Longest Day of the Year

Even though it is quite a common phenomenon, not many people are aware of the fact that there is something like the longest and the shortest day of the year. Technically put, a ‘day’ is the period of 24 hours, wherein the Earth completes a single rotation. Colloquially, however, the term is used to refer to the period between the sunrise and sunset, when it is bright outside. (In contrast, the term ‘night’ is used to refer to the period between the sunset and sunrise, when it is dark outside.)

On June 20th, 2016, the sunrise is scheduled for 05:47 and sunset for 19:59; which amounts to 14 hours and 12 minutes of daylight. The same was 9 hours and 18 minutes for January 1, 2016, (sunrise – 07:20 and sunset – 16:39), and will be 9 hours 28 minutes for December 1, 2016 (sunrise – 07:01 and sunset – 16:29). As you see, the length of a day increases and decreases over the course of a calendar year. Starting from January, it continues to increase till June 21st (at times June 20th or 22nd.) From this particular day, it starts decreasing, and continues to decrease till December 21st (at times December 20th or 22nd).

Summer Solstice and the Longest Day of the Year
Basically, days and nights are caused due to the rotation of the Earth, with the side facing the Sun experiencing day and other side experiencing night. As the Earth is tilted on its axis at an angle of 23° 26′, at one point it aligns in such a position that it is either inclined towards or away from the Sun. Such alignment, wherein the apparent position of the Sun is either perpendicular to the Tropic of Cancer or the Tropic of Capricorn, is referred to as solstice. It takes place twice in a year(;) once when the tilt of the Earth’s axis is inclined towards the Sun, and once when the tilt is inclined away from the Sun.

This phenomenon and the apparent position of the Sun in the sky enables the sunrays to reach the northern or southern extreme, which, in turn, determines the duration of a day. When the Sun is at the Tropic of Cancer, Northern Hemisphere receives more daylight, and therefore has longer days and shorter nights. When it is at the Tropic of Capricorn, things work the other way round, and the Southern Hemisphere experiences daylight for a longer period. Simply put, the hemisphere of the planet which is inclined towards the Sun experiences more daylight, and hence the days here are long and nights short.

Basically, the day on which the summer solstice occurs, with reference to a particular hemisphere, happens to be the longest day of the calendar year for that hemisphere. The length of a day will differ from one region to another depending on its latitudinal location. While the regions close to the Equator experience 12 hours of daylight, regions along the Tropics experience 14-15 hours daylight on this day. Interestingly, the places beyond 66.5°N and 66.5°S experience daylight for the entire 24 hours in summer, as the tilt of the Earth brings these areas directly under the Circle of Illumination for a part of the year. In fact, places like Canada, Greenland, Alaska and Sweden, witness a strange phenomenon referred to as the ‘midnight Sun’, wherein the Sun is visible even at midnight.
20th June or 21st June?

The alignment happens gradually over the course of time, and hence we witness the duration of the day increasing as we close in on June, and decreasing thereafter. On June 21st, the length of the day is at its peak, which again differs place to place. Though rarely, this phenomenon, which usually occurs on June 21st, can also occur on June 20th or June 22nd. (This change in the solstice dates can be attributed to the fact that we refer to the Gregorian calendar wherein every fourth year is a leap year.) In 2008, it occurred on 20th June; which was only the second time since 1975 when it didn’t occur on June 21st. In 1975, it occurred on 22nd June, and that will happen again only in 2203.

Though the actual astronomical event is restricted to a few seconds, the day on which this event occurs is informally referred to as the ‘summer solstice’. Being the longest day of the year, it also has a great significance in various cultures, where it is celebrated in the form of rituals, festivals and even gatherings, such as midsummer parties; all meant to welcome the Sun and the new season.

What is Solstice

In the field of geographical studies, the term ‘solstice’ refers to either of the two times of a given year wherein the Sun is farthest from the celestial Equator. While this definition is absolutely correct, there is a lot more to know about it. Did you, for instance, know that the December solstice (known as ‘winter solstice’ in the United States), which marks the beginning of winter in the Northern Hemisphere, actually marks the beginning of summer in the Southern Hemisphere? Not many people are aware of such facts about this phenomenon, and that has resulted in widespread myths about it.

