What is the shortest day ever recorded?

A day has 24 hours, right? That's 1,440 minutes. Or 86,400 seconds. That's to say, a day is 8,64,00,000 milliseconds. Only that, at that scale, hardly any of our days hits exactly that number. As the Earth's rotation speeds up or slows down, fractions of a millisecond are often added or subtracted, making our days a teensy bit longer or shorter on record.

June 29, 2022

On June 29, 2022, we had the shortest day ever recorded since scientists started measuring the length of each day with the precision of atomic clocks in the 1960s. June 29, 2022 was 1.59 milliseconds shorter than 24 hours.

In December 2020, the website Time and Date reported that that year alone had experienced the 28 shortest days since records were maintained. This included July 19, 2020, which was previously the shortest day on record at 1.47 milliseconds under 24 hours.

Speeding up or slowing down the rotation of any object comes down to its angular momentum, which has three components: mass of the rotating object, speed at which it moves, and the distance from the point it is rotating about. To help your understanding, imagine swivelling around in a chair. While your rotation will slow when you have your arms outstretched, you will spin faster when you pull your arms back in.

Remains a challenge

As Earth constantly redistributes its mass and angular momentum, its rotation rate and the length of the day keep changing. Scientists have a number of ideas as to why the Earth speeds up and slows down, but predicting the length of a day remains a challenge, even in the future.

This is because a number of factors are involved and there could even be a mix of several factors acting together. These include the wind, the gradual movements of mass within the Earth, the interactions where the Earth's core meets its mantle, and the fact that the Earth isn't exactly spherical, to name a few.

While understanding the planet's long-term changes that influence its rotation might put us on the path towards predicting the next shortest day, scientists believe that the most recent one could likely be the result of a brief climate phenomenon such as wind speed change high in the atmosphere. As for the next shortest day, we will just have to wait and see for the moment.

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Can reforestation alone save the Earth?

Trees are huge carbon sinks. They saok up the carbon. Planting trees will help mitigate the climate change and cool the planet to some extent. But that has to be combined with a dedicated effort to reduce carbon emission. Reforestation combined with the reduction of greenhouse gases, especially carbon dioxide (CO2), is the need of the hour. It is these gases that warm the earth, leading to climate change which we have been witnessing in many forms such as the melting of ice sheets, rising of sea levels, wildfires, floods, droughts and other natural calamities. So the carbon emissions need to be reduced by nations, on an industrial scale as well as individual level.

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WHAT IS THE FARTHEST WE HAVE GONE INTO THE EARTH?

What is the furthest down humans have gone? What is the Kola superdeep Borehole? Read on to find the answers.

In Jules Verne's science fiction novel, Journey to the Centre of the Earth (1864), three men reach the centre of the Earth. Is this ever possible? Our planet is made up of three main layers- the crust, the mantle and the core. The continents and oceans are situated on the crust which is about 8 km thick under the oceans and between 35 and 40 km deep under the continents. Below the crust is the mantle which is about 2,900 km thick. Next comes the core. The outer core, about 2.250 km thick, is made up of melted iron and nickel, and contained within it, is a ball-shaped inner core believed to be made up of solid iron and nickel.

The centre of the innermost core is the centre of the Earth. So there are thousands of kilometres to descend to reach the centre of the Earth, and what is the furthest down we've gone? When the Russians and the Americans were engaged in a race to the moon several decades ago, they also embarked on a race to inner space to see how far down they could go. While the Americans did not make much headway in this race downwards (Project Mohole'), the Russians went at it, hammer and tongs, in the Kola Peninsula and dug a hole 12.262 km deep over a period of 24 years from 1965 to 1989. They wanted to go at least 15 km down,  but just could not. This is the closest we've been able to go to the centre of the Earth. The Kola Superdeep Borehole, as it is now called, attracts curious visitors from around the world.

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BOLD AND OUTRAGEOUS ENERGY IDEAS

With World Environment Day falling in this month, it's time to see how we are faring. More importantly, we need to learn about the audacious ideas people have come up with to give Earth a chance to recuperate. How good are these eco-friendly strategies? You decide!

A grand plan for the skies

Just when we are all set to harvest energy from solar panels, the cloudy skies play spoilsport. So what's the solution? Japanese scientists have come up with an ingenious idea: send satellites into orbit carrying solar arrays up high where there are no clouds to block the sun's rays. Transmitters in the satellite will also convert the solar energy into microwave energy that can potentially provide power to millions of homes. Is it possible that the microwave beams miss the transmitter and fry up something on Earth? Let's hope that never happens.

