ⭕
⇒ Gravity: The moon's gravity is about one-sixth of Earth's gravity.
⇒ Surface: The moon's surface is covered with craters, mountains, and loose and hard dirt.
⇒ Atmosphere: The moon has a very thin atmosphere called an exosphere. It contains a small amount of atoms and molecules, including helium, argon, neon, ammonia, methane, and carbon dioxide.
⇒ Tides: The moon's gravitational pull causes tides on Earth, which impact the Earth's coastlines, ecosystems, and rotation.
⇒ Phases: The moon's phases depend on its position. The phases are new moon, waxing crescent, first quarter, waxing gibbous, full moon, waning gibbous, last quarter, and waning crescent.
⇒ Formation: The moon probably formed when a giant rock collided with Earth.
⇒ Movement: The moon is slowly moving away from Earth.
⇒ Quakes: The moon experiences quakes called "moonquakes".
Moon's Synchronous Rotation
Moon's rotation period (27.3 days) is the same as its revolution period (27.3 days) around Earth. This is called synchronous rotation. This Happens because of Tidal Locking.
⭕Additional iNFO: Tidal Locking⭕
⇒ Gravitational Interaction: The Earth exerts a gravitational pull on the Moon, which creates tidal forces. These forces have caused the Moon's rotation to slow down over millions of years. (Note: On Earth, the Moon's gravitational pull causes the oceans to bulge out on both the side closest to the Moon and the side farthest from the Moon)
⇒ Energy Dissipation: As the Moon rotated, the gravitational pull from the Earth created bulges on the Moon. The rotation caused these bulges to shift, leading to a torque that gradually slowed the Moon's rotation until it synchronized with its orbital period around the Earth.
Implications
⇒ Same Side Visibility: Because of this synchronous rotation, the same lunar surface (the near side) is always facing Earth, while the opposite side (the far side) remains hidden from view.
⇒ Long-term Stability: Tidal locking is a stable configuration for celestial bodies, and it can occur for moons around planets or planets around stars.
Craters
Circular pits or basins created by the impact of interplanetary debris. The lines extending from craters are called "ejecta rays" and are made from material blasted out of the crater.
Mountains
Some of the Moon's mountains are steep and high, and some are as tall as Earth's mountains.
Maria
The dark areas of the Moon that are visible from Earth. These are large, flat plains of solidified lava
Highlands
The highlands are light-colored, elevated regions on the moon's surface and make up about 83% of the Moon's surface. The lunar highlands are made of low-density rock that solidified on the Moon
Calculating Time Taken for Light to reach Earth
⇒ We know the Distance between Earth and Sun = 150 million kilometers
⇒ Speed of Light = 300000 km per second
⇒ 150000000 /300000 = 500s ≈ 8 Minutes
First Persons to Reach Moon
⇒ Neil Armstrong The first person to walk on the moon, Armstrong was also a naval aviator, test pilot, and university professor. He famously said, "That's one small step for [a] man, one giant leap for mankind".
⇒ Buzz Aldrin: The second person to walk on the moon, Aldrin was also an engineer and fighter pilot.
⇒ No Indian has ever landed on the moon. Note: Rakesh Sharma was the first Indian to travel to space
Satellite
⇒ Natural satellites: A natural satellite is a celestial body that orbits a planet, Also known as moons Examples include the moon orbiting Earth. Almost every planet has at least one natural satellite. Note Mercury and Venus are the only planets in our solar system that do not have moons
⇒ Man-made satellites: A man-made satellite is a machine that is launched into space to orbit a planet or other body. Also known as artificial satellites. Examples include the Hubble Space Telescope and the International Space Station Built by engineers and launched into space. Used for observation, communication, navigation, weather reporting, and research. The first artificial satellite, Sputnik I, was launched in 1957 by the Soviet Union
Animals and Plants requirements for survival
The animals and plants require water , solar energy, and air in order to grow and survive. Animals take in oxygen and exhale carbon dioxide while, Plants take in carbon dioxide and release oxygen back into the air.
What are Asteroids ?
Asteroids are rocky, airless remnants from the formation of our solar system. Most asteroids are found in the main asteroid belt, which orbits the Sun between Mars and Jupiter. Asteroids range in size from Vesta, the largest at about 329 miles (530 kilometers) in diameter, to bodies that are less than 33 feet (10 meters) across.
How did Asteroids from ?
To Understand Asteroid formation we need to understand other objects and their formation as well
⇒ About 4.6 billion years ago, a giant cloud of gas and dust collapsed.
⇒ Sun and Planetary formation: Most of the material in the cloud fell to the center and formed the sun, while some of the dust condensed into planets. This process, called accretion, continued until the material reached the size of Planets.
⇒ However, the gravity of Jupiter eventually stopped the formation of planetary bodies in this region, causing the small bodies to collide with each other and fragment into asteroids.
Milky Way Galaxy ? Label More Info for Detailed Regions
The Milky Way is a spiral galaxy that contains our solar system and billions of stars, gas, and dust.
