Mirages are optical illusions produced by extraordinary atmospheric conditions. They can be non-existent sheets of water or similar visions, inverted or over sized images of distant objects or various other distortions. All are caused by refraction or bending of light rays as they pass through two layers of air with different densities. The differences in density are usually due to unequal distributions of temperature in the atmosphere.

     Common type of mirage is seen in deserts where the heat of the sand rises the temperature of the lower air to make it substantially less dense than the rest of the atmosphere. This bends the light to such an extent that the images of the sky are projected on to the ground as patches of water. The phenomenon is known as an inferior image.

     If the layers of hot and cold air are reversed, the result may be a superior mirage, where distorted images of distant objects on the ground are projected into the sky. In this kind of mirage there are some times two images, the lower being upside down.

     A famous mirage known as the fatta morgana an be seen in the Strait of Messina, between Italy and Sicily. Here the distorted images or houses of the opposite cliffs are transformed into imaginary castles in sea and sky. The Italians name this mirage after the fatta morgana, legendary enchantress with the magical power of raising phantom castle from the waters.

     Christian Johan Doppler (1803-1853) was an Austrian scientist born in Salzburg who make an important discovery about the effects of sound and light when the sources are moving in relation to the observer. You may finds the Doppler effect easier to understand if you consider what happens to the noise of the train as it approaches you and then fades away.

     The Doppler principle states that the pitch of a sound is changed, if the object emitting it is moving relative to the observer. The light emitted, being a moving source, is changed in colour, as seen by a relatively stationary observer. In each case the actual sound and light frequency remains constant. That is to say, a diesel locomotive travelling at a constant speed will be producing exactly the same engine noise or "note" whether it is half a mile or a hundred yards from you. But as it gets closer, a change of tone appears. The second part of the principle can be applied to the change in the colour of a moving star.

     A more complex example is the Doppler navigational system for aircraft, which requires no ground installation. In a typical system four separate beams of microwaves energy are radiated from an antenna on the aircraft of the surface of the earth, and some of the energy is reflected back. The frequency of the reflected signal from each beam is shifted by an amount proportional to the plane’s speed. This information is processed by a computer and enables the pilot to fix his position.

     The earth is nearest to the sun on about the second or third day in January. The distance varies because the earth spins round the sun in an elliptical or orbit or path. The time when the earth is closest to the sun is called the perihelion. The time when it is farthest away – the aphelion – comes six months later on the first or second day in July. During the perihelion the earth is 147 million kms from the sun, but during the aphelion it is 152 million kms away.

     When planetary distances in the solar system are compared, the average distance between these two extremes is used. This is called astronomical unit and in the case of the Earth and Sun, measures 149 million kms. If it were possible for an aircraft to fly from the earth to the sun at a constant speed of 1000 miles an hour it would have to travel non stop for 10 years to reach its destination.

     The earth takes 365 ¼ days to travel round the sun and moves at a speed of nearly miles a second. As can be seen from the dates of the perihelion and aphelion, the nearness of the sun does not determine the season. Our seasons are decided by the amount of daylight directness of the sun’s rays on the earth’s surface.

These conditions vary as the axis on which the earth spins is titled.

      Albert Einstein is famous for his theories of relativity which say nothing in the universe is absolutely still and that all motion is connected or comparable. Einstein worked out a method of measuring the speed of moving objects, using the three dimensions of space-length, height and thickness-and adding the forth dimension of time. The three space dimensions tells us where the object is, while the fourth tells us when.

      In the relativity theories that the movement of any objects is represented by lines called ‘ world-lines', with the dimensions of time and space as a fourth dimensional graph. Is an object moves with an uniform speed and straight line, its world-line will be straight. If it moves under the force of gravity such as falling stone, it will drop at a uniform pace, but at an increasing speed. So its world line will be a curve

      His remarkable ability as a scientist did not stop him taking a keen interest in other affairs, and held passionate views on peace and world unity and he was also an accomplished violinist.

     If you stood on the shore looking across the sea to the horizon, you might be able to see about two and a half miles. But the higher you stood the further you would be able to see. As the earth is curved, the horizon would appear farther away with every increase in height above sea level.

     At a height of 20 feet you might see for 6 miles. For the top of 300 – foot cliff your view could extend for 23 miles, while on the summit of a 3500- foot mountain, it could lengthen to 80 miles. From an aircraft flying at 16000 feet you might have an uninterrupted panorama for 165 miles.

     If you look straight up into the sky, the distance you can see is immense. The moon is about 239000 miles away and the stars are millions of millions of miles distant.