Theory:

     “Here! Put on this sweater — or do you want Nabin Babu to order bed-rest tomorrow?”
 
     Like every other amateur astronomer, Duttada had a secret ambition that he would one day discover a new comet. For, comets can be new, coming as they do from the remote corners of the Solar System. Like planets, comets also orbit round the Sun but their orbits are highly eccentric. So once in a while a comet comes close to the Sun; it has a longish tail that is lit brilliantly by the sunlight and then it recedes into darkness not to be seen again for years, or for centuries.
 
     What chance did he stand with his eight-inch Dibya? Didn’t professional astronomers have gigantic telescopes?
Explanation:
 
When Duttada's wife arrived upstairs, she handed him the sweater that Duttada had forgotten to wear as the doctor (Nabin Babu) had advised. The next paragraph discloses Duttada's lifelong hidden goal. It was nothing more than a wish to find a new comet. These comets usually arrive from far out in the Solar System and they orbit around the sun like asteroids and planets. Even though these comets orbit the sun, their nature differs from that of planets, which is very unusual because, when a comet approaches the sun, the heat forces its gases to evaporate, releasing dust and microparticles. The movement of these components, which form a tail, is influenced by the sun's radiation pressure. The longish tail glows for a short while before disintegrating and fading for many years or centuries.
 
The comet.jpg
The Comet
 
In paragraph 9, the author himself posed a question to the readers, namely, 'On what basis did Duttada assume he could discover the comet with Dibya ahead of professional astronomers with massive telescopes?'. Also, we already have experienced astronomers and scientists in the field of astronomy who have a lot of expertise and whose work is far superior to Duttada's.
 
Meaning of difficult words:
 
S.No
Words
Meaning
1.
Comet
An object that revolves around the sun that has a tail of gas and dust
 2.
Recede
To move away to a great distance or to become less bright 
Reference:
National Council of Educational Research and Training (2008). The Comet I - Jayant Narlikar (pp. 73-80). Published at the Publication Division by the Secretary, National Council of Educational Research and Training, Sri Aurobindo Marg, New Delhi.