My Science School

                We know that the sun is much bigger than the earth but appears very small because it is very far from our planet. The sun is about 150 million kilometres from the earth. When the sun is overhead its distance is 6000 kilometres less than the rising and the setting sun, which is equal to the diameter of the earth. The distance of 6000 kilometres is negligible as compared to 150 million kilometres and would not make any difference in the size of the solar disc. In case of any difference, the sun at noon would have been looked a bit bigger than that of the size of rising and setting sun. Do you know why do we observe exactly the opposite effect? 

 

 

               The bigger solar disc seen in the morning or in the evening is an optical illusion. If you take a photograph of the morning, noon and evening sun, then you will see that the solar image is of the same size. The optical illusion works for the lunar disc also, and because of this, the rising moon appears quite big.

               The reason for this optical illusion is probably because we tend to compare the size of the rising or the setting sun with earthly objects. When we see a tree, or a building or a ship near the solar disc then the size of the sun appears to be big. At noon, when the sun is overhead, we are not able to compare it with any close by object near the sun. In short, we can say that the bigger appearance of the rising and the setting sun is nothing but just an illusion. In fact, the sun’s size always remains the same.

               We know that there are nine planets in our solar system: Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, Neptune and Pluto. In terms of distance from the Sun, Mars is the fourth planet. It is the outermost of the terrestrial planets and is often called the Red Planet. Do you know why?

               We know that Mercury is the planet closest to the Sun. It rises and sets almost with the Sun. Therefore, we can see it either before sunrise or after sunset. Similarly, we see Venus either sometime before sunrise or sometime after sunset (dusk). But Mars can be seen clearly only for a month or two every other year. Among all the planets Mars is next only to Venus in brightness. Also it is very striking not because of its brightness but for its reddish-yellow colour. To study Mars, man has sent many space probes. These spaceships have provided us with many valuable facts about it. In 1976, the American space probes Viking I and II landed on the Martian surface. They gave valuable information about the atmosphere of Mars. It has been found that the atmosphere of Mars contains 1 to 2 percent argon, 2 to 3 percent nitrogen, 95 percent carbon-dioxide and 0.3 percent oxygen.

               The surface of Mars appears to be made up of bright and dark areas. About 70 percent of the Martian surface is found reddish and yellowish which gives the planet its characteristic colour. These areas constantly change shape. It has many rocks containing rusty iron and is covered with reddish-brown deserts. The winds blow at very high speeds of about 400 km/hr over Mars and create heavy storms in Martian deserts. The storms raise a lot of red dust in the atmosphere. Since Mars has a weak gravitational pull, these dust particles remain in the atmosphere for weeks together. And so Mars, because of its red dusty surface and the dust particles in the atmosphere, appears reddish orange to us.