My Science School

Watching the full Moon rise over the horizon can be a spectacular experience. The Moon often looks humongous during this time, making people pull out their smartphones and capture the scene. As the night passes, the same Moon begins to look smaller higher up in the sky. But is there actually a difference in the size?

It's all in our head

The Moon never really changes in size. It remains the same whether you see it at the horizon or higher up in the sky. However, to our eyes the Moon looks different in size due to illusion. This illusion is popularly termed Moon Illusion.

Why do we see it?

Like several other mysteries that science is yet to find an answer for, there is no proven scientific explanation for Moon Illusion. However, many theories have been proposed.

Most theories on Moon Illusion revolve around how we visually perceive the world. Our brain perceives the size of objects nearer and farther away differently. Due to this, it is thought that the brain doesn't realise that the Moon's size doesn't change no matter at what point we see it in the night sky on a particular day.

Another theory is that the position and size of the objects in the foreground also plays a role. Trees, mountains, buildings or other objects in the foreground can trick the brain into thinking the Moon is closer and bigger than it actually is. Ponzo illusion is the term used to describe this effect. However, this is also not considered a perfect explanation since astronauts in orbit also see the Moon Illusion and they have no objects to act as distance cues.

Argue it out with the brain

There are a couple of ways to prove that what we are seeing is an illusion One of the simple ways is to hold up your outstretched index finger next to the Moon. You will notice that your fingernail and the size of the Moon is the same, no matter where you spot it.

Another way to check the size is through photographs. Take a photo of the Moon when it is near the horizon and another when it is higher up. Keep the camera zoom settings the same while taking both the photos. You will notice that the Moon's width is the same side-to-side. Note that the Moon might appear a little squashed in the vertical direction when it is near the horizon because the atmosphere acts like a weak lens.

 

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In biology, two related species or populations are considered sympatric when they exist in the same geographic area and thus frequently encounter one another. An initially interbreeding population that splits into two or more distinct species sharing a common range exemplifies sympatric speciation. Such speciation may be a product of reproductive isolation – which prevents hybrid offspring from being viable or able to reproduce, thereby reducing gene flow – that results in genetic divergence. Sympatric speciation may, but need not, arise through secondary contact, which refers to speciation or divergence in allopatry followed by range expansions leading to an area of sympatry. Sympatric species or taxa in secondary contact may or may not interbreed.

Syntopy is a special case of sympatry. It means the joint occurrence of two species in the same habitat at the same time. Just as the broader term sympatry, "syntopy" is used especially for close species that might hybridise or even be sister species. Sympatric species occur together in the same region, but do not necessarily share the same localities as syntopic species do. Areas of syntopy are of interest because they allow to study how similar species may coexist without outcompeting each other.

As an example, the two bat species Myotis auriculus and M. evotis were found to be syntopic in North America. In contrast, the marbled newt and the northern crested newt have a large sympatric range in western France, but differ in their habitat preferences and only rarely occur syntopically in the same breeding ponds.

 

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The largest bats in the world are the flying foxes, or fruit bats (family Pteropodidae), particularly those living in south-east Asia. Several species in the genus Pteropus have a head–body length of up to 45 cm (17.75 in), a wing-span of 1.7 m (5 ft 7 in) and a weight of 1.6 kg (3 lb 12 oz). The biggest are generally considered to be the large flying fox and the gigantic or Indian flying fox. Although certain other mammals are capable of gliding, bats are the only mammals capable of true flight.

It is primarily frugivorous, consuming several kinds of fig. However, its diet also includes some leaves. It forages at night and sleeps during the day in tree roosts. These roosts can consist of thousands of individuals, often including another species, the large flying fox. Not much is known about its reproduction; it gives birth annually from April through June, with females having one pup at a time. Predators of the giant golden-crowned flying fox include raptors such as eagles, the reticulated python, and humans.

Owing to deforestation and poaching for bushmeat, it is an endangered species. Though national and international law makes hunting and trade of this species illegal, these regulations are inadequately enforced, meaning that the species is frequently hunted nonetheless. Even in roosts that are more stringently protected from poaching, it is still affected by human disturbance via tourists who intentionally disturb them during the day.

 

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Kitti’s Hog-nosed Bat is the smallest species of bat and is the smallest mammal in length (the Etruscan shrew, Suncus etruscus, barely wins the title for smallest mammal by weight).

In addition to being very small, the Kitti’s Hog-nosed Bat is generally reddish-brown or grey in color, with a distinctive pig-like snout. They forage for insects in short bouts, and are thought to feed mainly on small flies and flying ants. Foraging ranges are very restricted, with most bats staying within 1 kilometer of the roost site. The roost in small groups within caves, averaging about 100 individuals.

With so few known populations, there is still limited information about this bat. Main threats to this bat are human disturbance due to religion visit and fertilizer collection, as well as limestone mining and forest habitat loss.

 

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Bats pop up in the fossil record around 50 million years ago during a time known as the Eocene. Paleontologists have recovered remains ranging from teeth and bits of jaw to stunning full skeletons in places as far-flung as Wyoming, Paris, Australia and India’s Vastan Mine.

