Search Pabitras

Category: Cosmology

Information About Solar System

Information About Solar System

OUR SOLAR SYSTEM is the family of sun including planets, dwarf planets, satellites, asteroids, comets and many other heavenly bodies in its periphery. Its outer boundary lies up to kupier belt. It is located in one of the arms of milky way galaxy, revolving around the galactic center.

Solar System
Solar System

Formation of Solar System

Solar system was formed from giant rotating cloud of gas and dust, called as solar nebula. Most of the materials in the nebula collapsed to form sun while other remaining particles formed smaller heavenly bodies which we call as planets, satellites, asteroids, etc.

The age of solar system is estimated to be 4.5 billion years and its mass is 1.0014 times the solar mass. We have got a star (sun) at the center of our solar system around which every components of solar system revolve.

Components of solar system

The sun

The sun is the most massive object located in the center of solar system. It constituents more than 99.85% of total mass of solar system. Sun is ultimate source of energy for us and is an active medium sized star.

Sun
Sun

Sun is made up of hydrogen gas which is continuously being changed into helium atom under extremely high pressure and temperature. The process of nuclear fusion in sun releases vast amount of energy. Thus the center of sun is very hot at about 35,000,000 k and surface temperature of about 6000 k. Sun emits electromagnetic radiations of all wavelengths in the form of radio waves, infra-red, UV-rays, visible light and other radiations.

Life cycle of sun is similar to other stars. It started its journey from nebula and changed gradually into active star. Visit: https://pabitras.com.np/life-cycle-of-a-star/

Solar wind is the stream of charged gaseous ions called plasma. It is emitted continuously by the sun with the speed of about 500 km/s. Sometimes, hot gases also shoot out from sun called prominences.

Planets

Planets are the heavenly bodies that revolve around the sun in their fixed path. Greek meaning of planet means ‘wanderer’. There are eight planets in our solar system (sorry pluto 😢). The path in which planets revolve around the sun is called orbit. Orbits are elleptical in shape and the orbits of different planets don’t lie in same plane. They also have their rotation in their own axis.

The definition of planet set in 2006 by the International Astronomical Union (IAU) states that in solar system. a planet is a celestial body that :

  • is in orbit round the Sun,
  • has sufficient mass to assume hydrostatic equilibirium, and
  • has “cleared the neighbourhood” around its orbit.

Since pluto don’t have its own fixed orbit, crosses the orbit of neptune and comparatively small, it was removed from the list of planets in 2006 AD. We will look more about it in dwarf planet section

Planets are classified into two categories: Inner planets and outer planets. Mercury, Venus, Earth and Mars are considered as an inner planet. Jupiter, Saturn, Uranus and Neptune are considered as outer ones. There lies an astronomical belt between Mars and Jupiter which separates outer planets form inner planets.

Inner Planets

The four inner or terrestial planets have dense, rocky composition, few or no moons and no ring systems. They are smaller than outer planets and have less duration for a revolution around the sun. These planets have volcanoes, mountains, plains, valleys, etc in their surface. Let’s look over a brief information about them below:

  • Mercury

    Mercury
    Mercury

    Mercury is the closest planet to solar system and also the smallest one among the eight planets. It is located about 0.4 AU from the sun and weighs only 0.055 earth masses. Because of its small size, it has low gravity in its surface (3.7 m/s²) and no atmosphere. It has got a large number of craters in its surface due to meteor shower and its surface is like that of moon. Mercury has a surface temperature of about 700 k during day and 93 k at night. It is the fastest revolving planet and completes its one revolution in 88 days.

  • Venus

    Venus
    Venus

    Venus is about 0.7 AU from sun and weighs of about 0.875 earth masses. It is also known as Earth’s twin. It is the hottest planet in solar system due to the presence of large amount of green house gases like carbondioxide. Its temperature rises to about 735 k. It has a regular volcanic eruptions and appears brighter than other planets. Its period of revolution (224.7 days) is nearly equal to that of earth. It also does not have any satellites.

  • Earth

    Earth
    Earth

    Earth is the largest and densest planet among inner planets, the only one known to have current geological activity, and is the only place in universe where life is known to exist till date. It has one moon, favorable atmosphere and suitable temperature. Its period of revolution around sun is 365 days 4 hours.

