Rosetta

Rosetta was a space probe launched by the European Space Agency whose mission is to orbit the comet 67P/Churyumov-Gerasimenko (comets are named as a combination of their catalogue number and their discoverers) and study it to learn more about the Solar System's origins.

This space probe consisted of two parts: Rosetta, the main spacecraft, and Philae, the lander that landed on the comet.

Rosetta was originally planned for launched in 2003, to study a totally different comet. But the launch was delayed, and a new trajectory was conceived. Rosetta was launched by the European Space Agency on March 2, 2004, beginning its hugely complicated series of flybys in space. No rocket could propel the spacecraft directly to the comet, so Rosetta's trajectory had to be long and complex. The first encounter was an Earth flyby, about a year after launch on March 4, 2005, where Rosetta tested its instruments and received a gravitational pull which sent it on orbit that would take it close to Mars. On February 25, 2007, Rosetta made a successful flyby of Mars, and it was set towards the Earth once again. As Rosetta approached the Earth for the flyby of November 13, 2007, an astronomer mistook the spacecraft for a small asteroid, about 75 feet in diameter, and predicted that it would pass within only a few thousand miles of the Earth. This caused momentary panic, until its track was recognized as Rosetta's.

After its second Earth flyby, Rosetta flew by by an asteroid, 2867 Steins, but did not use many instruments on it, to save most of its memory for the comet encounter. The asteroid was only about 2.5 miles across and Rosetta approached within 480 miles of the body on September 5, 2008. Although not much information was gathered on the asteroid, its orbit was verified more accurately than ever before.

Rosetta then made its last flyby of Earth on November 13, 2009.

On July 10, 2010, the probe encountered the asteroid 21 Lutetia. At its closest approach Rosetta was only 1960 miles away, and a significant amount of data was gathered. The ongoing analysis of this data will determine the composition of the asteroid. In addition, the exact orbit characteristics, mass, and rotation have been obtained, as well as many photographs.

Rosetta's image of the asteroid 21 Lutetia at closest approach.

After the second asteroid encounter, Rosetta shut off its systems in deep space in order to save its energy for the comet encounter. This stage is known has "Deep-Space Hibernation" and it began in May 2011. In total, this stage lasted for almost three years and ended on January 20, 2014. On this date, Rosetta sent a signal indicating that the hibernation had been successful and the spacecraft's systems were functioning normally. By this time, the comet had passed its apogee and it was once again approaching the Sun, so that Rosetta was close enough to power itself on the star's energy.

Even then, though, both the spacecraft and the comet were traveling relatively slowly. Rosetta began observations in January of that year as it approached the comet. In May, Rosetta began a series of maneuvers to prepare to orbit the comet. At the same time, a halo began to develop around the comet as it approached the Sun. The following image from early May shows this halo, or coma. This coma forms from sublimating ice and the release of gas trapped inside the comet's nucleus. In late June 2014, Rosetta measured that about 2 glasses of water a second were released from the comet in the form of vapor. This rate increased as the comet approached the Sun.

On July 14, Rosetta was close enough to obtain images of the body of the comet, revealing an unusual two-lobed structure (above). Images continued to increase in resolution as Rosetta approached.

Through July and early August 2014, the spacecraft continued to use fuel to decrease its speed relative to 67P/Churyumov-Gerasimenko, since orbit around such a small body ultimately required Rosetta's relative speed to the comet to be only 1 m/s (a typical walking speed)! In addition, Rosetta took its first temperature and surface readings. On August 6, 2014, Rosetta became the first spacecraft to ever enter orbit around a comet.

Rosetta had moved within 60 miles of the comet by this time, and began to map the surface with high-resolution imagery (such as the image above) to identify possible landing sites. By the end of August, 5 possibilities for a landing site had been chosen. During September, Site J, which the white plus sign marks on the image below, was selected for landing. In early November, this site was renamed "Agilkia" after an island on the Nile river.

On the days leading up to landing, Rosetta altered its orbit to release trajectory. During the morning of November 12, separation of Rosetta and Philae was confirmed. Seven hours later, the lander successfully touched down at the Agilkia site, but its harpoons did not activate, and the lander bounced twice, ultimately landing about a kilometer away from its original intended site.

