Why is the Earth Tilted?

Winter Solstice

Have you ever wondered why the Earth is tilted instead of just perpendicular with its plane of orbit? Scientists have taken a crack at answering that question. The main consensus is that it has to do with Earth’s formation along with the rest of the planets in the Solar system. This time in cosmic history is still a mystery to us but we do have some ideas about what went on. We know that the birth of the Sun created a new source of gravity in the young Solar System. The tidal forces between the young sun and the rest of the nebula the Sun was born from created further instability in the gases and dust left in the nebula. This allowed for the steady formation of the planets.

After millions of years passed enough matter collided to gain mass and its own gravity and become small versions of planets called planetessimals and protoplanets. These pre-planets collided to create even larger planets. This set the stage for how the Earth approached its final form. It looks like it probably collided with a another proto-planet and in the process it was tilted.

All the same the Earth’s tilt is very important. It is perfectly positioned so that it gives us the seasons and on top of that the seasons are near perfectly calibrated for life. When compared with other planets Earth’s tilt allows for season that are not too extreme in temperature but are pretty well balanced. At the same if it had stay in the “perfect” position one side of the Earth would be too hot at time and then too cold.

We have written many articles about the Earth’s tilt for Universe Today. Here’s an article about why Earth has seasons, and here’s an article about the Earth’s axis.

If you’d like more info on Earth, check out NASA’s Solar System Exploration Guide on Earth. And here’s a link to NASA’s Earth Observatory.

We’ve also recorded an episode of Astronomy Cast all about planet Earth. Listen here, Episode 51: Earth.

What Color is the Sky

Space Travel

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If you are a parent or are old enough to babysit younger relatives there is one question children ask that stumps most adults. It’s what color is the sky or why is the sky blue. This article will tell you why and do it in as simple a way as possible so that the next time a kids ask the question you have a good answer.

To understand why the sky is blue you need to remember how color works. Color is largely caused by how well an object absorbs the light spectrum. When you see a blue sky you only see blue because all the other colors were absorbed in the air. Any object with color works that way. For example a red ball is read because all the colors of light are absorbed by the ball except for red. This reflected light is what gives the object color.

This is what happens with the sky. The atmosphere is denser than we imagine and the different gases give the atmosphere unique properties in how it absorbs, diffuses, and reflects light. When sunlight passes through our atmosphere a portion of it is scattered and absorbed. The remainder either reaches the surface or is reflected back. The portion that makes it to us observers is 75 percent.

This process is called diffused sky radiation. So to review, we color because objects due to texture of dyes and surfaces absorb all light wavelengths and reflect back one or more. The reason we see the sky as blue is because the molecules in the air scatter the light absorbing most wavelengths of light except for blue.

In addition to this the sky is gray and overcast because of the water droplets in the atmosphere in the forms of clouds and humidity. water refracts light equally unlike air molecules in the atmosphere. This means we get the entirety of white light only it is dimmer just like when you shine a light through a white sheet.

The fact we see a blue sky is good thing because its shows that are atmosphere is at work shielding us from the full energy of the sun’s rays. While the sun is the largest source of energy to our planet, a lot of its high energy radiation that is deadly for living things. Our atmosphere plays it part by shielding us from that. So when you see a blue sky with your kid you can tell them it means the sky is acting like a huge shade blocking out the bad parts of the sun.

We have written many articles about the earth’s sky for Universe Today. Here’s an article about why the sky is blue, and here’s an article about how to find Venus in the sky.

If you’d like more info on the earth’s sky, check out an article about Strange Clouds. And here’s a link to NASA Space Place Article on Blue Sky.

We’ve also recorded an episode of Astronomy Cast all about Sky Survey. Listen here, Episode 118: Sky Surveys.

What Is The Largest Island In The World

Greenland. Image credit: NASA

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If you were asked what is the largest island in the world, what would you say? Australia maybe? Greenland is the worlds largest island. While Australia is an island, it is considered a continent. Greenland has an area of 2,166,086 square km, but a meager population of 56,452. The populations is over 85% Inuit. The remaining inhabitants are mainly Danish. The average annual temperature of Greenland varies between -9 to 7 °C.