Power from DIY tornadoes

A tornado is a powerful beast, capable of producing the same energy as a power plant... provided it is large enough. A Canadian engineer realized that taming such a beast would be the solution to our energy problems. All that was needed was an area bigger than two football fields and enough space above for manufacturing a spinning column. Some turbines here, and a generator nearby - bingo! You get loads of energy as long as the tornado does not go rogue and escapes its confines!

Hairy plants to the rescue! Who would have thought that hairy plants could one day save the planet? And no, they don't have to be brought down by aliens. There are quite a few on our planet itself. According to a team at the University of California, hairy plants absorb more light but less heat. Apparently, if there were more such plants across the world, the global temperature could go down. That would mean selecting and developing hairy versions. As long as they don't make us eat hairy spinach, this is worth a try!

Biogas to drive vehicle

Human waste can, in the future, seamlessly power cars and bikes when petrol is probably all gone. Under the right conditions, bio waste, crop stubble and leftovers from hotels can pool in to make commutes more eco-friendly. Think it's far-fetched? In Sweden. an entire fleet of buses run on biogas generated from manure and leftovers. The future isn't so bleak, after all!

The energy of hustling commuters

 Rushing to catch a train or even simply sitting in the train can be precious in the future. Swedish scientists are investigating how the air made warm by commuters at Stockholm Railway Station can be harvested through heat exchangers. And just like that, it would be possible to provide heating for a building nearby. Will cities across the world be able to make their citizens feel like superheroes - or at least power generators? Time will tell.

The energy of hustling commuters

Rushing to catch a train or even simply sitting in the train can be precious in the future. Swedish scientists are investigating how the air made warm by commuters at Stockholm Railway Station can be harvested through heat exchangers. And just like that, it would be possible to provide heating for a building nearby. Will cities across the world be able to make their citizens feel like superheroes - or at least power generators? Time will tell.

Store carbon dioxide underwater

What if we could suck up carbon dioxide emitted from power plants and store them in large flexible polymer bags deep under the sea instead of releasing it into the air? As stunning as it sounds, scientists argue that the idea isn't crazy. Pipes will feed the gas into these bags and they will remain for thousands of years undisturbed. Or at least, that's what we hope (and also pray that sharks don't sink their teeth into them!).

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HOW CYCLING IS GOOD FOR HEALTH AND EARTH?

Among the numerous days celebrated the world over, the one that profoundly impacts the present as well as future generations is World Bicycle Day. Well, on 3 June every year, since 2018, the U.N. General Assembly dedicated this day to celebrate the joy of riding bicycles. The simple structure of a bicycle requires only air and a bit of energy to function, however, it has proved itself to be both environmentally-friendly and a friend to all mankind. Prof Leszek Sibilski, a Polish-American sociologist, along with his sociology students, was the inspirer of this cause.

Apart from being an eco-friendly and economic means of transport, bicycling also promotes good physical as well as mental health. Cycling decreases the possibility of falling prey to cardiovascular diseases, aids in building body muscle, and reduces overall fat. It strengthens bones, improves joint mobility and relieves stress. In addition, it also facilitates the regulation and maintenance of healthy blood sugar levels in our system. Thus, cycling reduces the risk of depression, obesity, arthritis, diabetes, certain cancers, strokes and heart attacks.

The bicycle symbolizes adaptability and sustainability. Governments around the world are adopting and promoting eco-friendly conveyance systems. Many countries have dedicated bicycle tracks which make commuting by bicycle safe. India, too, has introduced bicycle tracks in cities like Delhi and Bangalore.

Though daily riding to work may be an inconvenience, taking into consideration climatic conditions, either having to face the scorching sun or heavy rain, however, despite these conditions, enthusiastic riders change their cycling gear once they reach their destination. It's a trend already prevalent in Europe.

Types of bicycles

If you are new to buying a bicycle, these guidelines will help you choose the right one.

Road bikes: Designed for normal roads.

Mountain bikes: Suited for hilly terrains.

Hybrid/commuter bikes: Combination of road bikes and mountain bikes.

Cyclocross bikes: A road bike feel for off-road trips.

Folding bikes: Commuting, leisure or touring for the short-on-space.