Name: The Milky Way gets its name from the way it appears as a milky band of light in the night sky. The name comes from the Classical Latin via lactea, which is derived from the Greek galaxías κύklos, meaning "milky circle".Its called Akash Ganga because it appears in the night sky as a wide, white river, similar to the River Ganga.
⭕Additional iNFO: Nearest Galaxy to Milky Way⭕
⇒ The Andromeda galaxy is the closest large galaxy to the Milky Way, and is about 2.5 million light-years away. It is also known as Messier 31 or NGC 224. The Andromeda galaxy is a barred spiral galaxy similar to Milky Way
What is a Galaxy ?
A galaxy is a massive collection of stars, planets, gas, dust, and dark matter held together by gravity. Galaxies come in a variety of shapes and sizes, and can range from a few thousand stars to trillions.
⭕Additional iNFO: The three main types of galaxies⭕
⇒ Elliptical galaxies: These galaxies are mostly made up of old stars and are shaped like spheres or ellipsoids. They have no spiral arms and are thought to be some of the oldest galaxies in the universe.
⇒ Spiral galaxies: These galaxies are large rotating disks of stars and nebulae surrounded by a dark matter shell. They are one of the most common types of galaxies, making up about 77% of all galaxies.
⇒ Irregular galaxies: These galaxies have a chaotic appearance and lack a nuclear bulge or spiral arms. They are thought to make up about one-quarter of all galaxies. Some irregular galaxies were once elliptical or spiral galaxies that were warped by an external gravitational force.
What is Universe? How Big is it ?
The universe is all of the galaxies – billions of them! Universe is all of space and time and their contents, including planets, moons, minor planets, stars, galaxies, the contents of intergalactic space and all other forms of matter and energy
How big is the Universe?
Not all of the Universe however is currently known to us; so, we can't quantify its exact size. The observable universe is a spherical region of the universe consisting of all matter that can be observed from Earth or its space-based telescopes. The observable universe is estimated to be about 93 billion light-years in diameter
Meteor
When meteoroids enter Earth's atmosphere (or that of another planet, like Mars) at high speed and burn up, the fireballs or “shooting stars” are called meteors.
Meteoroid
A meteoroid is a small rocky or metallic body in outer space. Meteoroids are distinguished as objects significantly smaller than asteroids, ranging in size from grains to objects up to a meter wide
Meteorite
When a meteoroid survives its trip through the atmosphere and hits the ground, it's called a meteorite. Meteorites are usually the size of a pebble or fist.
Molecular Clouds
Molecular clouds are the birthplace of stars and planets. The process of particles and gas coming together under gravity to form larger structures is called accretion. This process begins in molecular clouds and continues through the development of protoplanetary disks and planetary systems.
Perseus Arm
In a map of the Milky Way, the neighboring spiral arm just beyond (Outward) the Orion Spur is known as the Perseus arm. It is one of two major spiral arms of the Milky Way galaxy.
Orion Spur
The local spiral arm of our Galaxy, also called the Orion Spur as it is a partial arm located between the larger Sagittarius Arm and Perseus Arm.
Carina–Sagittarius Arm
It is a minor spiral arm in the Milky Way galaxy. It is the closest major spiral arm inward from the Orion Spur
Black Hole
The black hole at the center of the Milky Way galaxy is called Sagittarius A* It's a supermassive black hole with a mass that's about four million times that of our sun.
What is a Black Hole ?
A black hole is a region in space where the gravitational pull is so strong that nothing, not even light, can escape from it. They are formed when a massive star collapses in on itself at the end of its life, creating an incredibly dense object.
Galactic Bulge
As you go closer to the center of the Milky Way, the distribution of stars becomes vertically thicker. This has created a Bulge. The bulge is a dense region of stars packed together more closely than in the Solar neighborhood. It's made up of a mix of old, metal-rich stars and a large bar structure.
Hint: Compare - Composition, Light, Temperature, Size, Movement, Twinkling
Here are some differences between planets and stars:
⇒ Composition: Planets are made of solids, liquids, and gases, while stars are giant balls of hot gas.
⇒ Light: Stars produce their own light through nuclear fusion, while planets reflect light from an external source, usually the sun.
⇒ Temperature: Stars are very hot, while planets are relatively cool.
⇒ Size: Stars are much larger than planets.
⇒ Movement: Planets orbit the sun and spin on their own axis, while stars change position due to their distance.
⇒ Twinkling: Stars twinkle in the sky due to atmospheric refraction, while planets do not twinkle.
Hint: Sun + Planets + Other Elements
The Sun together with eight planets and the other group of celestial bodies forms the Solar system. These planets and bodies revolve around the Sun and are held by its attraction. Our solar system consists of an average star we call the Sun, the planets Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, and Neptune.
