planet mercury

Hello friends! , I am shubham from india, and this is spaceinfinite, whwere I share interesting facts about space, time planets, universe,etc.

I also have a youtube channel named ‘ space infinite’ related to this where I share similar facts to my audience in hindi, so if you belong to india then consider visiting my channel.

Before starting I would like to mention that there is my video if you scroll down on the similar topic i.e mercury , so you could watch it also as I have explained similar things in the video.

So… lets start..

Friends!  As we all know that mercury is the smallest as well as the nearest planet to sun in our so called solar system. Lets talk about some basic information related to mercury.

The orbital period of mercury around the sun on its orbit is just 87.97 earth days, the reason we all know , as it is the nearest to the sun among all the other planets, its obviously the fastest orbiting planet as well as the planet with least orbital period, wait! Did I mentioned the speed at which it revolves around the star? Hmm.. its 47.3km/s  , whoa its too fast! Even faster than a bullet!.

Friends as we all know that almost all the planets in our solar system are named after a roman god, so is true for mercury also, the mercury was named after a roman deity ‘mercury’, who is the messenger of gods.

Do you  know that none of the planets orbit is accurately circular, all of them rotate on an elliptical orbit, the mercury’s orbit is the nearest to the circular orbit, but its also not circular, as the eccentricity of mercury is 0.205, so it has an elliptical orbit. Here I would like to mention that in astronomy if the eccentricity of an object or its path is between 0 to0.7 then its elliptical and if its eccentricity is 0 (zero), then its perfect circular.

Now lets talk about the aphelion and perihelion of the mercury from the sun, friends aphelion is the farthest point of any object from the body its orbiting due to being gravitationally bound  to it.

And perihelion is the nearest point of the object from the object its revolving.

So aphelion of mercury from the sun is 69,816,900 kms .

And perihelion of mercury from the sun is 46,001,200 kms.

The mercury has no natural satellites or moon.

the mass of mercury is about 0.055 times the mass of earth, and its surface gravity is just 3.7 m/s^2

and its escape velocity that is the minimum speed at which any object should attain to escape its gravitational field is  4.25 km/s.

surface pressure of mercury is less than 0.5 pascals.

And its surface temperature fluctuates between 200k to 340k, the reason for it , is that the mercury is a tidally locked planet thus as a result it rotates in a unique way in solar system.

The planet rotates on its axis exactly one time for every two revolutions it makes around sun.

Because mercury is a tidally locked planet , so its one side  faces the intense  heat of sun and while other remains  in darkness  for a long time as its rotation is very slow on its axis.

Because mercury is so small thus it is not capable of holding its atmosphere , thus it has no atmosphere to retain heat. Thus the temperature difference between its dark side and solar facing side ranges from  -173 degree Celsius to 427 degree Celsius.

Internal structure

Now lets talk about the internal structure of the mercury.

So, as we all know that mercury is a terrestrial planet  i.e  a rocky planet.

It also comprises of three layers namely, crust,mantle,core.

When talking about crust , the crust of mercury is way thicker than that of our earth that is 100 to 300 kms thick!. It mainly comprises of solid silicates.

When talking about mantle , the mantle of the planet is the next layer under the crust and its neary 600km thick. It comprise of solid iron sulphide .

 Now  the next layer comes core with 1800 km of radius. The core comprises of two parts , namely outer core and inner core, the outer core mainly comprises of solid iron sulphide. And the inner core is completely liquid metal.

The radius of the mercury is just 2,439.7 km/s.

When talking about the total composition of minerals on the planet , the mercury comprises of 70%metallic minirals  and 30% silicate materials.

Did you know that mercury has the highest iron content in our solar system.

the mercury has been geologically inactive for billions of years  it could be said because of presence of craters on the planet that are easily visible from space.

The planet has some wave like structures which look like wrinkles , these are called  lobate scarps and were formed when Iron core cooled and contracted. This data was taken by NASA’s messenger spacecraft that was launched in 2004 and it orbited mercury 4000 times in four years before crashing on its surface.

parker solar probe

The probe

Hello, friends I am shubham and this is spaceinfinite . the place where I tell you about interesting space related stuff. So stay tunned because today I am going to share some information about NASA’s  solar mission of ‘parker solar probe’ which is surely going to be a historical space mission in the history of human kind.