Solstice Explained

The driving factors when it comes to solstice are Earth’s revolution around the Sun and its rotation along its axis, which is tilted at 23.5°―both of which contribute to Sun’s apparent position in the sky. Interestingly, these are also the driving factors when it comes to different seasons on the planet. As a result of revolution and rotation of Earth, the Sun is directly overhead at the tropic of Cancer and tropic of Capricorn. This journey of the Sun can be traced from the equator to the tropic of Cancer at 23.5°North, back to the Equator, and then down south to the tropic of Capricorn at 23.5°South over the year. When it reaches its northernmost or southernmost extreme, the Sun appears to stand still for sometime, before it resumes its journey. This very period when the Sun is still right overhead the tropic of Cancer or tropic of Capricorn, is known as solstice.

In fact, the term solstice is derived from the combination of two Latin words sol meaning the Sun and sistere meaning to stand still. Similarly, when the Sun is right at the Equator, it is referred to as equinox. As a result of the Earth’s tilted axis, the areas near the south pole experience darkness for 24 hours when the Sun is at its extreme north. Similarly, when the Sun is at its extreme south, the areas near north pole are in the dark for 24 hours.

Other Names for Solstice

Even though solstice is known by different names in different parts of the world, its naming on the basis of month and hemisphere has got worldwide acceptance. Basically, this astronomical phenomenon occurs twice a year―once in June, owing to which it is named June solstice, and then in December, thus December solstice. While these names are given on the basis of month in which the phenomenon occurs, it can be also named on the basis of hemisphere in which the Sun is positioned. When the Sun is at its northern extreme, it is referred to as northern solstice, and when it is at its southern extreme, it is referred to as southern solstice.

Winter Solstice and Summer Solstice

Other than these names, this natural occurrence is also referred to as summer solstice and winter solstice. That, however, can be misleading as the two hemispheres have different seasons at any given point of time. While the Northern Hemisphere experiences mid-winter in December, the Southern Hemisphere experiences mid-summer in December. So the solstice which marks the beginning of winter in the Northern Hemisphere, will mark the beginning of summer down south. Generally, the term winter solstice is used to refer to December solstice owing to the fact that most of the land area on the Earth falls in the Northern Hemisphere.

In astronomy, the term solstice is used to refer to the exact moment when this phenomenon occurs. Colloquially, however, it is used to refer to the day on which it occurs. While June solstice generally occurs on June 20 or 21 (which is thus the longest day of the year), December solstice generally occurs on December 21 or 22. That being said, even though rare, there have been instances of June solstice occurring on June 19 or 22 and December solstice on December

Coriolis Effect

The Coriolis effect is the apparent curvature of ocean currents, winds, and anything else that moves along or on the Earth’s surface. It is caused by the Earth’s rotation. Although an extremely important concept in physics and geography, it is often misunderstood. A manifestation of this is that, people believe it to be responsible for the water in a drain, swirling in a particular direction in the northern hemisphere, and in a different direction in the southern hemisphere. This is not true, because the effect has nothing to do with water swirling in the drain, that is solely down to the shape of the drain.

What is the Coriolis Effect?

This phenomenon is best explained as the tendency of any moving object, on or above the Earth’s surface, to stray sideways from its normal course, due to the Earth’s rotation. The deflection is towards the left in the southern hemisphere, while in the northern hemisphere, it is towards the right of the usual motion. Gaspard Coriolis, a French engineer, discovered this phenomenon and also came up with mathematical formulas to explain it.

The Earth’s surface does not rotate at all, at the poles, while the rotation speed is maximum along the equator. This is the reason why objects moving further from the equator drift eastwards, while the ones moving closer to the equator tend to drift westwards. All movements on or above the Earth’s surface, like winds, water flow, even artillery fired in the air, and ocean currents, are subject to this phenomenon.


The Earth’s rotation is known to be the main cause of the Coriolis effect. The Earth spins in an anticlockwise direction on its axis, and because of this, objects moving on or above the surface over a long distance, are deflected, as they are moving in the opposite direction, and that too at a faster speed.

