The Solar System & Universe

The Solar System & Universe

Universe

• The universe is commonly defined as the totality of everything that exists, including all physical matter and energy, the planets, stars, galaxies and the contents of intergalactic space.

• The study of universe is known as Cosmology.

Cosmology = cosmos (universe) + logos (science)

• The diameter of the universe is 10⁸ light years.

• After the birth of universe atoms came into existence. With these atoms dust and clouds of gases formed.

Galaxy

• A galaxy is a vast system of billions of stars, which also contains a large number of gas clouds (mainly of hydrogen gas) and dust, isolated in space from similar systems.

• There are about 100 billion galaxies (10¹¹ galaxies) in the universe, and each galaxy has, on an average, 100 billion stars (10¹¹ stars). So, the total number of stars in the universe is 10²² stars.

• The Milky Way Galaxy is the home of the Earth and our Solar System. It is spiral in shape.

• Milky Way Galaxy was formed 5 billion years after the Big Bang. The first person to see this galaxy was Galileo Galilei.

• Latest known galaxy is the Dwarf Galaxy.

• According to the modem thought, universe can be classified into two parts namely—(a) Atmosphere and (b) Space.

• Origin of the universe is explained by the Big Bang Theory, formulated and proposed by the Belgium Roman catholic priest, physicist, astronomer and cosmologist Georges Lemaitre.

• Andromeda is our nearest galaxy.

The Big Bang Theory

• All the matter in the universe was originally a concentrated lump called primeval atom.

• Big Bang was an explosion that occurred 13.798 billion years ago, leading to the formation of galaxies of stars and other cosmic bodies.

• Since then, all the galaxies have been flying away from one another causing expansion of the universe.

Higgs Boson

• On March 30, 2010, CERN conducted a major experiment in the 27 km Large Hadron Collider, colliding proton beams at light speed to produce Higgs Boson. Over 1,000 scientists took part to explore mysteries like dark matter, dark energy, extra dimensions, and the Big Bang.

• The Higgs Boson, often called the "God Particle," is seen as a key to understanding the universe. After 50 years of research, CERN confirmed a Higgs-like particle on July 4, 2012. The Large Hadron Collider was shut on February 14, 2013, and restarted in June 2015.

Star

• Clumps of dust and gas in a nebula come together due to gravity and form stars.

• Stars are made of hot burning gases. They emit light of their own and are very large and very hot.

• According to NASA, Light takes about 4.35 years to reach us from Alpha centauri and 4.25 years from the nearest star Proxima Centauri.

The Solar System

• The solar system consists of the Sun, the eight planets and their satellites (or moons), and thousands of other smaller heavenly bodies such as asteroids, comets and meteors.

• The Sun is at the centre of the solar system and all these bodies are revolving around it.

• The gravitational pull of the Sun keeps all the planets and other objects revolving around it. Thus, the motion of all the members of the solar system is governed mainly by the gravitational force of the Sun.

• Planets revolve around the Sun in elliptical orbit.

• In the solar system the planet nearest to the Sun is Mercury and the planet farthest from the Sun is Neptune (not Pluto).

• The size of solar system has been estimated to at about 10⁵ A.U.

• The solar system is dominated by the Sun which accounts for almost 99.9% of the matter in the whole solar system.

• The Sun is also the source of all the energy in the solar system.

• Pluto is a dwarf planet.

• Mercury, Venus, Earth, Mars are called terrestrial planets and Jupiter, Saturn, Uranus and Neptune are called gaseous planets.

Heliocentrism

• Heliocentrism, a cosmological model in which the Sun is assumed to lie at or near a central point (e.g, of the solar system or of the universe) while the Earth and other bodies revolve around it.

• In the 5th century BC, Greek philosophers Philolaus and Hicetas suggested Earth revolved around a "central fire." Later, Aristarchus of Samos proposed that Earth and other planets orbited the Sun.

