[These blogs are created for my online astronomy class in California State University Northridge. Since they may interest wider audience, I publish them on Blogger. All comments are welcome.]
Scale of the universe looking
at the sky
Debi Prasad Choudhary
Los Angeles, 1/30/2014
While growing up in a small
remote village, I used to listen stories from my granny about the mythological
characters who could change their size as they like and can move large
distances in a matter of fraction of a second. They can become like mountains
or like an ant in a moment. Once a Hindu God, known as Hanumanji in his
childhood, woke up in the morning and was hungry. His mother was attending to some other
household activity. He saw the rising sun and thought of it as a ripened fruit.
Immediately, he jumped and ate the sun. The whole world became dark. Other Gods
were afraid and prayed Hunmanji to eject the sun, which he obliged and saved
the creation. I was really fascinated with these stories and believed them that
gave me a sense of scale of the earth, sun and all others I saw around me.
Later in school, I read the story of Gulliver’s travels, where he encounters
Lilliput and giants. Even though I did not believe them, I wished they were
true.
Later, I went to far away
places from my village for higher studies that took 24 to 36 hours of train
journey. This really gave me a sense of the size of landscape in which I lived.
Much later, on my first visit abroad to Germany, when I used to talk to my wife
in India, some times I used to ask her go outside and see if it is daylight or
darkness of night. Even though, I knew that earth is round and my wife’s place
would be in nighttime when Germany would be in day, this fact fascinated me.
Even now, the fact that east and west coast of United States has two different
times separated by three hours fascinates me. Last summer, while attending a
conference, one of my old professors asked me “do you know how much is a trillion
dollar?” I was a bit confused, as I can never imagine what a trillion dollar
means. We figured out that if you place trillion of one dollar bills one over
the other, the height would be the distance to the moon!! You might like to
calculate this fascinating fact!!
Compared to my home, my town
and me the universe, of which I am a part, is big. There are, of course, much
tiny things around. They are so tiny that when you shine light onto them to
see, they move due to the push of light particles. So, it is impossible to
precisely determine their position. There is a whole different subject of
dealing with these tiny objects. But, astronomy is all about big things and
large distances.
It is fascinating to know
that there are things beyond what we know to exist like our home, our town or
our earth. There are other planets moving around the sun like our earth. There
are billions of suns in our galaxy and billions of galaxies are in this
universe. In this scale of structure, the nearest distance to a star, which is
our sun, is about 150,000,000 km called one astronomical unit. It is convenient
to write this in scientific notation as 1.5×108 km. The distance is so much that light takes about 8 minutes to come to us from
the sun. The speed of light is about 300,000 km/s and nothing in the universe
can travel faster then light. In order to express the size of a galaxy, we need
a bigger unit of distance. One convenient unit is the distance travelled by
light in one year. This is known as light year (Ly), a unit of distance NOT
time!! The size of a galaxy is 80,000 Ly, that means light takes 80,000 years
to come from one side of the galaxy to another side. If you go by a car it will
take many many years, during which time the sun itself will die!!
This is the vast universe we live in. Knowing
that make us smart and humbling. That is the single most benefit of learning
astronomy. How do we know that universe is this big? In past 100 years, we have
explored the universe with modern physics that has also given us airplanes, cars,
iPods and cell phones. We can watch a movie sitting on the college lawn. The
laws of physics that are used to make these devices are employed to explore the
universe. Sir Isac Newton, a British scientist showed that the same laws of
physics govern the motion of objects both on earth and in heavens. So, we are
confident that what we know is consistent. Today we are equipped to ask big
questions like: how the universe was created? How life was created? These are
the questions all civilizations asked. Every civilization answered in their own
way. We hope to give answer using robust science. We do not have answers to all
questions at this time. But my granny did not have an iPhone either. Exploring
the answer is the goal of modern science. We look at the sky and explore the
property of the stars and all that we can see.
While in elementary school, we used to sleep
outside in summer time and look at the sky. The village sky was much darker
those days, filled with bright and faint stars. Many bright stars gave an
appearance of patterns that are called constellations. These groups of stars
just appear as one pattern at this time and do not have any physical
association. Several thousand years ago, you might not see such patterns as the
stars move in the sky. My granny narrated stories about two group of
constellation that impressed me in my childhood. One of them was Orion
constellation depicted as the great warier, general of Gods, known as Mahakal.
The other one was great dipper, called saptarashi (seven sages). One of the sages is the sixth star
(located in the tail) named as Vasistha,
one of the great-learned sages of Hindu mythology. This is a visual binary star
that has a faint companion, named as the Arundhti,
the faithful wife of Vasistha. Many
years later, when my granny died, I wanted to name one of these stars after
her!!! This companion star is the limit of visibility for human eye, which can
often be used for eye test. If you can see this star with unaided eye, you are
good!!
There are twelve such prominent patterns known as
Zodiac. Since they happen to align with the plane in which the sun moves in the
sky, they have special significance in ancient time. Depending on the position
of the sun in the background of this zodiac constellation during the birth of
an individual, our constellation signs are decided. For example, I am a Leo.
When I was in 5th grade, my father invited an astrologer and found
out my major life events based the zodiac sign. He was worried, because I used
be sick very often for prolonged period, primarily because of lack of medical facility in the
village. Anyway, I took interest and waited for better times predicted by the
astrologer. Later, while in college, I used to look at the astrological predictions
printed in local newspapers. If the prediction was bad, I really used to get
depressed and look at another newspaper that gave prediction for a good day. I
used to convenience myself, may be the later newspaper is more correct. I gave
up this exercise after a while, when I did not find any such correlation with
what they say and what actually happens. Now, of course, I know that these
predictions are baseless and as good as my granny telling me how good my day is
going to be.
After my granny died, I started looking for the
brightest star for her. I learned that a star that looks bright might not be
really bright if it is located nearer to us compared to a bright star at a
greater distance. The brightness that appears is known as apparent brightness. The astronomers have devised techniques to
determine distances to the stars. So, they can tell their actual brightness,
known as absolute brightness. These
are measured in magnitude scale. In this apparent magnitude scale the sun is
-26.74. The brightest star is -1.47. A human eye can see a star of 6th
magnitude. The more negative is the brighter.
The stars are huge balls of glowing mostly
hydrogen located at far away distances. For us they are just point sources of
light, radiating energy in all directions. The energy received on earth over a
square meter per second is the energy flux (F) that actually decides the
brightness of the star. If two stars A and B differ by one magnitude, the flux
ratio would be FA/FB = (2.512)(mB-mA).
So, now while I know that Hanumanji could not
have eaten the sun or the star patterns do not decide my day, I know that the
laws of physics using which the TV set in my living room is made, govern the
motion of stars and their lifestyle. In my later career, I have been using them
to explore this amazing creation.
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You should use the material in the following links to explore the night sky in your locality with the help of Internet resources. Familiarizing the objects in the sky will not only give you intellectual pleasure but also help you in navigation and other useful activity.
(1) Install GoogleSky on your computer.
(2) Exercises to identify the constellations on local sky.
---------------------------------------------------------------------------------------
You should use the material in the following links to explore the night sky in your locality with the help of Internet resources. Familiarizing the objects in the sky will not only give you intellectual pleasure but also help you in navigation and other useful activity.
(1) Install GoogleSky on your computer.
(2) Exercises to identify the constellations on local sky.
