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Do we really know about a star?     Stars are heavenly bodies, which shine like our sun. Many shine brightly, the others have a dim glow. Some are red while others are blue. Stars are giant balls of gas made of hydrogen, bound together by their own force of gravity. The energy that makes them shine comes from a kind of power plant in their interior, where atomic nuclei of hydrogen atoms are fused together to form helium atoms. The stars do not live forever and ;die' at some point. Many simply get extinguished, while very heavy stars expand and explode. Their remains become either a neutron star of a 'black hole'.     The cradle of a star is a cloud of hydrogen and dust. There are numerous such clouds in the universe. By the action of external forces -such as the explosion of a star -this cloud gets compressed and keeps pulling itself together due to the increasing force of attraction among the particles. After a few hundreds of thousands of years, it begins to ...

Do we know?. why does the moon changes its shape? The moon, which causes high and low tides on the Earth, is a sphere. It does not changes its shape; only our view of it changes. The reason is that unlike the stars, the moon does not produce light, but only reflects the light of the sun. Since the moon goes around the Earth once in a month, the orientation of the moon, the sun, and the Earth respective to one another changes. For this reason, the illuminated part of the moon cannot always be seen clearly from the Earth. Sometimes we see it full, sometimes half, and sometimes not at all. The side of the moon that faces us remains the same. We can see the craters and dark spots on the moon, which are known as 'mares'. We always see the same side of the moon. It happens because of the moon rotates once on its axis during the time it complete one revolution around the Earth -which is 27 days, 7 hours, and 43 minutes. The mutual attraction between the Earth and the moon ha...

How can we classify the history of the Earth?   Like the history of human civilization, the history of the Earth too is divided into periods. However, these periods cover not just a few centuries, but millions of years. Broadly, we differentiate between the time preceding the period 550 million years ago and the time after that, during which life developed very quickly on the Earth. Researchers have gathered a lot of data regarding the different periods of the Earth's history by studying fossils. Thus, we came to know at what time fishes and birds appeared on the Earth, why plants and animals lived in the sea for so long, and what the different types of dinosaurs ate. After the 'Archeozoic' period of the Precambian era, which lasted till about 550 million years ago, came the Paleozoic era. This era is subdivided into Cambrian, Ordovician, Silurian, Devonian, Carboniferous, and Permian periods. In the Cambrian period, different types of organism lived in the sea. ...