Electric bikes: A hybrid, mountain or road bike with a battery and a motor.

Touring bikes: Designed for carrying loads over longer distances while remaining comfortable for the rider.

Taking into consideration the multiple benefits that cycling has to offer, using a bicycle whenever possible, if not regularly, will be advantageous to both our earth and ourselves. Look for ways in which cycling can be introduced into your daily routine; maybe riding to nearby places while carrying out daily tasks, to school, work or a friend's house. Let's try and adopt the culture of cycling and be the change our environment and our health needs.

Fun Facts

  • The longest tandem' bicycle seated 35 people; it was more than 20 metres long.
  • Every year, around a 100 million bicycles are manufactured worldwide.
  • The use of bicycles has conserved more than 238 gallons of gas yearly.
  • The Netherlands is the most bicycle friendly country in the world. 30 per cent of all transport is via bicycle. Seven out of eight of its residents over the age of 15 own bicycles.
  • The Tour de France, established in 1903, is the most famous bicycle race in the world. Bicycle track racing has been a sport in the Olympic Games since 1896.

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WHY DO THE CONTINENTS MOVE?

The surface of Earth is broken into giant fragments called tectonic plates. The continents are situated on top of these tectonic plates, which carry them much like cargo on rafts. The plates move at rates of between 2 and 17 cm per year, and over millions of years this moves the continents over many thousands of kilometres.

The earth’s crust is broken into separate pieces called tectonic plates. The crust is the solid, rocky, outer shell of the planet. It is composed of two distinctly different types of material: the less-dense continental crust and the more-dense oceanic crust. Both types of crust rest atop solid, upper mantle material. The upper mantle, in turn, floats on a denser layer of lower mantle that is much like thick molten tar.

Each tectonic plate is free-floating and can move independently. Earthquakes and volcanoes are the direct result of the movement of tectonic plates at fault lines. The term fault is used to describe the boundary between tectonic plates. Most of the earthquakes and volcanoes around the Pacific ocean basin—a pattern known as the “ring of fire”—are due to the movement of tectonic plates in this region. Other observable results of short-term plate movement include the gradual widening of the Great Rift lakes in eastern Africa and the rising of the Himalayan Mountain range. The motion of plates can be described in four general patterns:

  • Collision: when two continental plates are shoved together
  • Subduction: when one plate plunges beneath another
  • Spreading: when two plates are pushed apart
  • Transform faulting: when two plates slide past each other

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WHAT IS THE DIFFERENCE BETWEEN RAIN AND PRECIPITATION?

When a lot of water vapour fills the air, it begins to change and condense into droplets of water. These droplets fall back onto Earth as precipitation, which can take many forms - rain, hail, snow, sleet, fog, dew. So rain is just one form of precipitation.

The difference between Rainfall and Precipitation is that the Rainfall is a liquid water in the form of droplets that have condensed from atmospheric water vapor and then precipitated and Precipitation is a product of the condensation of atmospheric water vapour that falls under gravity.

Rainfall

Rain is liquid water in the form of droplets that have condensed from atmospheric water vapor and then becomes heavy enough to fall under gravity. Rain is a major component of the water cycle and is responsible for depositing most of the fresh water on the Earth. It provides suitable conditions for many types of ecosystems, as well as water for hydroelectric power plants and crop irrigation.

The major cause of rain production is moisture moving along three-dimensional zones of temperature and moisture contrasts known as weather fronts. If enough moisture and upward motion is present, precipitation falls from convective clouds (those with strong upward vertical motion) such as cumulonimbus (thunder clouds) which can organize into narrow rainbands. In mountainous areas, heavy precipitation is possible where upslope flow is maximized within windward sides of the terrain at elevation which forces moist air to condense and fall out as rainfall along the sides of mountains. On the leeward side of mountains, desert climates can exist due to the dry air caused by downslope flow which causes heating and drying of the air mass. The movement of the monsoon trough, or intertropical convergence zone, brings rainy seasons to savannah climes.

The urban heat island effect leads to increased rainfall, both in amounts and intensity, downwind of cities. Global warming is also causing changes in the precipitation pattern globally, including wetter conditions across eastern North America and drier conditions in the tropics. Antarctica is the driest continent. The globally averaged annual precipitation over land is 715 mm (28.1 in), but over the whole Earth it is much higher at 990 mm (39 in). Climate classification systems such as the Köppen classification system use average annual rainfall to help differentiate between differing climate regimes. Rainfall is measured using rain gauges. Rainfall amounts can be estimated by weather radar.