  • Mars

    Mars
    Mars

    Mars is at a distance of 1.5 AU from sun and has 0.107 earth masses. It has its own atmosphere which mainly consists of carbondioxide. There a lot of volcanoes in its surface like Olympus Mons. Mars has two small natural satellites, Phobos and Deimos. There is no sign of life on mars since it has relatively low temperature (223 K). It completes its one revolution sun in 687 days.

    Mars is also called a red planet since its surface is covered with red iron oxide.

Outer Planets

These planets lie behind asteroid belt and are also called as giant planets or Jovian planets. Saturn and Jupiter are the big giants of gas like hydrogen and helium while Uranus and Neptune are giants of icy object. They have a ring system around them among which Saturn’s ring is the largest one. A brief description on outer planets:

  • Jupiter

    Jupiter
    Jupiter

    The largest planet in our solar system, Jupiter, is 5.2 AU from sun and is 318 times the solar masses. It is made up of hydrogen and helium gasses and does not have any solid surface. There are a number of cloud band in its surface and the Great Red Spot is the most popular one. Astronomers have predicted that the red spot is formed due to disorder like atmospheric hurricane. It completes one revolution in 12 years.

    It has 79 known satellites. Among them Ganymede is the largest one. It is even larger than Mercury and Pluto! Some other satellites are Callisto, Europa, Lo, Ananke, etc.

  • Saturn

    Saturn
    Saturn

    Saturn, the planet of ring is 9.5 AU from the sun and is 95 times Earth mass. Its atmospheric condition and combination is similar to that of Jupiter. It is the second largest planet in solar system. Its rings are made up of small ice and rock particles. It completes one rotation in its axis in 10 hours 30 minutes and a revolution around sun in 29.5 Years.

    It has 62 confirmed moons. Titan is the largest among them. Some other moons are Enceladus, Mimas, Dione, etc. Titan is large enough to support even its own atmosphere.

  • Uranus

    Uranus
    Uranus

    Uranus is 19.6 AU from sun and is about 14 solar masses. Its axis is tilted over 90 degrees to the ecliptic. It rotates from east to west, which means that the sun will rise from west and set to east. Its temperature is very low of about 50 k. It has 27 named moons. Some of them are Titania, Ariel, Miranda, etc.

  • Neptune

    Neptune
    Neptune

    It is the farthest planet from sun. It is 30 AU from sun and is 17 earth masses. It is composed hydrogen, helium, neon, sillicate, water, etc. A great spot have been detected in its surface. It has 13 known satellites. Triton is the largest one. Other satellites are Proteus, Despina, etc.

Asteroid

Asteroids are small Solar System bodies composed mainly of refractory and metallic materials. They are mainly found at the asteroid belt which lies between Mars and Jupiter. There are millions of the asteroids whose size ranges from microscopic to few kilometers in diameter.

Asteroid
Asteroid

Largest asteroid is Ceres, which is large enough to maintain its nearly spherical shape. It has a diameter of 946 Km. It lies in the asteroid belt. Recently, it has been listed in the name of dwarf plant.

Meteoroid

Meteoroid is the small rocky or metallic particle in the Solar System. Most of the Meteoroid are the small asteroid, that escapes from its belt. They may also be the fragments of comets.

Meteorite
Meteorite

Those meteoroid that enters the surface of Earth’s (or any other body’s) atmosphere are called Meteor. It looks like the falling star from the surface of Earth and is called the shooting star. The color of these shooting star depends upon their chemical composition. Nitrogen or oxygen contained meteor gives red color. Similarly, iron containing Meteor gives Yellow color. Millions of meteoroid enter Earth’s atmosphere everyday and burn down typically in mesosphere due to friction with air.

There is very less chance of survival of a meteorite up to the surface of Earth. Those meteoroid that reaches the ground and survives impact is called meteorite. Large meteorites have a huge impact in the surface. Since Moon has no atmosphere, a number of meteorites hit moon everyday and large number of craters are formed in its surface.

