Guide to Space Archives

September 15, 2010December 24, 2015 by Jerry Coffey

What Is Solar Energy

What is solar energy? Solar energy is the radiant energy produced by the Sun. It is both light and heat. It, along with secondary solar-powered resources such as wind and wave power, account for the majority of the renewable energy on Earth.

The Earth receives 174 petawatts(PW) of solar radiation at the upper atmosphere. 30% of that is reflected back to space and the rest is absorbed by clouds, oceans and land masses. Land surfaces, oceans, and atmosphere absorb solar radiation, which increases their temperature. Warm air containing evaporated water from the oceans rises, causing convection. When the air reaches a high altitude, where the temperature is low, water vapor condenses into clouds and causes rain. The latent heat of water condensation increases convection, producing wind. Energy absorbed by the oceans and land masses keeps the surface at an average temperature of 14°C. Green plants convert solar energy into chemical energy through photosynthesis. Our food supply is completely dependent on solar energy. After plants die, they decay in the Earth, so solar energy can be said to provide the biomass that has created the fossil fuels that we are dependent on.

Humans harness solar energy in many different ways: space heating and cooling, the production of potable water by distillation, disinfection, lighting, hot water, and cooking. The applications for solar energy are only limited by human ingenuity. Solar technologies are characterized as either passive or active depending on the way the energy is captured, converted, and distributed. Active solar techniques use photovoltaic panels and solar thermal collectors to harness the energy. Passive techniques include orienting a building to the Sun, selecting materials with thermal mass properties, and using materials with light dispersing properties.

Our current dependence on fossil fuels is slowly being replaced by alternative energies. Some are fuels that may eventually become useless, but solar energy will never be obsolete, controlled by foreign powers, or run out. Even when the Sun uses up its hydrogen, it will produce useable energy until it explodes. The challenge facing humans is to capture that energy instead of taking the easiest way out by using fossil fuels.

We have written many articles about Solar Energy for Universe Today. Here’s an article about harvesting solar power from space, and here’s an article about the energy from the sun.

If you’d like more info on the Sun, check out NASA’s Solar System Exploration Guide on the Sun, and here’s a link to the SOHO mission homepage, which has the latest images from the Sun.

We’ve also recorded an episode of Astronomy Cast all about the Sun. Listen here, Episode 30: The Sun, Spots and All.

Sources:
Wikipedia
Wise Geek

September 15, 2010October 16, 2016 by Jerry Coffey

What Is Pangaea?

Continents might be necessary for life, especially complex life. This image shows super-continent Pangaea during the Permian period (300 - 250 million years ago). Credit: NAU Geology/Ron Blakey

So, you are curious about what is Pangaea? It was the supercontinent that existed 250 million years ago during the Paleozoic and Mesozoic eras. During the ensuing millenia, plate tectonics slowly moved each continent to its current position on the planet. Each continent is still slowly moving across the face of our world.

The breaking up and formation of supercontinents appears to have happened several times over Earth’s history with Pangaea being one among many. The next-to-last one, Pannotia, formed about 600 million years ago during the Proterozoic eon. Pannotia included large amounts of land near the poles and only a relatively small strip near the equator connecting the polar masses.

60 million years after its formation Pannotia broke up, giving rise to the continents of Laurentia, Baltica, and Gondwana. Laurentia would eventually become a large portion of North America, the microcontinent of Avalonia(a small portion of Gondwana) would become the northeastern United States, Nova Scotia, and England. All of these came together at the end of the Ordovician.

While this was happening, Gondwana drifted slowly towards the South Pole. These were the early steps in the formation of Pangaea. The next step was the collision of Gondwana with the other land mass. Southern Europe broke free of Gondwana. By late Silurian time, North and South China rifted away from Gondwana and started to head northward across the shrinking Proto-Tethys Ocean.

Movement continued slowly until the land masses drifted until their current positions. The list of oceans and microcontinents is too long to include in this article. We have many articles about this full process here on Universe Today. The evidence for Pangaea lies in the fossil records from the period. It includes the presence of similar and identical species on continents that are now great distances apart.

Additional evidence for Pangaea is found in the geology of adjacent continents, including matching geological trends between the eastern coast of South America and western Africa. The polar ice cap of the Carboniferous Period covered the southern end of Pangaea. Glacial deposits of the same age and structure are found on many separate continents which would have been together in the continent of Pangaea.

