When it was discovered that nearly all galaxies are moving away from us,scientists wondered whether the milky way might be situated at the centre of the universe.Plausible as the idea may seem,it is incorrect.In reality, galaxies scarcely move, it is the space between them that stretches - just like the surface of a balloon when it is inflated. Every point moves away from every point , surface.This would also be true if the universe were not curved like the balloon's surface but infinite.Although we may find this hard to imagine, even a universe of this kind would have no centre.
Many different methods are used to measure distance in space.Apollo 11 astronauts left a laser reflector on the moon, making possible to measure the centimetre the precise distance the moon and earth.
The distances of other bodies in our solar system, such as the planets & asteroids, can be measured by RADAR,that is reflecting radio waves off them.However,this method wonn't work for stars,which are much further away.For these, astronomers use a technique that measures tiny differences in the position of a star when it is observed from opposite side of the earth's orbit,that is at intervals six months apart.Since the diameter of the earth's orbit is known, the change in angular position of a star at either side of the orbit can be used to calculate it's distance known as the "PARALLAX" method this works for objects at distances of upto about 1000 light years.
For still more distant objects,such as galaxies astronomers use indirect methods.One of these involves cepheid variables, a type of star which has the convenient property of varying in brightness at regular intervals.We know that the length of the intervals depend on a star's luminosity,which means that by measuring a cepheid variable's brightness it is possible to calculate how far away it- and the galaxy that it is a part of- is from us.
There have been many attempts to explain the star of bethlehem said to have guided the three wise men to the birthplace of "JESUS" as a natural celestial phenomenon.It has been suggested that it might have been a comet or even a supernova, an exploding star.
Many researchers believe the most likely possibility to be the meeting of two or more bright planets - a celestial event known as a conjunction- and there are a number of candidates in the relevant period of time.Among the possibilities are the rare triple conjunction of jupiter and saturn in 7 BC or the conjunctions of venus & jupiter in 3 BC and again in 2 BC. However none of these hypotheses has so far been proven and none may ever be.
GALAXIES are mixture of several hundred billion stars. Stars are not evenly scattered across the universe,instead they form large systems that's what i call as a galaxy. Galaxies exist in a variety of different shapes and sizes,from gigantic elliptical galaxies,through to spiral galaxies like our own "MILKY WAY", and small, irregular galaxies such as the large and small magnetic clouds.
what are clusters of galaxies?
well galaxies themselves are not distributed randomly or evenly through the cosmos.They collect in groups and clusters.For example,our milky way belongs to the local group of galaxies which comprises about 30 star systems. Other galaxies are located in the clusters which have several thousand members. One example is a cluster within the constellation VIRGO, which is made of more than 2000 galaxies.
HOW MANY GALAXIES CAN WE SEE?
Between september 2003 and jan 2004, The "HUBBLE" space telescope took the longest ever exposure of the sky in the history of astronomy - more than 270 hours.Based on the number of galaxies visible in the spectacular "HUBBLE ULTRA DEEP FIELD" scientists estimate that with the technology available today some 50 billion galaxies can be observed.
How Far Is To The Nearest Galaxy?
It is currently thought that the "CANIS" major dwarf galaxy in the constellation of the great dog is the nearest galaxy closest to us. It is only 25,000 light years away from the centre of the milky way. This small system appears to be disintegrating as the gravitational pull of the much larger milky way is tearing it apart and absorbing it's stars.
Quasars are among the brightest objects in the universe,radiating more energy than entire galaxies! great aren't they? After speculating for years about the mysterious nature of quasars, astronomers had known that they lie at the heart of some galaxies.They draw their energy from enormous black holes which have masses billions of times greater than of our sun.Like cosmic vacuum cleaners these gravitational "MONSTERS" suck up matter from their surroundings,releasing unimaginable quantities of energy in the process.
now if anybody asks you what are the most brightest objects in our sky? you should say "quasars" but not stars.....
well u may be thinking it's nice knowing abt quasars but how are they "DISCOVERED"
Light rays are subject to the effects of gravity. If a ray passes close to a star or galaxy its path is curved by an effect known as "GRAVITATIONAL LENSING". This can produce some interesting effects.This is how scientists can observe quasars which would otherwise be hidden from us behind a much closer galaxy. Thanks to this phenomenon, astronomers have discovered several planets orbiting other stars.