So friends, NASA  officially  announced  the mission back in 2009, which was a source of curiosity for peoples that how NASA could send a probe to a huge fireball, in front of which our earth or any other planet in our solar system is nothing , so how could NASA send a spacecraft which could not only survive the intense heat of our sun, but also work properly and gather the information required by the scientists about the nearest star to our planet . but on 12^th august 2018 , NASA proved that it could be done by launching the parker solar probe on a long journey to our sun in order to understand it.

So friends what you think that how  scientists would be able to do that , lets talk about it .

Starting from the origin , friends I would like to mention that parker solar probe was first named as solar probe only , but later on NASA decieded to rename it to ‘Parker solar probe’ in order to give tribute to mr.   Eugene parker , professor in  university of California.

Parker solar probe ‘s aim is to reach the Corona of the sun , which is insanely hot place, even far away hotter than the surface of the sun, as per the scientific measurements the surface temperature of sun is approx  5,500 degree Celsius. But the temperature of Corona is about a million degree Celsius!!!  Well I don’t really know that how it could be possible but scientists have given many theories regarding this, but I don’t  think  any of them could be considered completely true.

The parker solar probe will approach within the 8.86 solar radii  i.e  6.2  million killometeres or 3.85 million miles  near the photosphere i.e the surface of the sun. well it sounds that the probe is not really close enough to the sun , but friends trust me it is insanely near to that giant fireball .

Did I mentioned the speed at which the probe will travel towards the star?

Well its 7,00,000 km/hr  i.e  7 lakh km/hr. that is incredibly fast speed and officially the fastest moving object made by the human kind ever, that’s a proud moment , isn’t it?

Talking  a bit technically , the parker solar probe mission is a heliophysics  mission, which means the mission which will include the complete study of the sun, whether it be inside the sun or outside , its neighboring environment and everything related to it, in short it is the study of complete physics about the sun. which would be very helpful in studying  the working or mechanism of  not only our sun but also other stars in our universe, specially the medium sized stars like our sun.

The structure and work

Well talking about the dimensions of the probe , so the launch mass of the probe was 685 kgs and the dry mass is 555 kgs. Its almost the mass of an average car.

NASA launched the probe from the Cape Canaveral air force station, Florida on 12^th of august 2018.

The orbit of the probe around the sun is of about 88 days.

Now comes the most important question that how would the probe will withstand the intense heat  of our sun ,  so here’s the answer to this.

Well the probe is protected with a solar shield of 2-3 metres which of hexagonal shape, which is about 11.4 cm thick . the shield is made up of reinforced carbon-carbon composite which could easily withstand the temperature of about 1370 degree Celsius.

Friends solar radiation in the corona is about 475 times more than that to the solar radiation on the earth’s orbit.

The spacecraft systems and scientific instruments are placed in the central position  behind the shield’s shadow. As the shield would be only at the solar facing side , and scientist would not like the instruments to face the sun directly as it would cause the instruments to destroy completely.

I would like to mention that the parker solar probe is the most autonomous probe ever .

As the distance of sun from the earth is about 150 million kms, so the radio communications from the earth to the probe would require about 8 minutes to reach the probe, and to make the probe work properly and to keep instruments safe from being  in direct contact from the sun, the probe should change its direction continuously in order to keep the solar shield to face the sun directly and avoid the instruments to be burned . and it was not a good idea to control the probe from the earth , so the scientists and engineers decided to make the probe nearly completely  autonomous machine , so that the things could be done smoothly and  right.

Friends ,  the main power source of the probe is obiviously solar panels, but it would not be a good idea to make solar panel face the sun all the time, so the panels wold face the heat and gather energy for a short time and get inside the probe , in order to avoid burning the probe  also include the pumped- fluid cooling system to maintsain operating temperature of the solar panels and instruementations .

Goals

When talking about the tasks to be performed by the probe then it includes a lot of tasks which are assigned to the probe.

1.       The first task of the probe is to trace the energy flow that heats the corona and accelerates solar winds .

2.       Second task is to determine the structure and dynamics of the magnetic fields and find out the source of origin of solar winds.