• In the 2nd century AD, Ptolemy proposed a geocentric model with Earth at the center and celestial bodies orbiting it. This view dominated science for about 1,400 years.

• In 1444, Nicholas of Cusa supported Earth's rotation, but heliocentrism gained ground with Copernicus's 1543 work. Galileo later backed this model, leading to his trial by the Inquisition in 1633.

Geocentric Model

• The Geocentric Model is a theory where Earth is considered the center of the universe. The most developed version was by Ptolemy in the 2nd century CE.

• This model was widely accepted until the 16th century, when Copernicus’s heliocentric model replaced it.

Members of the Solar System

The Sun

• The Sun is at the centre of the Solar System.

• Its size is thirteen lakh times as that of the Earth.

• It is the nearest star to the Earth.

• It is an ultimate source of energy for life on Earth.

• Its diameter is 14 lakh kms. (approx).

• It is composed of 71% Hydrogen, 26.5% Helium and 2.5% other elements.

• Hydrogen and Helium are the main gases present in the Sun.

• Within the Sun, hydrogen is converted to Helium due to nuclear fusion releasing a tremendous amount of heat and light.

• It has a surface temperature of 5778 K or 5504.85°C or 9940.73°F.

• A storm of hot atoms which dissipates from the photosphere of the Sun overcomes its gravity and goes into the outer space, is known as Solar Flares.

• When Solar Flares reach the earth's atmosphere, after colliding with the air and dust particles, it produces a spectacular colourful effect.

• In the North-Pole region, this effect can be seen as Aurora Borealis and in the South Pole region as the Aurora Australis.

• The Regions from where the solar flares originate some dark spots are seen and these are called Sun Spots.

• The Spots are relatively colder regions of the Sun, having temperature of about 1500°C. Sun Spots produce strong Magnetic Radiations which hamper the Wireless Communication Systems on earth. Sun Spots appear and disappear after every 11 years which is called Sun Spot Cycle.

• The temperature at the centre is around 1.571 x 10⁷ K or 15,000,000°C.Shining surface of the Sim is called photosphere, it appears like a disc, radiates energy and acts as a source of energy.

• The outer layer of the Sim's atmosphere made up of thin hot gases, is called Corona. Corona is visible only during a total eclipse of the Sun (or with a special solar telescope called Coronograph).

• The planet travels with the Sun through millions of stars in our galaxy at a speed of about 70,000 km per hour.

• The Sun is about 150 million kms away from the Earth.

• Light (at the speed of 3,00,000 km per second) takes about 8.5 minutes to reach the Earth from the Sun.

The Planets

• These are opaque bodies which continuously revolve around and are lighted by the Sun.

• The IAU General Assembly (2006) agreed that a 'planet' is defined as a celestial body that-

  • Is in orbit around the Sun,

  • It has sufficient mass for its self-gravity to overcome rigid body forces so that it assumes a hydrostatic equilibrium (nearly round) shape, and

  • It  has cleared the neighbourhood around its orbit.

• This means that the Solar System consists of eight 'planets' Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus and Neptune.

• A new distinct class of objects "dwarf planets" was also decided. It was agreed that "planets" and "dwarf planets" are two distinct classes of objects. The first members of the"dwarf planet" category are Ceres, Pluto and 2003 UB (temporary name).

• A ninth planet has been recently discovered by NASA named as Carla.

• The sequence of planets according to their distance from the Sun is Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, and Neptune.

• The sequence of planets according to their size (in descending order i.e. from big to small) is Jupiter, Saturn, Uranus, Neptune, Earth, Venus, Mars, and Mercury.

• Jupiter is the biggest and Mercury is the smallest planet of our solar system.

Classification of Planets

• The eight planets have been divided into two groups. All the planets of a particular group have some common features. 'Terrestrial planets' or 'Rocky planets' and 'Jovian planets' or 'Gaseous planets' (Gas giants) are the two groups of planets.