They draw their energy from enormous black holes which have masses billions of times greater than of our sun. this was my sentence in the very first paragraph. all may be amused at the first look at this sentence, wondering what exactly that sentence meant... well here i explain it clearly....
. Quasars Are So Bright, In Fact, That They Can Be Seen At Very Large Distances When The Universe Was Quite Young.
Although stars seem constant to us,there is in fact a relentless cycle of life and death going on in a space.Astronomers can identify regions where new stars are being born as well as the remains of stars that have exploded. the stars appear unchanged to us only because they take an almost inconceivably long time - millions & billions of years - to develop. Spectacular and rapid events like a "SUPERNOVA"- a star exploding- are very rare.The course of a star's life and it's eventual death depend on the amount of mass it accrued during it's formation.
how are stars and planets formed?
The life of a star begins with a gigantic cloud of cool hydrogen gas with an initial temperature no more than a few degrees above absolute zero(-273.15^o c). The cloud gradually collapses under it's own gravity and clumps of material begin to form inside it,causing it to collapse at ever increasing speeds,while the temperature of the gas rises steadily.The cloud eventually starts to glow,giving off thermal radiation which can be detected by infrared telescopes.The internal density and temperature ultimately increase to a point where "nuclear fusion" takes place.in which hydrogen is converted into helium,& so a new star is "BORN"
Typically many stars of different sizes emerge from one large gas cloud.Sometimes,stars clusters made up of thousands or even millions of stars are created all at once.A rapidly rotating cloud of gas and dust( the remnants of original cloud) floats around many of the young stars, and inside this cloud there are further clumps of matter which have the potential to develop into planets and other smaller celestial bodies. It is thought that planets may be formed around most stars.
what about age of stars?
The first stars found in the cosmos were formed 400 million years after the big bang.Some stars are very frugal in using their supply of fuel,that even today we are still able to see the stars belonging to the very first generations.This is especially the case with globular clusters,where we find stars that are more than 13 billion years old,although new stars are being formed all the time. One of the best known starbirth regions is the "GREAT ORION NEBULA". which is 1600 light years away and visible with the naked eye as part of the constellation orion. The hubble and spitzer telescopes have revealed that many young stars in the orion region have discs of matter rotating around them in which planets may be forming.
how long does a star live and how do they "die"?
The duration of star's life and the manner of it's death depend on it's "MASS".This is because large,high mass stars use up their energy reserves more rapidly than smaller,low mass stars.This is the reason why large stars shine brightly for no more than a few million years,while smaller stars can live for billions of years.Stars produce their energy as a result of a process known as nuclear fusion- during which hydrogen is converted into helium.However the time inevitably comes when all the hydrogen at the core of a star has been used up.
RED GIANTS & WHITE DWARFS
Once a star's hydrogen reserves are used up, the star enters the final phase of it's life.It swells up to become what is known as "red giant".Our own sun will one day turn into a red giant,and in so doing may even devour the earth,along with several more of inner planets.further fusion processes occur in the core of the enlarged star over millions of years,during which,for example helium is converted in to carbon and oxygen.when all of a star's stock of potential nuclear fuel has benn exhausted,it collapses and turns into a "WHITE DWARF". At this stage the star is only about the same size as "EARTH" and it takes billions more years for it to cool down
When a star has a mass of more than 8 times than that of our sun it's end is considerably more dramatic than that of most regular stars.In it's final stages the dying star hurls it's outer layers into space with a mighty explosion which is called as "SUPERNOVA".
at the same time,the star's interior's collapses to form a small,extremely dense body,which can form either of a "neutron star or a black hole".
The matter in a neutron star is packed as densely as the matter in an atomic nucleus.It is so tightly packed.that a tiny piece of a neutron star the size of a pinhead would weigh more than one million tonnes.The immense pressure in the interior of this kind of object pushes the electrons into the atomic nuclei's protons- leaving nothing but neutrons behind.Neutron stars have a diameter of only about 20 km but contain about the same mass as our sun.