Greenland is an autonomous country within the Kingdom of Denmark. Greenland is a group of islands and Greenland is the name of the largest, most populated one. Greenland has been inhabited on and off since 2500 BC. Denmark established rule in the 18th century. In 1979 Denmark granted home rule, in a relationship known as the Commonwealth of the Realm and in 2008 Greenland voted to transfer more powers to the local government. The Danish royal government is only in charge of foreign affairs, security, financial policy, and providing a subsidy to each citizen.

Greenland is bordered by the Atlantic Ocean to the southeast, the Greenland Sea to the east, the Artic Ocean to the north, and Baffin Bay to the west. The nearest countries to Greenland are Iceland to the east and Canada to the west. The country also contains the world’s largest national park. Scientists have thought for decades that the ice sheet covering the country may actually conceal three separate island land masses that have been bridged by glaciers over the last geologic cooling period.

The Greenland ice sheet covers 1,755,637 square km. It has a volume of 2,850,000 cubic km. Gunnbjorn Fjeld is the highest point on Greenland at 3,700 m. The majority of Greenland is less than 1,500 m in elevation. The weight of the ice sheet has formed a basin that is more than 300 m below sea level.

Between 1989 and 1993, climate researchers drilled into the summit of Greenland’s ice sheet, obtaining a pair of 3 km ice cores. Analysis of the layering and chemical composition of the cores has provided a revolutionary new record of climate change going back about 100,000 years. It illustrated that the world’s weather and temperature have often shifted rapidly from one stable state to another. The glaciers of Greenland are also contributing to a rise in the global sea level at a faster rate than was previously believed.

Greenland is fascinating and intimidating at the same time. To live there is a daily struggle against the elements that has forged a tough people.

We have written many articles about Greenland for Universe Today. Here’s an article about the growing ice sheets in Greenland, and here are some images of Greenland from space.

If you’d like more info on Earth’s islands, check out NASA’s Solar System Exploration Guide on Earth. And here’s a link to NASA’s Earth Observatory.

We’ve also recorded an episode of Astronomy Cast all about planet Earth. Listen here, Episode 51: Earth.

Sources:
World Atlas
Geographia

What Is The Largest Continent

Asia Image Credit: NASA's Blue Marble project

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There are a few different ways to answer ‘what is the largest continent’. The first is by area and another is by population. By area, Asia is the largest continent at 44,391,162 square km. It is also the largest by population with more than 4 billion people.

There is quite a bit of debate as to how many continents there are. Some areas of the world combine Asia and Europe into one continent called Eurasia. In that case, the continent of Eurasia would be the biggest continent in both area and population.

The debate as to how many continents there are is based in the basic, yet confusing definition of what a continent is. A continent is understood to be large, continuous, discrete mass of land, ideally separated by an expanse of water. Many of the seven most commonly recognized continents identified by convention are not discrete landmasses separated by water. The criteria of being large is used arbitrarily. Greenland has an area of 2,166,086 square km and is considered an island. Australia has an area of 7,617,930 square km, but it is called a continent. The distinct landmass separated by water criteria is sometimes ignored in the case of Europe and Asia. All of the criteria are a consensus, not a rule, so some countries teach a different number of continents.

Whether you have been taught that there are 6 or 7 continents, you need to know that here have been changing numbers of continents since the formation of the Earth. There have been anywhere from 1 to 7 continents. As the tectonic plates have shifted, the continents have broken apart and collided together again. The Earth’s tectonic plates are still moving, so it is hard to predict how many continents there will be in 500,000 years, 1 million years, and so forth.

The answer to ‘what is the largest continent’ is pretty cut and dry. If you consider that there are seven continents, then Asia is the largest in area and population. If you combine Europe and Asia into the continent of Eurasia, it is still the largest by area and population.

We have written many articles about Continent for Universe Today. Here’s an article about the number of continents in the Earth, and here’s an article about the Continental Drift Theory.

If you’d like more info on continents, check out NASA’s Solar System Exploration Guide on Earth. And here’s a link to NASA’s Earth Observatory.

We’ve also recorded an episode of Astronomy Cast all about planet Earth. Listen here, Episode 51: Earth.

