• The comprehensive exploration of the universe on a grand scale is termed cosmology. The universe encompasses planets, stars, galaxies, the contents of intergalactic space, the smallest sub-atomic particles, and all matter and energy.
• All celestial bodies, including stars, planets, satellites, asteroids, meteors, comets, dust, and gases, collectively constitute the universe. The scientific study of these heavenly bodies is referred to as astronomy, and individuals engaged in this field are known as astronomers.
• Theories about the Origin of the Universe have intrigued humanity since ancient times. Scholars have proposed various perspectives on the universe, and these theories can be categorized into two groups: early theories and modern theories.

Theories about the Origin of the Universe

Early Theories:

• Proposed by Ptolemy in 140 AD, the geocentric theory asserts that the Earth is the center of the universe.

Geocentric Theory:

• Introduced by Johannes Kepler in the 16th century, this theory explains the laws of planetary motion. According to Kepler, each planet follows an elliptical path around the Sun, with the Sun located at one of the foci of the ellipse.

Heliocentric Theory:

• Proposed by Copernicus around 1343 AD, the heliocentric theory asserts that the Sun is the center of the universe. Copernicus is acclaimed as the father of modern astronomy.
• In 1805, British astronomer Herschel Studied the solar system using a telescope and concluded that it constitutes only a small part of the galaxy.
• American astronomer Edwin P. Hubble (1925): Stated that the universe has a diameter of 2.5 billion light years and is composed of several galaxies.
• Stephen Hawking (England, 1974): Proposed the significant discovery that black holes emit radiation.
• Varahamihir (sixth century AD): Propounded that the Moon revolves around the Earth, and the Earth revolves around the Sun.

Modern Theories

Big Bang Theory:

• Proposed by Georges Lemaitre in 1927 and later strongly evidenced by George Gamow.
• States that, at the beginning, all matter forming the universe existed in the form of a tiny ball (singular or primeval atom) with an unimaginably small volume, infinite temperature, and indefinite density.
• Around 15 billion years ago, a vast explosion occurred, leading to the expansion of the universe.
• Confirmed by the discovery of Cosmic Microwave Background Radiation (CMBR) and Wilkinson Microwave Anisotropy Probe (WMAP).

Higgs Boson Theory:

• Recent experiments at the Large Hadron Collider (LHC) aim to recreate conditions just after the Big Bang.
• Higgs Boson, known as the God particle, is the fundamental force-carrying particle associated with the Higgs field, giving mass to other particles.
• Discovered at CERN on July 4, 2012.

Red Shift Theory:

• Based on the observation of the Doppler effect and redshift.
• Indicates the expansion of the universe, confirmed by the Cosmic Microwave Background Radiation (CMBR) and Doppler effect.
• After the Big Bang event, the solar system developed about 4.5 billion years ago, leading to the formation of planets and satellites.
• These theories provide insights into the origin and evolution of the universe, combining ancient views with modern scientific explanations.
• When a star is moving towards an observer, the light it emits shifts towards the blue end of the spectrum. Conversely, when the star is moving away, the light shifts towards the red end. This phenomenon is known as the Doppler effect or Doppler shift.
• Galaxies exhibit a Doppler shift, indicating their recession and pointing to the universe's rapid and accelerated expansion. This observation is commonly referred to as redshift.

Steady State Theory:

• Developed by Bondi, Gold, and Fred Hoyle, this theory posits a constant number of galaxies in the observable universe. 
• New galaxies continually emerge from empty space, filling gaps left by galaxies crossing the observable universe's boundary. 
• The overall mass and size of the observable universe remain constant, maintaining a steady state.

Pulsating Theory:

• Proposed by Dr. Allen Sunder, this theory suggests that the universe alternately expands and contracts, pulsating in a cyclical manner.
• Currently, the universe is in an expanding phase, but gravitational forces may cause it to contract. The pulsating cycle involves periods of expansion and contraction.

Age of the Universe:

• Astronomers estimate the Big Bang occurred between 12 and 14 billion years ago. Based on measurements of Cosmic Microwave Background Radiation (CMBR), the accepted age is 13.7 billion years. Our solar system is estimated to be 4.5 billion years old.
• The fate of the universe hinges on the interplay between expansion momentum and gravitational pull. If density is less than critical density (proportional to the Hubble constant squared), the universe will expand indefinitely. If density exceeds critical density, gravity will prevail, leading to a collapse known as the "big crunch." Dark energy, a mysterious form of matter, may influence the universe's evolution, potentially causing continued expansion.

