Basics of Astronomy

Basics of Astronomy

The most incomprehensible thing about the Universe is that it is comprehensible. 

- Albert Einstein

When you look up at the Moon on a full moon day, you see a very bright white colored disk in the sky. On the disk, you also see few dark colored spots. This view alone can explain so many things of Basic Astronomy. Like, the light of moon is nothing else but is reflected sunlight. Moon does not produce its own light. This understanding was not there few hundred years ago. The dark spots on the moon are nothing else but huge craters formed by bombardments of meteorites over the course of billions of years. The craters are deep and thus shadows form resulting in gray colored spots on the surface of the moon. 

Moon is at an average distance of 3,84,000 Kilometres from us or 0.384 million Kilometres and in comparison Sun is at a distance of 15 crore Kilometres (15 million Kilometres). More or less, we find the size of both Sun and Moon almost same. But, if you know that Sun is 400 times more farther than the Moon is, it shall come to your notice that Sun must be much much bigger than the Moon. 

 

The diameter of the Sun is 14 lakh kilometres. Earth's diameter is appx 12500 kilometres only. And the Moon is even smaller. Here, distance plays an important role. 

Velocity of light is 3,00,000 kilometres per second. Even at such great speed, a ray of light takes 8 minutes to reach Earth after it leaves from the surface of the Sun. How much time it must be taking for the moonlight to reach us? A little over 1 second only. Next nearest star to earth is a group of 3 stars known as Alpha Centauri. The light takes 4.25 years to reach us from those stars!

The galaxy in which we are wandering is very big. From one side to opposite side light takes around 2 lakh years to cover that much distance. Our solar system is appx. at a distance of 30,000 light years from the centre of our Galaxy.

This will give you some idea about how big the system is. In our galaxy alone, there are 100 to 500 billion stars. And, there are 400-500 billion such galaxies in the Universe. 

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