Comet

Comet is the small icy object of solar system with rocks and frozen fluids. It revolves around the sun in highly elliptical orbit. They have a wide range of orbital period ranging from few years to thousands of years.

When comet comes near the sun during its revolution, fluid on its surface evaporates into gases. The gases rush out by rapid vaporization in the form of jets, carrying solid particles with them. This forms the tail of the comet and is headed away from the sun. When comets move away from the sun, all of its gaseous matters disappears and it becomes solid block of icy mass.

Comet around sun
Comet

Many comets have been observed since ancient times. Some of them are Halley’s Comet, Temple-tutle, Enke, Schwasman-washman, Bennet, Shoemaker Levy, etc.

Satellite

Satellite is a small heavenly body revolving around the planet. The number of satellite of each planet ranges from 0 to 79. Numbers of satellite of each planets are:
Mercury – 0
Venus – 0
Earth – 1
Mars – 2
Jupiter – 79
Saturn – 62
Uranus – 27
Neptune – 13

First Ever Image of Black Hole Supports Einstein’s Theory of Relativity

First Ever Image of Black Hole Supports Einstein’s Theory of Relativity

Introduction to Black Hole

Black holes are supermassive objects from where nothing can escape, not even light. The edges of black hole are the point of no return called event horizon. But scientists finally succeeded in designing the first ever image of the shadowy edge of a supermassive black hole. This huge discovery in the history of mankind has led us to a different way of understanding the universe.

Although we have got an image of a black hole, the topic of black hole is not new. The existence of black hole was predicted by Albert Einstein’s general theory of relativity more than 100 years ago. Many scientists supported it including latest great scientist, Stephen Hawking. Now we have got a solid proof the existence of black hole after about 65 years of passage of Einstein.

First ever image of black hole
First Image of Black Hole

About First Image of Black Hole

On Wednesday, April 10, 2019, scientists have released the image of an active supermassive black hole which is located in the center of an elliptical galaxy. The black hole is named as Meisser 87 (M87)and is present about 15 million light years from us. It is 6.5 billion times the solar mass and 40 billion kilometers across. The image was captured by using the Event Horizon Telescope (EHT).

It is circular but on one side, light is brighter because the light is approaching the earth.

“The image had an orange, yellow and black ring which was obviously a black hole and its surrounding”, said Havard’s shepherd Doelemon, Director of EHT team.

An EHT team member and astronomer at University of Waterloo, Broderick said,” The shadow exists in nearly circular and the inferred mass matches estimates due to dynamics of stars 100,000 times farther away.”

Prediction by Einstein’s General Theory of Relativity

It was theoretically predicted by Einstein’s general theory of relativity more than 100 years ago. The image of black hole fully supports the theory of relativity. It is crescent – shaped as predicted by Einstein. The circular disc is an event horizon from where nothing can escape. The portion is the core of black hole and is totally black. Einstein’s prediction about the shape and glow of a big black hole is also proved right.

Einstein’s theory has not only passed this test but every challenge over the last 100 years. He has been right all along.

E.g. Einstein predicted gravitational wave which is created by massive accelerating objects.
In 2015, LIGO (Laser Interferometer Gravitational Waves Observatory) confirmed the ripples in space-time which were gravitational waves.
It was observed when two small black holes were merging.

Conclusion

After a decade, we have finally figured out about black hole which Einstein explained earlier. It took a lot of efforts for many scientists working for years and collecting millions of GBs of data to create a single picture of black hole. Hats off to all the scientists who theorized, supported, researched and proved about the existence of black hole.

Life Cycle of a Star

Life Cycle of a Star

Introduction to Star

You must have seen a number of stars in the sky at clear night. Have you ever tried to count them?
Obviously, impossible.
But, have you ever thought that from where these stars come from?
How do they appear to us although they are thousands of light years away?
Some are even millions and billions of light years away form us.
There are trillions of stars in our universe. Our nearest star is alpha centauri after sun. The collecion of a large number of stars forms a galaxy and collection of many galaxies forms the whole universe.
Well let’s see, how these stars are formed ,how do they die and how the life cycle of a star is completed.

