Then a gun is fired, explosive gunpowder is ignited. The explosive creates a high-pressure pulse of hot gases, forcing the bullet down the barrel. It exits at a supersonic speed with a bang that breaks the sound barrier.
A gun silencer suppresses that sound. It consists of a tube of small chambers separated by baffles. When the gun is fired, the pressurised gas now has lots of holes to expand into, so the pressure is far lower when the bullet exits the barrel, reducing the sound.
Stars twinkle when there appear to be variations in their brightness. Astronomers call this phenomenon atmospheric scintillation, and it’s caused by motion in the atmosphere.
Specifically, changes in atmospheric temperature cause small fluctuations in the air’s density. As starlight passes through the atmosphere, it’s refracted or slightly alters direction, creating a twinkling effect.
This is more obvious when viewing stars closer to the horizon because there’s a thicker layer of atmosphere. Astronomers compensate for atmospheric scintillation by using special adaptive optics on the most sophisticated telescopes. Space-based observatories like the Hubble also allow us to view stars and other objects without atmospheric scintillation.
The wax that makes up a candle’s body is made of a carbon and hydrogen compound called paraffin. As a solid, it isn’t actually very flammable and if you were to hold a flame against it, it would melt and then evaporate rather than burn.
This is where the wick comes in When you light the string at the top of the candle, the liquid wax is drawn up the wick by capillary action (the ability of a liquid to flow upwards against gravity in a small tube). It becomes so hot that it turns into a gas, which mixes with oxygen in the air and combusts.
We take for granted that a candle burns with a yellow, cone shaped flame, providing light. The reason this happens is due to a process called incomplete combustion, which produces bits of soot. This soot gets extremely hot, causing each particle to glow and produce the characteristic yellow colour.
Regular rainbows occur when moisture in the air refracts sunlight in such a way that it is broken up into its constituent colours. The phenomenon occurs when the Sun is positioned behind you and sunlight passes through the airborne water. The light refracts (bends) inside the droplets and the white light is broken up. Each colour has a different wavelength so, depending on the angle of refraction, a different colour of light will be reflected outwards, the result of this process is what we observe when we see a rainbow.
Every rainbow is accompanied by another, secondary rainbow. but it’s usually too dim to see. This double rainbow effect is due to the continued reflection of light inside each water drop. Sunlight is actually reflected twice inside a drop: once to produce the primary rainbow and a second time at the back of the drop. This second reflection inverts the light but undergoes the same refraction, so exits in the same way as before – though upside down. This second reflection reduces the intensity of the sunlight, but it also produces a second inverted rainbow, creating a double arc of multicoloured light.
They’re known as cryovolcanoes, and though scientists don’t have cast-iron proof that volcanoes spouting ice from a sub zero caldera exist on Enceladus, there is strong evidence for it.
The flyover by Cassini two years ago revealed jets spurting from four cracks along the moon’s surface, named Alexandria, Cairo, Baghdad and Damascus. The eruptions were so high that they could easily be seen in profile from space.
Volcanoes found on Earth and also Jupiter’s moon Io spout silicate lava that is heated by the pressure beneath the crust. Ice volcanoes work in a similar way: scientists believe that subterranean geological activity on Enceladus warms the freezing surface into a slush of water, ice and organic compounds, which is then ejected out by force through the surface by ice sheets grinding up against one another.
Enceladus has an elliptical orbit similar to our moon, so as Saturn’s gravity pulls unevenly at Enceladus it creates a bulge that generates the friction and heat necessary to cause this previously unheard-of phenomenon.
Birds of prey boast the greatest visual acuity of all animals and zoologists believe some hawks and eagles have vision eight times sharper than ours. An eagle’s retina sports around 1 million sensory cells per square millimetre – around five times what you’d find in a human retina.
It pays off: some birds of prey can spot and track a rabbit 1.5km (0.9 miles) away!
If you gauge eyesight in terms of light spectrum perception instead of acuity, the mantis shrimp is the champ.
Mantis shrimp perceive 11 or 12 primary colours, putting our three to shame, and they see ultraviolet and infrared light too.