Hint: My Very Efficient Mother Just Served Us Nuts
⇒ Mercury - 57.9 million km
⇒ Venus - 108.2 million km
⇒ Earth - 149.6 million km
⇒ Mars - 227.9 million km
⇒ Jupiter - 778.3 million km
⇒ Saturn - 1,427.0 million km
⇒ Uranus - 2,871.0 million km
⇒ Neptune - 4,497.1 million km
Hint: Water, temperature, atmosphere, plate tectonics, ecosystems, climate
Earth is a unique planet because it has the right conditions to support life. These conditions include:
⇒ Liquid water: Earth is mostly covered in liquid water, which is essential for life.
⇒ Moderate temperature: Earth's temperature is not too hot or too cold, which allows liquid water to exist for long periods of time.
⇒ Protective atmosphere: Earth's atmosphere contains oxygen and other gases that are necessary for life.
⇒ Active plate tectonics: Earth's surface is made up of rigid plates that move and collide, causing earthquakes, volcanoes, and mountain building.
⇒ Diverse ecosystems: Earth has a wide variety of ecosystems that support many different life forms.
⇒ Stable climate: Earth has a stable climate that allows life to thrive.
Hint: Synchronous Rotation -Tidal Locking
Moon's rotation period (27.3 days) is the same as its revolution period (27.3 days) around Earth. This is called synchronous rotation. This Happens because of Tidal Locking.
⭕Additional iNFO: Tidal Locking⭕
⇒ Gravitational Interaction: The Earth exerts a gravitational pull on the Moon, which creates tidal forces. These forces have caused the Moon's rotation to slow down over millions of years. (Note: On Earth, the Moon's gravitational pull causes the oceans to bulge out on both the side closest to the Moon and the side farthest from the Moon)
⇒ Energy Dissipation: As the Moon rotated, the gravitational pull from the Earth created bulges on the Moon. The rotation caused these bulges to shift, leading to a torque that gradually slowed the Moon's rotation until it synchronized with its orbital period around the Earth.
Implications
⇒ Same Side Visibility: Because of this synchronous rotation, the same lunar surface (the near side) is always facing Earth, while the opposite side (the far side) remains hidden from view.
⇒ Long-term Stability: Tidal locking is a stable configuration for celestial bodies, and it can occur for moons around planets or planets around stars.
Hint : Everything that exists
The universe is everything that exists, including all matter, energy, space, time, and all the structures they form
⇒ Matter: Atoms, subatomic particles, and everything they compose
⇒ Energy: Radiation, high energy particles, and magnetic fields
⇒ Space: All of space, including the space between stars and planets
⇒ Time: The universe includes time itself
⇒ Structures: Galaxies, planets, stars, dust clouds, nebulae, and more
✔ True
Venus is called Earth's twin because it's similar in size, mass, and composition to Earth.
✔ True
The earth is the third nearest planet to the sun. The planets in order from the sun are Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, and Neptune.
✔ True
When an object moves or revolves around the other object in an elongated path, it is called Elliptical orbit. All the planets in our solar system move in an elongated path around the sun. The same is with our natural satellite which is the moon.
✔ True
The North star indicates the north direction. It is also called the Pole Star. It always remains in the same position in the sky. We can locate the position of the Pole Star with the help of the Saptarishi.
Local Galactic Group
Groups of galaxies are the smallest aggregates of galaxies. They typically contain no more than 50 galaxies in a diameter of 1 to 2 megaparsecs. Our Galaxy Group is Called the Local Group. The Milky Way and Andromeda galaxies are the two large galaxies in the Local Group. There are a few dozen smaller galaxies in the group, including the Magellanic Clouds, the dwarf elliptical Messier 32, the small spiral galaxy Messier 33, and many small dwarf galaxies.
Virgo Supercluster
The Local Galaxy Group is contained in much larger entity called the Virgo Supercluster. When we talk of the Observable Universe then Superclusters are one of the biggest entities. There are usually many clusters of galaxies in a supercluster, or a single very large cluster at its center, along with many other groups and collections of galaxies that are collected in the supercluster’s central gravitational field.
Laniakea Supercluster
The Laniakea Supercluster is the supercluster that contains the Virgo Cluster, Local Group, and by extension on the latter, our galaxy; the Milky Way
Pisces–Cetus Supercluster Complex
The Pisces–Cetus Supercluster Complex is a galaxy filament that's about a billion light-years long, and includes the Laniakea Supercluster. Galaxy filaments are thread-like structures and are the largest known structures in the universe.
✔ True
Most of the asteroids lie in the main asteroid belt, which is the region between the orbits of Mars and Jupiter.
Similar to asteroid belt there is another belt of remnants in the Universe located between the orbit of Neptune and the Oort Cloud which is the Kuiper belt is much larger than the asteroid belt —20 times as wide and 20–200 times as massive. Like the asteroid belt, it consists mainly of small bodies or remnants from when the Solar System formed but these are ices compared to the silicates (rocks) and metals of the Asteroid Belt.
Moon
If we consider Planets, Venus is Earth's closest planetary neighbor when considering the closest approach to Earth, but not when considering the average distance. When averaged over time, Mercury is the closest planet to Earth.