Source:
Wikipedia

Equator

GOES-8 Satellite Image Captures Earth

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An equator is an imaginary line that runs around the surface of a planet, perpendicular to the sphere’s axis of rotation. Of course, the one we’re most interested in is the Earth’s equator. Regions north of the equator are called the Northern Hemisphere, and then south of the equator is the Southern Hemisphere.

Here on Earth, the equator has a length of 40,008.6 kilometers, and its latitude is 0°. And if you can stand on the equator, you’ll see the Sun rise in the East and travel overhead through the day, and then set in the West; on the March and September equinox, the rays from the Sun fall straight down. This is also the spot with the quickest sunrise and sunset times, since the Sun moves exactly perpendicular to the horizon, rising straight up, without moving at an angle to the horizon.

Because the Earth is rotating, turning once a day on its axis, the Earth’s equator bulges out further from the center than from the poles. The Earth isn’t a sphere, but it’s actually an oblate spheroid. The equatorial diameter of the Earth is actually 43 kilometers greater than the polar diameter.

Since it’s the region of Earth that receives the most sunlight, the climate near the equator is hot – it’s summer all the time. People who live near the equator will generally distinguish between a long hot dry season and a long hot wet season. Some of the countries with the equator include Gabon, Congo, Uganda, Kenya, Somalia, Indonesia, Ecuador, Columbia, and Brazil.

The equator is the best place to launch a spacecraft on Earth. That’s because the rotational speed of the planet adds to the launch velocity of a rocket. Rockets launched from the equator can launch with less fuel, or carry more mass into orbit with the same amount of fuel. This is why the Guiana Space Centre is located in Kourou, French Guiana. And this is also why the Sea Launch platform travels from Los Angeles down to the equator before launching rockets.

We have written many articles about the Equator for Universe Today. Here’s an article about the temperature of the Earth, and here’s an article about the circumference of the Earth.

If you’d like more info on Equator, check out NASA’s Article about Latitude and Longitude. And here’s a link to NASA’s Earth Observatory.

We’ve also recorded an episode of Astronomy Cast all about planet Earth. Listen here, Episode 51: Earth.

Source: Wikipedia

Terminator

Geological Period

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No, this isn’t a movie about robots. The terminator is the line that separates day from night on an object lit by a star. You can see evidence of this terminator when you look at the Moon. When we see the Moon, half in light and half in darkness, we’re seeing the terminator line going right down the middle of the Moon.

From our perspective here on Earth, we see the Sun rise from the East, go through the sky and then set again in the West. But if you could see the Earth from space, you would see half the planet is always illuminated, and half the planet is always in shadow. Since the Earth is rotating, we can watch different parts of the planet illuminated, and other parts darkened. The people on the surface of the planet are experiencing the Sun moving through the sky, but really it’s them who are doing the moving.

The location of the terminator depends on the axial tilt of the object. Since the Earth is tilted by 23.5° away from the Sun’s axis, the position of the terminator changes depending on the season. During summer in the northern horizon, the Earth’s north pole never goes into shadow, so the terminator never crosses the pole. And then in winter in the northern horizon, it never comes out of shadow.

If you could orbit the Earth, just above the equator, you would see the terminator line speeding away at approximately 1,600 km/h (1000 miles per hour). Only the fastest supersonic aircraft can match the terminator’s speed. But as you get closer to the poles, the terminator moves more slowly. Eventually at the poles, you can walk faster than the speed of the terminator.

When you see a terminator from afar, it can tell you a lot about a planet or moon. For example, the Earth’s terminator is fuzzy. This means that our planet has a thick atmosphere that scatters the light from the Sun. The Moon, on the other hand, is airless, so its terminator is a crisp line. When you’re standing on the surface of the Moon, it’s either bright or dark, not the in-between twilight that we experience here on Earth.

We have written many articles about the terminator for Universe Today. Here’s an article about why the Sun rises in the East and sets in the West, and here are some Earthrise photos.

If you’d like more info on Earth, check out NASA’s Solar System Exploration Guide on Earth. And here’s a link to NASA’s Earth Observatory.

We’ve also recorded an episode of Astronomy Cast all about planet Earth. Listen here, Episode 51: Earth.

