Tag Archives: Space

How can space or the universe be both infinite and expanding at the same time?

By using the word “expanding,” we’re given the assumption that the universe must be expanding into something, from a central, fixed point. In order to explain it in a somewhat concise manner, you have to realize that space isn’t something that is just there and stellar objects are just moving throughout it, space bends and stretches.

An accurate analogy would be the dough/raisin analogy that’s commonly used: the universe is a blob of dough with raisins spread throughout it. When you put the dough into an oven, the dough expands, taking the “stationary” raisins with it, increasing the distance (space) between the raisins.

Without any way to leave our little raisin, there is no way to see the “end” of the dough – so, if we assume that the universe is truly infinite, then it simply doesn’t have anything to “expand” into. Using a mathematical analogy, you have a series of whole integers that start with one to infinity. If you took every number and multiplied by any factor, the numbers in your series have stretched away from each other; yet the list hasn’t expanded. You still have a series that progresses from a number to infinity.

How was the Moon formed?

Even though it is lit up by thousands of stars, the night sky would seem vacant to most of us without the presence of Moon. The only natural satellite of Earth, the Moon has been the subject of interest of man forever. Moon had a position of reverence in ancient civilizations and has a great stature in various mythologies.
Myths and stories aside, the cosmic body has been one of the favorites of scientific world. The scientists are more interested in Moon now than ever, even so far as researching about the possibility of living there. As long as they have been mulling over the formation of the universe and solar system and Earth, the scientists have been after Moon as well.
There are a number of theories regarding the origin of Moon. Each one has its merits and faults. One of the earliest modern theories about Moon’s formation was the Fission Theory proposed by George Darwin, son of Charles Darwin. He argued that Moon was a piece expelled from Earth while the latter was still in its rapidly spinning molten state. This theory was popular in late 1800s.
Other notable hypotheses are the Capture theory which states that the Moon was captured by Earth and the Accretion theory stating Earth and Moon were formed together. However, the most widely accepted theory of Moon’s formation is the Giant Impact Hypothesis. It was first put forward by Canadian professor Reginald Daly in 1940s. Later many scientists gathered evidence in support of this hypothesis.
According to GIH, the Moon originated as a result of collision between the Earth and a Mars-sized body named Theia billions of years ago. This collision produced a large amount of debris around the Earth, some of which accumulated to form the Moon. The Moon rotated about one tenth of the distance today, and gradually became tidally locked with Earth.
The Giant Impact Hypothesis has been able to explain some of the aspects of the Moon, like its angular momentum, the difference between the cores of two bodies. However, a number of conflicts have arisen challenging the Giant Hypothesis. One of them is the isotopic comparison between Earth and Moon. The lunar isotope samples show great similarities with Earth. It is against the belief that much of Moon’s mass came from Theia. Also the volatile elements in Moon are not being depleted as fast as they are supposed to be, considering the energy unleashed during the collision. More and more research is being conducted on the subject, and one day we might have the sufficient explanation.

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Why do we only see one side of the moon?

Moon, the natural satellite of Earth, is also the planet’s closest neighbor in space. About a quarter of Earth’s size, the Moon rotates around Earth with a velocity of 1.03 km/s.
Click to enlarge
When we look from Earth, we always see the same side of the moon, about 59% of its surface. We call this side ‘near side’. The other one, which we call the ‘dark side’, is not actually dark, but permanently turned away from us. Moon, just like Earth, also goes through the cycle of day and night.
The reason for the far side of the moon being never visible from Earth is the uniformity between the periods of Moon’s rotation on its axis and around Earth. The phenomenon is known as synchronous rotation or tidal locking. The Moon takes same amount of time, 27.3 ‘Earth days’, to spin about its axis and to complete a revolution around the Earth. If they were even slightly different, we could see the entire surface of the satellite. But, these two periods have been same for all of the known history, and is likely to remain so for millions of years in future.
The reason for this phenomenon is called tidal friction. It can be explained in regard to the effects created by gravitation. The Earth and Moon exert gravitational force on each other. This mutual force creates tidal bulges on each other. One bulge faces in the direction of the other body, and one faces away. Over time, they siphon energy away from the rotational momentum of both bodies, producing a breaking effect.
Since the gravitational force of the Earth on Moon is considerably greater than that of Moon on Earth (about six times), the Moon experiences a greater breaking effect. While it attempts to go on a straight line, the Earth attracts it towards it. Millions of years ago, Moon used to rotate at much faster rate than now. Over time, Moon’s rotation has gradually slowed until the rate of rotation matches the rate at which the tidal bulges move around the body; that is tidally locked. At present, lunar tidal bulges are located at a constant position with respect to the rotation of the Moon, forming a sort of equilibrium. Now the Moon is locked into this period, with the same hemisphere always turned towards Earth.
Even though we should only be able to see half of the surface according to this theory, we get to see 59%, as said earlier. This discrepancy is because the moon orbits around Earth in an elliptical trajectory rather than a perfectly circular one, and it creates differences in angular and linear velocities.

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How long can a person survive in the vacuum of space?