A star has a life span of billions of years. So, it is not possible for one to observe its complete life from its birth to death. However, by observing different stars, their ages and their other characters, scientists have given an acceptable model for the life cycle of a star form its birth to its death.
Firstly, let’s look upon the formation of a star.

Image of life cycle of a star
Life cycle of a star
Image credit: cyberphysics.uk

Formation of a star

There are a lot of cloud clusters and dust particles present in the space. These matters start to come close to each other and attract each other.. Slowly they form a large mass of cloud and dust. It is called Nebula.

Nebula has extremely low temperature and mainly consists of hydrogen. Their mass is usually more than an average star mass. They are opaque to visible light and don’t reflect light at all. So they must be detected by the IR and UV-rays. The nebula begins to contract by the action of its own internal gravitational force. It becomes more denser and denser. This process continues for million of years depending upon the size of nebulae.

he temperature of the nebula starts to rise slowly and becomes highly packed. As a result, formation of protostar takes place. Protostar has relatively high density and temperature. When its temperature reaches to certain limit, nuclear binding energy of its constituent particle breaks and nuclear fusion reaction initiates. After the initiation of the nuclear reaction, large quantity of heat energy is produced. This results in the birth of a star.

A Living Star

After the birth of a star, the star starts its life of a billion of years. The life of a star depends upon the amount of matter it is composed of. Small stars have low temperature and use up their fuel slowly while large stars use up their fuel in vast amount and have very high temperature. Colour of a star also changes constantly along with the life cycle of a star. It changes as:

  • Violet
  • Indigo
  • Blue
  • Green
  • Yellow
  • Orange
  • Red

Our sun is now somewhere in the yellow-orange phase and is going to end up. But we don’t have to worry about it, because it will take several billions of years to finish the life of the sun.

Finally, the fuel of the stars become almost finished and the star starts its journey towards death.

Final Stage of a star

After the red-phase of a star, there comes possibility of formation of two types of stars, red supergiant star and red giant star. It depends upon the mass of the star.

1. Star having the mass less than five times the mass of our sun

Formation of Red Giant Star

Formation of Red Giant Star during life cycle of a star
Red Giant Star

If the star has the mass less than five times the mass of our sun, the star starts to contract. The star becomes dense. But some of the remnants hydrogen in the outer parts of star starts of fuse and produce large quantity of heat energy. Due to this, the star enlarges. This star of this stage is called red giant star.

Formation of Planetary Nebula

After the hydrogen of the star is completely used up, upper layers will expand and eject the materials to its surrounding while its core starts to shrink. This process continues until the pressure becomes equal to the central electron cloud. It results in the formation of a nebula called as planetary nebula.

Formation of red supergiant star during life cycle of a star
Red Supergiant Star

If the mass of the star is more than the five times the mass of our sun, the star expands enormously and changes into red supergiant.

The red supergiant cannot balance its inner and outer pressure and hence it explodes. This explosion of red supergiant star is called supernova.

After supernova, either neutron star or a black hole is formed.

For small remnant of supernova:

Formation of Neutron Star

If the remaining mass is relatively less, it starts forming the neutron star. The remaining hydrogen of the mass is converted into the helium. Its mass is large enough to convert helium into carbon and carbon into other elements like silicon, iron, etc. The core becomes so dense that even electrons cannot remain in the orbit. The electron then combines with the protons forming neutrons. Then the star becomes a ball of neutrons, which is called neutron star.
The neutron star has only neutrons as its constituents. So, it has a very large mass and small volume. Typically, a neutron star weighs about 5-10 solar masses and a radius of 10-20 KM. Its escape velocity also becomes very high ( about 108 m/s ).

For large remnant of supernova:

Formation of Black Hole

If the remnant of supernova is more than about 3 times the solar mass, the force towards the centre cannot be balanced by the repulsive force of neutrons. As a result, the mass further shrinks and forms a tiny mass. It causes the formation of black hole.
The black hole is a body whose escape velocity is more than that of the speed of light. So, even light cannot escape from the black hole and anything inside the black hole cannot be observed form outside the event horizon.

Concluding the life cycle of a star

Hence, a life of a star starts form the dust particles and clouds, passes through different phases and finally end up being white dwarf, neutron star or black hole, depending upon its size.