We know that the existence of supercontinents has been proven. We know that they have existed at different times in the Earth’s history. Also, we know that the tectonic plates are still moving. Is it possible that there will be another supercontinent someday in the distant future.

We have written many articles about Pangaea for Universe Today. Here’s an article about the Continental Drift Theory, and here’s an article about the continental plates.

If you’d like more info on Pangaea, check out the Pangaea Interactive Map Game. And here’s a link to NASA’s Continents in Collision: Pangaea Ultima.

We’ve also recorded an episode of Astronomy Cast all about Plate Tectonics. Listen here, Episode 142: Plate Tectonics.

Sources:
http://en.wikipedia.org/wiki/Pangaea
http://pubs.usgs.gov/gip/dynamic/historical.html
http://library.thinkquest.org/17701/high/pangaea/

September 15, 2010December 24, 2015 by Fraser Cain

Sand Storm

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A sand storm, also known as a dust storm is an atmospheric event when strong winds lift dust from one region and carry it into another. They’re most common in arid, desert regions where there’s little vegetation to hold the topsoil and sand down. Large sand storms can carry dust thousands of kilometers; dust that started in the Arabian desert can be dropped into the Pacific Ocean.

Sand storms get going when there’s a very dry region, without wet soil to hold the particles together. The smallest particles of sand can be pulled out of the ground by the wind, and held in suspension by the wind. It’s thought that static electricity in the storm can cause even more particles to pull out of the ground in addition to the wind effect. In some cases the dust is held low to the ground, but with the right atmospheric conditions, the sand can be carried more than 6 km high in the atmosphere.

Although sand storms are a natural event, it’s believed that poor farming techniques contribute to the problem. As the topsoil is depleted and erodes away by farming and grazing animals, it exposes the underlying sand and dust. This situation led to the huge dust storms of the Dust Bowl in the 1930s in the United States.

A dust storm can be quite a hazard if you get caught in one. The storms can spread over hundreds of kilometers, with driving winds that can be over 40 km/h. The sand can be thick enough to obscure visibility down to a very short distance. The dust can also be a danger to people with asthma and other respiratory illnesses.

Dust storms don’t just happen on Earth, they can also happen on Mars. In fact, dust storms can become so large on Mars they obscure the entire planet. When NASA’s Mariner 9 spacecraft arrived at Mars in 1971, there was a huge dust storm raging. Only the volcano Olympus Mons was visible above the haze of the dust storm. The most recent planet-wide dust storm occurred in 2007, posing a risk to the Mars Exploration Rovers. They rely on sunlight to power their solar panels, but the dust settling on their panels was reducing their power output.

We have written many articles about sand storms for Universe Today. Here’s an article about the black sand beaches, and here are some sandstorm pictures.

If you’d like more info on sandstorms, check out Visible Earth Homepage. 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.

September 15, 2010December 24, 2015 by Fraser Cain

Transit

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Although the word “transit” can have many meanings, here on Universe Today, we’re talking about astronomical transits. This is where one object in space moves directly in front of another, partly obscuring it from view.

The most famous example of an astronomical transit is a solar eclipse. From our vantage point on Earth, the Moon appears to pass directly in front of the Sun, obscuring it, and darkening the sky. When seen from space, the Moon casts a shadow on the surface of the Earth; only people within that shadowed area actually see the transit.

In order to have a transit, you need to have a closer object, a more distant object, and then an observer. When all three objects are lined up in a straight line, you’ll get a transit. There can be transits of Mercury and Venus across the surface of the Sun, or a transit of Earth across the Sun, seen from Jupiter. We can also see the transit of moons across the surface of their planets. Jupiter often has moons transiting in front of it.

Astronomers use the transit technique to discover extrasolar planets orbiting other stars. When a planet passes in front of a star, it dims the light from the star slightly. And then the star brightens again as the planet moves away. By carefully measuring the brightness of the star, astronomers are able to detect if they have planets orbiting them.

Transits are also helpful for studying the atmospheres of objects in the Solar System. Astronomers discovered that Pluto has a tenuous atmosphere by studying how it dimmed the light from a more distant star. As Pluto began transiting in front of the star, its atmosphere partly obscured the star, changing the amount of light observed. Astronomers were then able to work out the chemicals in Pluto’s atmosphere.

The next transit of Mercury will occur in 2016, and the next transit of Venus is scheduled to occur in 2012.

We have written many articles about astronomical transit for Universe Today. Here’s an article about the transit of Mercury, and here’s an article about the transit of Venus.