Philae took images, such as the above, showing the comet from 40 m above during its initial descent.

Upon its final descent, Philae unfortunately landed on its side, with most of its solar panels facing the ground or in shadow. On November 15, after using its battery for 57 hours, the lander entered hibernation. However, during its 57-hour period of activity, Philae successfully used all 10 of its scientific instruments. This included a drill, which chemically analyzed a sample from the comet's surface and relayed the data to Earth via Rosetta. Notably, Philae did detect the presence of organic molecules on the comet's surface.

Important observations continued to pile up from the Rosetta orbiter over the next several months. During December 2014, Rosetta measured the composition of water vapor released from the comet as it approached the Sun. This vapor had more deuterium (the isotope of hydrogen with one neutron) than the water found on Earth. The measurement suggested that comets such as 67P/Churyumov-Gerasimenko (theoretically originating in the Kuiper Belt near Pluto) may not have been the primary source of water for Earth's oceans, which were likely filled by impacting solar system bodies.

In February 2015, as the comet continued to approach the Sun and grow more active, Rosetta departed its near circular orbit and positioned itself for several close flybys to collect gas released from the comet. The first of these flybys took place on February 14 at a distance of less than 4 miles!

Rosetta took the above image of the two-lobed comet on March 14, 2015. It has been enhanced to indicate the increasing volume of dust and gas streaming from the comet as it approached perihelion.

The same month, Rosetta also completed the first ever detection of molecular nitrogen at a comet. This offered crucial information as to the comet's origin, because molecular nitrogen can only become trapped within a comet's ice at very low temperatures. Therefore, the measurement supported the theory that 67P/Churyumov-Gerasimenko originated in the Kuiper Belt. During the spring, researchers also used data from both Rosetta and Philae to conclude that the comet was not significantly magnetized, the first such measurement for a comet. This was significant because iron was a major component of protoplanetary dust and some models indicated that assembled objects would have been magnetized in the early Solar System. The result gives another way to test theories of the formation of the Solar System.

During June, communication with the lander Philae was sporadically established as its solar panels were illuminated. However, no more investigations were able to be made. Later that month, the ESA officially granted an extension to the Rosetta mission through mid-2016.

The above images show the higher comet activity as it approached perihelion. The comet's closest approach to the Sun did not take it inside Earth's orbit, but it reached a minimum distance of 1.28 AU on August 13, 2015.

The mission continued to yield new results after perihelion had passed. For instance, using data from July 2015, it was able to measure and investigate the size of the diamagnetic cavity surrounding the comet's nucleus. This cavity is a region where the gas streaming off of the comet deflects incoming charged particles from the solar wind. Assuming the comet itself is not magnetized (which Rosetta determined it wasn't), this region should be free of magnetic fields. However, it only becomes appreciable in size near perihelion, when more material is ejected from the comet.

The above chart shows the magnetic field measured by Rosetta during a period of a few hours on July 26, 2015. The blue highlighted region (in which the field is nearly 0) corresponds to when the spacecraft passed through the diamagnetic cavity along its orbit. Rosetta passed into the edges of the cavity many times, allowing for detailed measurements of its size.

Continued analysis of data from near perihelion in August indicated that certain organic substances were present on Rosetta, including glycine, the simplest of the amino acids. Though the discrepancy in isotope ratios discussed above indicates that comets of this exact type did not transport these compounds to Earth in its early history, it supports the general claim that glycine can originate from comets, a conclusion hinted at by earlier study but never unambiguously verified.

Data from the probe indicated that the comet "breathed out" primordial oxygen near perihelion; that is, heating up the body of 67P released gases that had been trapped there for billions of years. While other mechanisms had been proposed for the molecular oxygen found around the comet, the Rosetta mission verified that a majority must have appeared via this process.

On September 5, 2016, as Rosetta began its final approach toward the comet, it spotted the lander Philae from a distance of 2.7 km after its precise location had not been known for two years! The image below has an astonishing resolution of 5 cm/pixel, and shows the lander in the bottom right, wedged in a crack. This explains why Philae was not able to operate under solar power after its landing.