Rain is also known or suspected on other planets, where it may be composed of methane, neon, sulfuric acid, or even iron rather than water.

Precipitation

In meteorology, precipitation is any product of the condensation of atmospheric water vapor that falls under gravity. The main forms of precipitation include drizzle, rain, sleet, snow, graupel and hail. Precipitation occurs when a portion of the atmosphere becomes saturated with water vapor, so that the water condenses and “precipitates”. Thus, fog and mist are not precipitation but suspensions, because the water vapor does not condense sufficiently to precipitate. Two processes, possibly acting together, can lead to air becoming saturated: cooling the air or adding water vapor to the air. Precipitation forms as smaller droplets coalesce via collision with other rain drops or ice crystals within a cloud. Short, intense periods of rain in scattered locations are called “showers.”

Moisture that is lifted or otherwise forced to rise over a layer of sub-freezing air at the surface may be condensed into clouds and rain. This process is typically active when freezing rain occurs. A stationary front is often present near the area of freezing rain and serves as the foci for forcing and rising air. Provided necessary and sufficient atmospheric moisture content, the moisture within the rising air will condense into clouds, namely stratus and cumulonimbus. Eventually, the cloud droplets will grow large enough to form raindrops and descend toward the Earth where they will freeze on contact with exposed objects. Where relatively warm water bodies are present, for example due to water evaporation from lakes, lake-effect snowfall becomes a concern downwind of the warm lakes within the cold cyclonic flow around the backside of extra tropical cyclones. Lake-effect snowfall can be locally heavy. Thunder snow is possible within a cyclone’s comma head and within lake effect precipitation bands. In mountainous areas, heavy precipitation is possible where upslope flow is maximized within windward sides of the terrain at elevation. On the leeward side of mountains, desert climates can exist due to the dry air caused by compressional heating. Most precipitation occurs within the tropics and is caused by convection. The movement of the monsoon trough, or inter-tropical convergence zone, brings rainy seasons to savannah climes.

Precipitation is a major component of the water cycle, and is responsible for depositing the fresh water on the planet. Approximately 505,000 cubic kilometres (121,000 cu mi) of waterfalls as precipitation each year; 398,000 cubic kilometres (95,000 cu mi) of it over the oceans and 107,000 cubic kilometres (26,000 cu mi) over land. Given the Earth’s surface area, that means the globally averaged annual precipitation is 990 millimetres (39 in), but over land it is only 715 millimetres (28.1 in). Climate classification systems such as the Köppen climate classification system use average annual rainfall to help differentiate between differing climate regimes.

Precipitation may occur on other celestial bodies, e.g. when it gets cold, Mars has precipitation which most likely takes the form of frost, rather than rain or snow.

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WHAT IS HUMIDITY?

When water evaporates it forms the gaseous water vapour. The amount of water vapour in the air at any one time is known as its humidity. AS more and more water vapour saturates the air, humidity increases, eventually resulting in rain, fog or mist, depending on the heat and temperature of the place.

Humidity is the amount of moisture or water vapour or water molecules present in the atmospheric gas. The more water in the vapour, the higher the humidity. Humidity arises from water evaporating from places like lakes and oceans. Warm water evaporates quickly. That’s why; you may find the most humid regions near to warm water bodies in places like the Red Sea, the Persian Gulf, and Miami.

Types of Humidity:

  1. Relative humidity: A meteorologist uses the term ‘relative humidity’. The relative humidity is a comparison of the amount of moisture present in the air to the amount of moisture air can hold. The amount of moisture the atmosphere can hold totally depends on the temperature.
  1. Specific humidity: We define specific humidity as the mass of water vapour present in a given unit mass of moist air.

Specific humidity is equal to the ratio of water vapour mass and the air parcel’s total (including dry) air mass.

Specific humidity is also known as the humidity ratio. It does not change with the expansion or compression of an air parcel.

We usually express specific heat as grams of vapour per kg of air, or in air conditioning as grains per pound.

The specific humidity has great usage in meteorology.