Components of the Universe:

• The visible universe exhibits a foamy structure, composed of filaments, superclusters, galaxy groups, and clusters. Superclusters form walls, which are components of filaments. 
• The visible universe is concentrated in specific regions, surrounded by vast cosmic voids.
• In addition to visible matter, scientists have identified dark matter—an unseen substance that contributes significantly to the universe's composition.
• Various phenomena, such as gravitational lensing, temperature distributions, and the behaviors of galaxies, indicate the presence of dark matter in the universe, despite being invisible on the electromagnetic spectrum. Dark energy, another unseen entity, is believed to be responsible for the accelerated movement of galaxies.
• The nuclear fusion process has minimally altered helium quantities in the universe, maintaining a consistent proportional composition since its early years.

Galaxy:

• Galaxies, large groups of stars, come in diverse sizes and shapes, categorized as normal or radio galaxies. The dark regions between galaxies remain unlit due to the absence of stars.

Normal Galaxies:

• Emitting relatively small radio radiations, normal galaxies are bright at the center, gradually dimming towards the edges. They consist of billions of stars traveling together. Depending on shape, they can be elliptical (spheroid), spiral (rotating disk), or irregular.
  • Elliptical Galaxies: Shaped like a spheroid or elongated sphere, these galaxies often contain older, low-mass stars.
  • Spiral Galaxies: The most common type, spirals are large rotating disks surrounded by dark matter, like the Milky Way.
  • Irregular Galaxies: Irregular in shape, these galaxies lack the structure of spirals or ellipticals.
  • Radio Galaxies: Comprising only 2% of galaxies, these emit significantly more radio radiations, believed to originate from large radio sources within them.
• Approximately 18% of galaxies are elliptical, 80% are spiral, and 2% are irregular. Irregular galaxies are the youngest, spirals are mid-aged, and ellipticals are quite old. The observable universe contains around 170 billion galaxies, with the largest having nearly 400 billion stars, including our Milky Way with approximately 100 billion stars.

Stars

• A star is a luminous celestial body with its own light and heat energy. The Sun, the nearest star to Earth, takes 8.3 minutes (500 seconds) for its light to reach us, while Proxima Centauri, the closest star beyond our solar system, is 4.3 light years away.
• Stars are primarily composed of hydrogen (70%), helium (28%), carbon, nitrogen, neon (1.5%), and iron elements (0.5%). They can exist as single stars, though they are rare (only 25%), or in pairs known as binary stars (about 33%). Alpha Centauri, for example, consists of three stars.
• Variable stars, like Delta Cephei, exhibit varying degrees of luminosity, fluctuating between periods. Pulsars emit regular pulses of electromagnetic waves, and quasars are powerful sources of radio radiations.
• Stars form when dust and gas clump together due to gravitational forces, and nuclear reactions release energy to keep them hot. Planets, on the other hand, form from smaller amounts of dust and gas clumping together due to gravitational forces.
• Throughout their lifetime, stars like the Sun change into various forms, such as red giants, white dwarfs, neutron stars, and black holes, depending on their mass. High-mass stars burn through their hydrogen fuel more quickly and have a shorter lifespan.
• The Polar Star, currently Polaris, appears nearest to either celestial pole at any particular time. Stars twice as massive as the Sun burn through their fuel supply in 800 million years, while a 10 solar mass star burns much brighter but has only a 20 million year fuel supply.
• After the solar system, the closest star to Earth is Proxima Centauri, and its orbiting planet, Proxima Centauri-B, is similar to Earth. Sirius, also known as the Dog Star, is the next closest star, 8.6 light-years away, and is the brightest star visible at night.

Color Temperature and Age of Star

• The temperature of a star determines its color and age, ranging from dark red (175°C, aged) to blue-white (1150°C, young star). As stars age, they expand, and their core contracts, leading to the formation of red giants or red supergiants, which eventually collapse and transform into black dwarfs, neutron stars, or black holes through processes like explosion.

Black Hole

• The prediction of black holes originated from Albert Einstein's theory of relativity in 1916. The term "black hole" was introduced by physicist John Wheeler in 1967 to describe stars of varying sizes and high masses that reach the end of their lifetimes and collapse, forming black holes.
• In essence, a black hole forms when the mass in a neutron star concentrates at a single point or when its time period ceases. The density of matter in a black hole is immeasurable, and its gravitational field is so powerful that not even light can escape from it.