The Earth’s rotation speed decreases with latitude, while this effect increases. When a plane flies above the equator, it would continue moving without any major deflection. However, if the plane flies even a little away from the equator, the plane is sure to drift, and the drift is maximum at the poles.

Hurricanes are never formed along the equator, as there is not much of an Coriolis effect there. Storms formed north of the equator develop into hurricanes, as they start rotating and gaining strength. Apart from the distance from the equator and the Earth’s rotation, speed of the moving object also determines the extent of this phenomenon. Faster the object, more the deflection. Also, on which side of the equator the object is present, determines the direction of its drift.


The most crucial impact of the Coriolis effect is on the ocean currents and wind directions. Apart from this, planes, artillery, and missiles, are certain man-made objects which are affected by this phenomenon. Its impact on wind patterns is very prominent. When air rises up from the Earth’s surface, its speed is greater than otherwise. This is because the air now does not have to move across the various landforms on the surface and as a result, its drag reduces. As faster moving objects have a greater Coriolis effect, the rising air is deflected, forming winds.

As the wind traveling across the ocean water helps in formation of ocean currents, the effect also has a bearing on the movement of ocean currents. Huge ocean currents circulate around high pressure and warm areas, formed mainly due to the deflection caused by this phenomenon. Deflecting bullets, missiles, and planes, are also a result of the same.

For instance, assume that a flight is traveling from Los Angeles to New York. If there was no rotation of the Earth, there would be no Coriolis effect and plane could travel straight to the east, but because of it, the plane movement needs to be constantly monitored so that it is in sync with the Earth’s movement below. If it is left to fly straight, the plane would reach somewhere south.

Coriolis effect is therefore an indispensable tool when it comes to understanding many important concepts of physical geography.

Earth’s Core

The earth’s core is both, solid and molten, and is believed to be cooling down gradually. The iron-nickel composition within is responsible for the electromagnetic field generated around the planet and the consistent seismic activity observed. Earth, the planet we inhabit, is the third from the sun. It is not only the largest terrestrial planet in the solar system, but also ranks in terms of mass, diameter and density. Our planet is home to millions of living species and is the only planet known to support life. Formed more than 4.50 billion years ago, the biosphere has consistently altered its atmosphere and abiotic conditions. The presence of aerobic organisms, the ozone layer, and the magnetic field, all make the planet unique.

Vital Information

The planet’s outer surface or crust is made up of a number of segments or tectonic plates. These plates migrate over the surface, which is covered by 71% water and 29% land. The interior is persistently active and homes a layer of solid mantle, liquid outer, and an inner core that is concentrated in iron content. This is the reason behind the magnetic field generated around the planet. The planet’s mineral resources, biosphere components, their interdependency, and the presence of water are responsible for the survival of life forms.


The earth is an oblate spheroid. It is a sphere that bulges around the equator. With a mass of 5.98 × 1024 kg, the planet is composed of iron, oxygen, silicon, magnesium, sulfur, nickel, calcium, aluminum, and traces of other elements. The core is mainly composed of iron, nickel, and sulfur. Its interior is subdivided into chemical and physical layers, each with its own unique properties. The solid outer crust is held in place by a solid mantle that is viscous in nature. Beneath this mantle region, lies a liquid, outer part that protects a solid, inner, molten one that displays angular velocity. These two layers make up the total core of the planet.

How Hot Is the Core?

The inner center of our planet has a temperature that could rise beyond 10,340.33°F and the generated pressure could build up to more than 300 GPa. Volcanic activity and seismic waves contribute to and arise from these extreme conditions. It is about 1,220 km in radius, and primarily comprises an iron-nickel alloy. The temperature within it is believed to be similar to that on the sun’s surface. Very little is actually known about its inner part. It is believed that the region is gradually cooling to a homogeneous, clean layer. However, seismologists reveal that it enables the passage of seismic waves rapidly, in all directions. The molten inner center is believed to be composed of layers. Each of these is separated by some sort of transition zone.

Why Is the Core So Hot?

