Posted on by Tega Jessa

What are Photons

Faraday's Constant

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When we think about light we don’t really think about what it is made of. This was actually the subject one of the most important arguments in physics. For the longest time physicists and scientist tried to determine if light was a wave or a particle. There were the physicists of the eighteenth century who strongly believed that light was made of basic units , but certain properties like refraction caused light to be reclassified as a wave. It would take no less than Einstein to resolve the issue. Thanks to him and the work of other renowned physicists we know more about what are photons.

To put it simply photons are the fundamental particle of light. They have a unique property in that they are both a particle and a wave. This is what allows photons unique properties like refraction and diffusion. However light particles are not quite the same as other elementary particles. They have interesting characteristics that are not commonly observed. First, as of right now physicists theorize that photons have no mass. They have some characteristics of particles like angular momentum but their frequency is independent of the influence of mass They also don’t carry a charge.

Photons are basically the most visible portion of the electromagnetic spectrum. This was one of the major breakthroughs Einstein and the father of quantum physics, Planck made about the nature of light. This link is what is behind the photoelectric effect that makes solar power possible.Because light is another form of energy it can be transferred or converted into other types. In the case of the photoelectric effect the energy of light photons is transferred through the photons bumping into the atoms of a giving material. This causes the atom that is hit to lose electrons and thus make electricity.

As mentioned before photons played a key role in the founding of quantum physics. The study of the photons properties opened up a whole new class of fundamental particles called quantum particles. Thanks to photons we know that all quantum particles have both the properties of waves and particles. We also know that energy can be discretely measured on a quantum scale.

Photons also played a big role in Einstein’s theory of relativity. without the photon we would not understand the importance of the speed of light and with it the understanding of the interaction of time and space that it produced. We now know that the speed of light is an absolute that can’t be broken by natural means as it would needs an infinite amount of energy something that is not possible in our universe. So without the photon we would not have the knowledge about our universe that we now possess.

We have written many articles about photons for Universe Today. Here’s an article about how the sun shines, and here’s an article about why stars shine.

If you’d like more info on Photons, check out the Mass of the Photon. And here’s a link to an article about How Gravity Affects Photons.

We’ve also recorded an episode of Astronomy Cast all about the Atom. Listen here, Episode 164: Inside the Atom.

Source:
Wikipedia

Posted on by Tega Jessa

What Color is the Sky

Space Travel
Atlantis Breaks Through the Clouds

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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.

Posted on by Nancy Atkinson

Fleet of Solar Sail Spacecraft Envisioned for Future Data Gathering Missions

Artist concept of data clippers in space. Credit: Thales Alenia Space

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Future missions to explore the outer planets could employ fleets of ‘data-clippers’, maneuverable spacecraft equipped with solar sails, to ship vast quantities of scientific data back to Earth. According to Joel Poncy of satellite developer Thales Alenia Space, the technology could be ready in time to support upcoming missions to the moons of Jupiter and Saturn.

“Space-rated flash memories will soon be able to store the huge quantities of data needed for the global mapping of planetary bodies in high resolution.” said Poncy. “But a full high-res map of, say, Europa or Titan, would take several decades to download from a traditional orbiter, even using very large antennae. Downloading data is the major design driver for interplanetary missions. We think that data clippers would be a very efficient way of overcoming this bottleneck.”

Poncy and his team have carried out a preliminary assessment for a data clipper mission. Their concept is for a clipper to fly close to a planetary orbiter, upload its data and fly by Earth, at which point terabytes of data could be downloaded to the ground station. A fleet of data clippers cruising around the Solar System could provide support for an entire suite of planetary missions.

“We have looked at the challenges of a data clipper mission and we think that it could be ready for a launch in the late 2020s. This means that the technology should be included now in the roadmap for future missions,” said Poncy.

Spurred by the success of the Japanese Space Agency’s current solar sail mission, IKAROS, Poncy’s team have assessed the communications systems and tracking devices that a data clipper would need, as well as the flyby conditions and pointing accuracy required for the massive data transfers. Recent advances in technology mean that spacecraft propelled by solar sails, which use radiation pressure from photons emitted by the Sun, or electric sails, which harness the momentum of the solar wind, can now be envisaged for mid-term missions.

“Using the Sun as a propulsion source has the considerable advantage of requiring no propellant on board. As long as the hardware doesn’t age too much and the spacecraft is maneuverable, the duration of the mission can be very long. The use of data clippers could lead to a valuable downsizing of exploration missions and lower ground operation costs – combined with a huge science return. The orbiting spacecraft would still download some samples of their data directly to Earth to enable real-time discoveries and interactive mission operations. But the bulk of the data is less urgent and is often processed by scientists much later. Data clippers could provide an economy delivery service from the outer Solar System, over and over again,” said Poncy.