Gravitational Waves

• When two black holes orbit each other and merge, they create ripples in space known as gravitational waves. These waves are invisible and travel at the speed of light (186,000 miles per second). The first direct observation of gravitational waves occurred on September 14, 2015, at the Laser Interferometer Gravitational-wave Observatory (LIGO).

Chandrasekhar Limit

• The Chandrasekhar Limit is the upper bound on the mass of bodies made from electron-degenerate matter, such as white dwarfs. Subrahmanyan Chandrasekhar calculated the maximum mass of 1.44 solar masses for a white dwarf. This limit signifies that for masses above 1.44 solar masses, there is no balance between electron degeneracy and gravitational force, leading to the continued collapse of the star. This limit is also known as the Chandrasekhar Limit.

Life Cycle of Stars

• Stars have life spans ranging from millions to billions of years, acting as gigantic nuclear furnaces. The nuclear reactions inside stars convert hydrogen into helium through fusion, providing them with energy. Stars begin their lives as nebulae—clouds of gas (hydrogen) and dust. These nebulae collapse under gravitational forces, forming protostars, which further collapse to become main sequence stars.
• The life span of stars depends on their size, with massive stars burning their fuel faster than smaller ones. As a star's fuel runs out, it expands to form a red giant, lasting until it exhausts its remaining fuel. At this point, the pressure from nuclear reactions is insufficient to counteract gravity, causing the star to collapse.
• When a star uses all available hydrogen at its core, it starts fusing helium into carbon. If the star's mass is only a few times the solar mass, the fusion process does not go beyond this, leading to the formation of a white dwarf. As it cools down, a dark ball of matter known as a black dwarf remains.
• A white dwarf is a lifeless star as it no longer undergoes the fusion process to generate energy. Instead, it radiates heat accumulated during its active lifetime. Giant stars, nearly three times the mass of the Sun, follow a different life cycle.
• Upon depleting their fuel, these giants expand into red supergiants. The culmination of their existence often involves a spectacular explosion known as a supernova, and depending on their mass, they may transform into neutron stars or black holes.

Constellation

• A constellation refers to a group of stars forming a recognizable shape in the sky, assigned a specific name. According to the International Astronomical Union (IAU), there are officially 88 recognized constellations, including well-known ones like Ursa Major, Orion, the Hunter, and Ursa Minor, the Little Bear. Constellations serve various purposes, from naming stars and meteor showers to aiding navigation.
• Asterism, on the other hand, represents a pattern of stars that does not qualify as a constellation, forming any alignment unlike constellations. Generally, there are 27 asterisms.

The Solar System

• The solar system is primarily governed by the Sun, accounting for nearly 99.9% of the system's total matter and serving as the source of light and heat. The Sun's mass exerts gravitational force, controlling the movement of planets and other celestial bodies.
• Positioned at the center, the Sun is orbited by eight planets—Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, and Neptune—along with their satellites, dwarf planets, asteroids, meteors, and comets. Pluto, once considered the ninth planet, lost its planetary status in 2006 due to a redefinition by the International Astronomical Union (IAU).

The Sun

• The Sun, believed to have formed around 5 billion years ago, continues to emit significant heat and light. It is anticipated to maintain this radiance for the next 5 billion years. The Sun, our nearest star, is the primary source of energy for the entire solar system, with its radius nearly 100 times that of Earth and a mass about a million times greater.
• Situated approximately 150 million km away from Earth, it takes about 8.3 minutes for the Sun's light to reach us. The Sun's light is also responsible for lighting up the nearest star, Proxima or Alpha Centauri, in about 4.3 light years.

Layers and Related Concepts of the Sun

The Sun comprises various layers and related concepts:

• Photosphere: The outer layer emitting most radiation, particularly visible light. It exhibits extreme unevenness, with an outer surface temperature of 6000K.
• Chromosphere: A thin layer of burning gases situated just above the photosphere.
• Solar Flares: Storms of hot atoms emerging from the photosphere, overcoming gravity, and dissipating into outer space.
• Sunspot: A sunspot refers to a dark patch on the Sun's surface, representing relatively cooler regions with a temperature of about 1500°C. These sunspots undergo a cycle, appearing and disappearing approximately every 11 years. Each spot consists of a black center or umbra and a lighter region or penumbra.
• Lagrange Points: These are positions in space where the gravitational forces of the Sun and Earth create areas of mutual attraction.
• Corona: During a total solar eclipse, when the Sun's disc is completely obscured, the outermost layer, known as the corona, becomes visible. It appears like a crown encircling the Sun.
• Auroras: Solar flares reaching Earth's atmosphere result in charged particles colliding with gaseous particles, producing a vibrant and colorful effect. In the South Pole region, it manifests as Aurora Australis, while in the North Pole region, it appears as Aurora Borealis.
• Solar Day: The time interval between two successive transits of the Sun across a specific meridian. The mean solar day is 24 hours, with slight variations based on latitude due to the Earth's elliptical orbit inclined toward the equator.
• Sidereal Day: The time interval equivalent to one complete rotation of the Earth in relation to the Sun. Its duration of 23 hours, 56 minutes, and 4.09 seconds is nearly 4 minutes shorter than that of a mean solar day.