Found out that something is missing or incorrect?
Comment below and let us know 🤗

Theory of Light

Theory of Light

Introduction to light

Generally, light is a electromagnetic radiation of visible wavelength. Visible light ranges from the wavelength of 400 to 700 nm (nanometer). But in scientific context, light refers to whole electromagnetic spectrum of any wavelength. Theory of light describes how and why light shows its properties and nature .Light is composed of elementary particle called photon. It is produced by different luminous sources like fire, light bulb, etc.

Light shows different properties like reflection, refraction, diffraction, interference, photoelectric effect, etc. Optics is the branch of science which deals with these kinds of optical phenomena.
Ray optics deals with the geometric of the light like reflection, refraction, rectilinear propagation of light etc. while physical optics deals with the production, emission, propagation of light like interference, diffraction and polarization of light.

Different theories of light

From the very ancient time, people have been presenting different views about light. It has become one of the interesting field of research in modern world also. Scientists have made many discoveries regarding the light.

Ancient theories of light

In the ancient time, some people had purposed some theories in light . Earlier people considered it as one of the elements of nature. Later on, some assumptions were made as:

  • Light is composed of extremely small particles (though not mentioned clearly).
  • It travels at the speed of infinity.
  • Light always travels in straight path.
  • Colors of light are made up of darkness and brightness.

However, due to lack of further supports and proofs, these assumptions are negleted now.

These assumptions were based upon two different perspectives. They were tactile theory of light and emission theory of light.

  • Tactile Theory of Light:

    This theory was based upon the ability of eye to ‘touch’ objects. According to it, eye sends out streamers towards the object. When these streamers come into contact with an object, we would be able to see the object.
    But this theory lacked enough support and evidence.
  • Emmision Theory of Light:

    It is opposite to tactile theory of light. This theory is explains that the objects sends out light signals which is received by our eyes and we see the objects. This theory was accepted by all and all the modern theories are based upon it.

Corpuscular Theory of Light

This theory was given by the great scientist, Sir Issac Newton in 1678 AD. It supports the particle nature of light. Some of his assumptions on light were:

  • Light is composed of tiny, light(not heavy) and perfect elastic particles called corpuscules, emitted by luminious sources.
  • The size of corpuscules determine the colour of light.
  • The bouncing back of these corpuscules from the surfaces causes reflection of light.
  • The particles present in denser medium attract the corpuscules which cause them to accelerate. It explains the refraction of light.

He also explained that the white light is made up of seven colours (i.e. Violet, Indigo, Blue, Green, Yellow, Orange and Red) by the process of diffraction through triangular prism. Similarly, he made different optical instruments and contributed a lot in the field of physical optics. He also published a book named “Opticks” in 1704 AD.

His theory could not explain the wave nature of light like interference, polarization, diffraction etc. But this theory successfully explained particle nature of light. Since photoelectric effect was not discovered at that time, this theory was discarded.

Huygen’s Wave Theory

This theory was purposed by Christian Huygen in 1678 AD. It explains light as a longitudinal wave in which particle vibrate simple harmonically along the direction of propagation of wave. For the transmission of the longitudinal wave, a medium is necessary. So Huygen assumed that a hypothetical ether medium was present in the space which is responsible for transmission of light waves.

This theory could explain reflection, refraction, dispersion and total internal reflection of the light. Moreover, Frensnel and Young explained interference phenomenon on the basis of this wave theory.

However, this theory failed to explain the phenomena of polarization of light. Also, the existence of ether could not be verified by the experiments

Maxwell’s Electromagnetic Theory of Light

James Clerk Maxwell in 1860 AD mathematically proved that light is the electromagentic wave which travels with the speed of 3×108m/s in vacuum. He used the following equation to find out the speed of light.

Equation of Maxwell's Electromagentic Theory of Light

According to this theory of light, light is a form of electromagentic waves in which the electric and mangnetic field vectors oscillate transversely in the mutually perpendicular directions. Such wave needs no material for the propagation. So, the ether hypothesis is no longer required.

But the phenomena like compton effect, emission and absorption of light etc could not be explained by this theory. Hence, Physicists started further study of light naure.

