Stargazer

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Why are there no stars during the day ?

Even when I was young, I was always fascinated by the stars in the night sky. I always stare at them for I treated them as the most awesome things in the universe. Oh how they sparkle in the sky. The strange thing is that they always vanish during the day and I asked everybody, “Why is that?”

After the sunset the stars become visible in the sky. When the darkness of sky increases, the number of stars and their brightness also increases. As the sun come up to the sky, the number of visible stars decreases. At that time we can see only some bright stars. All the stars vanish as the sun rise.

It is believed by people that as the sun disappear at night, the stars also disappear in the day time. But it is wrong as the stars never disappear. They only become invisible in day light due to the brightness of the sun rays. In reality, the sun rays are scattered in all directions by the water vapors, gas and dust present in the atmosphere. Because of this, the whole atmosphere starts shining.

The light of stars is very weak as compare to sunlight therefore it can not make any impact on our eyes. Due to this reason we can not see stars in day time. Actually this can be proved by observing a burning lamp. Since at night the burning lamp is visible from a long distance but in day light the same lamp is not visible to us even from a short distance. Even if the weak light is able to reach our eyes at night, similarly the stars become visible to us at night. The stars would have been visible in day light if there had been no atmosphere.

How many stars are there in the sky?

My interest about the stars have grown even more intense as I wondered how many of this awesome things exist in the universe. Some adults only laughed at me when I raised the question. They always say that it is like counting the strands of my hair or counting all the fish in the sea.

Stars are not scattered randomly through space, they are gathered together into vast groups known as galaxies. The Sun belongs to a galaxy called the Milky Way. Astronomers estimate there are about 100 thousand million stars in the Milky Way alone.

It has been said that counting the stars in the Universe is like trying to count the number of sand grains on a beach on Earth. We might do that by measuring the surface area of the beach, and determining the average depth of the sand layer. If we count the number of grains in a small representative volume of sand, by multiplication we can estimate the number of grains on the whole beach.

For the Universe, the galaxies are our small representative volumes, and there are something like 1011 to 1012 stars in our galaxy, and there are perhaps something like 1011 or 1012 galaxies. With this simple calculation you get something like 1022 to 1024 stars in the Universe. This is only a rough number, as obviously not all galaxies are the same, just like on a beach the depth of sand will not be the same in different places.

Knowing how fast stars form can bring more certainty to calculations. Herschel will also chart the 'formation rate' of stars throughout cosmic history. If you can estimate the rate at which stars have formed, you will be able to estimate how many stars there are in the Universe today. Why can not I stare at the sun?

It seems that I really love stars and I am really interested in the biggest star in our galaxy, the Sun. I was amazed when I realized that the Sun was also a star and the only star that appears during the day. But it seems I can not look at it for a very long time. Thus I got curious and asked, “Why?”

The Sun is very bright and by focusing the light onto the back of your eye (the retina) with or without a telescope, you are putting a lot of energy (both optical light and infra-red) onto a tiny area. At some point in your life you may have tried to set paper on fire using a magnifying glass, so just think about that being done to the back of your...
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