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If you look up at the sky and find that
white band of light wondrous, read on…
Imagine a faint band of light stretching
from horizon to horizon against a background of deep black -- a
truly magnificent sight it would make.
The best thing is
that it exists in the sky. And it mystified the early Egyptians into
believing that it was the heavenly Nile flowing down to the Earth
from the land of the dead, while the ancient Greeks referred to it
as a River of Milk.
Through cosmology (a term that means study of the universe and which
has been derived from two Greek words, kosmos, which means
order and harmony and world; and logos, which means word or
discourse), astronomers through the ages have tried to
unravel this mystery. |
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Through their efforts, we now know that the band of light mistaken
for the Nile or the Milky River is but a continuous stream of
countless stars. The band appears continuous line without a break
because the stars are close together. The naked eye cannot
distinguish separate bodies at such a distance.
However, astronomers have proved their existence with the help of
telescopes. Such vast collections of stars are called galaxies, a
word derived from the Greek word for milk.
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A galaxy is,
thus, a massive collection of innumerable stars, each
interacting with the other gravitationally. All the stars that
we can see with our naked eyes belong to the Milky Way, the
galaxy that we are a part of.
Astronomers have estimated the presence of 125 billion
galaxies in the universe. During the early part of the
nineteenth century, noted British astronomers
Sir William
Herschel, Caroline Herschel and Sir John Herschel identified
and catalogued thousands of galaxies.
As we know,
the sun that shines on our earth is also a star. Similarly
each visible star is also a sun in its own right. Some stars
are in fact brighter than the sun but we receive much less
light from them as compared to the sun because they are much
farther away from the earth than the sun. |
The Milky Way |
Can stars die?
After millions or maybe billions of
years, some stars become smaller and cooler and gradually stop
burning. Some stars explode and these are called supernovas. These
are some of the ways in which stars die.
Scientists say it is difficult to pinpoint the average life span of
a star because there is no ‘average’ star. The stars are so varied
in size that an average cannot be arrived at. The diameter of some
stars measures around 1/ 70,000 that of the sun, and there are stars
with diameters thousand times larger than the sun’s diameter.
What are sunspots?
Sunspots are dark spots that can be
seen on the surface of the sun.
Generally they
are found in pairs. They vary in size and
a single sunspot could measure about 1,85,000 miles in length.
Sunspots are caused by the magnetic fields of the sun. They appear
darker, or rather less brighter than the areas around them because
they are cooler. Here, cooler simply means that they are relatively
cooler.
That is to say, the temperature of the sun’s surface is about 11,000
0 F, whereas the gases over a sunspot may be around 7,200
0 F hot. |