3. Absolute humidity: We define the absolute humidity in the two following sentences:

Absolute humidity is equal to the mass of water vapour per unit of volume of air, i.e., grams of water/cm3 of air. The formula for the absolute humidity is given by:

             Absolute humidity = Mass of water/volume in cm3

Absolute humidity does not take temperature into consideration.

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WHY IS THE STRATOSPHERE VITAL?

The stratosphere has a layer of ozone gas, which acts like a thick umbrella covering the layers beneath. By absorbing most of the harmful UV radiation from the Sun, the ozone layer prevents it from reaching the surface of the Earth, thus enabling the survival of life on the planet.

Stratosphere could be aptly called the ‘protection blanket’ of Earth. It extends up to 600 kms from the surface of the earth and it is the second layer of the Earth’s atmosphere, right above troposphere.

Stratosphere houses in it the most important layer called Ozone (O3), which acts as an absorber of the harmful UV radiations of the Sun (of about 90%) and thereby protecting us from diseases like Cancer, skin burn etc.

Its non-turbulance and stable, non-convection character makes it possible for the jets to cruise easily, hence they are flown here.

When Volcanic eruptions occur, the ejected material reaches as high as Stratosphere and it stays there for long period, as it doesn’t allow the circulation, there by leading to stratifying the volcanic particles and cooling down of the Earth surface.

However, such an important layer is being perforated by us through the extensive use of the chloro-fluro-carbons which happen to destroy the ozone molecules.

There is also an idea which the scientists are considering that could result in the slowing down of the Earth’s heating, i.e., by adding the man-made materials to stratosphere. Though the feasibility of this idea is yet to be verified. Thus, is the importance of the Stratosphere layer.

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IS THE ATMOSPHERE BUILT UP IN LAYERS?

Yes, the atmosphere has five layers. The lowest layer, closest to the surface of the Earth, is the troposphere. This is where weather is made, and most of the atmosphere’s gases are concentrated in it. Above it is the Stratosphere. No winds blow in this layer, nor are there any clouds. Beyond it lies the cold mesosphere, with very few gases. It is followed by the thermosphere, the thickest and hottest layer of the atmosphere, and lastly, the exosphere, on the edge of outer space.

Earth’s atmosphere is all around us. Most people take it for granted. Among other things, it shields us from radiation and prevents our precious water from evaporating into space. It keeps the planet warm and provides us with oxygen to breathe. In fact, the atmosphere makes Earth the livable, lovable home sweet home that it is.

The atmosphere extends from Earth’s surface to more than 10,000 kilometers (6,200 miles) above the planet. Those 10,000 kilometers are divided into five distinct layers. From the bottom layer to the top, the air in each has the same composition. But the higher up you go, the further apart those air molecules are.

Troposphere: Earth’s surface to between 8 and 14 kilometers (5 and 9 miles)

This lowest layer of the atmosphere starts at the ground and extends 14 kilometers (9 miles) up at the equator. That’s where it’s thickest. It’s thinnest above the poles, just 8 kilometers (5 miles) or so. The troposphere holds nearly all of Earth’s water vapor. It’s where most clouds ride the winds and where weather occurs. Water vapor and air constantly circulate in turbulent convection currents. Not surprisingly, the troposphere also is by far the densest layer. It contains as much as 80 percent of the mass of the whole atmosphere. The further up you go in this layer, the colder it gets.

Stratosphere: 14 to 64 km (9 to about 31 miles)

Unlike the troposphere, temperatures in this layer increase with elevation. The stratosphere is very dry, so clouds rarely form here. It also contains most of the atmosphere’s ozone, triplet molecules made from three oxygen atoms. At this elevation, ozone protects life on Earth from the sun’s harmful ultraviolet radiation. It’s a very stable layer, with little circulation. For that reason, commercial airlines tend to fly in the lower stratosphere to keep flights smooth. This lack of vertical movement also explains why stuff that gets into in the stratosphere tends to stay there for a long time. That “stuff” might include aerosol particles shot skyward by volcanic eruptions, and even smoke from wildfires. This layer also has accumulated pollutants, such as chlorofluorocarbons. Better known as CFCs, these chemicals can destroy the protective ozone layer, thinning it greatly. By the top of the stratosphere, called the stratopause, air is only a thousandth as dense as at Earth’s surface.

Mesosphere: 64 to 85 km (31 to 53 miles)

Scientists don’t know quite as much about this layer. It’s just harder to study. Airplanes and research balloons don’t operate this high and satellites orbit higher up. We do know that the mesosphere is where most meteors harmlessly burn up as they hurtle towards Earth.

