Recently Hubble discovered a spiral in Antilia constellations claiming to be millions of light years away. Besides it is a thing of distant past as the nearest star is four and half light years away?
Sundaresan,
One basic consideration is that the constellations are only groupings of luminous objects that, to a casual unaided observer, appear near each other in the sky and seem to move generally together. Actually, though those objects may be at vastly different distances from us - and each other, and totally unrelated except in their recent positions within our sky. I'm not a physicists or astronomer, but as I understand the more distant an object is, the less it seems to move in relation to other objects in the sky. Of course, most of the apparent motions of constellations is the result of the rotation of the Earth, our orbit around the Sun and relative motions of Earth's rotational axis. I hope this helps without being too rudimentary...
My point was what we see is actually 1000's of years prior as light years are involved.If so how does our observation apply to real life?
The most distant objects emitted their observed light nearly 13 billion years ago, for example. As the universe is estimated to be 13.7 billion years old, the information that can be derived from such observations contributes to our knowledge and understanding of the prevailing conditions in the ancient, early universe, and therefore its development to the present day.
Dear sir James
Thank you very much for your kind and sincere reply.These observations really invoke the philosophical thoughts to man and his limitations. The never say die man will be endlessly pursuing the secrets of Nature. There is more than what the eyes see and man's words keep changing with time.
Typical differential star velocities are of the order of 20Km/sec. Typical distances to the stars of constellations are about 1000 parsecs. At such distances, the projected separations in the plane of the sky for the individual stars that make up the constellation are about 150 parsecs. Now at 20 Km/sec, a star moves 20 parsecs
in a million years, or about 1/7 of the separation of constellation stars.
As a result, constellations will appear to show subtle changes over periods of about 100,000 years, and when a constellation star is nearby, it will be seen to move
substantially over periods as short as 1000-2000 years. This is how Halley noticed that Sirius and Arcturus had moved from their positions recorded in Ptolemy's catalog.
made some 1500 years earlier
Sir Woolf,
It is an honour to receive your explanation. Frankly it will take me some time to get a good feel . It looks as long as we live we will be witnessing a great Painting of our Universe drawn by One and seen by all. The Universe seems still and to shock us a new thing is revealed now and then from nowhere defeating our time concept and makes us spellbound. We humans as strong as we are never give up and some unseen Force is having a hearty laugh.
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