If you’d like more info about Astronomical Transit, check out NASA Homepage, and here’s a link to NASA’s Solar System Simulator.

We’ve also recorded related episodes of Astronomy Cast about the Eclipse. Listen here, Episode 160: Eclipses.

Source: Wikipedia

September 15, 2010September 18, 2016 by Fraser Cain

What Are Tornadoes?

Tornado at Union City, Oklahoma Credit: NOAA Photo Library

Also known as a twister, a tornado is a rotating column of air that can cause a tremendous amount of damage on the ground. Tornadoes can very in size from harmless dust devils to devastating twisters with wind speeds greater than 450 km/h.

A tornado looks like a swirling funnel of cloud that stretches from bottom of the clouds down to the ground. Depending on the power of the tornado, there might be a swirling cloud of debris down at the ground, where it’s tearing stuff up. Some tornadoes can look like thin white ropes that stretch from the sky down to the ground, and only destroy a thin patch of ground. Others can be very wide, as much as 4 km across, and leave a trail of destruction for hundreds of kilometers.

Tornadoes appear out of special thunderstorms known as supercells. They contain a region of organized rotation in the atmosphere a few kilometers across. Rainfall within the storm can drag down an area of this rotating atmosphere, to bring it closer to the ground. As it approaches the ground, conservation of momentum causes the wind speed to increase until it’s rotating quickly – this is when tornadoes cause the most damage. After a while the tornado’s source of warm air is choked off, and it dissipates.

When a tornado forms over water, it’s called a waterspout. These can be quite common in the Florida Keys and the northern Adriatic Sea. Most are harmless, like dust devils, but powerful waterspouts can be driven by thunderstorms and be quite dangerous.

Scientists have several scales for measuring the strength and speed of tornadoes. The most well known is the Fujita scale, which ranks tornadoes by the amount of damage they do. A F0 tornado damages trees, but that’s about it, while the most powerful F5 tornado can tear buildings off their foundations. Another scale is known as the TORRO scale, which ranges from T0 to T11. In the United States, 80% of tornadoes are F0, and only 1% are the more violent F4 or F5 twisters.

Although they can form anywhere in the world, tornadoes are mostly found in North America, in a region called Tornado Alley. The United States has the most tornadoes of any country in the world; 4 times as many as the entire continent of Europe. The country gets about 1,200 tornadoes a year.

We have written many articles about the tornado for Universe Today. Here’s an article about the biggest tornado, and here’s an article about how tornadoes are formed.

If you’d like more info on tornadoes, check out the National Oceanic & Atmospheric Administration (NOAA) Homepage. 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.

September 14, 2010December 24, 2015 by Fraser Cain

Terminator

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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

September 14, 2010May 16, 2016 by Fraser Cain

What Is Terminal Velocity?

The higher you are when you jump, the more it hurts when you hit the ground. That’s because the Earth’s gravity is constantly accelerating you towards its center. But there’s actually a maximum speed you reach, where the acceleration of the Earth’s gravity is balanced by the air resistance of the atmosphere. The maximum speed is called terminal velocity.

The terminal velocity speed changes depending on the weight of the object falling, its surface area and what it’s falling through. For example, a feather doesn’t weigh much and presents a very large surface area to the air as it falls. So its terminal velocity speed is much slower than a rock with the same weight. This is why an ant can fall off a tall building and land unharmed, while a similar fall would kill you. Keep in mind that this process happens in any gas or fluid. So terminal velocity defines the speed that a rock sinks when you drop it in the water.

So, let’s say you’re a skydiver jumping out of an airplane. What’s the fastest speed you’ll go? The terminal velocity of a skydiver in a free-fall position, where they’re falling with their belly towards the Earth is about 195 km/h (122 mph). But they can increase their speed tremendously by orienting their head towards the Earth – diving towards the ground. In this position, the skydiver’s velocity increases to more than 400 km/h.

The world skydiving speed record is held by Joseph Kittinger, who was able to fall at a speed of 988 km/h by orienting his body properly and jumping at high altitude, where there’s less wind resistance.

The gravity of the Earth pulls at you with a constant acceleration of 9.81 meters/second. Without any wind resistance, you’ll fall 9.81 meters/second faster every second. 9.81 meters/second the first second, 19.62 meters/ second in the next second, etc.

The opposing force of the atmosphere is called drag. And the amount of drag force increases approximately proportional to the square of the speed. So if you double your speed, you experience a squaring of the drag force. Since the drag force is going up much more quickly than the constant acceleration, you eventually reach a perfect balance between the force of gravity and the drag force of whatever you’re moving through.