Parker Solar Probe Mission:

• Parker Solar Probe Mission: Launched by NASA in 2018, the Parker Solar Probe aims to observe the outer corona of the Sun. It embarks on a journey through the Sun's atmosphere, approaching closer to the surface than any previous spacecraft. Enduring extreme heat and radiation conditions, the mission provides humanity with unprecedented observations of a star.

The Planet

• Planets revolve around the Sun. They have their own elliptical path of movement known as the orbits.
• Movement around its own axis is called rotation and movement around the Sun is revolution. They have their own speed too. 
• Planets, unlike stars, have no light or heat of their own. They are lit by the light of the stars.

Formation of Planets

• Stars are clumps of gas inside a nebula. In these clusters, due to the force of gravity, a core was formed in the gaseous cloud and around this gaseous core, a rotating plate of gas and dust particles developed.
• In this stage, the condensation of the gaseous cloud started and the material covering the core developed in the form of small spheres. These small spheres evolved as planetesimals by a process of mutual attraction from adhesion molecules.
• Earth and Mars, the inner planets, orbit the Sun closer than the outer planets—Jupiter, Saturn, Uranus, and Neptune. Inner planets, also known as terrestrial planets, have fewer moons, while the outer planets boast a ring system and more moons.
• Terrestrial Planets: Mercury, Venus, Earth, and Mars share similar structures with Earth.
• Jovian Planets: Planets beyond Mars are Jovian, resembling Jupiter in structure.

Mercury:

• The closest planet to the Sun, Mercury is the smallest, comparable in size and mass to the Moon. It orbits the Sun in 88 days, completes one axial rotation in 59 days, and lacks a moon. With no atmosphere, its surface is rocky and mountainous, with extreme temperature variations between its sunlit and shaded sides. Often hidden by the Sun's glare, Mercury is observable before sunrise in September and October.

Venus:

• Venus, similar in size to Earth, lacks a moon and rotates unusually from east to west. Taking 224.7 days to orbit the Sun and 243 days to rotate on its axis, Venus has a thick atmosphere primarily composed of carbon dioxide (96.5%) and nitrogen (3.5%). Its cloudy atmosphere causes a significant greenhouse effect, making it the hottest planet. Venus alternately appears in the eastern sky before sunrise or the western sky after sunset.

The Venera Programme:

• Soviet space probes under the Venera programme (1961–1984) explored Venus, marking milestones such as the first man-made device to enter another planet's atmosphere (Venera 3, March 1, 1966).

The Earth:

• Rotating west to east, Earth has a geoid shape—slightly flattened at the poles. As the third-closest planet to the Sun, Earth is the fifth largest. Its composition, resembling Venus, presents a blue-green appearance due to water and landmasses, earning it the title of the "blue planet."

Satellite: The Moon

• A celestial body orbiting a larger celestial body is known as its satellite. The Moon is Earth's natural satellite, and planets are satellites of the Sun. Satellites, like planets, do not emit their own light or heat.
• Due to the Moon's orbit around Earth and the Sun, its position changes daily in relation to the Sun, causing varying phases. The different shapes of the bright part of the Moon throughout a month are termed lunar phases.
• The Moon takes approximately 27 days and 7 hours to complete both its rotation and revolution, always presenting the same side to Earth. It lacks an atmosphere, and its diameter is only one-fourth that of Earth.
• The Moon is situated about 384,400 km away from Earth, and the reflected sunlight reaches us in about one and a quarter seconds. Notable explorers Neil Armstrong, Edwin Aldrin, and Michael Collins set foot on the Moon on July 21, 1969, discovering a dusty and barren surface with various-sized craters and steep mountains.
• The total gravitational forces of the Moon and the Sun are in a 9:4 ratio, with the Moon's gravitational pull being 1/6th that of Earth. The Moon's density is 3.34 g/cm³, about 60% of Earth's density. It is the second densest planetary moon and has the second-highest surface gravity.
• Selenology is the study of the Moon, and Moonquakes can occur due to tectonic plate shifts, Earth's tidal pull, meteor impacts, or temperature changes on the Moon's surface. Mons Huygens, the Moon's tallest mountain, stands at 18,046 ft and is named after Dutch astronomer Christian Huygens.

