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The Kármán line is a boundary 62 miles (100 kilometers) above mean sea level that borders Earth's atmosphere and the beginning of space. ○ The Kármán line is an imaginary line that demarcates the Earth’s atmosphere from space.
Troposphere → Earth’s Dynamic Weather and Life Zone: It is the lowest layer with an average height of 12-13 kilometres. Stratosphere → Guardian of Life with the Ozone Shield: It is located above the tropopause and extends to a height of 50 kilometres. ○ It contains the ozone layer, which absorbs harmful ultraviolet radiation from the sun, protecting life on Earth. Mesosphere → Cold Depths and the Mesopause Boundary: It extends up to 80 kilometres, and is characterised by decreasing temperatures with altitude, reaching as low as minus 100°C at its upper boundary, known as the mesopause. Ionosphere → Electric Heights and Radio Wave Reflection: This region spans from 80 to 200 kilometres. It contains electrically charged particles called ions and reflects radio waves back to Earth. Exosphere → Earth’s Boundary with the Cosmos Beyond: It is the uppermost layer of the composition of the atmosphere.
Space:
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Universe
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Universe includes all of the matter, time and energy. It contains both physical (planets, stars, asteroids, comets) and non- physical (light, gravity, waves, time, sound, etc) components. Galaxies and Black Hole: Almost every large galaxy contains a supermassive black hole at its center. These black holes can be millions or even billions of times the mass of the Sun. Milky Way Galaxy: The Milky Way galaxy, like most large galaxies, harbors a supermassive black hole at its center, known as Sagittarius A* (Sgr A*). The Milky Way galaxy is estimated to contain between 100 and 400 billion stars. Orion Arm: The Orion Arm is a minor spiral arm of the Milky Way galaxy.
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● Supercluster of Galaxies: The structure of the universe is not a homogeneous distribution of matter. It is clumpy with galaxies forming clusters and these in turn forming superclusters.
Fig: The first supercluster of galaxies, the Shapley Supercluster, was discovered in 1989, and the second, the Sloan Great Wall in 2003. The Milky Way galaxy is part of the Laniakea Supercluster, which was discovered in 2014. ●
In 1927, an astronomer named Georges Lemaître said that a very long time ago, the universe started as just asingle point. He said the universe stretched and expanded to get as big as it is now, and that
Galaxies in Universe: The Milky Way, which contains our solar system, is one of billions of galaxies in the observable universe.
Big Bang Theory: The Big Bang Theory is the most widely accepted explanation for the origin of the Universe. It states that the Universe began around 13.8 billion years ago from a single, extremely hot and dense point called asingularity. There was a sudden explosion which led to the origin of the Universe. Singularity: An infinitesimally small point with infinite mass and infinite density from where our Universe originates. Hubble Law: In the year 1920, Edwin Hubble proposed a hypothesis known as ‘Expanding Universe Hypothesis’ which was based on Hubble’s Law.
Extra Edge:
How DidtheUniverseOriginate?
it could keep on stretching. Just two years later, an astronomer named Edwin Hubble noticed that other galaxies were moving away from us and the farthest galaxies were moving faster than the ones close to us. This meant that the universe was still expanding, just like Lemaître thought. Hubble Space Telescope: The space telescope, conceived in the 1940s, designed in the 1970s, and built in the 1980s, was designed to give astronomers an unparalleled view of the solar system, the galaxy, and the universe. It was launched on April 24, 1990 and operates about 320 miles ( kilometres) above Earth. It is named after Edwin Hubble.
Terrestrial and Jovian Planets
● Terrestrial Planets: The inner, rocky planets are Mercury, Venus, Earth,^ and Mars. These worlds also are known as terrestrial planets because they have solid surfaces. Venus: Venus is the sister planet of Earth , the hottest planet. Hottest Planet: Venus is the hottest planet in the solar system. Venus is the second planet from the Sun, but is still hotter than Mercury. This is because the atmosphere is very thick and is made up of greenhouse gases such as carbon dioxide. It also has traces of nitrogen, and the clouds on Venus are made up of sulphuric acid. Moons: Most of the major planets except Mercury and Venus have moons.
