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The OZONE LAYER which lies in Stratosphere (16 to 48 kilometers above earth's surface) protects us from harmful UV radiation.


Ozone layer help us by trapping harmful radiation from the sun. Ultraviolet(UV) rays are harmful rays which come from the sun.

Ozone layer is made up of #O_3# or three atoms of oxygen. When UV rays of 230 to 320 #mum# hit the ozone layer, #O_3# absorbs its energy and gets converted into #O_2# & then #O#. #O_2# molecule combine with this #O# molecule and form #O_3# by this ozone is formed again. This happens continuously in the whole layer.

The use of Chlorofluorocarbons (which is used in refrigerator) stops the ozone to form again & it damage the ozone layer


When UV rays strike chlorofluorocarbon(#CFCl_3#) its carbon-chlorine bond breaks. This produces a Chlorine atom & this atom reacts with #O_3# breaking it apart, which causes a hole in ozone layer.

Gamma ray and X-ray are also harmful radiation which comes from space. Just a single high-energy photon of gamma rays can cause significant damage to a living cell. But our earth's atmosphere protect us by absorbing it.



Mostly nothing but....


In between galaxies, it is mostly just empty space. And by empty, I don't mean the kind of empty in an empty jar but empty as in a vacuum - an area with no particles or atoms at all. However, there are a few "rogue stars". These lonely stars are not part of a larger body (galaxy), but sit on their own in space.

There is something else that fills space, but whether it counts as anything depends on what you class as something. I am, of course, talking about dark matter.
Physicists have found that there is not enough mass in the detectable universe to account for certain phenomena (e.g. there are galaxies that spin so fast that their observable mass couldn't possibly keep them together - there must be some mysterious form of mass that is contributing to it).

We don't really know anything about dark matter. It doesn't interact with the electromagnetic force, so we can't look at light or heat to discover more. Instead, we sort of just give it a label to account for it and sit rather puzzled.

It is worth mentioning this Dark Matter though, as it is thought to make up around 83% of the universe (or about 91% including dark energy).

For more on dark matter and rogue stars, here are two very interesting websites:

I hope this helps; let me know if I can do anything else:)


Gamma-ray bursts are short-lived bursts or flashes of gamma-ray light with extremely energetic explosions that have been observed in nearby galaxies.


  • The meaning of gamma-ray burst

Gamma-ray bursts (also called GRBs) are flashes of gamma rays associated with extremely energetic explosions that have been observed in distant galaxies.

Most observed GRBs are believed to consist of a narrow beam of extreme radiation released during a supernova or nova as a rapidly rotating, high-mass star collapses to form a neutron star or black hole.

Gamma-ray burst (GRBs) are the brightest and most powerful singular events in whole universe. GRBs can last from ten milliseconds to several hours.

Gamma-ray burst were first observed by accident while detecting gamma radiation pulses emitted by nuclear weapons tested in space by the U.S. Vela satellites. They occur at random positions in the sky several times each day.

  • Types of Gamma-ray Burst

There are two types of Gamma-ray bursts:

#1.# Short-duration gamma-ray bursts
#2.# Long-duration gamma-ray bursts

#1.# Short-duration gamma-ray bursts - Short bursts last no more than two seconds.

#2.# Long-duration gamma-ray bursts - Long bursts can last up to just over fifteen minutes. Long-duration gamma-ray bursts produce a total energy output of about #10^44# joules.


  • Gamma-ray Burst Explosions

Gamma-ray bursts can release more energy in 10 seconds than the Sun will emit in its entire 10 billion-year lifetime! But you should not have to worry about it because all of the bursts we have observed have come from outside the Milky Way Galaxy.

Scientists believe that a gamma-ray burst will occur once every few million years here in the Milky Way.

Gamma ray bursts can only be observed directly from space, as the atmosphere blocks gamma rays.

Scientists theories about the source of gamma-ray bursts are many but I don't think so that anyone is accepted yet.


Yes - not only do they age in space but they age faster (assuming they are in orbit around the Earth) by about 2 minutes/year.


Do astronauts age while traveling in space? Let's explore that question:

I believe the question is getting to the fact that astronauts travel at faster speeds than what can be achieved on Earth. So let's take a look at the equation that deals with time contraction while traveling at high speed:


This is Einstein's Special Theory of Relativity, where #t# is astronauts's time, #t'# is relativistic or an observer of the astronaut's time, #v# is the speed of travel of the astronaut, and #c# is the speed of light.