3.       The third task is to determine that what mechanism accelerate and transport the energetic particles.

For performing such tasks many systems are included in the probe which are:

1.       FIELDS:  To measure the electric and magnetic fields around sun.

2.       ISOISl: This investigation system will measure the energetic electrons , protons, and heavy ions.

3.       WISPR: optical telescopes that will acquire image of corona and inner Heliosphere.

4.       SWEAP: To  count the electrons, protons and helium ions and measure their properties such as velocity, density, temperature.

5.       HelioSPP: theory and modeling investigation for good results from the mission.

So, friends these were the five major tasks to be performed by the parker solar probe.

Hope you liked the information about the parker solar probe.

Keep visiting the spacinfinite.blogspot.com  for more space related interesting  content.

Origin of matter

I could write a book land story about this question that what is the origin of the gaseous matter comprising the stars and galaxies? Surely something cannot be created out of nothing .
 the story will contain many definite truths.
 it will have a lot of extrapolation and it might still leave out several big holes.

 let me begin by first stating some things we now understand rather well . we have found out that the familiar world around us is made up of less than 100 elements. hydrogen, oxygen, nitrogen, iron, carbon, copper, zinc etc right up to Uranium represents examples of elements .

 elements are defined through the number of protons in the nucleus. this we learnt later. first, we learnt to recognise them through their chemical properties .

 it is amazing that whenever we look, the earth ,the moon and the stars or  interstellar and intergalactic space is the very same Limited list of elements are found .

 the richness we see on our planet is all derived from the multitude of ways in which these elements combine .
 this includes oceans, rocks and little Hills And The Mighty Himalayas .

 besides, it also includes all things living - the fantastic world of plants and flowers as also of butterflies and babies . tens of millions of species on earth are all ultimately made up of stuff we are familiar with .
 the magic comes from differences in structure and architecture . much of this structure is the result of forces whose nature we now understand reasonably well .
 this also includes the question "why has nature been constraint to have only 92 elements and not just 20, or as many as 500 "? There are no real exceptions to the rules that govern the world of things we have encountered . perhaps that is not strictly true but almost show .

 we cannot fully understand do not post and ultimate violation but only represent our current inability to comprehend and calculate .
 so now, let us move to question ;

how did all these things come into being?
 The variety they represent does not appear to be arbitrary .there is a deep related - Ness .
therefore, the process of creation also cannot be arbitrary .
Our broad understanding in this regard is the following :

We know by now that given enough concentration of energy, various forms of matter, such as protons neutrons ,electrons etc can be created and can transmute into Each Other .

 Einstein proved that theoretically exactly 100 years ago and this is now well established in a large number of experiments .
the ratio of particles produced depends on the details of interactions and of subsequent decay interactions .
we now understand a great deal in this regard, through decades of theory - making and experiments .

 the question arises as to what are the conditions and sources of such concentrations of energy?

One of the moments where conditions might have existed was the moment of the big bang ,hypothesized to exist at the "beginning" of the universe .

it might also be possible under special conditions involving high concentrations of mass , a scenario favoured by scientist who are not happy with the Big Bang hypothesis .

one should not be too worried about the availability of energy, because it can be shown that the positive energy of the particles produced is balanced by the negative gravitational energy .

 there is no Generally Accepted theory about the reason for the universe deciding to exist .

some people think that it was due to a Quantum fluctuation in space time! If all this is a little baffling do not feel to unhappy .

scientists are still struggling with some of these aspects . but a lot about evolution of matter and energy in subsequent epochs is well understood . we think that the light elements, like deuterium, Helium Lithium and beryllium were produced in the super hot stage like the Big Bang .

the heavier elements were synthesized through thermonuclear reactions inside stars and those heavier than iron during supernova explosion of the stars .

 stars can be considered as element manufacturing factory ; they also produces heat, light and other forms of energy as a byproduct .

our sun is one such element manufacturing factory . all this is not just science fiction or a loose story ,The interactions involved and other aspects of Stellar structure and evolution are fairly well understood .