The outer center does not have the ability to allow shear waves to pass through, and hence, compressional waves are generally observed in the region. The composition of the inner part, a nickel-iron alloy, is what makes the region very hot. These elements keep heating at the high temperature ‘locked’ within, with even the iron content melting at the dramatically high pressure generated. Research reveals that there is a super-rotation of seismic waves within the inner crux, and this property is responsible for one degree of extra rotation every year. The composition and trapped heat within the region is what generates a magnetic field due to a dynamo action. The dynamo action is generated within the liquid, outer surface.

This was a short summary about the earth’s core. It is important to know about this topic in order to have general awareness about our planet and the problems it is facing.

Could Archimedes have lifted the Earth?

Archimedes was a native of Syracuse, Sicily. It is reported by some that he visited Egypt and there invented a device now known as Archimedes screw. This is a pump, still used in many parts of the world. It is presumed that, when Archimedes was a young man, he studied with the successors of Euclid in Alexandria. Certainly he was completely familiar with the mathematics developed there, but what makes this conjecture much more certain, is that he knew personally the mathematicians working there.

“Give me a place to stand and I will move the earth!”

This is a legend ascribed to the famous Archimedes, genius of antiquity who discovered the laws of the lever. “Archimedes,” Plutarch says, “Once wrote to King Hiero of Syracuse, whose kinsman and friend he was, that this force could be used to move any weight. Carried away by the power of argument, he added that, were there another earth, he would go there and lift our own planet from it.”

King Hiero, who was absolutely astonished by the statement, asked him to prove it. In the harbor was a ship that had proved impossible to launch even by the combined efforts of all the men of Syracuse. Archimedes, who had been examining the properties of levers and pulleys, built a machine that allowed him to single-handedly move the ship from a distance away.

Archimedes knew that by applying a lever, one could lift the heaviest of weights by applying even the weakest of forces. One had only to apply this force to the levers longer arm and cause the shorter one to act on the load. He therefore thought that by pressing with his hand on the extremely long arm of a lever he would be able to lift a weight, the mass of which would be equivalent to that of the earth (For the sake of conceptual clarity, we shall take the “moving” or lifting of the earth to mean the lifting on the earth’s surface of a weight whose mass would be equivalent to that of the earth).

But, if this great scholar of antiquity would have known what an enormous mass the earth possesses, he would have most likely “eaten his words”. Let us imagine for a moment that he had at his disposal “another earth” and also the point of support he sought. Further imagine that he was even able to manufacture a lever of the required length. I wonder if you can guess the amount of time he would need to lift a load equivalent in mass to that of the earth, by at least a centimeter? Thirty million million years- and no less!!

Astronomers know the earth’s mass. On earth a body possessing such a mass would weigh in round numbers.
6,000,000,000,000,000,000,000 tons

Supposing a man could lift only 60 kg directly, to “lift the earth” he would need a lever with a long arm that would be longer than the shorter arm by
1,000,000,000,000,000,000,000 times!!

You can easily figure it out that to have the end of the short arm rise by one centimeter; the other end must describe through space the huge arc of 1,000,000,000,000,000,000 km.

That is the colossal distance Archimedes would have had to push the lever to lift the earth by just one centimeter. So how much time would he need? Presuming Archimedes could have lifted 60 Kg one meter in one second- the work of almost one horsepower! – to lift the earth by just one centimeter, even then he would need 1,000,000,000,000,000,000,000 seconds
or 30 million million years. Though he lived to a ripe old age, Archimedes and his lever wouldn’t have lifted the earth by so much as even the thinnest of hair.

No artifices would have helped him to cut the time noticeably – despite all his brilliance. For according to the “golden rule” of mechanics, the mechanical advantage derived will always be accompanied by a loss in displacement, or, in other words, in time. Even if Archimedes had been able to push the lever with a speed of 0.34 km/sec the speed of sound, he would have lifted the earth by one centimeter only after 93,264,094,069,895.84265 years.

If he had pushed the lever with the speed of light, 300,000 km/sec, nature’s fastest possible – he would have lifted the earth by one centimeter only after ten million years of pushing.

– Lewis, Albert C. “Archimedes.” Encyclopedia of World Biography. New York: McGraw- Hill, Inc., 1973. vol. 1, pp.219-223.
– Various history books

Take Your Pick – Vacuum or Nothing!