Late on September 29, 2016, Rosetta's thrusters fired for the last time, sending it on a collision course with the comet. The spacecraft continued to transmit valuable data and images during its descent, taking advantage of its only opportunity to collect information from such a low altitude above the comet. The last image transmitted from Rosetta, shown below, was taken at an altitude of only about 20 meters, just before impact. The final impact occurred on September 30, ending communication with the probe.

The 12-year Rosetta mission provided invaluable knowledge about the structure, composition, and evolution of the comet 67P, and through it a better understanding of the formation of our Solar System billions of years ago. Comets are among the most pristine of time capsules for investigating the beginning of the Solar System as well as possible sources of water and other important molecules on Earth. The Rosetta mission will continue to shape our conception of our origin for years to come.

Sources: (Photos from ESA) ESA-Rosetta, http://en.wikipedia.org/wiki/Rosetta_(spacecraft),http://www.bbc.com/news/science-environment-27498534, http://www.astronomy.com/news/2014/07/the-twofold-comet-comet-67pchuryumov-gerasimenko, http://www.esa.int/Our_Activities/Space_Science/Rosetta/Rosetta_arrives_at_comet_destination, http://www.esa.int/var/esa/storage/images/esa_multimedia/images/2014/09/philae_s_primary_landing_site/14819792-1-eng-GB/Philae_s_primary_landing_site.png, http://www.esa.int/Our_Activities/Space_Science/Rosetta/Rosetta_s_comet_contains_ingredients_for_lifehttp://www.esa.int/Our_Activities/Space_Science/Rosetta/Rosetta_and_Philae_find_comet_not_magnetised, http://www.esa.int/Our_Activities/Space_Science/Rosetta/Rosetta_finds_magnetic_field-free_bubble_at_comet,http://www.esa.int/Our_Activities/Space_Science/Rosetta/Rosetta_s_comet_contains_ingredients_for_life, http://www.esa.int/Our_Activities/Space_Science/Rosetta/Mission_complete_Rosetta_s_journey_ends_in_daring_descent_to_comet

Tornadoes

This is the second part of a two part post. For the first part see here.

Simple thunderstorms are simply clouds developing at a frontal boundary, and these are the most common, but other, more complicated types also exist.

Although some thunderstorms from exclusively on the frontal boundary, many spawn other thunderstorms miles, or even tens of miles away whenever there is warm, humid air present. This is because thunderstorms cause downdrafts, or cool air to flow down from upper altitudes. When this air hits the ground, it spreads out and flows parallel to the ground. This moving air can help to create new thunderstorms in two different ways. Either the cold air pushes the warm air up, and as we already know, a warm updraft causes thunderstorms, or, a cool wind gust can encounter another one, and they push each other up, creating additional thunderstorms.

In many cases, thunderstorms are composed of individual units, called cells. These cells form and die in minutes, but as one dies, its downdrafts produces another cell, and on. The progression of these cells tend to move because cells form in humid air at the boundary of air masses, and as the boundary moves, the area of formation moves. However, there are cells that form in a more independent way then this.

The most powerful type of cell is known (rather appropriately) as the supercell. Like a normal cell, the supercell has an updraft fueling its development: a mesocyclone. A mesocyclone is a rotating column of air that feeds the storm with the moisture and rotation it needs to be powerful. A mesocylone is typically between 1 and 5 miles in diameter and can extend up to 10 miles in to the sky. It forms when strong high altitude winds and weak ground winds blow past each other, creating a tube of air. An updraft lifts this tube, and it eventually breaks into two tubes, one spinning clockwise, the other counterclockwise. Due to the Coriolis Effect, the clockwise column is neutralized in the northern hemisphere and the counterclockwise column is strengthened, while this is reversed in the southern hemisphere.

Once the mesocyclone has formed, if there is a frontal boundary present, a colossal anvil shaped cumulonimbus cloud is formed, often stretching over 60,000 feet into the air! Warm middle layer winds feed the cyclone, while upper level winds spark fierce downdrafts. In addition, the supercell creates such a temperature difference in the air, that its downdrafts create their very own mini-frontal boundary. All this, coupled with the powerful mesocyclone at the center, brings heavy rain or hail for hours, and a supercell can travel over 300 miles before dying out.