■ Mars has two moons, Phobos and Deimos Jovian/Gaseous/Non-Terrestrial Planets: The outer planets are gas giants Jupiter and Saturn, and ice giants Uranus and Neptune. These are called Jovian planets (or Jupiter-like planets) that do not have solid surfaces. Instead, they are composed primarily of hydrogen and helium, with traces of methane, ammonia, water, and other gases in their atmospheres. ○ (^) Moons: Jupiter (95 moons) and Saturn (274 moons) have the most moons. ■ Jupiter: Jupiter also has the biggest moon (natural satellites) in our solar system, Ganymede (icy moon). It is even bigger than the planet Mercury. ● The other icy moons are Europa, Io, Callisto.
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The solar system has eight planets: Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, and Neptune.
Solar System
Fig: Europa Clipper will not directly search for life, but will assess whether Europa's environment could support it. ■ (^) Saturn: One of Saturn's moons, named Titan, even has its own (dense) atmosphere, which is very unusual for a moon.
Fig: Astronomers say they have discovered more than 100 new moons around Saturn, possibly the result of cosmic smashups that left debris in the planet’s orbit as recently as 100 million years ago.
Goldilocks Zone: The distance Earth orbits the Sun is just right for water to remain a liquid. This distance from the Sun is called the habitable zone, or the Goldilocks zone. It is where the possibility of life is highest.
IAU Classification of Solar System Objects
The International Astronomical Union (IAU) which was founded in 1919, defines the criteria for all objects presents in solar system in three different categories (except moon) ● (^) Planets: Revolve around the Sun ○ (^) Must have sufficient mass for its gravity to overcome rigid body forces, achieving hydrostatic equilibrium (near spherical shape). ○ Must have cleared the neighborhood objects around its orbit. ● Dwarf Planets: Revolve around the Sun. ○ Have enough mass to attain a spherical shape (hydrostatic equilibrium).
Large rocky bodies in space revolving around the sun. They do not have atmosphere Some asteroids have their own moons. Example: Bennu, Eros, Oumuamua, 16 Psyche, Lucy, Ryugu,
Have not cleared the neighborhood around their orbit. Example: Ceres, Pluto Small Solar System Bodies/Objects: It Includes ○ Asteroids, Meteoroids, Comets, Meteorites, Meteors, etc
Asteroids
Fig: Psyche’s destination is a by the same name that orbits the sun within the main asteroid belt between Mars and Jupiter.
Bennu Asteroid: Bennu is a small, near-Earth asteroid that passes close to Earth about every six years. Bennu is a carbon-rich asteroid that is about one-third of a mile (half a kilometre) wide at its equator. Bennu’s average orbital distance from the Sun is about 105 million miles (168 million kilometres), which is only slightly farther than Earth’s average orbital distance of 93 million miles. NASA Exploration: Bennu was the target of NASA's first asteroid sample return mission (collect an asteroid sample and bring it to Earth), OSIRIS-REx. The spacecraft dropped off a sample of Bennu on Sept. 24, 2023. New Mission (Apophis): The spacecraft was renamed OSIRIS-APEX and sent on a new mission to explore asteroid Apophis in 2029. Apophis: Near-Earth asteroid Apophis (discovered in 2004) is said to safely pass close to Earth in April 2029.
Extra Edge:
While most meteors burn up completely in the atmosphere, some large or dense ones survive and fall to the ground as meteorites. When a large meteorite strikes the Earth, it creates a depression or hollow on the surface called an Impact Crater. ● Impact Craters in India: ○ ○ ○
Dhala Crater in Madhya Pradesh Lonar Crater in Maharashtra Ramgarh Crater in Rajasthan
Meteorites in India: India has three of these meteor impact craters – Ramgarh in Rajasthan, Lonar in Maharashtra and Dhala in Madhya Pradesh. ● Lonar^ Crater^ Lake:^ Lonar^ crater^ lake^ (Buldhana identified as a unique geographical site by C J E Alexander, a British officer, in 1823. ○ ○
Lonar lake in Maharashtra, the only crater lake of India. In 2020, the Lonar lake was added to the list of recognised Ramsar sites ● Dhala Crater:^ It is located in Shivpuri district in Madhya Pradesh. Estimated to have formed some 2500 million years ago, the Dhala Crater is the oldest and the largest impact crater in India. Dhala Crater is a massive 11 km in diameter, making it the largest in Asia. Ramgarh Crater: Approximately 165 million years ago, a large meteorite fell on Earth, some 110 km from Kota in Rajasthan, and formed an unusual crater with a diameter of approximately 10 km. Its diameter is 3.5 kilometres.