Mars

• Mars is approximately half the size of Earth, with a diameter slightly over half of Earth's and only one-tenth of Earth's mass.
•  It takes 687 days for one orbit around the Sun and one day for one spin on its axis. 
• The Martian atmosphere is much thinner than Earth's, primarily composed of nitrogen and argon, with traces of oxygen.
• Known as the red planet due to its reddish appearance, Mars has two small natural satellites, Phobos and Deimos.
• In July 2018, researchers unveiled evidence of a liquid lake beneath the ice cap at Mars' Southern pole. Mars is observable from Earth for a significant part of the year, but optimal viewing occurs when it is opposite the Sun's position in the sky, bringing it closer to Earth.

MAVEN

• MAVEN (Mars Atmosphere and Volatile Evolution mission) embarked on its mission in November 2013 to explore Mars' upper atmosphere, ionosphere, and interactions with the Sun and solar wind.

InSight mission

• The InSight mission, a component of NASA's Discovery Programme, deployed a robotic lander on May 5, 2018, with the aim of studying Mars' interior using geophysical measurements. It successfully landed on November 26, 2018, in the Elysium Planitia region of Mars.

Jupiter

• Jupiter, the largest planet in our solar system, orbits the Sun every 11 years and 11 months.
•  It completes one spin on its axis in 9 hours and 56 minutes and boasts 67 satellites, along with faint rings.
•  The Great Red Spot, a complex storm enduring for centuries, is a distinctive feature. 
• Jupiter's massive size exerts a strong gravitational pull on nearby objects, and its bright appearance in the sky is due to a reflective atmosphere.

Jupiter’s Mission Juno

• Juno, NASA's space probe orbiter around Jupiter, entered a polar orbit in 2016. Launched in 2011, it aims to study Jupiter's temperature, clouds, water composition, gravitational and magnetic fields, and other properties.

Saturn

• Saturn, the sixth planet from the Sun, stands out with its yellowish hue and three prominent rings. It takes 29 years and 5 months for one orbit and 10 hours and 40 minutes for one rotation. Saturn's density is less than water, and it has 82 satellites.

• Ring-plane crossings occur approximately every 14.7 years, causing the rings to temporarily disappear.

Uranus

• Uranus, discovered by William Herschel in 1781, was the first planet identified with a telescope.
•  Hydrogen and methane are present in its atmosphere, and its unique feature is a highly tilted rotation axis, causing it to appear to roll on its side during orbital motion. 
• Uranus completes one orbit every 84 years and one rotation every 17 hours and 14 minutes, with 27 satellites in tow.

Neptune

• Neptune, identified by Sir William Herschel based on Sir Isaac Newton's law of gravitation nearly 180 years after its formulation, completes one orbit around the Sun in 164 years and one rotation on its axis in 16 hours and 7 minutes. 
• With 14 satellites, Neptune and Uranus, both faint and imperceptible to the naked eye, remained unknown in ancient times until the advent of telescopes in astronomy.

Pluto

• Pluto, discovered by Clyde Tombaugh in 1930, was initially acknowledged as the ninth planet in our solar system. However, the revelation of similarly intriguing celestial bodies within the distant Kuiper Belt led to its reclassification as a dwarf planet in 2006.
•  Pluto's revolution spans 248 years, and it completes a rotation in 155 hours. Hosting five known moons—Charon (the largest), Styx, Nix, Kerberos, and Hydra—Pluto and Charon are occasionally regarded as a binary star system.

Additional Members of Our Solar System

• Several other constituents of our solar system are outlined below.

Asteroids (Starlike Celestial Bodies)

• Numerous minuscule celestial bodies exist between the orbits of Mars and Jupiter, orbiting the Sun. These bodies, referred to as asteroids, each follow their distinct orbit, collectively forming a dispersed band.
• Some asteroids exhibit elongated orbits that extend beyond Jupiter's orbit.
• Asteroid sizes vary from pebble-sized to a few hundred kilometers. 
• The largest, Ceres, boasts a diameter of approximately 1000 km. Scientists posit that asteroids are remnants of matter that couldn't coalesce into a planet, constituting small, rocky bodies. During their orbits, asteroids frequently collide and fragment into smaller pieces.