What would it take for an astronaut to not age? Or in other words, what would it take for an observer on Earth to look at an astronaut and observe he is not aging? The answer is the astronaut would have to be traveling at the speed of light:






So no matter the value of #t#, the amount of time the astronaut experiences, an observer would not see that the astronaut had aged at all. But keep in mind that the astronaut would experience time in what s/he considered normal!

But perhaps an astronaut will age slower in space than on Earth. Let's explore that - first let's start with the equation again:


According to "the internet", the ISS (International Space Station) travels at around #7.66 (km)/s# so let's assume the astronaut travels that fast, so we have our #v#. A rough approximation of #c=300,000 (km)/s#. So let's work that out for a period of 1 year of space travel (which is roughly #3.154xx10^7# seconds (that's 31,540,000 seconds):







#t'=31539999.9905# seconds

So in a year of traveling on the ISS, an astronaut would be observed to have aged roughly #1/1000# of a second less than an observer on Earth.

Einstein also developed General Relativity, which predicts that someone in a gravitational field will age slower than one outside of it. Since our astronaut will be in a lesser gravitational field than the observer on Earth, the astronaut would be observed to be aging faster! But as we can see from the above, the effects are very very slight.

These effects work to cancel each other out on the surface of the Earth, but do have an impact on satellites in space. According to http://metaresearch.org/cosmology/gps-relativity.asp, "For GPS satellites, GR predicts that the atomic clocks at GPS orbital altitudes will tick faster by about 45,900 ns/day because they are in a weaker gravitational field than atomic clocks on Earth's surface. Special Relativity (SR) predicts that atomic clocks moving at GPS orbital speeds will tick slower by about 7,200 ns/day than stationary ground clocks."

So the net result is that clocks on satellites, and the astronauts aboard ISS, they will appear to age faster by 38,700 nanoseconds per day, which is .00000387 seconds, or about 122 seconds per year - so about 2 minutes/year.


String-Theory is the theory that replace the particles(atoms, electrons, photons) to vibrating strings.


In the early Twentieth century, two frameworks of physics were published:

#1.# Theory of Relativity by Albert Einstein
#2.# Quantum Mechanics

Both these theories try to explain the formulated laws of Physics that we use now. But the problem arises when we try to reconcile Quantum Mechanics with Theory of Relativity because of Gravity.

String Theory try to solve this problem by replacing particles with strings. That's why it is a member for Theory of Everything.

On large scale distances, the string have normal properties like mass, charge, etc. It is a vibrating string that vibrates in all different ways.

When we get electromagnetic field in space-time, it is called as Quantum Field Theory. As we know that, quantum mechanics is based on probabilities, we can compute that with the help of Perturbation Theory.

But how string theory relates to space-time? If a closed string is traveling in a curved space-time, then the coordinates of the string in spacetime feel this curvature as the string propagates. The answer lies on the string worldsheet or stringy space-time. In order for their to be a consistent quantum theory in this case, the curved space in which the string travels must be a solution to the Einstein equations.

This was a very convincing result for string theorists. Not only does string theory predict the graviton (A hypothetical gravitatioal force carrier) from flat spacetime physics alone, but string theory also predicts the Einstein equation will be obeyed by a curved spacetime in which strings propagate.(Credit)

The problem with string theory is that it is not experimentally discovered yet. If we will get results, we can be able to reconcile gravity with quantum mechanics.


The Oort cloud explains the existence of long period comets.


Long period comets with periods of over 200 years have to come from somewhere. One problem with such comets is that they will eventually either fall into the Sun or be expelled from the solar system.

The comets had to have been around from the early solar system, so they must have been somewhere for a long time before becoming a comet.


The Oort cloud explains this. The comets would have been in the Oort until some gravitational perturbation caused them to fall into cometary orbits.

Also, models of the early solar system predict that the large outer planets, particularly Jupiter, would have ejected material as they moved to their current positions.

The problem with actually detecting the Oort cloud is that it is between 2,000 and 50,000 AU away. It is possible that modern space telescopes, such as Kepler, may be able to detect Oort cloud objects transiting a star.

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