Poncy will be presenting an assessment of data clippers at the European Planetary Science Congress in Rome on Monday September, 20, 2010.

Source: European Planetary Science Congress

Posted on by Nancy Atkinson

LRO Finds Bridges on the Moon

A natural bridge on the Moon. Credit: NASA/GSFC/Arizona State University

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“Just when you think you have seen everything, LROC reveals a natural bridge on the Moon!” said Mark Robinson, Principal Investigator of the Lunar Reconnaissance Orbiter Camera (LROC), writing on the LROC website. “Who would have thought?” The natural bridge seen in this image is about 7 meters (23 feet) wide on top and perhaps 9 meters (30 feet) on the bottom side. Scientists estimate it would be a 20-meter (66-foot) walk to cross from one side to the other. While there are natural bridges here on Earth (which usually form as a result of wind and water erosion — see here for images of a natural bridge in Virginia in the US) how would such a natural structure form on the Moon? The answer might include another intriguing feature that has been found recently on the Moon: lava tubes.

Lunar bridge in 3-D. Image credit: NASA, GSFC/Arizona State University. Stereo image by Nathanial Burton-Bradford.

Robinson said the most likely way this feature formed is from a dual collapse into a lava tube. These are deep holes on the Moon that could open into vast underground tunnels, and could serve as a safe, radiation shielding habitats for future human lunar explorers.

There are actually a couple of these natural bridges that were found in just one region on the Moon, in the midst of an impact melt in the 15 km-wide King crater. Nathanial Burton-Bradford has created a few stereo images, which provide a unique perspective on these lunar bridges. Nathanial called the one below a “strange ‘twiglet’ ‘Monster Munch’ shape bridge.”

Another natural lunar bridge. Credit: NASA/GSFC/University of Arizona. Stereo image by Nathanial Burton-Bradford.

How can the lunar scientists be certain this feature really is bridge over a cavern? Look closely at the top image and in the pit on the west or left side, there is a small crescent of light on its floor. That patch of light came from the east, under the bridge.

Although Robinson and his team do not know for certain the details of how the bridge formed, here’s one possible scenario: The impact melt that was thrown out of the crater pooled on the newly deposited ejecta and must be many tens of meters thick, allowing its interior to stay molten for a long time. As the local terrain readjusted after the shock of the impact, the substrate of this massive pool of melt was jostled to some degree. Local pressures built up and the melt moved around under a deforming crust. You can see that the south end of the bridge extends from a small local rise, shaped something like a blister. Perhaps some melt was locally pushed up forming the rise, then the magma found a path to flow away, leaving a void which the crusted roof partially collapsed.

The LROC team is working on making their own stereo images, but in the meantime, thanks to Nathanial Burton-Bradford for providing us with a preview!

See more on the LROC website, and at Nathanial’s Flickr page.

Posted on by Nancy Atkinson

Satellite Images Show Hurricane Igor Likely to Make Direct Hit on Bermuda

Hurrican Igor as seen by one of the GOES satellites, taken on Sept. 19, 2010 at 17:15 UTC. Credit: NOAA

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The massive Hurricane Igor is now a Category One storm, with maximum sustained wind speeds of 140 km per hour, (85 miles per hour). As of this writing at 2:30 EDT, it looks as if it is on a direct collision course with Bermuda and is about 220 km (135 miles) southwest of Bermuda. The intensity of the storm has decreased over the past few days, but the size and rotation of the Igor means that Bermuda will be hit repeatedly as the arms of the hurricane spin over the 54 square kilometer (21 sq mi) island nation. In the satellite image above, Bermuda is the small white dot near the center of the image.

Projected track of Hurricane Igor. Credit: NOAA

Damaging sustained winds of hurricane force will reach the Bermuda late Sunday afternoon, and they will continue into early Monday morning. Wind gusts are predicted to be near or just over 160 km/hour (100 mph) as Igor makes its closest approach to Bermuda. Here’s a link to even more hurricane images.

The hurricane threatens to leave widespread tree damage and power outages in its wake. Some structures will also sustain damage; but fortunately, many buildings on Bermuda are made of stone with foundations into bedrock.

Flooding is also a serious concern across Bermuda. Igor will not only drop 4 to 8 inches of rain but will also trigger a 6- to 10-foot storm surge. Worsening the situation is the fact that waves pounding Bermuda will rise to heights in excess of 40 feet into this evening.

The massive size of Igor will cause the hurricane to keep battering the island well into Monday afternoon.