Stars

Suppose we have a large cloud of dust and gas .it is quite likely that because of random fluctuations or some other causes, some part of this cloud may come to be denser than its neighbourhood ,in that case, the surrounding regions would begin to gravitate towards the denser part. 
This is an accelerating process . denser the inner part, more is its attraction.
We therefore have a situation where the dust and the gas start falling inwards, leading to a compaction of the cloud . 
the following material is subject to collisions leading to heating up of the dense cloud.The gravitational energy is being converted into heat energy. the central part of this cloud will be the hottest .
When we say that a gas is hot, we also imply that its particles are moving with random velocity and continuously colliding with each other . in fact, temperature is a measure of the velocity of these particles.Then something new happens . at very high temperatures, atoms are ionized that we do not have neutral atoms anymore . the most abundant element is hydrogen, which after ionization is broken up into protons and electrons . through a well understood series of nuclear reactions and radioactivity, 4 protons are fused into one Helium nucleus resulting in a lot of energy.Energy is released because the mass of helium nucleus is significantly less than the mass of a Proton . 
this can happen only if the thermal energy of the protons is high enough to overcome the electrostatic repulsion between particles of like charges .as the temperature at the centre of the dense cloud Rises, the rate of the fusion reactions also increases . rising temperature leads to a high gas pressure which is enough to support the inward gravitational pressure . 
At that stage, the dense cloud is stabilized. it has become a star.Our sun is one such star. this Star would keep shining at about the same rate till the hydrogen supply in the core is exhausted.Notice the remarkable mechanism that gives long term stability to stellar furnaces. Any increase in the internal temperature that would increase the energy production would also increase the internal pressure . as a result the Star would expand, leading to a drop in the temperature and ,hence, the rate of energy production . the reverse would happen if the internal temperature decreased .stars are self regulating furnaces.
From the above discussion it should be clear that if the material from which stars are formed is about the same the only thing that controls the brightness of the star is its Mass.
Very heavy stars will be able to compress the centre to much higher temperature before the internal pressure Rises enough to counter the force of the gravitational compression.  a higher temperature also implies that the rate of reactions inside is much higher, resulting in the stars being much brighter. this is a sensitive function .
 it turns out that stars that are 10 times more massive than our Sun would produce energy and consume their hydrogen fuel at such a rate that they live a thousand times less than moderate stars like our Sun .
 even among stars the fat and the spendthrifts do not last long! While we talk about energy production in stars, let us not over look that the Stellar furnace is also creating heavier elements through fusion of light elements .
 we will not go at this time into the details of how and when that happens .we should only say that the stars are believed to be the generators of all chemical elements of mass equal to and greater than carbon.
In the end let me say that nothing is permanent does not even the 'saptarishi' . our life span is too short compared to that of the stars .even our recorded history of a few Thousand Years is minuscule in length .
we humans have not been here for a long enough period to see a significant change in the appearance of the heavens . yes ,the changing relative positions of Stellar conditions can be discerned.Life of star depends upon its mass. Strange as it might seem, bigger the mass shorter is its life! While a star with the mass like our Sun might Shine for about 10 billion years, very heavy stars might die in a few million years . To understand this we have to have a General understanding of the way stars are Bond, how they live and the way they Die.this process does not stop at making of helium from hydrogen but in later stages of the Stellar life, also leads to the synthesis of heavier elements . To be aware of big changes, we have to look at the largest sample of astronomical observations .there we do se reminents of supernova ,neutron stars and evidence of black holes.
 these are all stages of the way some stars and their lives sometimes to be born again in States completely unpredictable at the time of their birth.

Protostar- in a nutshell

The current wisdom about the formation of a star goes something like this. first, you need a lot of matter containing various elements, mostly hydrogen, along with a lot of dust that might be the result of earlier happenings in space. 

Large clouds of such matter are visible in many parts of our Galaxy and in other galaxies in the universe. these clouds roam around, sometimes with turbulent motion, rotating and interacting with other clouds and stars. 
All particles in the cloud interact with each other due to force of gravity.
Fluctuations might lead to situation where the concentration of mass is Greater at some point as compared to the neighbourhood. 
This would lead to more and more particles being drawn towards that point of concentration. the big one continuous to become bigger. As the particles fall in together, the progress accelerates.

While this is happening, we have also to remember that the cloud was originally rotating, howsoever slowly . 
the particles that come from the direction of the axis of rotation can fall straight in towards the centre while those along the equator have to content with the centrifugal force. 
Therefore, the concentration of matter does not lead to a ball but to a disc - like shape. All this might take millions of years .In later stages , the particles falling in begin to collide with each other rather frequently and their energy becomes the chaotic energy of heat. 
Does the gravitational energy is converted to heat ;concentrated near the centre of attraction . 