● Chicxulub Crater (Gulf of Mexico): This asteroid impact, which formed the Chicxulub crater, is widely believed to have caused the mass extinction of dinosaurs around 66 million years ago. Note: If a large asteroid, approximately the size of Mount Everest, collided with Earth, it could result in catastrophic global devastation and resulting in extinction of earth.
Comets
Meteorites
A meteorite is the remnant of a meteoroid that survives its passage through the Earth’s atmosphere and lands on the Earth’s surface.
district, Maharashtra)^ was
Comets are like dirty snowballs mainly made up of ice and frozen carbon dioxide with some dust and organic molecules left over from the formation of the solar system. They are mostly found in the Kuiper belt. Kuiper Belt: The width of the belt is approximately 1 AU. Halley's Comet: A "periodic" comet, it returns to Earth's vicinity about every 76 years. It was last here in 1986. The comet, officially called 1P/Halley, is named after English astronomer Edmond Halley. Structure of Comet:
○ The Sun’s heat causes them to release gas and dust, forming a glowing cloud called a coma around the solid core. The dust tail , made of tiny particles, looks yellowish-white. The plasma (or ion) tail, made of charged gas, glows blue due to carbon monoxide ions.
Life Cycle of Stars (Stellar Cycle)
Nebula
A nebula (plural: nebulae) is a vast cloud of gas and dust in space, primarily composed of hydrogen and helium. These cosmic clouds are often the birthplaces of stars and can span thousands of light-years across. Within the densest regions of a nebula, gravity begins to pull gas and dust together to form clumps, eventually giving rise to new stars.
As gravity continues to pull hydrogen gas inward, the clump begins to spin and heat up, forming a protostar—a star in the making. At this stage, nuclear fusion has not yet started, but the temperature keeps rising. When the core temperature reaches approximately 10 million Kelvin (K), hydrogen fusion begins. This marks the transition from a protostar to a main sequence star.
Protostar
This is the longest and most stable phase of a star’s life. During this period: ○ ○ ○
The star fuses hydrogen into helium in its core. The energy released from fusion creates an outward pressure. This outward pressure balances the inward pull of gravity, maintaining equilibrium. Example: Our Sun is currently in the main sequence phase.
Main Sequence Star
Mass of a Star and the Star’s Life Cycle
A star’s mass determines its entire life cycle. More massive stars have stronger gravity and burn through their fuel more quickly, resulting in shorter lifespans. Based on mass, stars are generally categorized into two types:
Chandrasekhar Limit: Named after Subrahmanyan Chandrasekhar determines whether a star ends its life as a smouldering white dwarf, or explodes in a supernova to become a neutron star or black hole. According to this limit white dwarf stars are generally considered to be 1.4 solar masses (M ☉). 1.4 M ☉< or <3 M☉ (Solar Mass): After the supernova explosion the remnant core is a superdense neutron star if its solar mass is greater than 1.4 and smaller than 3. One teaspoon of neutron star would weigh roughly around 10 million tons. > 3 M ☉: If the mass is above 3 solar mass then it would become black hole. Black Holes are huge concentrations of matter packed into very tiny spaces. A black hole is so dense that gravity just beneath its surface, the event horizon, is strong enough that nothing – not The event horizon isn’t a surface like Earth’s or even the Sun’s. It’s a boundary that contains all the matter that makes up the black hole.
even light – can escape.
They are rapidly rotating neutron stars that blast radiation pulses from seconds to milliseconds. These 'cosmic lighthouses' can spin as fast as 700 rotations per second.
Neutron Star: If the mass of the collapsed core is between 1.4 and 3 solar masses, it forms a neutron star. ○ Neutron stars are created when massive stars reach the ends^ of their lives. They are some of the most dense objects in the universe, having a mass up to two times our sun, but a diameter ranging only between 10 - 20 kilometers. Composed mostly of neutrons, formed when electrons and protons are squeezed together under immense pressure.
