2.1. The universe

The Universe

Introduction
Theories of Space
Important Points

The Universe – Introduction

• The Universe is all of space and time and their contents,including planets, stars, galaxies, and all other forms of matter and energy.
• It was termed as Cosmos when first conceived as an orderly unit and its study is called as cosmology. Normal matters all that are visible (star, planet and galaxies) make up less than 5 % of the total mass of the universe rest are made of dark matters.
• These dark matters are not seen by the astronomers but can study their effects.The observable universe is about 28 billion parsecs (91 billion light-years) in diameter at the present time.
• Generally scientists agree Universe is 13.82 billion years old.
• Modern studies indicate the existence of between 100-200 billion galaxies in the visible universe.
• These dark matters are not seen by the astronomers but can study their effects.The observable universe is about 28 billion parsecs (91 billion light-years) in diameter at the present time.

Planet – Earth

Star – Sun

Solar System

Galaxy

Universe

Our own galaxy, called the ‘Milky way’ or ‘Akash ganga’, which appears as a river of bright light flowing through the sky, belongs to a cluster of some 24 galaxies called the ‘Local group’.

Origins of the Universe 101 National Geographic

Theories of Space

THE EXPANDING UNIVERSE

• Edwin Hubble, in 1920, provided evidence that the universe is expanding. As time passes, galaxies move further and further apart.
• It is a general law that all material bodies are heated when compressed and cooled when expanded.
• The primordial Universe, being highly compressed, must have experienced high temperatures. Heat as we know, tends to expand matter. High temperatures, therefore, must have, at some point, started an expansion of the Universe.

Theories of Space

BIG-BANG THEORY

• It is also called expanding universe hypothesis.
• Later Big bang theory was proposed by Georges Lemaitre in 1927.
• According to this theory billion of years ago cosmic matters were in highly compressed state and expansion started with primordial explosion which was bang in super dense ball. These exploded particles are still travelling at a speed of thousands miles per second and gave rise to our galaxies.

Steady state model

• The steady state theory was governed by Hermann Boudi and Thomas Gold.
• It is also known as theory of continuous creation.
• According to this theory universe has always existed and will always exist and will always look essentially the same, so there is no overall evolution thus balancing the average density despite the expansion.
• As old galaxies move apart the new galaxies are being formed.
• The Oscillating Universe Theory was advocated by Dr. Alan Sandage.
• This theory postulates that the universe not only expands but it also contracts.
• The time interval between the two phases is presumed to be billions of years.
• It is a mixture of both Big Bang an Big Crunch theory.

A cyclic model (or oscillating model)

BIG-BANG THEORY

• It is also called expanding universe hypothesis.
• Edwin Hubble, in 1920, provided evidence that the universe is expanding. As time passes, galaxies move further and further apart.
• Later Big bang theory was proposed by Georges Lemaitre in 1927.
• According to this theory billion of years ago cosmic matters were in highly compressed state and expansion started with primordial explosion which was bang in super dense ball. These exploded particles are still travelling at a speed of thousands miles per second and gave rise to our galaxies.

The primordial explosion is the hallmark of the big-bang theory. It also differs from other theories in two important respects:

• It disagrees with the Steady State claim, that new matter is being continuously created in the Universe,
• It differs from the Pulsating theory, in that, it does not admit, that matter will revert to the original congestion point.

Galaxies

• A galaxy is a gravitationally bound system of stars, stellar remnants, interstellar gas, dust, and dark matter.
• The solar system where our earth exists is in Milky Way Galaxy. It is also known as Akash Ganga.
• The Milky Way is a barred spiral galaxy with a diameter between 150,000 and 200,000 light-years (ly).It is estimated to contain 100–400 billion stars and more than 100 billion planets.
• The nearest galaxy to Milky way is Andromeda.
• Andromeda is a spiral galaxy and approximately 2.5 million light-years from the earth.
• Andromeda is also known as NGC224 and M31

Structure and composition of Galaxies

• Elliptical Galaxies – Elliptical galaxies can be classified on the basis of their ellipticity, ranging from nearly spherical (E0) to highly elongated. These have low portion of open clusters and low rate of new star formation.