As if this wasn't enough, sudden huge downdrafts called microbursts can also form during the duration of a supercell. Often, this downdraft pushes down another coil of air spinning parallel to the ground, again forming two columns. The counterclockwise swirl near the ground is expanded by updrafts to form one huge rotating air mass, from the ground way into the clouds. This is the tornado.



Tornadoes are immensely powerful and are actually, contrary as it is to common belief, invisible. Only when debris is picked up by the tornado does it assume a color and this depends totally upon the terrain. Tornadoes range from virtually harmless to incredibly deadly and can last from seconds to hours. Also, multiple tornadoes can come from one mesocyclone and often orbit around each other within it, assuming the form of a funnel cloud, which appears to be one tornado and can be largely hidden among clouds until it hits.



A funnel cloud hidden in the atmosphere. There is a vague suggestion of a rotation in the cloud structure, but there is no obvious tornado, like there is above.

Although a majority of tornadoes are spawned from supercells, some do not. It is possible for a weak tornado to develop from a regular thunderstorm, but this is uncommon, and a tornado in this situation is usually so weak that it is virtually undetectable. In some cases, tornadoes also from over water, forming what is known as a waterspout. As with land tornadoes, the waterspout assumes the color of water, and in most cases, appears blue. Some waterspouts have been known to develop mysteriously in fair weather, but most, known as tornadic waterspouts, form in thunderstorms. Hurricanes can be a source of tornadoes and waterspouts, when circulations form in their thunderstorm bands, and some hurricanes have caused over 100 tornadoes! Three Atlantic hurricanes have attained this: Hurricane Beulah in 1967, with about 115, Hurricane Frances in 2004, with 103, and Hurricane Ivan in 2004, with 117. Of Frances's tornadoes, 6 were considered significant, or with winds exceeding 110 mph, and Ivan had 19 significant tornadoes.



A waterspout off Florida's coast.

Also, dust devils, or swirling gusts of wind, can form in a dry environment, usually a desert. One last type of rotating mesocyclonic structure is a "fire whirl" or "steam devil". If there is a significantly heated environment, as in a fire, or heated water, the updrafts caused by the heated air can be strong enough to start a mesocyclone. The latter types of rotating mesocyclonic structures are not associated with thunderstorms, but are related since they are similar to tornadoes. They are usually weak in comparison to a real tornado.



A dust devil that formed in Nevada. Note the fair weather conditions.

Until recently, most areas used the Fujita scale to measure tornado strength. However, the U.S. thought the categories and their respective damages educated guesses at best, and the scale was changed into what is now known as the Enhanced Fujita Scale.



A comparison of the original Fujita scale introduced in 1971, and the new Enhanced Fujita Scale, which was first used in 2007. Although the Fujita scale covers a higher range of wind speeds, the Enhanced version gives more accurate damage information, and considers that anything under 65 mph is not a tornado at all, but perhaps a spinning funnel cloud that doesn't reach the ground.

The most powerful tornado recorded had peak winds around 300 mph, and wreaked havoc in Oklahoma City in 1999. This tornado also caused the second most damage of any single one, with adjusted damages of $2 billion. However, a tornado in 1896 has the greatest adjusted damage value, at a stunning $2.9 billion. In terms of width, one tornado had a damage path width of 2.5 miles in 2004. In terms of path length, the infamous Tri-State Tornado is the record holder, traveling 219 miles over three states, Missouri, Illinois, and Indiana. It also holds the record for the deadliest U.S. tornado with 695 deaths recorded. The huge F5 tornado wreaked havoc in 1925. In the world, the deadliest tornado probably belongs to the Bangladesh 1989 tornado which took an astounding 1300 lives. Finally, the largest tornado outbreak occurred in 1974, on April 3 and 4 of that year. An extremely powerful system spawned an amazing 148 tornadoes recorded and probably more weak ones going unrecorded. Among these, 23 were F4 and 6 were F5! The number of major tornadoes was simply unheard of, and this outbreak is still, after over 35 years, the largest one in history.