Comets

• Comets traverse highly elliptical paths around the Sun, typically with extended revolution periods. They become visible from Earth when in close proximity to the Sun, appearing as bright heads with long tails.
• The tail's size increases as the comet nears the Sun and diminishes as it moves away, always pointing away from the Sun. Some comets, like Halley's comet, reappear periodically—Halley's comet, for instance, returns approximately every 76 years, last observed in 1986. Research into comet tails has revealed the presence of carbon, nitrogen, and hydrogen molecules.
• Given that these molecules can contribute to the formation of complex molecules vital for life's origin, some scientists propose that comets transported life's building blocks to Earth from outer space.

Meteoroids, Meteorites, and Meteor Showers

• Meteoroids are small, stone-like objects orbiting the Sun.
• Their presence becomes noticeable when some of them occasionally enter Earth's atmosphere, traveling at high speeds.
• Due to atmospheric friction, these meteoroids heat up, glow, and quickly evaporate, creating bright streaks of light in the sky. Although commonly referred to as shooting stars, they are not actual stars.
• Meteorites Some meteoroids are large enough to reach Earth before completely evaporating, and the fragments that make it to Earth's surface are called meteorites. These meteorites may crash into the ground, forming craters. Examples include the Meteor Crater in Arizona, USA, and Lonar Lake in Maharashtra, India.
• Meteor Showers When Earth passes through the debris trail of a comet, swarms of meteors become visible, resulting in meteor showers. Some meteor showers occur at regular intervals each year.

Orbits

• An orbit is the curved path of an object, such as a planet around a star, a natural satellite around a planet, or an artificial satellite around an object in space.

Types of Orbits:

• Geostationary Orbit Circles the Earth above the Equator from West to East at a height of 36,000 km. Satellites in Geostationary Orbit appear stationary over a fixed position, following Earth's rotation.
• Geosynchronous Orbit Orbits Earth with a pattern matching Earth's daily rotation on its axis (sidereal day).
• Sun-Synchronous Orbit Polar orbits synchronized with the Sun, typically occurring at altitudes of 600 to 800 km.
• Low Earth Orbit (LEO) Typically at an altitude of less than 1,000 km, with the International Space Station located in low Earth orbit.

Altitude could be as low as 160 km above the Earth's surface.

Prelims Facts

• Which evidence(s) support the Big-Bang Theory on the origin of the Universe?
  • - Expansion of the Universe (UPPSC (Pre) 2016
• The terms Event Horizon' Singularity, String Theory' and "Standard Model' are related with the study of
  • -Observation and Understanding of the Universe [IAS (Pre) 2017)
• Who gave the Hypothesis that the planets were formed out of a cloud of material associated with a youthful Sun?
  • -Immanuel Kant (Nebular Hypothesis) (MPSC (Pre) 2019]
• At which place, the Polar Star appears at the lightest angle in the sky that is at an angle of 30°?
  • -Phalut, West Bengal (WBCS (Pre) 2014)
• If the stars are seen to rise perpendicular to the horizon by an observer, it is located on which point?
  • - Equator (UPPSC (Pre) 2001)
• Which scientist said for the first that the Earth revolves around the Sun and that the Earth is not the centre of the universe?
  • - Copernicus (MPPSC (Pre) 1998)
• A group of stars arranged in a particular shape is called
  • -Constellation (UPPSC (Pre) 2013
• The Black Hole Theory was propounded by
  • -S Chandrashekhar (UPPSC (Pre) 1996]
• The unit of measuring distance between the stars is known as
  • -Light Year (UKPSC (Pre) 2006]
• The Big Bang Theory is related to avode ITH
  • - Origin of the Universe [RAS/RTS (Pre) 2007]
• The Milky Way is classified as
  • - Spiral Galaxy (UPPSC (Pre) 2001]
• In irregular galaxies, quantity of gases and dust is More than stars [UPPSC (Pre) 2003]
• The distance between the Sun and the Earth varies from a maximum point to a minimum. What is the average distance between them?
  • - 150x106 km [UPPSC (Pre) 2001]
• Which planet has its day and tilt of its axis as almost indentical to those of the Earth?
  • faint and consists mainly of Silicates [UPPSC (Mains) 2001
• The Jovian Ring system is dust, the composition of dust is formed by
  • - Silicates (UPPSC ( mains 2014
• What is the name of small pieces of rock revolving around the Sun between the orbits of Mars and Jupiter
  • - Asteroids [IAS (Pre) 1997
• In order of their distance from the Sun, which planetsi between Mars and Uranus? What is the name
  • - Jupiter and Saturn (UPPSC (Pre) 2008
• mission that gave mankind its first ever walk on the Moon's surface?
  • -The Sea of Tranquility [MPPSC (Pre) 2005
• What is the name of the planet, which takes 29.5 years to complete one revolution around the Sun?
  • - Saturn [BPSC (Pre) 2000
• Which planets are the only planets in our solar system, which do not have any natural satellites?
  • - Mercury and Venus [UPPSC (Mains) 2016]
• The atmosphere of Saturn contains which gas in a large quantity?
  • Nitrogen [UPPSC (Pre) 2022)
• Size of the Sun is many times bigger than that of the Earth?
  • 109 times (MPPSC (Pre) 2014]
• Time taken by the Sun to revolve around the centre of our galaxy is
  • - 25 crore years [IAS (Pre) 1994]
• The group of stars that indicates the direction of poles is
  • - Saptarishi [BPSC (Pre) 1996]
• Which is the largest and heaviest planet of our Solar System?
  • Jupiter [CGPSC (Pre) 2003-
  • - When the Earth is farthest from the Sun then that Mars and Jupiter [UPPSC (Pre) 2008
• phenomenon is known as
  • Aphelion (MPPSC (Pre) 2015