• Spiral Galaxies – Spiral galaxies have a central nucleus with great spiral arms trailing round it resembling pin wheel. Andromeda Galaxy and Milky Way are the examples of such galaxy. The spiral arms are thought to be areas of high-density matter, or “density waves”.

• Irregular Galaxies – Irregular galaxies are youthful in nature with no sharp and boundary thinning out gradually, these galaxies contain large amount of gas and dust. This type of galaxy is the result of gravitational interaction or collision between formerly regular galaxies.

Stars

Planets – A planet is an astronomical body orbiting a star or stellar remnant that is massive enough to be rounded by its own gravity, is not massive enough to cause thermonuclear fusion.

• A star is type of astronomical object consisting of a luminous spheroid of plasma held together by its own gravity. The nearest star to Earth is the Sun.
• The nearest star to the earth (other than the sun) is Proxima Centauri.
• Star looks-Red with low temperature, Yellow with higher and blue with very high temperature.

THE STAR FORMATION

THE STAR FORMATION

• The distribution of matter and energy was not even in the early universe. These initial density differences gave rise to differences in gravitational forces and it caused the matter to get drawn together.
• These formed the bases for development of galaxies. A galaxy contains a large number of stars. Galaxies spread over vast distances that are measured in thousands of light-years. The diameters of individual galaxies range from 80,000-150,000 light years.
• A galaxy starts to form by accumulation of hydrogen gas in the form of a very large cloud called nebula.
• Eventually, growing nebula develops localised clumps of gas. These clumps continue to grow into even denser gaseous bodies, giving rise to formation of stars.
• The formation of stars is believed to have taken place some 5-6 billion years ago

Important Points

The light-year is a unit of length used to express astronomical distances and measures about 9.46 trillion kilometres (9.46 x 1012 km). As defined by the International Astronomical Union (IAU), a light-year is the distance that light travels in vacuum in one Julian year (365.25 days). Because it includes the word “year”, the term light-year is sometimes misinterpreted as a unit of time.

An Astronomical Unit (AU) is the average distance between Earth and the Sun, which is about 93 million miles or 150 million kilometers. Astronomical units are usually used to measure distances within our Solar System.

A black hole is a region of spacetime exhibiting such strong gravitational effects that nothing—not even particles and electromagnetic radiation such as light—can escape from inside it. Objects whose gravitational fields are too strong for light to escape were first considered in the 18th century by John Michell and Pierre-Simon Laplace.

2.2. The solar system

SOLAR SYSTEM

INTRODUCTION
PLANETS
THE MOON
ASTEROID
THE RINGS OF SATURN
DWARF PLANET
SOLAR SYSTEM KEY FACTS

Introduction

• Solar System constitute of heavenly bodies revolving around an average star known as SUN.
• Our solar system consists of the sun (the star), 8 planets, 63 moons, millions of smaller bodies like asteroids and comets and huge quantity of dust-grains and gases. The Nebula from which our Solar system is supposed to have been formed, started its collapse and core formation some time 5-5.6 billion years ago and the planets were formed about 4.6 billion years ago.
• Eight Planets – Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus and Neptune

Solar System

THE SUN

Core The core of the sun consists of hydrogen atoms which fuse together due to compression and creates helium. This is called as nuclear fusion.

Radiative Zone Energy produced in core slowly rises in the radiative zone outside the core. It takes around one million years for energy to travel out.

Convection Zone Convection zone is just beneath the Sun’s surface.

Photosphere Photosphere is the visible surface of Sun where temperature is around 5500°C. This part gives us light, which takes around 8 minutes to reach Earth surface.

Chromosphere Chromosphere is a thin layer of gas above the photosphere. Along with Corona, it makes the atmosphere of Sun.