• The four planets nearest to the Sun-Mercury, Venus, Earth and Mars are called terrestrial planets, because their structure is similar to the earth.

• Other four planets-Jupiter, Saturn, Uranus and Neptune are called Jovian planets.

• Planets are classified into the following two groups inner and outer planets. These are separated by asteroid belt.

Some Notable Facts about Various Planets and Satellites

Mercury

• Mercury is the closest planet to the Sun.

• It is extremely hot planet. It is visible two hours before sun rise.

• Its special feature is the presence of magnetic field in it.

• It is the smallest and lightest of all the planets. It has no moon.

• The planet has no water on it.

• Mercury planet has no gases like CO₂, N₂, H₂ and O₂ which can act as building blocks of life.

• Mercury planet has no protective blanket like Ozone around it to prevent us from harmful radiations.

Venus

• Venus is the second planet in distance from the Sun. This planet is nearest to the Earth and is also the brightest planet.

• Venus is known as the 'Evening Star' as well as 'Morning Star'.

• Venus is surrounded by a thick cloud cover, hence known as the 'Veiled Planet' ('veil'means undear/cover).

• Venus is like the Earth in size and mass, and hence also known as the 'Earth's twin'. It also rotates clockwise like Uranus.

• Venus is the hottest planet (even hotter than Mercury) of our Solar System, due to its veil of cloud.

• Venus has no water on it. There is no sufficient oxygen on the Venus.

The Earth

• Earth is the largest of the inner planets and the fifth largest planet of our solar system.

• The Earth is 23° tilted on its axis and thus makes 66 ° angle. The earth rotates by 1° in 4 minutes.

• It takes 23 hours 56 minutes and 4.091 seconds to rotate on its axis with a speed 1,610 km/h.

• It takes 365 days, 5 hours and 48 minutes to revolve around the Sun. Mean velocity = 29.8 km/sec

• The Earth is known as the 'watery planet' or the 'blue planet' due to the presence of huge amount of water on it.

• The Earth is the only known planet which provides sustenance or life on it. It has a large quantity of oxygen which supports life.

The Moon

• The Moon is the only satellite of the Earth.

• It has a diameter of 3,475 km and its circumference is 10,864 km while its orbit is elliptical.

• The maximum distance (apogee) of the Moon from the Earth is 4,06,000 km, the minimum distance (perigee) is 3,64,000 km and approximate average distance is 3,84,400 km.

• It takes 27 days, 7 hours and 43 minutes to rotate on its axis (this period of about 27% days is called the sideral month) and approximately the same period of time it takes to revolve around the Earth.

• The Moon's period of revolution with reference to the Sim is about 29.53 days (29 days, 12 hours, 44 minutes and 2.8 seconds). This period is called a synodic month.

• Only 59% of the total surface of the Moon is visible from the Earth.

• Mass (compared to that of the Earth) - 1:81.30

• Density (relative to that of the water) - 3.34

• Density (relative to that of the Earth) - 0.6058

• Hidden part of Moon's surface - 0.41 (41%)

• Highest point on the Moon - Mt. Leibnitz (35,000 ft.) situated on the South Pole of the Moon.

• The bright part of the Moon is full of mountains whereas the dark patches are low lying plains.

• 'Sea of tranquility' made of the plain of dust particles, is on the rear side of the Moon, which always remains dark.

• The Moon has no atmosphere, no twilight and no sound.

• The temperature during daytime is about 100°C and during night it drops down to about -180°C.

• The light from the Moon takes 1.3 seconds to reach the Earth.

• The size of the Moon is one-fourth (1 /4th) the size of the Earth.

• Gravitational pull of Moon is one-sixth (l/6th) that of the Earth.

• Mainly silicon, iron, magnesium etc elements are found on the Moon's surface.

• The study of the Moon is called 'Selenology'.

• Moon is also known as the fossil planet.