This 3-D image of Igor's cloud heights and rainfall from NASA TRMM satellite. Credit: Credit: NASA/SSAI, Hal Pierce

This 3-D image of Igor’s cloud heights and rainfall from NASA TRMM data shows a large area of heavy rainfall (falling at about 2 inches per hour) shown here in red on Sept. 15 at 0353 UTC. The yellow and green areas indicate moderate rainfall between .78 to 1.57 inches per hour. The image reveals that Igor’s eye was still very distinct but the southwestern portion of the eye wall had eroded.

Sources: NOAA, AccuWeather, JPL

Posted on by Steve Nerlich

Astronomy Without A Telescope – Not So Ordinary

The Small and Large Magellanic Clouds - not the kind of things you usually find near large spiral galaxies. Cerro Tololo observatory, Credit: Fred Walker.

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Sorry – a bit of southern sky bias in this one. But it does seem that our favourite down under naked eye objects are even more unique than we might have thought. The two dwarf galaxies, the Large and Small Magellanic Clouds, orbit the Milky Way and have bright star forming regions. It would seem that most satellite galaxies, in orbit around other big galaxies, don’t. And, taking this finding a step further, our galaxy may be one of a declining minority of galaxies still dining on gas-filled dwarf galaxies to maintain a bright and youthful appearance.

We used to think that the Sun was an ordinary, unremarkable star – but these days we should acknowledge that it’s out of statistical mid-range, since the most common stars in the visible universe are red dwarfs. Also, most stars are in binary or larger groups – unlike our apparently solitary one.

The Sun is also fortunately positioned in the Milky Way’s habitable zone – not too close-in to be constantly blasted with gamma rays, but close-in enough for there to be plenty of new star formation to seed the interstellar medium with heavy elements. And the Milky Way itself is starting to look a bit out of the ordinary. It’s quite large as spiral galaxies go, bright with active star formation – and it’s got bright satellites.

The Lambda Cold Dark Matter (CDM) model of large scale structure and galaxy formation has it that galaxy formation is a bottom-up process, with the big galaxies we see today having formed from the accretion of smaller structures – including dwarf galaxies – which themselves may have first formed upon some kind of dark matter scaffolding.

Through this building-up process, spinning spiral galaxies with bright star forming regions should become common place – only dimming if they run out of new gas and dust to feast on, only losing their structure if they collide with another big galaxy – first becoming a ‘train wreck’ irregular galaxy and then probably evolving into an elliptical galaxy.

The  Lambda CDM model suggests that other bright spiral galaxies should also be surrounded by lots of gas-filled satellite galaxies, being slowly draw in to feed their host. Otherwise how is it that these spiral galaxies get so big and bright? But, at least for the moment, that’s not what we are finding – and the Milky Way doesn’t seem to be a ‘typical’ example of what’s out there.

The relative lack of satellites observed around other galaxies could mean the era of rapidly accreting and growing galaxies is coming to a close – a point emphasised by the knowledge that we observe distant galaxies at various stages of their past lives anyway. So the Milky Way may already be a relic of a bygone era – one of the last of the galaxies still growing from the accretion of smaller dwarf galaxies.

Supernova 1987a, which exploded near the Tarantula Nebula of the Large Magellanic Cloud. Credit: Anglo-Australian Observatory.

On the other hand – maybe we just have some very unusual satellites. To a distant observer, the Large MC would have nearly a tenth of the luminosity of the Milky Way and the Small MC nearly a fortieth – we don’t find anything like this around most other galaxies. The Clouds may even represent a binary pair which is also fairly unprecedented in any current sky survey data.

They are thought to have passed close together around 2.5 billion years ago – and it’s possible that this event may have set off an extended period of new star formation. So maybe other galaxies do have lots of satellites – it’s just that they are dim and difficult to observe as they are not engaged in new star formation.

Either way, using our galaxy as a basis for modelling how other galaxies work might not be a good idea – apparently it’s not so ordinary.

Further reading: James, P. A. And Ivory C.F. On the scarcity of Magellanic Cloud-like satellites.

Posted on by Jon Voisey

The Case of the Missing Bulges

The Hubble sequence is astronomer’s main tool for classifying galaxies. On one side, you have elliptical galaxies with defined structure. As you progress, the galaxies become more stretched out, but still lack definition until suddenly, there’s a bulge in the center and spiral arms! Oh yeah, and then there’s the cousins that no one really likes to hang out with, the “irregular” galaxies, hanging out in the corner.

But there’s another class of galaxies that seems to have fallen off the Hubble wagon. Some spiral galaxies seem to lack defined bulges. These oddities pose a challenge to our understanding of galactic formation.