Self Check

1. In order of their distances from the Sun, which of the following planets lies between Mars and Uranus.

(a) Earth and Jupiter

(b) Jupiter and Saturn

(c) Saturn and Earth

(d) Saturn and Naptune

2. Messenger satellite has been launched by NASA for the study of

(a) Mercury

(b) Venus

(c) Saturn

(d) Jupiter

3. Milky Way galaxy was first seen by

(a) Galileo

(b) Martin Schmidt

(c) Marconi

(d) Newton

4. Which of the following statements are helpful in probing the Big Bang Theory?

1. Study of Cosmic Microwave Background Radiation (CMBR).
2. Measurement by Wilkinson Microwave Anisotropy Probe (WMAP).
3. Red shift observation.
4. Information about the Large Hadron Collider.

Select the correct answer by using the codes given below.

Codes

(a) 1 and 3)

(b) 1, 2 and 3

(c) 3 and 4

(d) All of the above

5. Consider the following statements.

1. When a star moves away from the observer then the light coming from it looks red gradually shifting from white.
2. This observation is useful to explain the origin of the universe.

Which of the statements given above is/are correct?

(a) Only 1

(b) Only 2

(c) Both 1 and 2

(d) Neither 1 nor 2

6. Consider the following statements.

1. Our galaxy 'Milky Way' is a spiral galaxy.
2. Our solar system is located in the approximate center of the Milky Way.

Which of the statements given above is/are correct?

(a) Only 1

(b) Only 2

(c) Both 1 and 2

 (d) Neither 1 nor 2

7. Consider the following statements.

1. Pulsars emit regular pulses of electromagnetic waves.
2. Quasars emit radio radiation.
3. Origin of stars are traced back to nebulae.
4. It is predicted that after 5 billion years the Sun may expand enough to engulf all its planets and collapse itself

Which of the statements given above is/are correct?

(a) 3 and 4

(b) 1 and 2

(c) 1, 2 and 3

(d) All of these

8. Assertion (A) A black hole is an astronomical entity that cannot be seen by telescope.

Reason (R) The gravitational field on a black hole is so strong that it does not allow even light to escape. UPPSC (Pre) 2001, 03

Codes

(a) Both A and R are true and R is the correct explanation of A

(b) Both A and R are true, but R is not the correct explanation of A

(c) A is true, but R is false.

(d) A is false, but R is true.

9. Which of the following statements are correct?

1. Most of the stars in our universe exist single.
2. High mass stars have a shorter duration of life span.
3. In the future, 'Sun' may become a black dwarf not a black hole.
4. Chandrasekhar limit deals with the finding of black holes

Select the correct answer by using the codes given below.

(a) 1 and 4 

(b) 1. 2 and 3

(c) 2 and 3

(d) All of these

10. Which of the following statements is/are correct? 

1. Supernova is a stage when a star explodes and loses its characteristics.
2. Stars having similar mass like our Sun have similar rotational speed.
3. Stars having mass lower than the Sun never explode. 4. Once a star turns to white dwarf, it is rapidly converted to black hole.

