Answers to last issue's Do You Know?
1. I have seen "night vision goggles" in movies. How do they actually work?

ANSWER: In movies, military people go around wearing goggles which generate green pictures on a television-like screen. These equipment use a technique called Light Amplification. This is nothing but a gigantic photomultiplier tube to "see" at night. As the name suggests, small amounts of light in the area surrounding the object (which you are viewing) are converted into electrical energy. Electrons pass through a thin disk, and are multiplied. These electrons bounce off a phosphor screen which converts them back to light. This light is what the viewer sees and enables the viewer to see in the dark. 
In more detail, as an individual photon (light particle) enters the night vision goggle, it strikes a highly charged cathode plate, which emits multiple electrons. That spray of electrons then strikes the phosphor plate (just like it does inside a television) and what you "see" is an image at night that looks like it does in the day. It is possible for things to be so dark that you cannot see even with such goggles.
There is another technique used by night vision equipment for visibility in darkness, it is called Thermal Imaging. This method uses the heat emitted by objects to its advantage and shows that to the viewer. The infrared light is detected by infrared-detectors and a detailed temperature pattern is created, called Thermogram. The thermogram is then converted into electric impulses, and these impulses are sent to a unit which processes the signals, which are sent to a display and the image is shown.
Modern systems use Gallium Arsenide chips for the cathode plate, which have a very special sensitivity to Infrared light. 
With all this technology, night vision is not of very good quality, as we do not get depth perception or vision of activity. They usually have only a 40 degree field of view. At best you can have 20/25 to 20/40 vision with such goggles, even in "perfect" light. This is very different from the 20/20 daytime vision you probably have!

2. Can stars become planets ever and go around other stars?
ANSWER: Short answer: yes, it is possible for stars to turn into planets, but this happens only for a very special kind of stars, called brown dwarfs.
Brown dwarfs are often called "failed stars". Sad for them, isn't it? They are objects that are too compact in size to be stars, but too huge to be planets. They have mixed features of both stars and planets. Their sizes range from twice the mass to 90 times the mass of Jupiter. Like a regular star, they are generally found at the centre of their solar system and have planets orbiting around them. Unfortunately, they do not have enough gravitational force to support the nuclear fusion of hydrogen.
Even though a brown dwarf cannot support the fusion of hydrogen, it can support the nuclear fusion of heavy hydrogen, called deuterium. Thus, early in its life, it gets energy from this reaction and gives off heat and light, just like a regular star. However, deuterium is found only in limited amounts in the universe. As a result, a brown dwarf exhausts its deuterium fuel very quickly. After this, all reactions stop, and the brown dwarf stops the emission of heat and light altogether. It dims and cools down and starts resembling a planet. The result of this is a group of planets in orbit around a giant, central planet.
To date, only about 3,000 brown dwarfs have been discovered. The number is so small because brown dwarfs stop emitting light very early on in their life cycle. They are cool and dark for almost their entire life, which makes it difficult to spot them with conventional telescopes. It is suspected that the number of brown dwarfs in the universe may be close to that of regular stars. For all we know, brown dwarfs make a small, yet substantial contribution to the mysterious identity called dark matter!
BOX Types of Stars
Stars are of different kinds. The Sun falls into a category of stars called main-sequence stars. These stars produce their energy by the nuclear fusion of hydrogen to form helium inside their cores. This energy is released in the form of heat and light. The energy released also maintains the pressure required, so that they do not collapse inwards. In general, stars stay in this phase for about ten billion years.
The amount of hydrogen that a star contains in its core is limited. Once it has exhausted all the hydrogen in its core, the nuclear fusion reaction in the core stops. The core starts collapsing inwards and its temperature increases. As the core becomes hotter, the star starts getting rid of its outermost layers. This causes the star to expand and its outer layers to become cool, giving it a reddish glow. The star is now called a red giant.
This red giant stage lasts for about 1 billion years. During this phase, the star tries to produce more energy to stay alive through complex nuclear reactions that use up the helium it contains. These reactions can only support the star temporarily. Gradually, these reactions start becoming unstable, so the star starts losing even more of its outer layers. Stars like the Sun continue this process until all the layers are shed and the core is exposed. At this stage, it is now called a white dwarf, and will slowly cool and fade away.
For a star with a mass greater than 1.4 times that of our sun, its first core will collapse inwards and then blow up in a gigantic explosion. This is called a supernova explosion. A supernova releases such an enormous amount of energy, that it can shine brighter than an entire galaxy for a few weeks. Such an explosion leaves behind either a neutron star or a black hole.
End of BOX
BOX How planets form
When a star is formed, there is often a disc of gas, dust and debris around it. Particles of dust in this disc are the building blocks of rocky planets. Due to gravity and other forces, these particles collide with each other. If the collision is mild, these particles stick together. This process continues until rocks with slightly larger masses are formed. Now these rocks can pull even more particles towards them with the help of gravity. Through these processes, small planetary bodies called planetesimals are created. Similar to the smaller particles, these planetesimals collide and fuse to form planets.