Paleontologists are familiar with such conundrums. For decades, anatomists and zoologists were confounded by the origin of whales. Then, at the end of the 20th century, a wealth of fossil finds provided a detailed outline of how hoofed land mammals became the sea’s largest swimmers. Birds presented a similar problem, with their origin from an unknown reptile ancestor stumping experts until some new ideas about the “terrible lizards” and amazing fossil finds proved that birds are living dinosaurs. Until recently, turtles presented an odd case similar to that of bats; the shelled reptiles seemed to appear out of nowhere in the fossil record. During the past two decades, experts have identified new species of transitional turtles and revised their opinions of already-known species to explain how turtles got their shells.

 

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All the stars you can see at night belong to our galaxy, the Milky Way. To get a grasp of the size of the Milky Way, let's consider the time for light to travel from one place to another. It takes about one second for light to reach us from the surface of the Moon, eight minutes from the Sun, and four years from the nearest other star. But from the edges of the Milky Way, light takes tens of thousands of years! And despite its vastness, the Milky Way is just one galaxy amongst billions of other galaxies scattered in the immensity of the universe.

Our closest neighbours are small galaxies orbiting the Milky Way. Beyond them, the Andromeda Galaxy is bigger than the Milky Way. The Milky Way will eventually collide with it. For the moment though, its light takes more than two million years to reach us. Even farther away lies the Virgo duster, which comprises more than a thousand galaxies. But this is still the neighbourhood of our Milky Way. The farthest galaxy ever observed is so far it takes light 13 billion years to reach us. Wherever telescopes look, they spot thousands and thousands of galaxies!

 

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Legend has it that during the height of the space race in the 1960s, NASA scientists figured that pens could not function in space. So, they spent millions of dollars developing a pen that could write in space, while their Soviet counterparts used the humble pencil.

This story has been floating around the Internet for way too long. However, it is just a myth.

The truth

According to NASA historians, NASA astronauts also used pencils. In 1965, NASA ordered 34 mechanical pencils from Houston's Tycam Engineering Manufacturing, Inc. at the rate of $ 128.89 per pencil. When the public got to know about these rates, there was an outcry, and NASA had to find something much cheaper for its astronauts to use.

The pencil loses out

The pencil wasn't an ideal choice for writing in space because its tip could flake and break off, drifting in microgravity with the potential to harm an astronaut or an equipment. Apart from this, pencils are flammable, and NASA wanted to avoid anything flammable aboard a spacecraft.

And the pen?

Regular pens that work on Earth did not work in space because they rely on gravity for the flow of ink to the nib. This was understood quite early by scientists and hence astronauts used pencils. But with both the pencil and the pen creating issues, what did NASA finally resort to?

The saviour

Around the time NASA was embroiled in the mechanical pencils controversy, Paul C. Fisher of the Fisher Pen Co. designed a ballpoint pen that could work in space. His company invested one million dollars to fund, design, and patent the pen on its own.

Fisher's pen operated seamlessly, not just in space, but also in a weightless environment, underwater, in other liquids, and in temperatures ranging from -50 F to +400 F.

The company offered the pen to NASA, but the space agency was hesitant to buy it due to the mechanical pencil controversy.

However, a few years later, after rigorous testing, NASA agreed to equip its astronauts with the space pen. The space agency bought 400 pens from Fisher. And a year later, the Russians also ordered 100 pens and 1,000 ink cartridges to use on their Soyuz space missions. Both NASA and the Soviet space agency received a 40 % discount on bulk purchase of the pens, paying about $ 2.39 per pen.

Over the years, Fisher's company has created different space pens, which are still used by NASA and the Soviet space agency.

If you would like to get your hands on one of these space pens, it would cost you approximately $ 50.

 

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At one time people thought that shooting stars were a sign of coming disasters. Now we make wishes when we see them and hope they will come true. In both cases the reality behind shooting stars is less exciting.

Although we call them stars, they are really no more than bits of space dust which burn up as they enter the earth's atmosphere. Great heat is generated by the friction of their flight through the atmosphere and this causes them to flare up into a brief streak of light as they race across the sky and disintegrate.

On average you can see a shooting star every ten minutes on a clear night. From time to time the earth passes through a cloud of dust left by a comet, and when this happens shooting stars occur much more frequently.

Spacecraft returning to earth have to be fitted with special shields to protect them as they enter the earth's atmosphere. The American space shuttle, for example, has heat-reflecting tiles. Without these it would burn up on re-entry.

 

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This looked like being a major problem in the early days of radio communication. Knowing that radio waves travel in straight lines, many scientists thought they would just go straight out into space and be lost. Fortunately an English scientist called Oliver Heaviside and an American colleague, Arthur Kenelly, had other ideas. They predicted that high up in the earth's atmosphere there is a layer that would reflect radio waves and send them bouncing back down to earth again. They were proved to be absolutely right, and the atmospheric layer that reflects radio waves was named the Kenelly-Heaviside layer in their honour.