Select the correct answer by using the codes given below.

(a) Only 1

(b) 1 and 2

(c) 1, 2 and 3

(d) All of the above

11 . Which is true about planets? UPPSC (Pre) 1992

(a) Planets are non-luminous bodies and don't shine. 

(b) Planets shine though they are non-luminous bodies. 

(c) Planets do not shine though they are luminous bodies.

(d) Planets have a luminous body and also shine.

12. Consider the following statements regarding the solar system.

1. All the planets constitute less than 2% of the total matter of the solar system.
2. All the Jovian planets have rings.
3. At the edge of the solar system, there are numerous small celestial bodies.

Which of the above statements are correct?

(a) 1 and 2

(b) 2 and 3

(c) 1 and 3

(d) All of these

13. Consider the following statements regarding Mercury

1. One part of the planet is very hot while the other is very cold.
2. Its surface is rocky and mountainous
3. It can be seen in sky in September and October 'just after sunset

Which of the above statements are correct?

(a) 1 and 2

(b) 2 and 3

(c) 1 and 3

(d) All of these

14. Which of the following statements relating to the planet Venus is/are correct?

1. It is the nearest planet from the Sun.
2. It is only slightly smaller than the Earth.
3. It has no atmosphere.

Select the correct answer by using the codes given below.

(A) 1 and 2

(b) 1 and 3

(c) Only 2

(b) 1 and 3

(d) All of these

15. Which of the following statements relating to the solar system is/are correct?

1. Venus and Uranus rotate opposite to the direction of rotation of the Earth.
2. Venus is the nearest planet to the Earth.

Select the correct answer by using the codes given below.

(a) Only 1

(b) Only 2

(c) Both 1 and 2

(d) Neither 1 nor 2

16. With reference to Mars, which of the following statements is/are true?

UPPSC (Pre) 2014

1. Mars is also called 'Red planet', is a neighbor planet of the Earth.
2. It has two satellites called Deimos and Callisto.
3. It is the most explored planet by man in the solar system other than the Earth.
4. It is the smallest planet in the solar system.

Select the correct answer by using the codes given below.

(a) Only 1

(b) 1 and 3

(c) 1, 2 and 3

(d) All of the above

17. Which of the following pairs is not correctly matched?UPPSC (Mains) 2011

(a) The largest planet of the solar system: Jupiter

(b) The smallest planet of the solar system: Mercury

(c) The brightest planet of the solar system: Venus

(d) The slowest moving planet of the solar system: Mars

18. Consider the following statements regarding the Moon of the Earth.

1. In terms of size, the Moon is similar to planet Mercury.
2. In terms of mass, Moon is about two-third of the planet Mercury

Which of the statement(s) given above is/are correct) 

(a) Only 1

(b) Only 2

(c) Both 1 and 2

(d) Neither 1 nor 2

19. Consider the following statements about the Flute

1. Pluto is the largest dwarf planet in our solar system. 
2. Pluto is located in the Kuiper belt.
3. Pluto has no natural satellites.

Which of the statements given above is/are correct?

(a) Only 2

(b) Only 3

(c) 1 and 2

(d) All of these

20. Which of the following describes the Geostatio-nary Orbit (GEO) correctly?

 (a) Altitude of 20000 km above the sea level and the Slisorbital period is 12 hr.

(b) Altitude of 36000 km above the sea level and the No bull orbital period is 24 hr.

c) Altitude of 400 km above the sea level and the orbital period is 90 min.

(d) None of the above

21. What are the differences between asteroids and comets? UPPSC (Pre) 2011

1. Asteroids are composed of rocks and metals, while comets contain lot of ice along with rocks and hydrocarbons.
2. Asteroids are found mostly in Kuiper belt beyond the orbit of Neptune and in Oort cloud in outer solar system, while comets are found in the belt between Mars and Jupiter.
3. The surface of asteroids is solid and stable, where the surface of comets is very unstable and changeable.

Which of the statements given above is/are correct?

(a) 1 and 2

(b) 1 and 3

(c) Only 3

(d) All of these

Know Right Answer

1 (b)

2 (a)

3( a)

4(d)

5 (a)

6( a)

7(d)

8(a)

9 (c)

10 (a)

11 (b)

12 (d)

13 (a)

14 (c)

15 (d)

16 (b)

17 (d)

18 (a) 

19 (a)

20 (b)

21 (b)