Featured Answers

Active contributors today


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.



The elements Lithium, Beryllium and Boron are made by cosmic rays.


The elements Hydrogen and Helium were made during the Big Bang. Helium is also made by fusion reactions in stars.

The elements Lithium Beryllium and Boron can't be made in any quantity is stars as they are intermediate steps in other fusion reactions. Any of these elements present at the birth of a star will get consumed by later reactions.

These intermediate elements (Lithium, Beryllium and Boron) are produced by cosmic rays. These are high energy protons and other particles. These collide with nuclei of Carbon and Oxygen which breaks them down and produces Lithium, Beryllium and Boron.

Carbon is produced by reactions such as the triple Helium reaction. This reaction explains what happens to Beryllium.

#""_2^4He+""_2^4He rarr ""_4^8Be#
#""_4^8Be+""_2^4He rarr ""_6^12C#

enter image source here
The diagram shows where all of the elements are created.


Nuclear fusion is the process of two small atomic nuclei coming together to make a larger nucleus which is stable.*


Nuclear fusion is the reverse process of nuclear fission. This process also results in the conversion of mass into energy.

Nuclear fusion is the energy source which causes stars to "shine", and hydrogen bombs to explode.

Nuclear fusion in star
The enormous luminous energy of the stars comes from nuclear fusion processes in their centers. Depending upon the age and mass of a star, the energy may come from proton-proton fusion, helium fusion, or the carbon cycle

(Credit- http://hyperphysics.phy-astr.gsu.edu/hbase/astro/astfus.html)

Fusion releases energy. The energy released is related to Einstein's famous equation, #E=mc^2.#

To start nuclear fusion, protons and neutrons must be exposed to temperatures approaching 10 MK Celsius (180 million degrees Fahrenheit). In these reactions too much energy is released.

When nuclei fuse together, part of their mass is converted into energy. The sun and other stars convert this energy into light.

#=># For example - Fusion of deuterium with tritium creating helium-4, freeing a neutron, and releasing 17.59 MeV of energy, as an appropriate amount of mass changing forms to appear as the kinetic energy of the products, in agreement with kinetic E = Δmc2, where Δm is the change in rest mass of particles. (Source : Wikipedia)



It did have a huge effect on the philosophies of science and astronomy!


First of all, what do you mean by "bigger effect"? It did have quite a huge impact in cosmology and astrophysics that we had to rewrite entire libraries with the new discovery and its implications. Nowadays, all astronomy books include this unexplained "dark energy" and the mass-energy density pie-chart of the universe had to be revised.

Perhaps you felt it wasn't as big as the paradigm-shift that occurred in the early-1900s when Edwin Hubble proved that Andromeda and other spiral clouds were in fact entire galaxies similar to our own (which made the known universe to substantially increase in size, plus its expansion meaning that the universe had a beginning), or as big as the discovery of the Cosmic Microwave Background in the 1960s (which proved once and for all that the Big Bang really occurred and that the universe had a beginning).

The omega value, or critical density of the universe, is very close to 1 (i.e. flat universe), and since the expansion rate of the universe seems to be accelerating, it will keep expanding forever and faster and thus its geometry MAY be slightly open (but we don't know that for sure and it is up to debate, and if that is the case, the extent of the universe beyond the observable one could be infinite).

I realize that I need to explain more in my answer about another question asking for the volume of the universe, to which many of us replies that the "universe is infinite", as it would only make sense if the geometry is either really flat or open.

The current standard model of cosmology that best describes the universe is called the lambda CDM model and takes into account the cosmological constant (first introduced by Einstein but to have the opposite effect of what it is used for today, the dark energy). There are many references in the literature (perhaps not popular science), but I find the WMAP and Planck websites to be quite good to get a grasp of the current model. That's why, it still had a great effect.


The decadal oscillations cause temporary changes in world-wide climate, both global warming and global cooling.


One theory is that the present observed trend in global warming is at least partially the result of the decadal oscillations. The effects of the oscillations can be seen in the arctic ocean and the glaciers of Greenland.

During the 1930s and 1940s there was a global warming effect due to the decadal oscillations. During this time the Arctic Ice melted and the Northwest passage was open for a time in 1939 and 1940. Planes landed on the glaciers of Greenland were later covered with very thick layers of ice. These planes have recently been uncovered by the present trend in global warming.


Similar oscillations have been seen in the past. Vikings settled in Greenland, raised crops, grapes and cattle during a warming trend.
A later cooling trend forced the Vikings to abandon their settlements on Greenland and closed the Northwest passage that had allowed the Vikings to settle in what is now Russia.

Another theory is that the oscillations have nothing to do with the present trends in global warming. The oscillations are by definition are always moving back and forth. While the oscillations have a temporary affect on world climate the present trends are thought to be independent of the temporary affect of the oscillations. The theory is that the present trend in global warming is linked to the increased production of Carbon Dioxide.


Planets orbits are defined by conservation laws.


Johannes Kepler discovered by observation that planets follow elliptical orbits. A few decades later Isaac Newton proved that by applying the law of conservation of energy that a planet's orbit is an ellipse.

When two bodies orbit around each other, they both always orbit about the centre of mass. This centre of mass is called the barycentre. The Moon doesn't orbit around the Earth. In fact both the Earth and Moon orbit around the Earth-Moon Barycentre (EMB).

When it comes to something more complex like the solar system a similar principle applies. None of the planets etc actually orbit around the Sun. In fact the Sun, planets, asteroids, comets and other bodies all orbit around the centre of mass of the solar system which is called the Solar System Barycentre (SSB).

The SSB is in constant motion and can be anywhere from near the centre of the Sun to over a Su radius outside of the Sun. So, everything in the solar system is orbiting around a point which is in constant motion.

The diagram shows the path of the SSB over several decades. The points where the SSB is furthest from the Sun occur when the planets are aligned.

enter image source here

View more
Ask a question Filters
This filter has no results, see all questions.
Question type

Use these controls to find questions to answer

Need double-checking
Practice problems
Conceptual questions