The space, beyond the atmosphere of Earth, has always fascinated humans. Now it is accessible to us, even if it is for scientists or the rich. It is difficult to meet someone who hasn’t got the desire to go up there, and float in the vast expanse of vacuum. However, the space is as oppressive as it is attractive. One can’t survive much longer there, without the help of a space suit. There are a number of things that make your life in space very short; from the absence of oxygen to the high-speed projectiles wandering up there.
Since there is no oxygen, which we need the most to survive, a person would lose consciousness in as little as 15 seconds. If he was to be brought back into the standard environment within two minutes or so, he can be saved.
The lack of atmosphere also means the lack of air pressure in the space. The pressure is what keeps our blood and other body fluids in liquid state, and in its absence they would ‘boil’. It would result in a rapid loss of energy, and the fluids would freeze before the evaporation. This can happen in a period between 30 seconds and 1 minute. Also the tissues of skin and the internal organs like heart and lungs would expand because of the boiling fluids and the expanding air. However, the tight structure of the skin would prevent itself from tearing apart. Due to the freezing of blood, the circulation will stop within a minute as well.
Notwithstanding all of the threats above, the space is crowded with various celestial particles that move at high velocity, with no apparent destination. Some are controlled by the gravitational forces and orbiting certain celestial bodies. Anyone of them can collide with you causing fatal damages to you. The space is also filled with various types of harmful radiations emitted by the Sun and other stars. These can cause very serious damages to the body.
Then there is the temperature. The temperature in space shows an extreme range of difference which can be withstood by no human. It can range from minus 100 degree Celsius to 120 degree Celsius. All of these situations taken into account, a person can survive barely a minute or two in outer space without any kind of protective gears.
Most of these conclusions, apart from that about cosmic objects and radiations, come from studies on animals, especially dogs and chimpanzees. Experiments proved that chimpanzees can survive longer in space than dogs. Also, a few human accidents have also contributed to these findings.

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Who named our galaxy the Milky Way? And why it is named so?

Galaxies are huge congregations of stars held together by the gravitational force. They are often called island universes due to their size. There are more than a trillion galaxies in the visible universe alone. Our home galaxy, the Milky Way, is a part of a collection of 24 galaxies, named Local Group, that travel through space together.
Milky Way is a spiral galaxy. The diameter of its globular nucleus is about 16,000 light years. It has far-stretching spiral arms in one of which our solar system is located. The galaxy extends to a length of 100,000 light years and consists of hundreds of billions of stars. Its centre is occupied by a massive black hole.
A major feature of the Milky Way is the bright band of light that runs in an almost perfect circle through it. The band is actually made up of millions of glittering stars which appear to be situated in close proximity, when seen from far away. It is this river of light what gives the galaxy its name.
It is not entirely clear who named the Milky Way so, the stories of which are long lost to history. Long ago, the Romans used to call the galaxy ‘Via Lactea,’ which translates to ‘road of milk’ in Latin. However, the Romans are believed to have got the name from the Greeks, who used to call it ‘Galaxias Kyklos, which translates into ‘milky circle.’ All these are owing to the appearance of the galaxy in night sky, which looks like a long silver line.
There is a Greek myth about the formation of galaxies which may have contributed to its name. Once, the supreme god of Greeks, Zeus, brought his son Heracles home for Hera to breastfeed while she was sleeping. Heracles was born of one of Zeus’ affairs and was half-mortal. Hera did not like him. When Hera awoke, Heracles was feeding and she quickly pushed the child away, causing a few drops of milk to spill into the night sky. These milk drops became Milky Way, according to the myth. Other languages have different names for the Milky Way, though most of those are some kinds of variations of the phrase. In Germany, the galaxy is called ‘Milchstrasse’ and Norwegians have named the galaxy ‘Melkeveien.’ In most of the European languages, the word for the galaxy is derived from the Latin name.
In Chinese, the word for Milky Way means ‘silver river’ and its Sanskrit name ‘Mandakini’ means calm. The South Indian languages refer it to as ‘Aakasha Ganga’, meaning ‘Ganges of Space’. In any way, its appearance and local legends have contributed greatly to its nomenclature in various languages.

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Is our Milky Way a static object or rotates like planets and stars?

There is no object in the Universe that does not rotate on its axis and our Milky Way is no exception. This vast system of stars, shaped like a flattened disc, is a spiral, with stars, dust and gas clouds visibly concentrated along enormous spiral arms which curve away from the galactic center to its edge.
The whole system is rotating, but not like a solid body. Gravity makes its inner regions swirl around far more rapidly than those parts as far out as the Sun, so that a star in an inner orbit will do a lap in only a few thousand years — a trip which takes our Sun 250 million years to complete, even though it is travelling at almost 1 million kilometers per hour! The net result of this differential rotation should be to wind up the spiral pattern after just a few revolutions, but this clearly hasn’t happened. Nor do any of the million of other spiral galaxies how any signs of being wound up. One of the biggest puzzles facing astronomers today is to explain how spiral galaxies keep their shape.

Additional reading:
Milky Way (Wikipedia)

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Has any spacecraft ever been hit by space debris in orbit around the Earth?