All of the tracks of the tornadoes in the Super Outbreak of 1974. They are numbered in order of development, from 1 to 148.

There have been many exceptional tornado oddities, most involving debris and people being picked up and placed back down unharmed. There have been many claims of this type and some have been disputed. For more information, see here.

Tornadoes are among the most violent weather events on the Earth, and they are the most deadly, there being no accurate way to predict them. Although tornado watches and warnings are put into effect when there is a risk or a sighting of a tornado, these can only be given a few minutes in advance. Climatology wise, tornadoes occur in various parts of the world. As well as the U.S. southern Canada and northern Mexico, much of Europe, South Africa, areas of Argentina, Australia, and Eastern Asia also experience tornadoes regularly.

Currently, Earth is the only celestial body on which tornadoes have been detected. There are rotating systems on other planets, such as Jupiter (the Great Red Spot and various other systems), and many of these may feature mesocyclones, but no real evidence for extraterrestial tornadoes has been collected.

Sources: The Weather Book by Jack Williams, http://www.srh.noaa.gov/mfl/?n=waterspouts, http://www.nssl.noaa.gov/edu/safety/tornadoguide.html, National Hurricane Center

Introduction to Tornadoes: Thunderstorms

Thunderstorms are powerful rain storms that usually have heavy rain, wind, thunder, and lightning associated with them. For a specific post on thunder and lightning, see here.

A thunderstorm is caused by a low pressure system, usually extratropical in nature. An extratropical low is one that is not tropical. A tropical low is usually a tropical storm or hurricane. Furthermore, extratropical lows are usually asymmetrical, and most rainfall with them comes with frontal boundaries. There are two main types of frontal boundaries, cold and warm. For convenience, a brief description is described below.

A cold front is an area of cold air advancing against an area of warm air. The warm air, being lighter, is pushed up. At this boundary, moisture forms, causing clouds. In a cold front, the clouds start low, and billow upward, as the cold air pushes higher up into the sky. The clouds often reach five miles in height and are then called cumulonimbus clouds. Heavy rain or even hail fall form these clouds. Then, as the boundary moves on, the clouds expend all their moisture into rain and dissipate.



A warm front is an area of warm air advancing against an area of cold air. Unlike a cold front, the effects of a warm front start at high altitudes as the warm air pushes the cold from above. The first clouds are usually high-level, such as cirrus or cirrostratus. Then, as the warm front continues to advance, the clouds come at lower altitudes, typically ending in the low altitude nimbostratus cloud. Lighter rain, or, if in winter, snow, can fall from these clouds. Then, as the clouds empty out their moisture, the clouds thin, sometimes ending in a white stratus cloud.



There are other types of fronts as well, that are not as well known. One is the stationary front, which is as boundary of cold and warm air in which neither is advancing. There is usually little storm activity associated with these fronts. Another rarer type of front is the occluded front, where a cold front catches up and combines with a warm front, ending in a boundary of cold and cool air. Since the difference in air temperature is less prominent in these systems, the fronts usually subsequently dissipate.

An area of thunderstorms form in a line, usually along a cold frontal boundary. Along this front, a squall line forms. A squall line is a thin area of heavy rain and wind that trails from a low pressure system, often hundreds of miles away.



A low pressure over northwestern Pennsylvania and an accompanying squall line to the south.

The internal structure of the thunderstorm is one of rising air. Usually warm air on the surface rises, cools, forms a few cumulus clouds, and then sinks when it cools to past the temperature of the surrounding air. However, in a cold frontal boundary, abnormally warm air is rising into cold air, and it therefore does not stop. The clouds continue upwards until they reach cumulonimbus stage, where the air finally cools and sinks. A healthy thunderstorm is a series of updrafts and downdrafts balancing each other out. The downdrafts help water particles to condense and become rain. However, although contrary to what would be thought at first glance, hail forms during the warmer seasons, when there are thunderstorms. Hail forms when water droplets form in the part of the cloud where the temperatures are below freezing. The updrafts send the ice higher into the cloud, until the plummet, attach to other droplets in the lower atmosphere, and then are swept up again. This continues until the ice droplets get heavy enough to fall. In strong updraft conditions, hail can reach over half a foot in diameter and weigh over a pound.