This heat can be sent through infrared emissions. if the cloud is large enough, the process can proceed towards star formation of the clouds .

Before it gets there you can call the child star only a protostar. the true star phase of its life begins when the interior temperature rises to several million degrees or more . 
At those temperature the kinetic energy of protons and light chemical elements are high enough for thermonuclear reactions to occur ; the energies of particles can overcome the electrostatic repulsion of nuclei. fusion of four protons to form a Helium nucleus and a couple of positrons and some neutrinos can produce more energy per mass unit than any other fuel period ,this is the energy that ultimately enables the protostar to shine, and continue to shine till the fuel inside is exhausted .
 Depending on the mass of the stars that might take a few million years to many billions of years . the heavier ones Shine brighter and die earlier . our sun will continue to give us light and heat for several billion years.

Incidentally ,let us not forget the matter around the edges of the accreting disc . it is believed that planets are coagulated in those regions.

Planets-The Spheres(nutshell)!

Spherical shape of planets

As matter accretes, its gravitational attraction increases. Continous accertion leads to an inward gravitational force that can overwhelm the forces that give solid- state structures their integrity. Under a gravitational force that is large enough, even rocks melt and flow. Each particle on the surface of the aggregate wants to get as close to the centre as possible and the shape of the aggregate tends to become spherical - that is what natural equity or democracy would demand. 
Extremly high mountains- protrusions beyond the spherical surface- are not viable because their weight would make them sink down. When we get to aggregations of planetary levels, the height of the highest mountain is inversely proportional to the mass of the planet. Mars has higher mountains and deeper valleys then does the earth because it is less massive then the Earth, even our tiny satellite, the moon , surpases the earth in this regards, whose highest mountain peak sticks out to a height of barely 9km on a sphere whose diameter is nearly 13,000km.

The spherical shape of heavinly bodies testifies that gravitational force of matter in bulk can overcome all other sustaining forces.

Zero weight - possible???

This innocent sounding question requires some detailed consideration. Scientists distinguish between the words "weight" and "rest mass ". In ordinary life on earth, the two are the same . Rest mass or (more simply, mass) and weight are proportional to each other and the unit of measurement are so choose that they are the same. A weighting balance determine the weight; this is the force with which the earth attracts the object.

However, if the same object is in orbit around the earth, it is freely falling the towards the earth and is weightless. If you were that object and stood on a balance while both you and the balance were orbiting the earth the balance would show a reading of zero. Both the balance and you would be weightless, even though both would have the same mass as they had on the surface of the earth.
Therefore, I will assume that we are  interested in finding out whether there is any entity in the universe that has zero "rest mass"? 
The answer to that the last question is yes, and the very obvious "object", if you can call it that , is light . 

We
Light photon have energy but zero rest mass. In addition, there are other particles called neutrinos that have zero or near zero rest mass. The existence of neutrinos was theoretically postulated to explain certain observations , and experimental evidence has since been gathered for their existence. There is some recent evidence that the neutrino mass may not be exactly zero, but they are very close to being mass-less. 
Mass-less particles have an initial role in the universe. This is obvious as far as light and heat are concerned . It has been found that neutrinos are also central in determining the nature and evolution of the universe.

Comets - the formation(nutshell)

Comets are believed to be coagulations of material left over during the formation of the solar system through gravitational contraction and spinning up of the solar nebula. The spinning up is a consequence of conservation of angular momentum. In this process , a time came when the spinning material was concentrated into an ever-thinking disc. The shape was ordained by the fact that the epuitorial regions of the spinning cloud could overcome the gravitational contraction while the polar regions could  not. Finally when the central core of  the cloud became dense and hot inside, thermonuclear reactions started, thereby converting hydrogen into helium and producing a lot of energy.

Outflow of this energy produced the outward pressure to stabilise the sun against the contracting force of gravity.

Density fluctuations in the disc led to coalescence of mass into planets going around the sun. But a lot of mass in the outer fringes of the thin disc escaped congregation into large aggregates and was retained as dispersed material in the far reaches of the solar system. The additional pressure of the solar wind probably aided dispersal . This cloud is known as the Oort cloud .

