Why solar eclipse should not be viewed with naked eyes?

One should not see the Sun during eclipse as the sudden change in light intensity may damage the eye.The human eye, as a protective measure, can adjust automatically to varying light conditions-under bright illumination, as during the day, it closes partially and under dark conditions,as in the night,it opens fully.However this process of adjustment takes some time, a few minutes.

As it is dark during a total solar eclipse, the eyes is fully open to let in more light.After totality, as the sun emerges the increase in light intensity is so sudden that it catches the eye unawares.Being very bright it can damage the retina even in few seconds.

Does the sun rotate?

Yes, the sun too rotates about its axis.But unlike the earth, which has rotation period of one day, the sun has a 'differential rotation'.i.e.All the parts of the sun do not have the same period of rotation.The period of rotation near its equator, sun spot zone, and pole are 26.9, 27.3, and 31.1 days.

The sun's enormous core temperature of 15 million degree Kelvin and a surface temeprature of 6,000 degree Kelvin, leaves all its constituents in the state of a high pressure, gaseous  plasma.For the purpose of certain calculations, the top and the bottom ends of the visible sphere of the sun are designated as north and south poles respectively.

Photographs are taken daily and the movements of the spots, filaments and plages are observed for various latitudes and longitudes, for a long period of time.From this, the sidereal rotation period is calculated.The reason behind this phenomenon is still a puzzle to solar physicists.

Why do we have sodium vapour lamp in the streets and not mercury vapour lamp?

White light consists of seven colours-VIBGYOR.During foggy days,air is highly humid and contains lots of tiny water droplets which can act like a prism.So, if white light is used in automobile headlights and street lamps, water droplets will split it into its componet colours, thereby, creating a circular rainbow around each light source.This will affect clarity of vision and lead to acccidents.In order to avoid this effect, a monochromatic(yellow) light source is used.Yellow is chosen because, being in the middle of the visible spectrum, it undergoes medium refraction and medium reflection while passing through a water droplet.Also, it is next only to whilte in brightly illuminating all objects in their original colour.

However, mercury vapour lamps are used in the interiors because, white light is more pleasing to our eyes, and slight reduction of vision due to fog is not of great concern.

What is the difference between a hydrogen and an atom bomb?

An atom bomb is a fission device.Here a heavy atom (like uranium) is split into two or more lighter atoms.In such a nuclear fission process, one or two neutrons are also released from each atom.If these neutrons are captured bythe surrounding heavy atom, further fission takes place leading to further neutron release.In atomic power reactors, this chain reaction is controlled so that the energ released during the reaction can be used beneficially.

But in the case of an atom bomb, the chain reaction is not controlled but left free.This leads to the release of large amount of heat energy in a very short time resulting in a catastrophic explosion.

In a fusin bomb, such as a hydrogen bomb, two or more lighter atoms fuse together to form a heavier atom.Such fusion reactions can take place only at very high temperature, say a few million degrees Celsius.Only at such temperatures can the starting atoms overcome the repulsive forces acting between them.

In this case also, when uncontrolled fusion takes place a large amount of energy is suddenly released resulting in explosion far bigger than an atomic explosion.

It may be noted that the temperature needed to initiate a fusion reaction is normally obtained by a fission reaction.

What is red eye reduction and its function?

Many Compact cameras and some SLR cameras have built-in flash.The flash cannot be detached from these cameras and may result in "red eye" that is,the pupils of a subject's eyes appear red in coloue photographs.

Red-eye occurs when the light from the flash is reflected off the back of the retina.Subjects pupils are dilated and the On-Camera flash actually illuminates the blood vessels in the eye.The only way to avoid this is to close down the pupils i.e.contract the iris by raising the room lights,or using "red eye reduction flash mode".

This feature is available in sophisticated compacts.This mode fires a pre-flash or a bright lamp prior,thereby reducing the affect.In compacts where there is no red-eye reduction feature,the following technique may be employed to reduce the red-eye effect.The flash light may be bounced off the ceiling or wall,before it reaches the subject.

Why should we not sleep north-south?

Researchers at the Chennai Institute of Magnetobiology,say that sleeping in the north-south direction could make one lack a sense of well being at times.According to Dr.Sankaranarayanan,director of the institute,when a man lies with his head towards north in a pulsating magnetic field,his brain's electrical activity is suppressed or damped.Measurements reveal that blood circulation in fingure tips are affected and the balance between neurochemicals is upset.In addition,it gives subjective experiences like headache,confused thinking and lack of a sense of well-being.
     
As opposed to this,he says,if one sleeps east-west,in the pulsed field,the brain's activity is considerably enhanced.Also,the peripheral blood circulation all over the body is enhanced.Hence he feels relaxed and alert.

It is known that the Earth's magnetic field pulses at extremely low frequencies and is typically in the range of human brain's electrical activity.These pulses are not present always but they peak during certain periods generally associated with solar activity.If one sleeps north-south during such activity headache,general discomfort,nausea and confusion may result.On inactive nights,there may not be any change in the body,he says.