Reference:
NASA Earth Observatory

What Is Lithosphere

Inner Earth

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Every rocky planet has a lithosphere, but what is lithosphere? It is the rigid outermost shell of a rocky planet. Here on Earth the lithosphere contains the crust and upper mantle. The Earth has two types of lithosphere: oceanic and continental. The lithosphere is broken up into tectonic plates.

Oceanic lithosphere consists mainly of mafic(rich in magnesium and iron) crust and ultramafic(over 90% mafic) mantle and is denser than continental lithosphere. It thickens as it ages and moves away from the mid-ocean ridge. This thickening occurs by conductive cooling, which converts hot asthenosphere into lithospheric mantle. It was less dense than the asthenosphere for tens of millions of years, but after this becomes increasingly denser. The gravitational instability of mature oceanic lithosphere has the effect that when tectonic plates come together, oceanic lithosphere invariably sinks underneath the overriding lithosphere. New oceanic lithosphere is constantly being produced at mid-ocean ridges and is recycled back to the mantle at subduction zones, so oceanic lithosphere is much younger than its continental counterpart. The oldest oceanic lithosphere is about 170 million years old compared to parts of the continental lithosphere which are billions of years old.

The continental lithosphere is also called the continental crust. It is the layer of igneous, sedimentary rock that forms the continents and the continental shelves. This layer consists mostly of granitic rock. Continental crust is also less dense than oceanic crust although it is considerably thicker(25 to 70 km versus 7-10 km). About 40% of the Earth’s surface is now covered by continental crust, but continental crust makes up about 70% of the volume of Earth’s crust. Most scientists believe that there was no continental crust originally on the Earth, but the continental crust ultimately derived from the fractional differentiation of oceanic crust over the eons. This process was primarily a result of volcanism and subduction.

We may not walk directly the lithosphere, but it shapes every topographical feature the we see. The movement of the tectonic plates has presented many different shapes for our planet over the eons and will continue to change our geography until our planet ceases to exist.

We have written many articles about the lithosphere for Universe Today. Here’s an article about the lithosphere, and here’s an article about the tectonic plates.

If you’d like more info on the Earth’s lithosphere, check out NASA’s Solar System Exploration Guide on Earth. And here’s a link to NASA’s Earth Observatory.

We’ve also recorded an episode of Astronomy Cast all about planet Earth. Listen here, Episode 51: Earth.

What Is A Continent

Map of Earth

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You know that there are 7 continents(6 if you were taught geography in Europe) right now, but do you really know the definition of what is a continent? There are many different, and confusing definitions of what a continent is. The most widely accepted one says that a continent is defined as a large, continuous, discrete mass of land, ideally separated by an expanse of water. This definition somewhat confuses things. Many of the current continents are not discrete landmasses separated by water. The word large leads to arbitrary classification: Greenland, with a surface area of 2,166,086 km2 is considered the world’s largest island, but Australia with a land mass of 7,617,930 km2 is a continent. The qualification that each be a continuous landmass is disregarded because of the inclusion of the continental shelf and oceanic islands and is contradicted by classifying North and South America and Asia and Africa as continents, without a natural separation by water. This idea continues if the land mass of Europe and Asia is considered as two continents. Also, the Earth’s major landmasses are surrounded by one, continuous World ocean that has been divided into a number of principal ‘oceans’ by the land masses themselves and various other geographic criteria.

The number of continents has changed throughout the evolution of the Earth. Plate tectonics and continental drift have forced changes on continental composition. The planet began with one single land mass(the Mesezoic Era). This continent was not suddenly there. It was the result of partially solidified magma being smashed together by plate tectonics and continental drift. Those forces remain at work today.

To further confuse things, different parts of the world teach different versions of the continents. The seven-continent model is usually taught in China and most English speaking countries. A six continent model combining Europe and Asia is preferred by the geographic community, the former parts of the USSR, and Japan. Another six continent model combining North and South America is taught in Latin America and most of Europe.
The answer to ‘what is a continent’ is more by convention than strict definition. Hopefully, this will help to clear some of the confusion that you had before you started reading this article.

We have written many articles about the continents for Universe Today. Here’s an article about the biggest continent, and here’s an article about the continental drift theory.