Super Moon

• Super Moons happen when a full Moon is closest to the Earth, appearing bigger and brighter than normal. They are called 'super' because they are 15% brighter and 30% bigger than regular full moons.

Blue Moon

• If in a calendar month there are two full moons then the second full moon is referred as Blue Moon. It is because of the gap between the two moons which is less than 31 days.

• If in any specific year Blue Moon appears in two or more than two months then it is referred as Blue Moon Year.

Blood Moon

• A "Blood Moon" is the name given for a view of the Moon during a total lunar eclipse. Because of the way light passes through the Earth's atmosphere during an eclipse, red light from the Sun is reflected on to it.

• The Moon's reddish colour earns it the nickname—"Blood Moon".

Lunar Tetrad

• A sequence of four total lunar eclipses including no partial eclipses is called a tetrad.

Chandrayaan-1

• On 22nd October, 2008 Indian Space Research Organization (ISRO) has successfully established CHANDRAYAAN-1 in the moon's orbit from Satish Dhawan Space Centre in Sri Harikota of Andhra Pradesh by polar satellite launch vehicle PSLV-C-1.

• Chandrayaan-1 was India’s first lunar mission, carrying 11 instruments to study the Moon’s surface, minerals, ice, and temperature. It included a Moon Impact Probe and sent back high-resolution images and chemical data.

Chandrayaan-2 Mission

• India’s GSLV MKIII-M1 successfully launched Chandrayaan-2 on July 22, 2019, from Sriharikota. The mission included an Orbiter, Lander (Vikram), and Rover to explore the Moon’s South Pole.

• After multiple orbit-raising maneuvers, Chandrayaan-2 entered lunar orbit on August 20. Vikram attempted landing on September 7, but communication was lost at 2.1 km altitude.

• However, the Orbiter, equipped with the highest-resolution lunar camera (0.3 m), continues to provide valuable data.

Chandrayaan-3 Mission

• Chandrayaan-3, ISRO's third lunar mission after Chandrayaan-1 and 2, focused on achieving a soft landing on the Moon.

• Launched in June 2023 aboard GSLV MkIII, it included the Vikram lander and Pragyan rover.

• Aimed near the site of Chandrayaan-2’s crash-landing, the Rs 250 crore mission incorporated key improvements.

• On August 23, 2023, Chandrayaan-3 successfully landed on the Moon, marking a major milestone for India’s space exploration.

Mars

• Mars, known as the 'Red Planet' due to its iron-rich soil and pink sky, is a small, rocky, cold desert world—about half the size of Earth.

• It has seasons, polar ice caps, volcanoes, and weather, with a thin atmosphere of carbon dioxide, nitrogen, and argon.

• A day on Mars is 24.6 hours, and a year is 687 Earth days. Mars has two moons: Phobos and Deimos.

• India’s Mars Orbiter Mission (MOM), launched by ISRO on November 5, 2013, entered Mars orbit on September 24, 2014, in its first attempt and completed over 1000 Earth days in space.

Jupiter

• Jupiter is the largest planet of the Solar System.

• Jupiter is also known as winter planet as its average temperature is very low (-148° C).

• Ganymede, (yellow in colour), largest satellite of Jupiter is the also largest satellite in the Solar System.

Saturn

• Saturn is the second largest planet in the Solar System.

• Saturn has bright concentric rings which are made up of ice and ice-covered dust particles which revolve around it.

• Titan is the largest satellite of Saturn,

Uranus

• Uranus is about four times the size of the Earth. This planet appears greenish in colour because of methane gas present in its atmosphere.

• Uranus was discovered in 1781 by Sir William Herschel. Uranus is the 7th planet from the Sun.

• Uranus is the first planet to have been discovered by the use of a telescope.

• Uranus is the third largest planet of the Solar System.

• Uranus is extremely cold, having surface temperature (-) 190°C and is surrounded by 13 rings namely zeta (G)/R1986U2,6,5,4, alpha (α), beta (β), eta (∈), gamma (Y), delta (δ), lambda (γ), epsilon (∈), nu (v) and mu (μ).