The mass in the thinning edge of the pre -solar disc was too sparse to form large bodies through coagulation and was left alone to form it's own small colonies. Comets could be considered as colonies  of this kind and are the transformed components of Oort cloud .  They also go around the sun in long period elliptical orbits that are often perturbed when they travel into the inner solar system. In the early history  of the solar system, they occurred more frequently  and there is a feeling that much of the water on earth and other planets was brought in by comet collisions.

The Mars & Life

Mars , some basic information

The scientists have not found any evidence for remnants of plants, animals or other significant life forms on mars. But search for life beyond the earth is a natural urge. It is true that our Earth is a wonderful planet but it is only a tiny little rock around an ordinary star. There are billions upon billions such stars in the universe. Even if life is an extremely rare and wondrous natural happening, surely it could have also found a foothold at some other places. One finds that organic molecules of the type used by life forms are found in abundance in many molecular clouds in our own galactic vicinity. If life is not a unique miracle but a natural outcome of far-from-equilibrium thermodynamics in the evolution of matter and energy, one cannot stop Looking for its presence in all sorts  of near - congenial locations .

If we look at other planets of our solar system , we do not find many good candidates. The moon is too small and cannot sustain an atmosphere. Mercury is horribly hot and cold during its days and nights respectively, and cratered much like our moon because it lacks the protection of an atmosphere. Venus seems to have done something wrong during its evolution . It is subject to a runaway greenhouse effect, raising it's temperature to hundreds of degrees Celsius . Jupiter is enormous and has thick atmosphere , with its lower parts at thousands of degrees , altogether in congenial from the point of an earth-centric scientist, even if we were to grant a latitude of few hundred degrees Celsius for survival of life. The moons of Jupiter (like Europa) are beginning to look attractive  because they might have pools of liquid water. Mars on the other hand , seems like an attractive  candidate . There is evidence that it did have flowing water at some time. It probably still has some frozen water below the surface. It's atmosphere is thin , but might not  be completely hopeless in terms of supporting life. We certainly cannot expect elephants , monkeys or men running around there. Signs of even rudimentary life forms would be useful and extremely instructive . Because of all these reasons , I am very partial towards scientists who are devoting an enormous amount of effort to detect evidence of life processes on Mars . Our solar system itself is a tiny part of the universe. We could go on looking for evidence of life having emerged somewhere or the other . Some searches have been made but we have not looked hard enough. Universe is vast, even bigger than we can imagine , search for life by us and giving conclusion that there is no other intelligent life form or simply other life form in the universe is like that taking a glass of water from the Pacific ocean and concluding that there are no fishes in the ocean. The search for life is just beginning , humanity has a very long way ahead to discover more.

DARK ENERGY-THE DARK SECRET

We are passing through a unique period in the history of science. Based on observations and experiments in our laboratories and on internal consistency of the of the theories we had built, we were convinced that our universe is structured and controlled only by four types of forces . These were gravitation, electromagnetism, the weak force, and the strong force. These forces seemed to account for everything we saw or measured , here on earth or amongst stars and galaxies . There was no measurement or observation that was considered unexplainable. The basic principles incorporating these theories were not violated. The world of physics, chemistry, biology, geology, and astronomy threw up nothing that required the existence of an other type of force or energy. With e had also worked out theories that helped us to unify at least theree of these four interactions . The only residual agenda in this connection was the unification of gravity with all the other forces . Some ingenious experiments looked for a possible fifth force . These could only put upper limits of the order of a millionth the strength of gravity. Then came some surprising observations in astronomy and from cosmological theories. Some radical changes in the Constitution and the history of universe has been indicated , even though we are far from understanding the science behind them. The proposal for existence of dark energy was one of the new hypothesis .
This was entirely new . In addition, we did have mounting evidence that a dominant fraction of some matter in the universe is not visible to us. It has gravity like all other matter but it is dark, in the sense that it does not emit any detectable radiation. The nature of dark matter is still under discussion even though it's existence is observationaly strongly indicated.
I find a present situation rather uncomfortable. Till recently, we did our physics through observation and theory, connected with things happenings on earth. We had tremendous success in understanding the external universe using the very same physics. Now the distant universe is beginning to suggest objects and laws that are difficult, if not impossible to test here on earth! I , for one, am beginning to have some doubts about the validity of the evolutionary or bigbang model of the creation of the universe, in spit of the fact in many respect it seems so simple and compelling . In this regard, let me describe a piece of evidence brought forth to suggest that the bulk of the energy in the universe resides in a repulsive field called Dark energy.One of the methods used for determining the rate of expansion of the universe is to explore the relation between the red shift of astronomical objects and their distance . It is clear that we could get an approximate idea of the distance of an object if it were assumed to be a standard "candle" and it's brightness was measured. The rate at which it is receding from us would be known from the red shift of its spectral lines. A class of supernovae has been used to provide standard candles in this regard. It has been recently discovered that some of these supernovae at large red shifts appear to be too dim to be at the distance indicated by their red shifts if we use the standard value of the Hubble constant. This has been interpreted as indicating that universe has started to expand much faster than initially believed. A large repulsive force embedded in the fabric of the universe is believed to be responsible . The energy associated with this force is the so called Dark Energy!!.I cannot help being a little sceptical .Do we have enough confidence that the few supernovae we have used are truly standard light sources? Are we sure that the dimness of the sources is not due to absorption of their light by intervening dust clouds? Perhaps these doubts would be removed In time. However one is still left with a feeling that parameters are being chosen somewhat arbitrarily, to make the universe completely consistent with the dominant model of big bang  cosmology . We might end up getting a good parametric fit without a true physical foundation . That would be , at best , some tentative progress, not a proper understanding.