Black Hole: If the remaining core has a mass greater than 3 solar masses, it collapses further to form a black hole. ○ A black hole has: ■ (^) A gravitational field so strong that not even light can escape. The ability to distort space-time around it. The power to pull in surrounding matter, including gas, dust, and even nearby stars.
Post-SupernovaOutcomes
Pulsar (Rotating Neutron Star)
Other Stars
Cepheids
Cepheids are among the brightest stars in the universe. They are the stars that brighten and dim periodically. They act as a natural clock because the light fluctuations happen periodically
Events in Our Universe
Gamma Ray Bursts (GRBs)
GRBs are extremely energetic explosions that have been observed in distant galaxies
Fig: Millisecond pulsars emit radiations every few milliseconds. In 2023, Pune-based astronomers discovered two new Millisecond Pulsars (MSPs) using a novel, indigenously developed technique. This was part of an ongoing sky survey with the Giant Metrewave Radio Telescope (GMRT), located 80 km from Pune. Operated since 2000, the GMRT is the world’s largest low-frequency radio telescope and is managed by TIFR-NCRA, Pune.
They maybe be created in four ways: ○ During Supernova explosion forming blackhole When two neutron stars collide When two black holes merge. When one blackhole absorbs a neutron star GRBs can be of two types: ○ ○
Short GRBs: They last from a few milliseconds to 2.5 seconds. Long GRBs: They last for more than 2.5 seconds. Fermi Gamma-ray Space Telescope is a space observatory being used to perform gamma ray astronomy observations from low Earth orbit (LEO). This was launched by NASA in 2008.
GRB 221009A About two billion years ago, a massive star in adistant galaxy exploded in apowerful supernova, releasing an intense gamma-ray burst (GRB)—the most energetic form of electromagnetic radiation. These gamma rays traveled across the universe and reached Earth on 9 October 2022, where they impacted the atmosphere for approximately 13 minutes, causing a notable disturbance in the ionosphere.
Gravitational waves are the ripples in the fabric of space-time caused by some of the most violent and energetic processes in the universe.
Gravitational Waves
Fig: Massive objects (like black holes) create strong gravitational fields that curve and stretch the "fabric" of space-time. (Right) A 3D illustration of a black hole curving spacetime.
Laser Interferometer Space Antenna (LISA) is a constellation of three identical spacecraft arranged to form an equilateral triangle with 2.5 million kilometres distance between them. Project by European Space Agency (ESA) and NASA. This project is due for launch in 2030. LISA Pathfinder: In this LISA pathfinder, a testing mission was launched in 2015. Evolved LISA (eLISA) / Final Project: After the success of LISA pathfinder Evolved LISA (eLISA) is a plan of setting into space the three spacecraft.
Fig: LIGO's Dual Detectors (ground based observatory)
LISA Project
Fig: It would be a space based observatory. Three spacecraft (one mother and two daughters) arranged in an equilateral triangle.
Elements of the Universe
Visible Part : Only 5% of the universe consists of observable matter (ordinary matter), which includes everything we can see and detect, such as stars, planets, and galaxies. Dark Matter: Dark Matter is an invisible substance, because it does not interact with electromagnetic radiation.
Particle Physics is a branch of physics associated with the study of elementary constituents of matter, radiation and interaction between them. The Standard Model of Particle Physics is the theoretical framework that describes the fundamental particles and their interactions. It explains how the universe works at the smallest scales. All the particles existing in the universe can be classified into two heads: fermions and bosons.
Dark Matter constitutes about 25% of the total universe. It interacts with the rest of the universe only through gravitational waves & this was the primary reason that we came to know about its existence. Dark Energy: Dark Energy is a theoretical repulsive force that counteracts gravity. It drives the expansion of the universe, leading to galaxies moving further apart over time. ○ Dark Energy makes up about 70% of the universe.
STANDARD MODEL OF PARTICLE PHYSICS
Matter Providing Particles (Fermions)
Fermions are the building blocks of matter.^ They are divided
into two
Quarks combine to form particles called hadrons (the most stable of which are protons and neutrons). Proton = 2 Up Quarks + 1 Down Quark Neutron = 1 Up Quark + 2 Down Quark A combination of three quarks is called a baryon. ○ There are six types of quarks, known as flavours: up, down, strange, charm, bottom, and top.
