Theory:

    Next day when Tilloo’s father went to work, he found the Control Room full of excitement. People were crowded round the big TV screen. It showed a dot in an otherwise clear background.
 
    “It isn’t a star—for it’s changing its position. Our computer has given a trajectory for this ‘thing’. It’s heading towards us.” The Supervisor of the last shift explained.
 
    “A spacecraft?” Tilloo’s father asked. By now he was joined by his teammates on the new shift.

    “So we think; but it needs watching.”
 
    A spacecraft? Where from? The solar system wasn’t known to have any life anywhere else except on their planet. Tilloo’s father recalled the ancient days recorded in the archives at the Central Bureau when their ancestors had a well-developed space programme and had searched the solar system with manned and unmanned spacecraft and found that they were indeed ‘alone’. Now, in the days of energy shortage and underground life, they had no space programme. They could only watch impotently from their vantage point. Who were these strangers?
Explanation:
 
The next day, Tilloo's father went to work. When he arrived at his workplace, he noticed that the Control Room was full of excitement. The excitement might be because they had seen something unusual. In addition, a large crowd of people who had gathered in front of the large television screen were curious to know what was that. They observed something in the form of a dot that appeared in the plain background, telecasted on the television screen.
 
controls-1853330_1920.jpg
Control Room

Furthermore, a Supervisor working on the last shift remarked that it could not be a star because it kept on changing its position. In addition, he claimed that their computer was tracking the object's path and when he saw that, he realised that it was approaching them.

After seeing the object's movement, Tilloo's father asked whether it was a spacecraft. Other team members joined with him in the new shift while he was conversing with the Supervisor. Later the Supervisor stated they also think it would be a spacecraft. They also had to keep an eye on its movements to figure out what it was.

Tilloo's father later inquired as to how and from where the spacecraft had been sent. He thought it was because no other life had been discovered in the solar system except on their planet. It means that there was no life on the other neighbouring planet. Later, Tilloo's father recalled how his forefathers had a well-developed space programme and explored the solar system and discovered that they were "alone" in the universe. It means that no other life forms were there on the planet at that time.
 
solar-system-439046_1920.jpg
Solar system

Also, Tilloo's father stated that during his ancestors period, the manned and unmanned spacecraft were sent to identify whether any presence of lives was there. The manned spacecraft have been operated with the help of a crew member, and the unmanned spacecraft could be used without any crew member. Later, the spacecraft discovered that there were no signs of lives except them in the galaxy. Moreover, these pieces of information had been already recorded in the Central Bureau's records.

Tilloo's father later remarked that nowadays, there were shortages of energy and underground existence. They were allowed to survive under artificial conditions due to the upset in the natural equilibrium, which resulted in energy shortages. They had lots of vitality naturally during his forefathers' time. He also remarked that they no longer had a space programme and that all they could do was watch helplessly from the Control Room. Finally, the question of who these strangers remained. The reason behind the comment was if they had enough energy and spacecraft, they would have been able to identify the strangers and from where they had been sent to their planet.
 
Meanings of the difficult words:
 
S.No
Words
Meanings
1
ExcitementA feeling of great enthusiasm and eagerness
2
CrowdA large number of people gathered together in a disorganised or unruly way
3
Trajectory The path followed by a projectile flying or an object moving under the action of given forces
4
Ancestor A person, typically one more remote than a grandparent, from whom one is descended
5
Vantage A place or position affording a good view of something
6
StrangerA person whom one does not know or with whom one is not familiar
Reference:
National Council of Educational Research and Training (2007). Supplementary. An Alien Hand - Jayant Narlikar (66-73). Published at the Publication Division by the Secretary, National Council of Educational Research and Training, Sri Aurobindo Marg, New Delhi.