Corona Corona is a thick layer of gas above chromosphere. It extends millions of kilometers around the sun. Corona and Chromosphere are visible during a total solar eclipse when the sun’s surface is completely hidden behind moon.

Composition of Sun

The Sun’s mass is composed of 71 percent hydrogen, 27 percent helium, and 2 percent other elements.

Mass of Sun

The Sun has a mass of 1.99 million trillion trillion kilograms. The most massive supergiant stars have about one hundred times more mass than the Sun.

Rotation of Sun

It spins at different speeds depending on the latitude. The Sun spins once around its axis near its equator in about 25 days, and in about 35 days near its north and south poles. This kind of spinning, in which different parts move at different speeds, is called differential rotation.

Planets

• Eight Planets – Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus and Neptune.
• Inner Planets – Out of the eight planets, mercury, venus, earth and mars are called as the inner planets as they lie between the sun and the belt of asteroids.
• Outer Planets – the other four planets are called the outer planets.

Terrestrial Planets – Alternatively, the first four are called Terrestrial, meaning earth-like as they are made up of rock and metals, and have relatively high densities.

Terrestrial Planets – Alternatively, the first four are called Terrestrial, meaning earth-like as they are made up of rock and metals, and have relatively high densities.

Jovian Planets – The rest four are called Jovian or Gas Giant planets. Jovian means Jupiter like. Most of them are much larger than the terrestrial planets and have thick atmosphere, mostly of helium and hydrogen.

The terrestrial planets were formed in the close vicinity of the parent star where it was too warm for gases to condense to solid particles. Jovian planets were formed at quite a distant location. The terrestrial planets are smaller and their lower gravity could not hold the escaping gases.

All the planets were formed in the same period sometime about 4.6 billion years ago. Till August 2006, Pluto was also considered a planet. However, in a meeting of the International Astronomical Union, a decision was taken that Pluto like other celestial objects (2003 UB313) discovered in recent past may be called ‘dwarf planet’.

Mercury

• Mercury is the smallest planet.
• It is the closest planet to the sun at a distance of about 58 million km.
• One day on Mercury takes 59 Earth days.
• Only two missions have visited this rocky planet: Mariner 10 in 1974-5 and MESSENGER, which flew past Mercury three times before going into orbit around Mercury in 2011.
• Daytime Temperatures can reach 430° Celsius (8000 Fahrenheit) and drop to -180° Celsius (-290° Fahrenheit) at night.

Venus

• Venus is the second closest planet to the sun at a distance of about 108 million km.
• One day on Venus Lasts as long as 243 Earth days.
• Venus’ thick and toxic atmosphere is made up mostly of carbon dioxide (CC2) and nitrogen (N2), with clouds of sulfuric acid (H2S04) droplets.
• More than 40 spacecraft have explored Venus.
• The planet’s extreme high temperatures of almost 4800 Celsius.
• Venus spins backwards (retrograde rotation) when compared to the other planets. This means that the sun rises in the west and sets in the east on Venus.

Earth

• Earth is the third planet from the sun at a distance of about 150 million km. That’s one Astronomical Unit (AU).
• A day on Earth is 24 hours (the time it takes the Earth to rotate or spin once).
• Earth’s atmosphere Is 78% nitrogen (N2), 21% oxygen and l0% other ingredients – the perfect balance for Earthlings to breathe and live. Many planets in our solar system have atmospheres, but only Earth is breathable.
• Earth has one moon. Another name for a moon is natural satellite.
• Earth is the perfect place for life as we know it.
• Our atmosphere protects us from incoming meteorolds, most of which break up in our atmosphere before they can strike the surface as meteorites.

Mars

• Mars is the fourth planet from the sun at a distance of about 228 milLion km (142 million miles) or 1.52 AU.
• One day on Mars takes just a Little over 24 hours.
• Mars has a thin atmosphere made up mostly of carbon dioxide , nitrogen and Ar.
• Mars has two moons named Phobos and Deimos.
• The first true Mars mission success was Mariner 4 in 1965. At this time In the planet’s history, Mars’ surface cannot support Life as we know it.
• Mars is known as the Red Planet because iron minerals in the Martian soil oxidize, or rust, causing the soil and the dusty atmosphere to look red.