The current understanding of galactic formation is one of hierarchical merging. Small dwarf galaxies form first, and then form bigger galaxies which merge and continue to eat more dwarf galaxies until a fully fledged galaxy is formed. However, the collisional nature of this formation tends to scatter stars, favoring random orbits towards the center of flattened galaxies, which should create a classical bulge. Galaxies that do not have a bulge, or have a “pseudobulge” (small bulges created by gravitational sorting of stars within an already formed galaxy) don’t seem to fit this picture.

A recent review suggests that galaxies without true bulges are in fact common and include many well-known galaxies such as M101 (the Pinwheel Galaxy) and M33. The team, led by John Kormendy of the University of Texas, Austin, conducted a survey of spiral galaxies in the Local Group to determine just how common they were. To determine the status of the bulge, the team analyzed the physical size of the bulge, its luminosity as a fraction of the overall light output, and the color/age of the stars therein. Bulges that were small, indistinct, and contained stars similar to the color/age of the stars found in the disk were considered examples of the psuedobulges. Ones with significant, bright, and distinctly redder/older bulges were indicative of what would be expected in the classical merger bulge.

The team determined that as much as 58-74% of their sample did not contain a classical bulge. Furthermore, they state, “Almost all of the classical bulges that we do identify – some with substantial uncertainty – are smaller than those normally made in simulations of galaxy formation.” Indeed, included among these galaxies is our own Milky Way which has a very odd, box shaped bulge. The team notes that the velocity distribution of the apparent bulge merges seamlessly into the disk portion of the galaxy as opposed to a discontinuous fit in classical bulges.

Kormendy’s team finds that one way to form such “pure-disk” galaxies is to allow for the possibility of early star formation. According to the paper, this would “give the halo time to grow without forming a classical bulge.”

These findings stand in strong contrast with a study published by the same group in 2009, analyzing the Virgo cluster of galaxies. In that study they found that classical bulge galaxies (including in this study, elliptical galaxies) seemed to dominate. As such, they suggest that the formation of bulges is somehow related to the local environment. Although the question cannot yet be answered, it begs the question for future study: What about our environment is so special that we can form galaxies in a non-merger process? The answer to this question will require further study.

Posted on by Nancy Atkinson

Review: “Packing for Mars” (and win a copy, too!)

'Packing For Mars' by Mary Roach

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What happens if you vomit in your helmet during a spacewalk? Is it really difficult to burp in space? What happens if you don’t walk for a year? Is it possible for the human body to survive a bailout at 17,000 miles per hour? Which would be worse if you spent a year in space: not being able to have sex or not being able to have a beer? If questions like this keep you up at night, you really need to read Mary Roach’s new book, “Packing for Mars: The curious science of life in the void.” The book takes a look at the challenges of sending the human body – with all its requirements and desires — into space.


The life of an astronaut in space really isn’t very glamorous at all, and the topics Roach covers aren’t always the first things people think about when pondering the requirements for spaceflight. “Not the parts you see on TV, the triumphs and the tragedies, but the stuff in between,” she writes “ — the small comedies and everyday victories. What drew me to the topic of space exploration was not the heroics and adventure stories, but the very human and sometimes absurd struggles behind them.”

Yes, going to the bathroom in space is very much a part of this book. But there’s also things like how it took major research to figure out the politically correct way to plant a flag on the Moon.

To research her book, Roach toured the gamut of space research facilities and simulated space stations and ends up finding that space exploration is very much an exploration of what it means to be human. Though there is plenty of silliness and hilarity in this book, it also considers how humanity’s efforts to understand the great void have produced awe-inspiring results, such as the landing of a delicate scientific instrument upon the surface of Mars, more than 400 million miles away. As Mary Roach ultimately discovers, “space doesn’t just encompass the sublime and the ridiculous. It erases the line between.”

Mary Roach is the author of Stiff: The Curious Lives of Human Cadavers, Spook: Science Tackles the Afterlife, and Bonk: The Curious Coupling of Science and Sex.

Want to win your own copy of Packing for Mars? Universe Today has 5 copies to give away! Send an email to [email protected] with “Mary Roach Book” in the subject line and Fraser will randomly pick the winners. Deadline for entry is Tuesday, September 21, 2010. We’ll notify the winners by email.

For more information on the book, see Mary Roach’s website, or Amazon.com

Posted on by Jerry Coffey

What Is The Largest Island In The World

Greenland. Image credit: NASA
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

Posted on by Jerry Coffey

What Is The Largest Continent

Asia Image Credit: NASA's Blue Marble project
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