3. How fast can a human being run? Is there a limit and why?
ANSWER: This is such a natural and simple question, yet it is very hard to answer. Theoretically, humans could run at speeds up to 60 kilometres per hour (kmph), but in practice, even with the most advanced technology available, the maximum speed that humans currently reach is roughly 45 mph.
We all like athletics and admire sprinters like Usain Bolt. The Jamaican's 2009 record of running 100 metres in 9.58 seconds is the best among men. Among women, the 1988 record of 10.49 seconds by American Florence Griffith-Joyner stands unbroken. Bolt has reached a maximum of 44.64 kmph. 
But given how quickly records keep getting broken in sports, we all expect that it is a matter of time before someone comes to claim Bolt's crown. Is this only a belief, or is there any scientific evidence for it?
The main factor that determines how fast we move is the speed at which our muscles can move.
In 2010, an important study measured different forms of movement (hopping, forward running, backward running) on a highly sensitive treadmill. They found that the maximum amount of force our joints can withstand while running is actually higher than what the average sprinter experiences during a race. According to them, the true limiting factor is the amount of time our feet stay in contact with the ground. For the world's fastest sprinters, this is less than 1/10th of a second, and the time period during which the sprinter applies peak force to the ground is less than 1/5th of a second.
This time determines how fast the sprinters' muscles contract and hence their ability to benefit from the upward/forward force from the ground. The forward motion force that runners utilise to sprint is generated by using around 90% of the impact force on the ground. The study noted that the greater the force applied to the ground, the faster the speed of the sprinter.
Thus, if we could contract our muscles faster and utilise the maximum amount of force, humans would be able to exceed the 45 kmph “speed limit”. It is by extrapolating the maximum force from one style of movement (hopping), it is estimated that humans could theoretically achieve speeds of 65 kmph. 
Such theoretical predictions based on such studies are not wholly accepted by many scientists, as the studies are based on "current" humans. We are taller and healthier (on average) now than in the past, and modern medicine is making a big difference. Running tracks are now composed of meticulously designed material that absorbs less energy than the cinder tracks of the past. Athletes today are finely tuned machines, often spending decades perfecting a single ability, but this was rarely the case even two generations ago. It is also clear that some people's bodies are better suited to certain physical tasks: Kenyan long-distance runners have dominated the international marathon scene for decades, just as small Eastern European women seem to excel in gymnastics and men over 7 feet tall dominate professional basketball. So there may be much more room for improvement due to factors we do not understand yet.
So making predictions on human speed limits is difficult. For now, it is best for you to eat healthy food and have regular exercise!

4. Termites seem to work collectively. How do they manage to divide up the work?
ANSWER: Termites are indeed social insects that work together, dividing their tasks by assigning them to different groups. Subterranean termites make tunnels in the soil to look for food. How do they organise the tunnel construction?
What do you know about termites? Perhaps you’ve heard that some termites can infest your home. But there are many different species out there. For example, subterranean termites make tunnels in the soil to look for food. Like other social insects, termites divide their tasks by assigning them to different groups. So how do they organize the tunnel construction?
Termites have different groups (castes) which perform different tasks: Soldiers protect the colony, queens and kings produce and fertilise eggs, while workers find food in the soil by constructing tunnels. When workers build a network of underground tunnels, they leave chemical signals on the trail so that their mates can follow them. The workers construct tunnels and feed on wood. The soldiers have powerful jaws to protect the workers from enemies. Soldiers do not construct tunnels or feed on wood. They rely on workers to feed them. Termites resemble ants, which sometimes causes people to confuse the two orders of insects. In fact, termites are more closely related to cockroaches.
In a study in which scientists observed five groups of 30 workers of Coptotermes formosanus termites for three days, they found that within each group, three individuals (on average) transported most of the sand. In two of the five groups of termites, the same individuals moved most of the sand on all the three days. Specific individuals acted as top excavators, in both tunnel initiation and expansion. Inactive workers on the first day often remained inactive later as well. 
When the termites were moved to a new sand location, again the top busy workers were the ones who started the tunnel construction. Thus only a few individuals seem to play the key role in tunnel construction, and these same workers organise and determine the orientation of the tunnel and its branches. How, among the population, are these specific top workers determined? This seems to be unclear. 
Social organisation of insects is a fascinating area of scientific study. You can already start doing the research at home!
Compiled from: scienceabc.com, physlink.com and Science