Ever since the first rocket was launched into space, we have been polluting the environment above the Earth. Pieces of junk and debris from spacecraft have been accumulating in orbit around the Earth and are beginning to present a distance hazard to both manned spacecraft and artificial satellites. The space junk ranges in size from dead satellites and spent rocket stages to individual flecks of paint from spacecraft. Surveys carried out in recent years by NASA estimate that there are perhaps 1,00,000 pieces of debris 1 cm (1/2 inch) or more across and 10,00,000 pieces 1 mm across in orbit around the Earth. See the graphic below.
In February 1997, while the space shuttle Discovery was docked with the Hubble Space Telescope, mission control in Houston ordered the crew to fire the shuttle’s maneuvering jets in order to avoid a lethal chunk of debris. This piece of space junk was from a Pegasus rocket, which had exploded a few years earlier. Hubble was launched into space in April, 1990 and since that time it has been pitted with hundreds of holes ranging in size from less than 1 mm to a few centimeters. In 1996, a small British built satellite called CERISE was disabled when it was struck by a fragment from an Ariane rocket, which had blown up shortly after launch several years earlier.

Additional reading:
Space debris (Wikipedia)

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Why is the sky dark if there are billions of stars in the Universe?

Billions of stars
The dark night sky paradox, often called Olbers’ paradox, named after Heinrich Wilhelm Olbers(a German physicist of the early 19th century), arises from the fact that the number of stars in the sky is assumed to be essentially infinite, and hence the night time sky should be ablaze with light, not shrouded in darkness.
If the logic were correct, no matter where we looked in the sky, the canopy of stars would be continuous, with no dark gaps between any two stars. The result would be a heavenly vault as dazzlingly bright and as hot as the Sun’s surface. A paradox arises from the seeming conflict between logic and the observed darkness of the night sky. The solution comes from the landmark cosmological discovery made by American astronomer Edwin Hubble. He demonstrated that the universe is expanding and the light from the receding galaxies is shifting towards the red end of the spectrum–just short of becoming invisible.
It follows from this that beyond a certain distance, any star or galaxy will be receding from us so rapidly that its light will be shifted out of the visible spectrum into the infrared or radio spectrum. The radiation we receive from celestial body is therefore no longer visible to our eyes. This would greatly reduce the number of stars and galaxies visible in the sky, and could explain nighttime darkness. Scientists agree that this red shifting must contribute to the darkness of the night sky.
There is another supportive explanation based on the fact that the speed of light always remains constant and it can not be boosted any further. One consequence of the fixed speed of light is that we can not observe any object farther than about 15 billion light-years away from Earth. Even if there are more galaxies beyond that distance, light from them would not have the time to reach us.

Additional reading:
Olbers’ paradox (Wikipedia)

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What would happen if Earth passed through a comet’s tail?

Nothing, except that we would witness a breath-taking aerial fireworks display. The meteoritic dust in the comet’s tail would be burned up by the air’s friction, just as meteors are consumed and become what is commonly (and erroneously) known as shooting stars when they enter our atmosphere.

Moreover, while we tend to ridicule the ancients who considered comets omens of death and destruction, we should remember that the twentieth century had a same scare, too. On May 18, 1910, the head of the famed Halley’s Comet was scheduled to pass between the Earth and the Sun. Newspapers caused widespread apprehension by announcing that the tail contained a poisonous gas–cyanogens.

Comet pills label

A worldwide scare ensued and quite a few quacks has a field day. They encashed on the panic by selling comet pills, which according to their phony claim, would safeguard people from the ill-effects of the supposedly toxic gas. The long-awaited day arrived but nothing happened. In fact, no one saw the head of the comet against the Sun, although some reported the comet’s tail was faintly visible. The Earth had passed through the tail of Halley’s Comet, with all living beings remaining as safe and sound as they were before.

Additional reading:
Comet tail (Wikipedia)

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What is ‘Grandfather Paradox’ concerning time travel and how can it be resolved?

The paradox manifests itself when you stretch Einstein’s general theory of relativity to its extreme limit. The theory, in principle, allows you to go back in time and visit the past. All you need to do is to take a trip through what is called wormhole, a theoretical tunnel that connects one part of the universe with another. You would emerge in a different space-time, having accomplished time travel to an event in your own past.

Consider our nearest galactic star Alpha Centauri which is 4.2 light-years away. A light beam takes that much time to reach it when traveling through ordinary space, but you could beat a light beam by taking a shortcut through a wormhole. (See diagram.) You start your journey in the year 2012 and emerge at Alpha Centauri in 1912 instead. Now for the paradox that defies logic: What if you travel much further backwards and accidentally kill your grandfather, thereby preventing yourself from ever being born on the first place? If you were never born, you could never go back in time, and so you could not kill your grandfather.

This paradox is so potent that scientists are unable to offer any rational solution. However, science fiction writers, having more inventive minds and greater freedom of imagination, have a way of circumventing such conundrums. They say that after traveling through the wormhole you emerge in a new universe where you can not encounter your grandfather — so never have a chance to gun him down. Period.

Additional reading:
Grandfather paradox (Wikipedia)

Below is a video explaining the paradox. Note that HBA is not affiliated with creator(s) of this video.

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