Another uncommon occurrence with thunderstorms is thundersnow, which is a thunderstorm at below freezing temperatures. These are rare, because thunderstorms are prevalent in the warm seasons. This is because there is a greater difference between ground temperatures and atmospheric temperatures and air can more easily stay warmer than surrounding air. As a result, cold fronts are generally strong in summer and weak in winter, whereas warm fronts are generally strong in winter and weak in summer.

Most of the time, thunderstorms are relatively simple systems. However, when a tornado forms, the situation is much more complex. Tornadoes are discussed in the next part of this post, see here. For more information on particularly intense thunderstorms called derechos, click here.

DNA and RNA as the Basis of Evolution

DNA is familiar to most people as our genetic code, the stuff that makes us who we are. Although this is true, it does not nearly encompass all that DNA is responsible for.

In humans, you must travel into any organ, such as the heart, find a tissue, such as heart tissue, and find cells within that tissue. The cells, on their own, are as complex as some organisms. But within the cell, we must magnify even further, and find the blob in the center that is known as the nucleus. Inside this nucleus, we encounter DNA wrapped and doubled up upon itself many times to form X-shaped structures called chromosomes. The human body contains 46 of these chromosomes in each cell, and each one has a much longer DNA strand (n fact, uncoiled, the DNA in a chromosome stretches 10,000 times longer). To fully understand of what importance DNA is, one must understand the structure of DNA.

DNA, short for deoxyribonucleic acid, is in the form of a double helix, which resembles a twisted ladder. The sides of this twisted ladder are made of deoxyribose, which is a sugar. The "rungs" of this ladder are called base pairs and there are four types. These types are cytosine, adenine, guanine, and thymine. These are abbreviated C, A, G, and T, respectively. These four are DNA bases. The bases A and T, and the bases C and G, always bond at a molecular level to form each "rung".



A diagram of DNA labeling each of the base pairs.

DNA is present in all known living organisms, which suggests that DNA would be behind the origin of life. However, another component of the cell is needed to aid DNA for life to continue. This component is the all-important enzyme. Most enzymes are proteins, and they are responsible for many of the chemical reactions that occur in the body. Remarkably, the combination, breaking down, and transforming of chemicals within the body is controlled by enzymes. For example, the breaking down of food in the stomach is attributed to acids, but the breaking down of chemicals at a molecular level is handled by the enzymes. In fact, DNA is dependent on enzymes for its very survival! Enzymes help to split DNA and later replicate it and even "check" for errors in the DNA strand, which lowers the number of mutations and changes that occur, which, if left alone, have the potential to cause disease and genetic disorders. In conclusion, enzymes are, along with DNA, a huge success in evolution that has developed remarkably over the last few billion years.

Despite the fame and omnipresence of this remarkable pair, DNA and enzymes are not believed to have been the basis of life on Earth. The most widely believed hypothesis has RNA present before DNA and enzymes, and all the simple life forms that only had RNA have been extinct for several billion years. But first, a brief (or possibly not so brief) word about RNA.

RNA is another acronym, standing for ribonucleic acid. This name is the same as deoxyribonucleic acid, except without the "deoxy". As explained previously, the sides of the double stranded DNA ladder are made of deoxyribose. This differs from RNA, because RNA is single stranded, with the strand made of ribose. Due to the absence of a second strand, the base pairs of RNA are just hanging off of it, which makes RNA more unstable, but it also has its advantages. The final major difference is that one of the base pairs, thymine, is absent, and replaced by uracil (U). The new base uracil still bonds with adenine (A) to make a base pair. The unique structure of some types of RNA allows the strand to fold over on itself, forming a double helix shape with a "hairpin" on the end.



In this image, a section of RNA is starting to fold up upon itself.

However, the single stranded nature of the RNA molecule provides many more benefits that to simply fold up upon itself. It can also attach to other RNA strands, and that is where the different types of RNA come in. There are three main types of RNA: messenger, transfer, and ribosomal RNA. Although there are other types, the three above will be sufficient to explain the main purpose of RNA.

