My Science School

               When we look towards the surface of the moon with the naked eyes, we observe some dark smooth regions. The earliest astronomers believed that these dark regions on the moon’s surface were covered with water like the seas on earth. It was Galileo who first studied these dark areas through his telescope in 1609 and concluded that these were the areas covered with water. Galileo also studied some bright rugged regions of the moon’s surface and found that the bright areas were highlands. The highlands catch the sun’s rays. The darker patches are low lying plain areas of moon. Therefore once these were thought to be seas of the moon.

               In the later centuries, with the development of better telescopes, it became evident that the “Seas of the moon” were not seas at all, but low-lying and completely arid basins or plains. However, they continued to be called “Seas”. Astronomers called the dark areas Maria, meaning “Seas”. Strangely enough, no extensive Maria occurs on the lunar far side, which is almost entirely covered by mountainous terrae formations.

               The Seas of the moon can be divided into two types: the circular shaped and the ones with irregular outline. The circular type Seas are generally surrounded by mountains. Mare Imbrium (Sea of showers) and Mare Crisium (Sea of crises) on the near side and Mare Moscoviense (Sea of Moscow) on the far side are of this type. The irregular seas, such as Mare Tranquillitatis (Sea of Tranquillity) and Oceanus Procellarum (Ocean of Storms) have no extensive bordering mountain walls.

               The lunar seas are paved with successive lava flows. These might have been formed by the collisions of high velocity giant asteroids or meteorites. This would have ruptured the surface or triggered off volcanic eruptions allowing vast quantities of lava to well up from the lunar interior. The surface is made up of much the same elements as are volcanic rocks on earth but they contain no water. From the analysis of Maria basalts collected by the Apollo astronauts, it appears that the filling of the maria basins took place about 3500 million years ago. The terrae are much older regions than the maria. Most of these high ranges border the maria.

 

               We see a large number of stars in the sky every night. Since the ancient times they have helped man in more ways than one. He used to find out direction with the help of the Pole Star. He developed astronomy by studying stars and planets. Man has been trying to know more and more about these stars. Powerful telescopes have been made to provide valuable information about the stars. It is also possible to tell the date with the help of stars. Do you know how?

               To find out the date, take a large sheet of paper and draw a circle of at least eight inches in diameter. Divide this circle into twelve equal parts — just as a clock face is divided. On each division of the circle, write the name of each month. At the position of 12’O clock write the month of March. Keeping the usual order of the months, write them anticlockwise. Mark the centre of the circle as ‘North Star’. Imagine that the distance on the circle between each month is divided into 30 smaller divisions.

               Take your diagram outdoor on a clear night. Hold it in such a manner that the month of March is at the top. Imagine the diagram in the sky, with the North Star as the centre. Note the location of the Big Dipper. Now draw the Big Dipper on your diagram in the same location as you find it in the sky. Having done this, draw a straight line from the pointer to the North Star. This line will pass through the circle at a point that will indicate the date on which you are making your observation. If the line passes half way between the June and July positions on the circle, it is the day of 15th June. Of course, unless you have drawn a very large circle, it will be difficult to estimate 30 divisions between months on the circle. However, you can come within a few days of the exact date.

               The important thing is to note that on the diagram you have made on any particular date at midnight, the pointers are in line with that date on the star calendar. This is how we can find out the date by the stars.

                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.