The mesopause is also known as the Karman line. It’s named for the Hungarian-born physicist Theodore von Kármán. He was looking to determine the lower edge of what might constitute outer space. He set it at about 80 kilometers (50 miles) up.

The ionosphere is a zone of charged particles that extends from the upper stratosphere or lower mesosphere all the way to the exosphere. The ionosphere is able to reflect radio waves; this allows radio communications.

Thermosphere: 85 to 600 km (53 to 372 miles)

The next layer up is the thermosphere. It soaks up x-rays and ultraviolet energy from the sun, protecting those of us on the ground from these harmful rays. The ups and downs of that solar energy also make the thermosphere vary wildly in temperature. It can go from really cold to as hot as about 1,980 ºC (3,600 ºF) near the top. The sun’s varying energy output also causes the thickness of this layer to expand as it heats and to contract as it cools. With all the charged particles, the thermosphere is also home to those beautiful celestial light shows known as auroras. This layer’s top boundary is called the thermopause.

Exosphere: 600 to 10,000 km (372 to 6,200 miles)

The uppermost layer of Earth’s atmosphere is called the exosphere. Its lower boundary is known as the exobase. The exosphere has no firmly defined top. Instead, it just fades further out into space. Air molecules in this part of our atmosphere are so far apart that they rarely even collide with each other. Earth’s gravity still has a little pull here, but just enough to keep most of the sparse air molecules from drifting away. Still, some of those air molecules — tiny bits of our atmosphere — do float away, lost to Earth forever.

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HOW COLD IS THE ATMOSPHERE?

The atmosphere, with all its layers, extends up to 10,000 km from Earth’s surface. Temperatures vary in the different layers: the mesosphere can go down to -90 °C, the exosphere much, much lower, whereas the thermosphere can be as hot as 2000 °C!

Temperature varies greatly at different heights relative to Earth's surface and this variation in temperature characterizes the four layers that exist in the atmosphere. These layers include the troposphere, stratosphere, mesosphere, and thermosphere.

The troposphere is the lowest of the four layers, extending from the surface of the Earth to about 11 km (6.8 mi) into the atmosphere where the tropopause (the boundary between the troposphere stratosphere) is located. The width of the troposphere can vary depending on latitude, for example, the troposphere is thicker in the tropics (about 16 km (9.9 mi)) because the tropics are generally warmer, and thinner at the poles (about 8 km (5.0 mi)) because the poles are colder. Temperatures in the atmosphere decrease with height at an average rate of 6,5°C (11,7 °F) per kilometer. Because the troposphere experiences its warmest temperatures closer to Earth's surface, there is great vertical movement of heat and water vapour, causing turbulence. This turbulence, in conjunction with the presence of water vapour, is the reason that weather occurs within the troposphere.

Following the tropopause is the stratosphere. This layer extends from the tropopause to the stratopause which is located at an altitude of about 50 km (31 mi). Temperatures remain constant with height from the tropopause to an altitude of 20 km (12 mi), after which they start to increase with height. This happening is referred to as an inversion and it is because of this inversion that the stratosphere is not characterized as turbulent. The stratosphere receives its warmth from the sun and the ozone layer which absorbs ultraviolet radiation.

The next layer is called the mesosphere which extends from the stratopause to the mesopause, located at an altitude of 85 km (53 mi). Temperatures in the mesospere decrease with altitude and are in fact the coldest in the Earth's atmosphere.This decrease in temperature can be attributed to the diminishing radiation received from the Sun, after most of it has already been absorbed by the thermosphere.

The fourth layer of the atmosphere is known as the thermosphere which extends from the mesopause to the 'top' of the collisional atmosphere. Some of the warmest temperatures can be found in the thermosphere, due to its reception of strong ionizing radiation at the level of the Van Allen radiation belt.

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WHERE IS THE TROPOSPHERE THE THINNEST?

The troposphere can be found between the ground and an altitude of 7 to 20 kilometers (4 to 12 miles). The lesser thickness is found at the Polar Regions, since colder temperatures lead to a decrease in gas volume. The vast majority of the world's weather is formed in the troposphere and this layer also contains 80 percent of the atmosphere's mass. The temperature within the troposphere drops with altitude, since it is essentially being warmed by the ground. The pressure also drops within the troposphere as altitude increases, and this explains why mountaineers require oxygen masks.