If the mass of a star's collapsing interior is more than about 3 times that of our sun,it's gravity becomes so strong that even the neutrons can't halt the process. Inexorably, the star continues to collapse until it becomes a "BLACK HOLE". the name given to a region where gravity is so powerful that nothing,literally not even light, is able to escape. this is why these gravity holes are "BLACK".
what are star's?
Stars are nothing other than suns. just like our own sun, they too are huge balls of incandescent gas,inside which "NUCLEAR FUSION" transforms hydrogen into helium.This process releases enormous amounts of energy,which is why stars shine and radiate heat.It is only because stars are so far away that they appear in the night sky as no more than tiny points of light.In reality,many stars are considerably larger than our sun.
Mercury is the closest planet to the sun in our solar system.since it's average distance from the sun is only 58 million km(compare with 150 million km between the earth and the sun),it's position in the sky is also very close to the sun.seen from earth,mercury can't move any further from the sun than 28^o, and most of the time it is even closer than that,or even directly in front of or behind the sun.from earth the planet is nearly always obscured by the sun's brilliant light.mercury is only visible for most people when the sun is not in the sky at the same time - which is obviously at dawn and dusk.then mercury can be seen low on the horizon either rising or setting just before or just after the sun.
well everybody loves moon. don't they? but do you know what makes our earth and the moon in our solar system special?
well as all know there are 8 planets in our solar system, and most have moons, but there is something special about the earth and it's moon.
The fact that there is life on earth is one important factor that makes it special,but there is another- astronomical reason as well.
And that is "NO" other planet has such a large moon relative to the planet's size.This is why some scientists don't consider the earth and it's moon to be a typical planet moon system,but prefer to think of it as a "DOUBLE PLANET".
it's very difficult for the scientists to measure exactly the age of our universe.
coming to the question how scientists would have measured the age of our universe?
well, does anybody know about "cosmic microwave background radiation"?
cosmic microwave background radiation:- Cosmic microwave background reaches the earth from all the directions and is like an echo of the big bang.
The background pattern we see today emerged when the cosmos was only 400000 years old. by that time it's temperature had dropped to less than 2700 c. and what had been hot,opaque plasma became transparent gas through which electromagnetic radiation could travel freely.since then,the universe has expanded and cooled so that the temperature of the cosmic background radiation is now only 2.7 c above absolute zero(-273.15 c). so thanks to tiny variations in the cosmic background radiation we can hope to learn what happened at the time of big bang.
the most accurate measurement of cosmic microwave background radiation so far was made by,the US satellite "WILKINSON MICROWAVE ANISOTROPY PROBE.(WMAP). which found our universe to be "13.7" billion years old.by comparison, earth came into existence into being some "4.5" billion years ago.
1) firstly how many of you know that our universe is expanding day by day?
2)if so why? according to some space scientists our present universe is expanding day by day.coming to the point why the universe is expanding? In 1929 Edwin Hubble, working at the Carnegie Observatories in Pasadena, California, measured the redshifts of a number of distant galaxies. He also measured their relative distances by measuring the apparent brightness of a class of variable stars called Cepheids in each galaxy. When he plotted redshift against relative distance, he found that the redshift of distant galaxies increased as a linear function of their distance. The only explanation for this observation is that the universe was expanding.
take a keen look at this.this would do the understanding.
1) would you believe during the explosion of big bang the size of our universe was 10-36 m.
2)usually everyone loves moon. did anyone know that every year moon comes 3.7 cm close to earth?
3) does anybody knows a place on this earth where people can indirectly watch the earth's rotation? well there is a place named "pantheon" in paris. There people can observe the rotation of the earth indirectly by means of a "foucault" pendulum.
4)It(light ray emitted by moon) takes "8.3" seconds to reach the earth's surface. where as a sun ray takes 8.248 minutes.
4)It(light ray emitted by moon) takes "8.3" seconds to reach the earth's surface. where as a sun ray takes 8.248 minutes.