• Uranus rotates from east to west on its axis, which is opposite to other planets except Venus.

• The axis of Uranus has large inclination so that it appears to be lying down, hence it bears the name 'A Planet on its Side'.

Neptune

• Neptune is the 8th (farthest) planet of the Solar System.

• The temperature on the surface of Neptune remains low.

• Neptune is very similar to Uranus and can be considered as its twin.

• Neptune is surrounded by methane rings of sub zero temperature.

Pluto is not a Planet now

• On August 24, 2006, the International Astronomical Union (IAU) redefined what qualifies as a planet, leading to Pluto losing its planetary status.

• As a result, the Solar System now officially has eight planets: Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, and Neptune.

• Pluto, discovered in 1930 by Clyde Tombaugh, was considered a planet for 76 years before being reclassified.

Pluto Gets a Numerical Denomination

Weeks after it was demoted to a sub-planetary status, Pluto was given a new name to reflect its new status as a dwarf planet in September, 2006.

The former 9th planet was assigned the asteroid number 134340 by the Minor Planet Centre (MPC), the official organization responsible for collecting data about asteroids and comets in our Solar System.

• Pluto's companion satellites, Charon (Pluto's largest moon), Nix and Hydra are considered part of the same system and will not be assigned separate asteroid numbers.

• Instead, they will now be called 134340 I, II and III respectively.

• Before loosing its planetary status on 24th August, 2006 Pluto was the outermost planet of the Solar System.

Some Facts and Figures about the Planets (As on August 17, 2022)

Some more elements in the Solar System

Asteroids (or Planetoids)

• Asteroids, also called minor planets, are rocky objects that orbit the Sun, mainly between Mars and Jupiter in a region known as the asteroid belt.

• Over 5000 have been identified, varying in shape and size. They rotate on their axis every 5 to 20 hours and some have small moons.

• Trojan asteroids share Jupiter’s orbit, moving ahead or behind it. Scientists believe asteroids are remnants that couldn't form into a planet due to Jupiter’s strong gravity.

Meteors and Meteorites

• Meteors and meteorites, often called shooting stars, are rock fragments from asteroid collisions.

• Small meteors burn up due to air resistance before reaching Earth.

• Larger ones that survive and land are called meteorites.

• They mostly come from the asteroid belt and are pulled toward Earth by gravity.

Comets

• Comets, known as "hairy stars," are spectacular and unpredictable visitors of the Solar System.

• They orbit the Sun in long, elliptical paths, taking hundreds or even thousands of years to complete one revolution.

• Made of frozen gases, rock, and metal, comets become visible near the Sun as the ice melts, forming a glowing tail that always points away from the Sun—even when the comet moves away.

Features of a Comet

• A comet is characterized by a long luminous tail, which emits light. But, this is visible only when the comet's orbit passes close to the Sun.

• When the comet travels close to the Sun, the ice melts to a head of gas called a Coma.

• The Sun's radiation sweeps this into a gas tail. Dust particles are also swept back to form a dust tail.

Stars

Stars are glowing celestial bodies made of hot, burning gases that shine with their own light. Though they appear fixed in the sky, stars are actually in constant motion—just so far away that their positions seem unchanged over short periods.

According to NASA, the closest star to Earth after the Sun is Proxima Centauri, located about 4.24 light years away.

Some well-known stars include:

• Pole Star (Polaris)

• Sirius

• Vega

• Capella

• Alpha Centauri

• Beta Centauri

• Proxima Centauri

• Spica

• Regulus

• Pleiades (star cluster)

• Aldebaran

• Arcturus

• Betelgeuse

• And, of course, the Sun.

Facts about Stars

• On a clear, moonless night, about 2,000 stars can be seen without a telescope.

