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.

 

Picture Credit : Google

So far 12 humans have set foot on the Moon as part of NASA's Apollo missions between 1969 and 1972. While none of them was sent with the intention of walking the circumference of the Moon, have you ever imagined how many days it would take to actually do so?

Hypothetically speaking...

It would take 91 days to walk around the Moon non-stop. How do we arrive at this figure? In 2014, NASA published a study in the Journal of Experimental Biology. The study tested how fast humans could walk and run in simulated lunar gravity. Eight participants, three of whom were astronauts, were asked to use a treadmill onboard a McDonnell Douglas DC-9 aircraft, which flew special parabolic trajectories to simulate gravity on the Moon for up to 20 seconds at a time.

It was found that the participants were able to walk up to a speed of 5 km/hr before breaking into a run. Therefore, at this speed, it would take a human about 91 days to cover the 10,921-km circumference of the Moon if he or she walks non-stop.

In reality...

We arrive at the 91 days considering the average maximum speed at which humans can walk on the Moon and the circumference of the Moon. However, there are several other factors that could make the journey much longer.

First, we need to consider the weight of the spacesuits and the supplies. The participants in the study were able to pull off such speeds, because they were able to swing their arms freely and weren't wearing any spacesuits. While on the Moon, this speed could definitely come down since the spacesuits are not designed for optimal movements, and additionally, the astronauts would have to carry supplies such as oxygen and food.

Secondly, the moon's topography would also play a role as it is filled with meteor craters that can be several miles deep. So, astronauts would mostly likely need to find a route around the craters.

Third, the light and temperature factors as well as the lunar cycle where the Moon can go days without sunlight also need to be considered. The temperature on the Moon can vary from 100 degree Celsius during the day to minus 180 degree Celsius during night time.

Fourth, radiation levels on the Moon also play a role. Since the Moon doesn't have a magnetic field like the Earth, any major solar activity such as a solar flare or coronal ejection could send high amounts of radiation to the Moon

Finally, it is close to impossible for a person to walk non-stop for 91 days maintaining a speed of 5km/hr. Thus, while it might be possible to walk around the Moon, it can definitely not be done in just 91 days.

 

Picture Credit : Google

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!

 

Picture Credit : Google

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.

 

Picture Credit : Google

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.

 

Picture Credit : Google

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.

 

Picture Credit : Google

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.

 

Picture Credit : Google

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.

 

Picture Credit : Google

The idea of floating about completely weightless sounds great fun, but try to imagine what it must be like to lose normal control of your body. Astronauts have to learn to live in these conditions, sometimes for months on end, because when they are in space their bodies become apparently weightless. Once a spacecraft is in orbit around the earth, it remains held in position by the earth's gravity. The astronauts inside are moved by the same force, and since they and the spacecraft are moving in the same way, they are not drawn down to the floor but float about.

There is one curious side-effect of weightlessness which is encouraging to anyone who would like to be a little taller. Because their bodies are not pulled down to earth by the force of its gravity, astronauts find that they stretch a little in space. The effect does not last for long once they return to earth. Gravity soon pulls them back to their original height.

 

Picture Credit : Google

The universe is so enormous it is hard for us to imagine the distance in it. Trying to measure them in kilometres would be almost meaningless as well, because the numbers would be incredibly long with strings of noughts on the end. Instead, distances in the universe are measured in light-years. One light-year is the distance that light travels in a year. Since light travels at 299, 792.5 kilometres per second, in one year it travels an amazing 9,460,528,405,000 kilometres. That’s what a light-year represents.

To get an idea why such measurement is necessary, think about these statistics. It takes 75,000 light-years for light to reach earth from the most distant star in the Milky Way. Light from the most distant star we can see with the naked eye takes even longer. We have to wait 2,200,000 years for light to come from anything as far away in the universe as that.

Closer to home, it takes just under eight and a half minutes for light to reach us from the sun. The moon’s closer still. Light reflected off the moon comes to earth in only one and a quarter seconds.

Yes – the universe is a big place!

 

Picture Credit : Google