Messenger RNA, abbreviated mRNA, contains the genetic code needed for synthesizing chemicals, mainly amino acids, which make up the center of a protein. The genetic code is a sequence of base pairs, just like in DNA. Transfer RNA, abbreviated tRNA, "reads" the genetic code from the mRNA by attaching itself to the mRNA and matching up the base pairs. Together, tRNA and mRNA create the many different types of amino acids using their genetic code to cause chemical reactions. The amino acids are transported by the tRNA, hence their name, to the site of protein formation, the ribosome. The ribosome (one of the main parts of a cell) contains ribosomal RNA, abbreviated rRNA, which develops the "meat" of a protein, the amino acid being a main component. The tRNA carries the amino acid into the rRNA's construction area by attaching to the rRNA, therefore creating a finished protein.

From the above information one can conclude that although DNA and enzymes are better at their individual jobs, RNA is more flexible, capable of both carrying a genetic code in a double helix form and starting chemical reactions that produce important parts of a living thing, amino acids, and completed proteins. Therefore, RNA is hypothesized to be present without DNA and enzymes in the simplest forms of life, some of them, without a cell. We define "living things" as things with cells, which isn't necessarily an accurate definition. Although there is no absolute information from the era of the first living things (which was from 3-4 billion years ago), we can speculate on events that lead to the first single celled organisms, some of which survive today.

The only thing surviving from the era that could be a living thing but isn't considered one is the virus. The virus isn't an organism by our standards because they don't contain cells. They do reproduce, which is another requirement for being a living thing, but it cannot reproduce on its own; it needs a host cell to infect with its genetic material. The encoded genetic message tells the cell to make for viruses, therefore spreading the virus. Viruses, on their own, are mere balls of genetic material, some types have DNA and some types have RNA, surrounded by protein. My personal opinion is that life can exist without cells, and that life, if started on other planets besides ours, could lack cells as well.

The moral of this story is that for all terminology, including "living thing" "mammal" (the main debate here is the platypus, which lays eggs, but is still considered a mammal) and even "planet" (Pluto. The rest is history) does not draw a distinct line classifying things. Things that possess RNA could be considered living, some (not many, but some), consider everything with atoms "living" in a sense. At this point, "living" is not an appropriate word, and should be replaced by "has the potential for living when grouped together with enough of its own kind". Nothing in this realm is clear, and it cannot be solved. By dropping terminology though, we can say that RNA is the basis of the first organisms that have set the stage for all bacteria, protists, plants, fungi, animals, and ultimately, us.

Sources: http://dl.clackamas.edu/ch106-08/enzymes.htm, http://www.uic.edu/classes/phys/phys461/phys450/ANJUM04/RNA_sstrand.jpg (image), http://www.elmhurst.edu/~chm/vchembook/583rnatypes.html, The Ancestor's Tale by Richard Dawkins.

Irrational Numbers

Of the infinite set of numbers, the most known are the counting numbers, 1,2,3... The negative numbers and zero are combined with the counting numbers to form the wider set of integers. Integers can be divided to form fractions, therefore expanding the system to rational numbers.

All of the above is common knowledge, but the number system can be further expanded by taking the infinite sum of a convergent sequence of rationals, or, more commonly, simply taking the square root of a non-perfect square. Either method results in a number that has an infinite decimal expansion that never repeats. Mathematically, this means that the number cannot be expressed as a fraction. Numbers of this type are called irrational numbers.

Irrational numbers can also be subdivided further into two groups: the algebraic irrationals, and the transcendental irrationals. The algebraic irrationals are simply the ones that solve a polynomial equation with integer coefficients. This simply means any equation like x^2+3x+5=0, x^5-97x^3+4=0, etc. Other numbers can also be algebraic, and all rational numbers are. (for equations like 3x-2=0, the solution is 2/3. All fractions, and therefore all rationals, can be expressed this way) It is also obvious why square roots are algebraic, they all fit equations of the form x^2=n, where the solution will always be the square root of n. Cube roots, and all other roots come about in the same way. Finally, all numbers of the form a+square root of b can be reached by means of the quadratic formula. Some other irrationals are algebraic as well, but it is a lot less obvious.