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Earth history

How old is Earth

The clock used for measuring the geological age of the earth

Is a nuclear clock. 

The most common is called U238 pb206 clock. U238 has a half life of 4.51 billion years. 

After a long chain of decays the end element is pb206 and U238 in an old rock. This would tell us how long the uranium has been decaying in that rock that gives us the age of the rock. 
This has been done very carefully. Some other radioactive dating methods have also been used. 
The current consensus is that the age of the earth and the solar system is 4.6+0.1 or 4.6-0.1 billion years.

Weight of earth

Since the earth is suspended in space,"weighing" it is not the same thing as putting an object on a scale.
when we speak of the weight of the Earth, we mean the amount of matter that makes it up.
this is called its mass.

The earth's mass is about 6600 trillion tons. to give you an idea of how that number looks here it is ----       
 66 00000000000000000000 . 

how did scientist find out that this was the mass of the earth,?

To do this, they used a principle based on the fact that any two objects attract each other. 
this is what the force of gravity depends on. put in simple terms, the law of gravity states that two objects are attracted by force That depends on their mass and their distance apart .
the bigger the objects the greater the force that pulls them together . the farther apart they are, the smaller the Force.

To measure the weight of the Earth, the following is done- a small weight is suspended from a string .the exact position of that weight is measured .
now a tonne of lead is brought near the Hanging weight. there is an attraction between the weight and the lead and this causes the weight to be pulled just a tiny bit out of line . actually it is less than 0.00002 mm so you can see how carefully the measuring must be done.

After this is measured scientist can use mathematics to figure out the weight of the earth.
 they have measured the power of the earth's attraction on the weight and they have measured the power of the 1 ton leads attraction on the suspended weight. 

the relative difference can be calculated and tells them the mass of the earth.

What is this mass made of?

There is the crust of solid rock ; then a layer called the Mantle which is also solid Rock and goes down about 1800 miles ; and then the innermost part, which is the core and is about 2100 miles in radius . the material of the core is liquid because of the great heat at the centre of the earth.

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OUR SUPER STAR-THE SUN

The sun and its speed

The sun is the basic source of life on earth, earth and all other planets revolves around it, but does sun also revolves around something?? 

The answer is yess!!

It revolves around our galaxy, the milky way, and its speed of revolution is 220   km per second!, it sounds insane , but its true, but even at this speed itt takes about a million years to go around once, because the galaxy is so large. Humanity has not been around even for one revolution! It is useful to know that the matter and stars in the galaxy take on a spiral shape.

By analyzing the differential rotation of the stars as a function of distance from the centre of the galaxy, astronomers have concluded that besides the visible stars and clouds, there must be a lot more invisible matter that exerts a gravitational force on the visible matter in the galaxy. This invisible matter is referred to as the so-called dark matter. We still do not know the nature or identity of this matter.

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