Proton: ● ● ●
Composition: 2Up Quarks+1 Down Quark Charge Calculation: The proton has an overall positive charge. 2× (2/3 )+1× (−1/3 )=+ Neutron: ● ● ●
Composition: 2Down Quarks+1 Up Quark Charge Calculation: The neutron has an overall neutral charge. Chargeless:^ 2× (−1/3 )+1× (2/3 )= ● Ferminions: Neutrinos
subcategories:
Quarks (6 types)
● Bosons: Zboson, gluon, photons & Higgs. Massless (Only Bosons): ● Gluon, photon
Lepton are categorized into Electron, Electron Neutrino, Muon, Muon Neutrino, Tau, Tau Neutrino. Neutrino: They are leptons that interact only through a weak interaction force like gravity. They are named so because they are electrically neutral and its rest mass is so small that it was thought to be zero. ○ They^ are^ produced^ in^ various^ natural^ processes^ like^ nuclear^ reactions^ in^ the^ sun’s^ core, radioactive decays or supernova explosions. ○ Ice^ Cube^ Neutrino^ Observatory^ (South^ Pole located at the South Pole (Antarctica) to detect neutrinos and capture them.
Leptons (6 types)
Neutrino Observatory): The Observatory
In The News: Peter Higgs, whose ground-breaking work helped explain how everything in the universe attains mass, passed away in April 2024. Higgs Field: In 1964, he theorised the existence of the Higgs Boson, a fundamental force-carrying particle associated with the Higgs field. The Higgs field is a quantum field that gives mass to particles and exists throughout the universe. Nobel Prize: In 2013, Peter Higgs was awarded the Nobel Prize in Physics along with François Englert "for the theoretical discovery of a mechanism that contributes to our understanding of the origin of mass of subatomic particles, and which recently was confirmed through the discovery of the predicted fundamental particle, by the ATLAS and CMS experiments at CERN's Large Hadron Collider" God Particle: The Higgs boson is popularly known as the "the God Particle". The name originated from Nobel Prize-winning physicist Leon Lederman's book on the particle which he titled the "Goddamn Particle" - owing to frustration over how difficult it was to detect.
Particle Accelerator: LHC is the biggest and most powerful particle accelerator in the world started in 2018 at CERN (European council for Nuclear Research). Location: It is located near Geneva (Switzerland-France border).
Satyendra Nath Bose (S. N. Bose) In the News: In a significant milestone for India’s scientific community, the Science and Technology Minister virtually inaugurated the Centenary Celebrations of the iconic “Bose-Einstein” Statistics postulation at the S.N. Bose National Centre for Basic Sciences. Bose-Einstein (B–E) Statistics: B–E statistics describe the distribution of non-interacting, indistinguishable particles across energy states at thermal equilibrium. ○ In 1924, Satyendra Nath Bose proposed this approach to particle behavior, later developed with Albert Einstein.
Large Hadron Collider (LHC)
It also provided masses to W and Z Bosons
Higgs Boson
Built: LHC is positioned in a tunnel with a circumference of 27 km (17-mile) depth of 175 meters. Aim: It is designed to collide opposite particles at very high energy and speed (near to the speed of light) in order to study new fundamental particles emerging out due to this collision. India’s Contribution: India has been collaborating with the European Organization for Nuclear Research (CERN) since 1991 on the LHC experiment. ○ ○
India became an Associate Member of CERN in 2017. Indian scientists and India-made components are crucial in activating LHC much below the sanctioned cost.
Satellites stay in orbit due to a balance between: ○ Gravitational force (G^ f): The force exerted by the Earth on the satellite pulling it toward the center of the planet. ■ Acts radially inward
○ Centrifugal force (F^ ): The outward force experienced by the satellite due to its circular motion around the Earth.