Jupiter

• Jupiter is the fifth planet from the sun at a distance of about 778 million km (484 milLion miles) or 5.2 Astronomical Units (AU).
• One day on Jupiter takes about 10 hours (the time It takes for Jupiter to rotate or spin once).
• Jupiter is a gas-giant planet and therefore does not have a solid surface. Jupiter may have a solid, inner core about the size of the Earth.
• Jupiter’s atmosphere Is made up mostly of hydrogen (H2) and helium (He).
• Jupiter has 50 known moons, with an additional 17 moons awaiting confirmation of their discovery, that is a total of 67 moons.
• Jupiter has a faint ring system that was discovered in 1979 by the Voyager-i mission. All four giant planets in our solar system have ring systems.
• The Juno mission was arrived at Jupiter in 2016.
• Jupiter cannot support life as we know it. However some of Jupiter’s moons have oceans underneath their crusts that might support life.

Saturn

Saturn is the sixth planet from the sun at a distance of about 1.4 billion km (886 million miles) or 9.5 AU.

One day on Saturn takes 10.7 hours (the time it takes for Saturn to rotate or spin once).

Saturn is a gas-giant planet and therefore does not have a solid surface.

Saturn’s atmosphere Is made up mostly of hydrogen (H2) and helium (He).

Saturn has 53 known moons with an additional nine moons awaiting confirmation of their discovery that is a total of 62 moons.

Only a few missions have visited Saturn: Pioneer 11, Voyager 1 and 2 and Cassinl-Huygens. Since 2004, Cassinl has been exploiing Saturn, its moons and rings.

Fact: When Galileo Galilei was observing the planet Saturn in the iGOOs, he noticed strange objects on each side of the planet and drew in his notes a triple-bodied planet system and later a planet with arms or hand les. These “handles” were in fact the rings of Saturn.

Uranus

• Uranus is the seventh planet from the sun at a distance of about 2.9 billion km.
• One day on Uranus takes about 17 hours.
• Uranus is an ice giant. Most (80 % or more) of the planets mass is made up of a hot dense fluid of Icy” materials above a small rocky core.
• Uranus has an atmosphere made up of hydrogen and helium , with methane.
• Uranus has 27 moons. Uranus’ moons are named after characters from the works of William Shakespeare and Alexander Pope.
• Voyager 2 is the only spacecraft to have visited Uranus.
• Unlike any of the other planets, Uranus rotates on Its side, which means It spins horizontally.

Neptune

• Neptune Is the eighth and farthest planet from the sun at a distance of about 4.5 billion km or 30.07 AU.
• One day on Neptune takes about 16 hours.
• Neptune Is a sister Ice giant to Uranus.
• Neptune’s atmosphere is made up mostly of hydrogen , helium and methane.
• Neptune has 13 moons. Neptune’s moons are named after various sea gods and nymphs in Greek mythology.
• Neptune has six rings.
• Voyager 2 is the only spacecraft to have visited Neptune.

The Moon

• The moon is the only natural satellite of the earth.
• The Moon is thought to have formed about 4.51 billion years ago, not long after Earth.
• The Moon’s average orbital distance is 384,402 km or 1.28 light-seconds.
• The moon makes a complete orbit around Earth in 27 Earth days and rotates or spins at that same rate, or in that same amount of time. This causes the moon to keep the same side or face towards Earth during the course of its orbit.
• The Moon has an atmosphere so tenuous as to be nearly vacuum,called an exosphere.

Dwarf planet

• A dwarf Planet is a planetary-mass object that is neither a planet nor a natural satellite. It orbits the Sun, and is massive enough for its shape to be in hydrostatic equilibrium under its own gravity, but has not cleared the neighborhood around its orbit.
• The term dwarf planet was adopted in 2006. Currently, the International Astronomical Union (IAU) recognizes five dwarf planets: Ceres, Pluto, Haumea, Makemake, Seden and Eris.