Quantum Theory of Light

This theory considers light as a discrete packet of waves called quantum. Each quanta (singular of quantum) of light consists of a photon which carries energy equal to the product of plank’s constant and its frequency.
i.e. E = hν
where, h = 6.62607004 × 10-34 m2 kg / s
A photon travels with very high speed ( 3 × 108 m/s in vacuum). Higher will be the frequency of light, more will be the energy carried by the photon.
Quantum theory of light successfully explains the phenomena of photoelectric effect, compton effect, etc.

Conclusion

The experimental observations show that light sometime shows the behavior of wave and sometime it behaves as particle. E.g. light showed particle nature during interference while it showed particle nature during photoelectric effect.
In 1924 AD, de-Broglie suggested that a particle moving with the momentum ‘p’ has an associated wavelength of λ = h/p
i.e. λ = h/(mv)
However, light is found to have no rest mas. So the light never remains stationary and always travels with very high speed.

Hence we can conclude that light has dual nature of wave and particle. Photoelectric effect can be explained on the basis of quantum theory of light while interference, diffraction and polarization can ve explained on the basis of wave theory.


Finally, we have come to an end. You can leave your suggestions, queries or reactions below 😊.

Interesting facts about Earth

Interesting facts about Earth

Our Earth:

Our Earth is only a known planet which supports life. Although we have found many breathtaking discoveries in outer space, there is still much to study and find out about our own planet EARTH. It is full of mysteries and interesting facts. Scientists have been doing research on it for many years had have found some interesting facts. Some interesting facts about Earth are presented below:

Earth
Earth
  • The rotation of the Earth is gradually slowing down.

    The Earth is decelerating at a very slow rate of 15 milliseconds per every 100 years. This will certainly lengthen our day but will take about 140 million years to increase day length by one hour.

  • There is high amount of gold in earth core.

    Earth’s crust contains very large amount of gold. It is almost enough to create 1.5m layer of gold in Earth’s surface.

  • Earth has very high temperature at its core.

    The Earth’s inner core is very hot. Its temperature is nearly equal to that of sun.

  • Earth is the most dense planet in the solar system.

    The density of Earth is different in each part of the it – the core, for example, is denser than the Earth’s crust – but the average density of the planet is around 5520 kg per cubic meter.

  • Earth has one of the most circular orbits of all the eight planets

    It seems to be most interesting fact about Earth. The axis of rotation of Earth is tilted 23.4° away from the perpendicular of its orbital plane, which is responsible for the seasons we experience.

  • There is a leap year once in every four years.

    The duration of one year is actually 365 days plus 1/4 days. That is the reason we get leap year (with 366 days) once in every four years.

  • A huge amount of fresh water in Earth is frozen.

    Over 68% of Earth’s fresh water is frozen in permanent ice, which includes Earth’s ice caps and glaciers.

  • Antarctica contains large amount of meteorites.

    Antarctica is present is south pole which has very little vegetation. Scientists have found a lot of meteorites in Antarctica than any other place in the Earth.

     

meteroites in antartica
Meteorites in Antartica
  • Mt. Everest is not the closest point to space on Earth.

    It is obvious that is Mount Everest of Nepal is the highest point of Earth but it is not the closest point to space. Mt. Chimborazo, which is roughly equal to 20000 ft. of Andes mountain range is the closest point to space as it lies higher in the Earth’s bulge.

  • 380 ft. tall tree in Earth.

    The tree named “hyperon” is the known tallest tree in Earth which is about 380 ft. in height. It is a redwood tree present in California.

Tallest Tree in the World
Tallest Tree
  • Imaging Earth without moon.

    Our only satellite moon has the great impact in Earth climate and rotation period. Without moon, Earth will have drastic and extreme climate and thus would be inhabitable. The alternation of summer and winter seasons won’t be possible too.

  • Longest mountain range in Earth is underwater.

    The longest mountain range in the surface of Earth is Andes mountain range. But actually about 20 times longer mountain is present underwater which stretches over 80000 km all around the Earth.

These were some of the interesting facts about Earth. There are many others interesting facts about Earth that we can research and find out. You may add some others interesting facts in comment section too.

Feel free to leave comments below….