C
■ Acts radially outward. Here, three conditions arises ○ Satellites fall back towards Earth (F^ G> F^ C): If the gravitational force acting on a satellite is greater than the centrifugal force, the satellite would spiral downwards towards the Earth's surface. Satellites escape the Earth (F (^) C> F G): If the satellite’s velocity were too large (F C> F G), it could break away from Earth’s gravity (escape) and will continue to move in space. Satellites Are stable in Orbit (F (^) G= F C): The satellite does not fall to Earth or escape into space. This is done by the speed of the satellite
The satellite must travel at a specific speed to maintain a stable orbit. If the speed is too low, the satellite will spiral back to Earth due to gravitational pull. If the speed is too high, it may escape Earth's gravitational influence. Note: A lower orbit requires a higher orbital velocity for a satellite to maintain a stable orbit. Conversely, a higher orbit requires a lower orbital velocity.
SPACE TECHNOLOGYSPACE TECHNOLOGYSPACE TECHNOLOGY
Why Don't Satellites Fall intotheEarth?
Classification of Orbits
BasedonShape
Circular Orbit: The satellite moves around the Earth in a circular path. Elliptical Orbit: The satellite follows an elliptical path around the Earth.
Altitude: 2000-35,786 km
Usually a satellite takes ~90 minutes to revolve around the earth.
Types of Orbit
Fig: It is the first Earth-observing satellite to carry dual-frequency synthetic aperture radars, Nasa’s L-band and Isro’s S-band, which will allow it to monitor changes in Earth’s surface with unmatched precision
LowerEarthOrbit(LEO)
Medium Earth Orbit (MEO)
● Applications of MEO: Global navigation satellites ○ USA’s Global Positioning System (GPS) is a constellation of about 24 satellites.
Revolution of GSO Satellite = Rotation Period of Earth At altitude of 35,786 km)
Attitude: 35,786 (around 36000) km GSO: A geosynchronous orbit (GSO) is any orbit with a period of exactly one sidereal day, meaning the satellite will appear to complete one orbit per day as seen from Earth. ○ Satellites will be always seen but will move in vertical direction with respect to a point on^ earth.
GeosynchronousOrbit(GSO)
GEO: A geostationary orbit (GEO), on the other hand, is a specific type of geosynchronous orbit that's also circular, directly above the equator, and with zero inclination (no tilt). This means a geostationary satellite appears stationary (fixed) in the sky from the ground (earth’s position).
Applications: Used as a communication satellite for TV broadcasting, internet services and military communication
○ For regional navigation satellites Galileo which is Europe’s own global navigation satellite system GLONASS (GLObalnaya NAvigatsionnaya Sputnikovaya Sistema) which is a Russian global navigation satellite system that provides positioning, navigation and timing services BeiDou / Compass which is Chinese navigation system
High Earth Orbit (HEO)
It is a type of polar orbit where the satellite remains in a sunlit zone, never entering Earth's shadow. SSO is also known as “Dawn to Dusk”. The sun appears to always shine on SSO. This orbit ensured the satellite passes over the same part of Earth at the same local solar time each day.
Altitude: It is positioned at an altitude of higher than 35,786 km above Earth's surface. Applications: Deep space missions which involve a trip to the planets of the solar system outside of the earth. ○ Helps in navigation satellite to improve efficiency
It is a subtype of Low Earth Orbit (LEO) which revolves around the earth from pole to pole. This orbit has a period of approximately 90 minutes and it will cover the entire earth. This orbit allows for complete global coverage because the Earth rotates beneath the satellite as it travels from pole to pole. Application: Used for weather forecasting, environmental monitoring and reconnaissance satellites. Disadvantage: It is very difficult to maintain the balance of the satellite placed in polar orbit.
Halo Orbit
Satellites are placed at these special points (like Lagrange points) between two body systems where the resulting Gravitational force applied by these two bodies equating in opposite directions, revolves around the sun and maintains a similar vertical revolution around these Lagrange points.
Special Orbits
PolarOrbit
Sun-SynchronousPolarOrbit(SSO)
Halo orbits are periodic, three-dimensional orbits around a Lagrange Point (L1, L2 or L3). Lagrange Points There are special spots called Lagrange Points where the gravity of two large objects (like the Earth and the Sun) balance each other perfectly. This balance means a small object, like a satellite, can stay in that spot without using much energy. There are 5 Lagrange Points in total: ○ L1, L2, and L3: These are unstable points and are along a straight line between the two large objects (like Earth and the Sun). If something moves just a little away from these points, it will drift off. ○ L4 and L5: These are stable points and form the corners of an equilateral triangle, with