If you’d like more info on Earth’s continents, check out NASA’s Solar System Exploration Guide on Earth. And here’s a link to NASA’s Earth Observatory.

We’ve also recorded an episode of Astronomy Cast all about planet Earth. Listen here, Episode 51: Earth.

Source: Wikipedia

Does Zonal Swishing Play a Part in Earth’s Magnetic Field Reversals?

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Why does the Earth’s magnetic field ‘flip’ every million years or so? Whatever the reason, or reasons, the way the liquid iron of the Earth’s outer core flows – its currents, its structure, its long-term cycles – is important, either as cause, effect, or a bit of both.

The main component of the Earth’s field – which defines the magnetic poles – is a dipole generated by the convection of molten nickel-iron in the outer core (the inner core is solid, so its role is secondary; remember that the Earth’s core is well above the Curie temperature, so the iron is not ferromagnetic).

But what about the fine structure? Does the outer core have the equivalent of the Earth’s atmosphere’s jet streams, for example? Recent research by a team of geophysicists in Japan sheds some light on these questions, and so hints at what causes magnetic pole flips.

About the image: This image shows how an imaginary particle suspended in the liquid iron outer core of the Earth tends to flow in zones even when conditions in the geodynamo are varied. The colors represent the vorticity or “amount of rotation” that this particle experiences, where red signifies positive (east-west) flow and blue signifies negative (west-east) flow. Left to right shows how the flow responds to increasing Rayleigh numbers, which is associated with flow driven by buoyancy. Top to bottom shows how flow responds to increasing angular velocities of the whole geodynamo system.

The jet stream winds that circle the globe and those in the atmospheres of the gas giants (Jupiter, Saturn, etc) are examples of zonal flows. “A common feature of these zonal flows is that they are spontaneously generated in turbulent systems. Because the Earth’s outer core is believed to be in a turbulent state, it is possible that there is zonal flow in the liquid iron of the outer core,” Akira Kageyama at Kobe University and colleagues say, in their recent Nature paper. The team found a secondary flow pattern when they modeled the geodynamo – which generates the Earth’s magnetic field – to build a more detailed picture of convection in the Earth’s outer core, a secondary flow pattern consisting of inner sheet-like radial plumes, surrounded by westward cylindrical zonal flow.

This work was carried out using the Earth Simulator supercomputer, based in Japan, which offered sufficient spatial resolution to determine these secondary effects. Kageyama and his team also confirmed, using a numerical model, that this dual-convection structure can co-exist with the dominant convection that generates the north and south poles; this is a critical consistency check on their models, “We numerically confirm that the dual-convection structure with such a zonal flow is stable under a strong, self-generated dipole magnetic field,” they write.

This kind of zonal flow in the outer core has not been seen in geodynamo models before, due largely to lack of sufficient resolution in earlier models. What role these zonal flows play in the reversal of the Earth’s magnetic field is one area of research that Kageyama and his team’s results that will now be able to be pursued.

Sources: Physics World, based on a paper in the 11 February, 2010 issue of Nature. Earth Simulator homepage

Earth Surface Temperature

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The average Earth surface temperature is 14° C. That’s 287 kelvin, or 57.2° F.

As you probably realize, that number is just an average. The Earth’s temperature can be much higher or lower than this temperature. In the hottest places of the planet, in the deserts near the equator, the temperature on Earth can get as high as 57.7° C. And then in the coldest place, at the south pole in Antarctica, the temperature can dip down to -89° C.

The reason the average temperature on Earth is so high is because of the atmosphere. This acts like a blanket, trapping infrared radiation close to the planet and warming it up. Without the atmosphere, the temperature on Earth would be more like the Moon, which rises to 116° C in the day, and then dips down to -173° C at night.

We’ve written several articles about the temperature of the planets. Here’s an article about the temperature of all the planets, and here’s an article about the temperature of the Moon.

If you’d like more information on the Earth, check out NASA’s Solar System Exploration Guide on Earth. And here’s a link to NASA’s Earth Observatory.

We’ve also recorded an entire episode of Astronomy Cast all about Earth. Listen here, Episode 51: Earth.