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WHAT IS THE IONOSPHERE?

It is another layer, overlapping the mesosphere, thermosphere and exosphere, where radio waves are reflected.

A dense layer of molecules and electrically charged particles, called the ionosphere, hangs in the Earth’s upper atmosphere starting at about 35 miles (60 kilometers) above the planet's surface and stretching out beyond 620 miles (1,000 km). Solar radiation coming from above buffets particles suspended in the atmospheric layer. Radio signals from below bounce off the ionosphere back to instruments on the ground. Where the ionosphere overlaps with magnetic fields, the sky erupts in brilliant light displays that are incredible to behold.

Several distinct layers make up Earth's atmosphere, including the mesosphere, which starts 31 miles (50 km) up, and the thermosphere, which starts at 53 miles (85 km) up. The ionosphere consists of three sections within the mesosphere and thermosphere, labeled the D, E and F layers, according to the UCAR Center for Science Education.

Extreme ultraviolet radiation and X-rays from the sun bombard these upper regions of the atmosphere, striking the atoms and molecules held within those layers. The powerful radiation dislodges negatively charged electrons from the particles, altering those particles' electrical charge. The resulting cloud of free electrons and charged particles, called ions, led to the name "ionosphere." The ionized gas, or plasma, mixes with the denser, neutral atmosphere.

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IN WHICH LAYER OF THE ATMOSPHERE DO SATELLITES ORBIT EARTH?

You can consider most satellites to be in space, but in terms of the Earth's atmosphere, they occupy regions called the thermosphere and the exosphere. The layer through which a satellite orbits depends on the satellite's function and the kind of orbit it has. Since the launch of Sputnik in the 1950s, spacefaring countries have put thousands of satellites into orbit around the Earth and even other planets. They serve many different purposes, from complex space stations like the International Space Station to the Global Positioning System that helps you find your way home.

Thermosphere: High Temperatures

The thermosphere is a region of very high temperature that extends from the top of the mesosphere at around 85 kilometers (53 miles) up to 640 kilometers (400 miles) above the Earth's surface. It is called the thermosphere because temperatures can reach up to 1,500 degrees Celsius (2,732 degrees Fahrenheit). However, despite the high temperatures, the pressure is very low, so satellites don't suffer heat damage.

Exosphere: Farthest Reaches

Above the thermosphere sits a final layer called the exosphere, which extends up to 10,000 kilometers (6,200 miles) above the Earth, depending on how it is defined. Some definitions of the exosphere include all space up until the point where atoms get knocked away by solar wind. No distinct upper boundary exists since the exosphere has no pressure and molecules float freely here. Eventually, the exosphere gives way to space outside of the Earth's influence.

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WHAT IS AIR PRESSURE?

The air around you has weight, and it presses against everything it touches. That pressure is called atmospheric pressure, or air pressure. It is the force exerted on a surface by the air above it as gravity pulls it to Earth.

Atmospheric pressure is commonly measured with a barometer. In a barometer, a column of mercury in a glass tube rises or falls as the weight of the atmosphere changes. Meteorologists describe the atmospheric pressure by how high the mercury rises.

An atmosphere (atm) is a unit of measurement equal to the average air pressure at sea level at a temperature of 15 degrees Celsius (59 degrees Fahrenheit). One atmosphere is 1,013 millibars, or 760 millimeters (29.92 inches) of mercury.

Atmospheric pressure drops as altitude increases. The atmospheric pressure on Denali, Alaska, is about half that of Honolulu, Hawai'i. Honolulu is a city at sea level. Denali, also known as Mount McKinley, is the highest peak in North America.

As the pressure decreases, the amount of oxygen available to breathe also decreases. At very high altitudes, atmospheric pressure and available oxygen get so low that people can become sick and even die.

Mountain climbers use bottled oxygen when they ascend very high peaks. They also take time to get used to the altitude because quickly moving from higher pressure to lower pressure can cause decompression sickness. Decompression sickness, also called "the bends", is also a problem for scuba divers who come to the surface too quickly.

Aircraft create artificial pressure in the cabin so passengers remain comfortable while flying.

Atmospheric pressure is an indicator of weather. When a low-pressure system moves into an area, it usually leads to cloudiness, wind, and precipitation. High-pressure systems usually lead to fair, calm weather.

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