Outside the Earth’s atmosphere, though, there’s no terminal velocity. You’ll just keep on accelerating until you smash into whatever’s pulling on you.

We have written many articles about the terminal velocity for Universe Today. Here’s an article featuring the definition of velocity, and here’s an article about the X-Prize Entrant completing the Drop Test

If you’d like more info on the Terminal Velocity, check out a Lecture on Terminal Velocity, and here’s a link to a NASA article entitled, The Way Things Fall.

We’ve also recorded an entire episode of Astronomy Cast all about Gravity. Listen here, Episode 102: Gravity.

Sources:
NASA
Wikipedia
GSU Hyperphysics

September 14, 2010December 24, 2015 by Jerry Coffey

What Is Mechanical Energy

Millennium Force roller coaster Credit: Cedar Point

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The straight forward answer to ‘what is mechanical energy’ is that it is the sum of energy in a mechanical system. This energy includes both kinetic energy(energy of motion) and potential energy(stored energy).

Objects have mechanical energy if they are in motion and/or if they are at some position relative to a zero potential energy position. A few examples are: a moving car possesses mechanical energy due to its motion(kinetic energy) and a barbell lifted high above a weightlifter’s head possesses mechanical energy due to its vertical position above the ground(potential energy).

Kinetic energy is the energy of motion. An object that has motion, vertical or horizontal motion, has kinetic energy. There are many forms of kinetic energy: vibrational (the energy due to vibrational motion), rotational (the energy due to rotational motion), and translational (the energy due to motion from one location to another).

Potential energy is the energy stored in a body or in a system due to its position in a force field or its configuration. The standard unit of measure for energy and work is the joule. The term “potential energy” has been used since the 19th century.

Because of the different components of mechanical energy, it exists in every system in the universe. From a baseball being thrown to a brick falling off of a ledge, mechanical energy surrounds us. Defining what is mechanical energy is easy, but finding examples of it are even easier.

We have written many articles about mechanical energy for Universe Today. Here’s an article about how generators work, and here’s an article about what is energy.

If you’d like more info on Mechanical Energy, check out a Discussion on Energy, and here’s a link to an article about Momentum.

We’ve also recorded an entire episode of Astronomy Cast all about Gravity. Listen here, Episode 102: Gravity.

September 14, 2010December 24, 2015 by Jerry Coffey

What Is Lithosphere

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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.

September 14, 2010December 24, 2015 by Jerry Coffey

What Is Light Energy

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Just asking ‘what is light energy’ opens you up to a flood of other questions trying to narrow down the context that you are asking the question in. In photometry, luminous energy is the perceived energy of light. It can also be defined as the electromagnetic radiation of visible light. Since light itself is energy, then another definition is relevant: light is nature’s way of transferring energy through space.

The speed of light is about 300,000 km/s. To put that in perspective, when you watch the sun set, it has actually been 10 minutes since that light left the Sun. Light energy is measured with two main sets of units: radiometry measures light power at all wavelengths and photometry measures light with wavelength weighted with respect to a standardized model of human brightness perception. Photometry is useful when measuring light intended for human use. The photometry units are different from most units because they take into account how the human eye responds to light. Based on this, two light sources which produce the same intensity of visible light do not necessarily appear equally bright.

Light exerts a physical pressure on objects in its path. This is explained by the particle nature of light in which photons strike and transfer their momentum. Light pressure is equal to the power of the light beam divided by the speed of light. The effect of light pressure is negligible for everyday objects. For example, you can lift a coin with laser pointers, but it would take 1 billion of them to do it. Light pressure can cause asteroids to spin faster by working on them like wind pushing a windmill. That is why some scientist are researching solar sails to propel intersteller flight.

Light is all around us. It has the ability to tan or burn our skins, it can be harnessed to melt metals, or heat our food. Light energy posed a huge challenge for scientist up to the 1950’s. Hopefully, in the future, we will be able to use light energy and solar wind to travel among the stars.

We have written many articles about light energy for Universe Today. Here’s an article about the prescription for light pollution, and here’s an article about where visible light come from.

If you’d like more info on Light Energy, check out NASA’s Page on Atoms and Light Energy. And here’s a link to an article about How Photovoltaics Work.

We’ve also recorded an episode of Astronomy Cast all about Energy Levels and Spectra. Listen here, Episode 139: Energy Levels and Spectra.

Sources:
Johns Hopkins University
Wikipedia