Asteroid A small rocky body orbiting the sun is termed as asteroid. Large numbers of these, ranging enormously in size, are found between the orbits of Mars and Jupiter, though some have more eccentric orbits. The asteroid is categorized by their spectra, with most falling into three basic groups: carbonaceous (C-type), silicate (S-type), and metal-rich (M-type).

Asteroid A small rocky body orbiting the sun is termed as asteroid. Large numbers of these, ranging enormously in size, are found between the orbits of Mars and Jupiter, though some have more eccentric orbits. The asteroid is categorized by their spectra, with most falling into three basic groups: carbonaceous (C-type), silicate (S-type), and metal-rich (M-type).

Meteor A meteoroid is a small rocky or metallic body travelling through space and range in size from small grains to 1 meter-wide objects. When it enters the atmosphere to become visible is called as a meteor. It is also known as “shooting star” or “falling star.” One can see nearly 20 million of meteors in a day. On an average nearly each day nearly one to two reaches Earth.

Meteor A meteoroid is a small rocky or metallic body travelling through space and range in size from small grains to 1 meter-wide objects. When it enters the atmosphere to become visible is called as a meteor. It is also known as “shooting star” or “falling star.” One can see nearly 20 million of meteors in a day. On an average nearly each day nearly one to two reaches Earth.

Comet

• A comet is an icy, small Solar System body that, when passing close to the Sun, warms and begins to release gases, a process called outgassing.
• This produces a visible atmosphere or coma, and sometimes also a tail.
• These phenomena are due to the effects of solar radiation and the solar wind acting upon the nucleus of the comet.
• Comets are distinguished from asteroids by the presence of an extended, gravitationally unbound atmosphere surrounding their central nucleus.
• As of July 2018 there are 6,339 known comets.

Properties of some comets

• A supernova is the biggest explosion that humans have ever seen. Each blast is the extremely bright, super-powerful explosion of a star.
• This happens when a star at least five times the mass of our sun goes out with a fantastic bang!
• Massive stars burn huge amounts of nuclear fuel at their cores, or centers. This produces tons of energy, so the center gets very hot. Heat generates pressure, and the pressure created by a star’s nuclear burning also keeps that star from collapsing.

Supernova

List of the nearest stars to Earth

• Sun – about 8.2 light minutes from Earth
• Alpha Centauri star system – 4.24 to 4.36 ly
  • Proxima Centauri – 4.24 ly [YH]
  • Alpha Centauri A – 4.36 ly [YS]
  • Alpha Centauri B – 4.36 ly [YS]
• Barnard’s Star – 5.96 ly [YH]
• WISE 1049-5319 – 6.5 ly, aka Luhman 16, a binary of two brown dwarf stars
• Wolf 359 – 7.78 ly [Y]
• Lalande 21185 – 8.3 ly [YH]
• Sirius star system
  • Sirius A – 8.58 ly [YH]
  • Sirius B – 8.58 ly [YH]

SOLAR SYSTEM KEY FACTS

11. Densest Planet- Earth 12. Fastest Rotation in Solar System – Jupiter 13. Morning Star-Venus 14. Nearest Planet to Earth-Venus 15. Nearest Planet to Sun-Mercury 16. Red Planet-Mars 17. Slowest Revolution in Solar System-Neptune 18. Slowest Rotation in Solar System-Venus 19. Smallest Planet-Mercury 20. Earth’s Twin-Venus

1. Biggest Planet-Jupiter = 1300 Earths 2. Blue Planet-Earth 3. Green Planet-Uranus 4. Brightest Planet-Venus 5. Coldest Planet-Neptune 6. Evening Star-Venus 7. Farthest Planet from Sun-Neptune 8. Planet with maximum no of satellites-Saturn 9. Fastest revolution in solar system – Mercury 10. Hottest Planet-Venus