The compass app on your phone probably won’t work because it relies on radio signals that are easily blocked by rock or water, but for a compass with a wobbly needle, it just depends on how far underground.
A compass works because its magnetised needle lines up with the magnetic field that runs between Earth’s north and south poles, and that field is just as powerful if you go down a mineshaft or into the depths of the ocean.
But the field is created by swirling molten iron in Earth’s core, and if you could drill that far down, you’d find your magnetic needle going haywire.
Bats are the only mammals that can fly. They fly like birds do-by beating the air with their wings. However, the bat’s wing is not like a bird’s wing at all. A bat’s wings are actually its forelimbs that have grown very long. The wing has no feathers- rather, a thin membrane stretches across the ‘fingers’.
The toes of the hind limbs are long, with curved claws that the bat uses for hang ing from trees. Bats feed on insects in the evening. Because bats sleep during the day and are active at night, they are called ‘nocturnal’. They sleep upside down and use their feet to grasp onto a twig or board. When it is cold, they hang close together.
There are more than 1000 species of bats in the world, and they are found in every continent except Antarctica. Like other mammals, they give birth to live babies. The babies feed on their mother’s milk. Many bats have adaptations that let them find their way and their prey – in complete darkness!
Flying fox bat:- Flying foxes are a species of fruit bat. As you might have guessed, their diet consists mainly of fruits. They are named flying foxes because of their fox-like heads and red dish brown fur. There are over 160 species of flying fox found widely through South East Asia and North East Australia, where they inhabit tropical rainforests.
Like most bats, the flying fox is nocturnal, and roosts in trees during the day in large groups called ‘camps’ which may contain thousands of individuals. They sleep hanging from branches by their feet, and keep themselves cool by fanning themselves with their large wings. They are the largest bats – some attain a wingspan of one metre.
Vampire Bats:- A vampire is the only bat-and the only mammal- that feeds on blood. It preys on cattle, horses, large birds and pigs. Vampire bats don’t suck animals’ blood. They make a small hole with their two very sharp incisor teeth, and lap up the blood. The bat does not take enough blood to harm the animal- but the very fact that it drinks blood scares most people!
The elephant is truly a magnificent animal, and the largest living land mammal on Earth. Elephants are brown to dark gray in colour, and have long, coarse hairs that cover their bodies sparsely. They have very thick skin that keeps them cool.
Elephant ears are large, thin, and full of veins. This allows blood to circulate through them, and helps cool off this large mammal. When they fan their ears, they’re looking to cool off! Of all its specialized features, the elephant’s musculartrunkis perhaps the most extraordinary.
It is actually a fusion of the nose and lip, and contains almost 40,000 muscles! It serves as a nose, hand, extra foot, signaling device and tool for gathering food, siphon ing water, dusting, and digging.
Elephants eat leaves, bamboo, bark, roots. They are also known to eat crops like banana and sugarcane which are grown by farmers. Adult elephants eat 136-180 kilos of food per day.
Elephants form deep family bonds, and live in tight matriarchal family groups of related females called a herd.
The herd is led by the oldest, and often largest female in the herd, called a matriarch. Herds consist of 8100 individuals depending on terrain and family size.
Recent discoveries have shown that elephants can communicate over long distances by producing a sub-sonic rumble that can travel over the ground faster than sound through air.
Other elephants receive the messages through the sensitive skin on their feet and trunks. Elephants are extremely intelligent animals, and have memories that span many years. They also display signs of grief, joy, anger, and playfulness.
Dendrochronology is a scientific method of dating by studying the patterns of the growth rings in trees.
Trees have a single, thick and woody stem. If you look at the trunk of a tree that has been cut, you will see that it has a pattern of rings on it.
Each ring is made up of a new layer of tissue that is added every year. So, each ring represents a year of the tree’s growth.
Dendrochronologists are scientists who study the rings of trees. They use annual rings to date events in history – both in the history of the tree, and of the natural world.
Using dendrochronology, it is possible to date wood as far back as thousands of years.