Thanks to this it is possible to send radio signals from, say, New York to London, by beaming them up into the atmosphere and letting them bounce down to their destination.

Planets which have no atmosphere, like the moon, present a different problem. No atmosphere, no Kenelly-Heaviside layer and no bouncing radio waves that is what it amounts to. In these conditions radio signals would just shoot out into space. So if radio stations were ever set up on planets like this, the only way to send messages from one side to the other would be by bouncing them off an artificial satellite in space. Or, in the case of the moon, by bouncing the radio waves off the earth.

 

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It is only when the rays of sunlight are split that we can see white light is made of different colours. Rainbows have this effect of splitting sunlight and so does the triangular-shaped block of glass called a prism.

Red, orange, yellow, green, blue, indigo and violet are the seven colours into which light can be broken down, as any rainbow will show. These colours are waves of electromagnetic radiation from the sun which move through the air at different speeds. Together they are known as a spectrum. If a prism is placed in the path of a spectrum, it will reverse the ray-splitting process and combine the different colours into white light once more.

 

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Roy C. Sullivan of Virgina, USA, would certainly have been able to tell you a thing or two about this. During his life he was struck by lightning seven times over a period of thirty-five years. This makes him unique and in a way very lucky, because lightning can kill.

Lightning and thunder usually occur in humid weather when strong winds begin blowing and large clouds appear in the sky. Inside these clouds huge charges of electricity build up. When they are eventually released they zigzag to earth as flashes of lightning.

Lightning finds the shortest route to the ground. This is why it often strikes tall trees and buildings. Trees can be set on fire by lightning, and buildings have to be protected by lightning conductors which carry the electrical charge safely to earth.

Sheltering under trees during a thunderstorm can be dangerous. Walking across a flat, empty landscape can be risky too, as you are likely to be the tallest thing around.

As lightning passes through the air, it heats it to a very high temperature very quickly. The air expands, causing a violent bang - thunder. A flash of lightning and its clap of thunder happen at the same time, but because light travels much faster than sound, we see the flash before we hear the thunder. You can tell how far away a storm is by the gap between the two. The longer the gap, the further away the storm. If the gap gets shorter, the storm is moving towards you. And if the two happen almost simultaneously, the storm is right above you. So watch out. Remember what happened to Roy C. Sullivan.

 

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No one has ever seen a black hole and it is unlikely that anyone ever will. They exist only as complex scientific calculations. But evidence obtained from studying the universe suggests that they are out there somewhere.

The principle behind a black hole is that it is an object with a force of gravity so strong that nothing can escape from it not even light! This is not too easy to imagine. But space scientists reckon that anything falling into a black hole would never be seen again - pretty spooky. Their thinking goes that black holes are formed when massive stars, much bigger than even our sun, reach the end of their lives and shrink. As they shrink they squeeze everything inside to an infinite density.

The major clue to the existence of black holes is X-rays which have been detected by satellites outside the earth's atmosphere. These seem to come from gas falling into black holes. The gas gets so hot that it gives off X-rays which help pin-point where black holes might be.

 

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Our nearest star is the sun. Most of the stars that we see in the night sky are also suns, only they are much further away from us. Inside the sun and every other star fantastic amounts of energy are being created by enormous chemical reactions. They have been going strong for millions of years and will carry on for millions more. Stars contain vast quantities of hydrogen. At the very high temperatures inside the stars, the hydrogen, changes into another gas called helium. This process releases the energy which we see as light.

Eventually a star uses up all its hydrogen and dies. Our own sun will die one day too but not for another 5000 million years. Though if some of our awful summers are anything to go by, you would be forgiven for thinking it was on the way out already.

 

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The sky may not look very different each night, but the stars that light it up are moving away from each other at a speed of hundreds of thousands of kilometres a second. Even more amazingly they have been doing this for between 10,000 million and 20,000 million years! That is the period when scientists calculate that the universe began with a huge explosion. They call this the Big Bang. When the Big Bang happened, all the matter in the universe exploded from a tiny point of fantastic energy shooting off in every direction. The galaxies, stars and planets in the universe were formed from this matter. And the Big Bang was packed with such force that they are still hurtling away from each other at incredible speeds thousands of millions of years later.

 

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The moon orbits the earth - as everyone now knows. It takes about 27.32 days to complete each circuit. At the same time it is also spinning on its axis. This takes almost exactly the same length of time. So while the moon is revolving round the earth, it is also spinning at the same speed. This means that the same face is turned towards us all the time.

No man had ever seen the far side of the moon until 1959, when a Russian space probe went behind it for the first time and sent back the photo graphs of the hidden half. In some ways they were a bit of an anticlimax. There was not a man in the moon. Nor was it made out of blue cheese. The far side of the moon looks pretty much like the side we can see. The main difference is that it does not have any large dark plains known as 'seas'. These have never had any water so they are not seas as we know them. But they have level surfaces like the oceans on earth.

 

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