The history of vacuum and its applications. What is vacuum? Can you achieve perfect vacuum? Why isn’t the Earth’s atmosphere being sucked out into outer space? What applications & industries use the principle of vacuum? And more…

What is vacuum? Vacuum is the absence of anything and everything in a given space, therefore a perfect vacuum would be completely devoid of matter.

Till date it has not been possible to achieve pure vacuum, the nearest we have got is molecules one mm apart, not much one may say, but when you consider that at sea level, molecules are millionth of a millimeter apart, it is considerable, or rather considerably less. Also perfect vacuum is by definition obtained only at a temperature of zero degree Kelvin, and reaching zero degree Kelvin is practically impossible.

Of course nature as usual does a better job, there are vast sections of space where matter is ten centimeters apart and it is theoretically possible that billions of light years away, there are parts where matter is spread out more than one meter apart.

But then if one is to go by the saying that ‘nature abhors a vacuum’, why isn’t the Earth’s atmosphere being sucked out into outer space? What the saying essentially means is that air will move in swiftly (if it can) to fill up any vacuum created inside the atmosphere (this is because air is a constant state of flux and will move from a higher atmospheric pressure point to a lower atmospheric pressure point). As one goes up into the atmosphere, air pressure keeps reducing, and at the edge of the atmosphere there is no air pressure and individual air molecules move around freely. The reason they do not move away from Earth is that the Earth’s gravity attracts them and unlike on Earth, there is no air pressure in space to force the molecules to occupy the vacuum.

The first recorded instance of artificially created vacuum was by Evangelista Torricelli, an Italian, he was a physicist, mathematician and is perhaps best known for inventing the barometer, which is used to measure atmospheric pressure.

Around 1643, following a suggestion by Galileo, he filled an approximately four-foot-long glass tube with mercury and closing the open end with a finger, inverted the tube into a dish filled with mercury. When he removed the finger, some of the mercury did not flow out of the tube. When Torricelli measured the height of the mercury in the tube, it was approximately 70 mm. And he presumed, correctly, that the space above the mercury inside the tube was a vacuum.

In 1657, the German physicist Otto von Guerricke physically demonstrated the power of vacuum. He fitted together two copper bowls to make a hollow sphere and then removed most of the air to form a vacuum. Although the bowls were held together only by atmospheric pressure, two teams of horses, pulling in separate directions could not pull them apart.

Otto von Guerricke also invented the first vacuum pump. Of course many different kinds of vacuum pumps have now been devised for creating vacuum by removing molecules of gas from a closed space. But all of them belong to two basic types: air-powered or electric. An interesting fact is that pumps of the same capacity will create the same amount of vacuum, irrespective of the type of pump.

Applications of Vacuum

Since the beginning of time, humans have harnessed the power of inventions and discoveries for practical uses. It was no different with the vacuum.

In 1698, Thomas Savery, an English military engineer, patented the first steam engine. He was working on the problem of pumping out water from coalmines. Using a closed vessel filled with water, he introduced steam under pressure into it, this forced the water upwards, the steam was then cooled, creating a vacuum that sucked more water out of the mine.

In 1712, Englishman Thomas Newcomen used the principle of vacuum to run an atmospheric steam engine (he was helped in this by Savery).
Steam was first pumped into a cylinder and was then condensed to create a vacuum. This resulted in atmospheric pressure operating a piston to create downward strokes, which pumped the water up.

In 1765, James Watt, while working on a Newcomen engine, began to make several improvements. And soon his patented engines became the dominant designs for all steam engines.

The steam engine was one of the main reasons for the start of the industrial revolution; in fact the steam engine was the first major source of power after wind and water. Since then the power of vacuum is being utilized in many industries and has spawned many inventions including the vacuum cleaner and the vacuum flask.

Other practical applications include vacuum distillation, incandescent light bulbs (the vacuum ensures that air does not react with the hot filaments), television picture tubes, vacuum tubes, vacuum clamps (the main advantage is that the clamping force is on one side only) etc.

Some of the industries that use vacuum technology include
– Metallurgical
– Metal working
– Tool manufacturing
– Electrical, electronics & microelectronics
– Solar technology
– Medical technology
– Chemical
– Pharmaceutical &
– Food