• In total, around 8,000 stars are visible from Earth to the naked eye — 4,000 in the Northern Hemisphere and 4,000 in the Southern Hemisphere.

• However, at any given time, only half of these (about 2,000) are visible because the rest are in the daytime sky, hidden by the Sun’s brightness.

• Astronomers estimate there are about 10²² (10 sextillion) stars in the observable universe.

Constellations

• To enable astronomers to identify roughly the position of the stars, the sky has been divided into units. These units are known as Constellations.

• These constellations were named in the honour of mythological characters.

• At present 88 constellations are recognized.

Some well known Constellations

• Some well known constellations, with their Indian names are given below :

Earth's Galaxy: The Milky Way

• It is a large spiral-shaped galaxy, about 1,00,000 light-years wide and 10,000 light-years thick at the center.

• The Milky Way appears as a milky band of light in the night sky because it is made up of billions of stars, too far away to be seen individually.

• Galileo discovered that this soft glow is actually a collection of countless stars.

• Our galaxy rotates slowly and takes about 250 million years to complete one full revolution.

Andromeda: Earth's closest Galactic neighbour

• It appears as a faint, fuzzy patch of light in the night sky and contains millions of stars.

• It is the farthest object visible to the naked eye from Earth.

• Andromeda and the Milky Way are part of a galactic cluster called the Local Group, which contains about 30 galaxies.

• The Local Group itself is part of a larger cluster known as the Virgo Cluster.

• Galaxies are often found in clusters, and these clusters may form superclusters, which are scattered across the universe.

Nebulae

• Nebulae are vast clouds of gas and dust in space that look like faint, misty patches in the sky.

• Some shine brightly, while others appear dark against the background.

• Their brightness depends on nearby stars—hot stars can make nebulae glow by ionizing hydrogen, cooler stars only reflect light, and without any nearby stars, nebulae stay dark and are seen only by the way they block starlight behind them.

There are five types of nebulous objects in the sky –

1. Planetary nebulae,

2. Emission nebulae,

3. Reflection nebulae,

4. Dark nebulae and

5. Supernova remnants.

The Earth: Shape Size & Statistical Data

Shape of the Earth:

Pythagoras, a Greek philosopher, was among the first to suggest that the Earth is spherical. If the Earth were flat, the Sun would rise at the same time everywhere, but it doesn't.

When ships approach the shore, their tops appear before the rest of the body, which suggests a curved surface.

During eclipses, the Earth always casts a circular shadow, which also supports the idea that the Earth is a sphere.

• At the North Pole, the Pole Star is directly overhead (90° angle).

• Moving south, its angle lowers, becoming 0° at the Equator—showing a curved surface.

• Sun, Moon, and other celestial bodies appear spherical, suggesting Earth is too.

• Space photos confirm Earth is round.

Refined measurements of the Earth have proved that the true form of the Earth resembles a sphere that has been compressed at the poles and made to bulge at the Equator. This form is known as an oblate spheroid.

The various factors which make the earth suitable for life to evolve and survive are:

Why Earth Supports Life

• Earth has essential elements like carbon, hydrogen, nitrogen, and oxygen.

• It has the right temperature—not too hot or cold.

• Water is abundant in lakes, rivers, and oceans.

• Oxygen in the atmosphere supports breathing.

• The ozone layer protects life from harmful UV rays.

Biodiversity

• Biodiversity means the variety of life on Earth.

• It is richest near the equator, especially in tropical regions.

Statistical Data of the Earth

The Earth, third planet from the Sun, is the fifth largest planet in the Solar System in terms of size and mass.

• Average diameter of Earth is 12,742 km, which was first calculated by Eratosthenes, the Greek mathematician.

• 29.1% of the total surface area of Earth is covered by continents (land), while 70.9% is covered by oceans.

• The total water area of the earth including the oceans, lakes, rivers, ice sheets and the water in the atmosphere is called hydrosphere and it covers about 71% of the earth's surface.