Transcendental numbers are all irrational, and these are simply the remaining numbers that do not fit the above category. Among these are π (pi), e, and any nonzero powers of either of them. There are still some numbers, like the square root of two to the power of the square root of two, π-e, and others that it is not known whether they are algebraic or transcendental.

Another method for representing the irrational numbers is the continued fraction. A continued fraction looks like this:



In the above picture, the first constant a0 must be an integer, and the remaining numbers must be positive integers. If this conditions are filled, the expression is a continued fraction. Continued fractions can represent all real numbers, rational and irrational (technically, complex numbers are the sum of two continued fractions, one real, one imaginary). Unlike decimal expansions, where rational numbers can go on forever (Ex. 1/3=.333333...) every continued fraction for a rational number is finite, meaning that there are a limited number of constants in the continued fraction. Conveniently, all irrational numbers have infinite continued fractions. The continued fraction for the square root of 2 has the constants 1,2,2,2,2,2... with the two repeating indefinitely. Another interesting property of continued fractions is that the constants of a algebraic irrational number repeat (Ex. square root of three has constants 1,1,2,1,2,1,2,1,2) while transcendental irrationals have a non-repeating sequence of constants (Ex. π has the constants 3, 7, 15, 1, 292, 1, 1, 1, 2, 1...). In a sense, the number is a irrational irrational!

There are infinite irrational numbers, but three notable ones are listed below.

π (pi)
A detailed article on pi in available elsewhere on this blog, see here.

e
Type: Transcendental irrational
Decimal Expansion: 2.71828182845904523536...
Continued Fraction Constants: 2,1,2,1,1,4,1,1,8,1,1,16...(this sequence of constants does have a pattern, but it still does not repeat, making e a transcendental irrational)
Description: The constant e is important in many aspects of mathematics, particularly calculus, and it appears in many functions. e is the limit of the function (1+1/x)^x as x approaches infinity and is the base of the function e^x, which is the only function of x that when differentiated stays the same. e is also the base of the natural logarithm, denoted ln(x) which has many properties. e is related to the notable constants π, i, 1, and 0, through Leonhard Euler's famous eqaution e^πi+1=0. Overall, the constant e shows up in many unlikely places in various regions of mathematics.

φ (phi)
Type: Algebraic irrational
Decimal Expansion: 1.6180339887
Continued fraction constants: 1,1,1,1,1,1,1...
Description: φ is an irrational number that is also commonly known as the golden ratio. This is because it is the ration between two line segments that makes it also the ratio between the longer segment and the sum of the two segments. The image below illustrates this property.



φ is also the only number whose reciprocal is itself minus one (1/φ+1=φ). Interestingly, φ is also related to the Fibonacci Sequence (the sequence that starts 1,1 and each new number is the sum of the previous two). The ratio of two consecutive terms of the Fibonacci sequence approximates φ, and the approximation becomes more accurate with higher Fibonacci numbers. φ has numerous properties, and is the only number to satisfy many formulae throughout mathematics.

There are many other irrationals but the above are the most notable.

Sources: http://en.wikipedia.org/wiki/Continued_fraction (info and image), http://en.wikipedia.org/wiki/E_(mathematical_constant) (info)

Notable Hurricanes: Longevity; Part 3

This is the conclusion of a three part post. For the first part see here. For the second part see here.

#3 Hurricane Inga (1969) September 20-October 15 24.75 days (from formation to final extratropical transition)

The depression that became Inga formed on September 20 from a tropical wave that moved off of Africa a few days before. The system quickly became a tropical storm, but then was a depression again until the 28th. Upon turning northward, Inga became a hurricane and made a very tight loop southeast of Bermuda, before making a bigger loop and becoming a major hurricane, reaching its peak intensity of 115 mph winds and a pressure of 964 millibars. Still moving slowly, Inga started to weaken halfway through its loop and dissipated on October 15. Although Inga was very long lived, it didn't affect land and no damage resulted. Inga had an ACE of 31.64.



Track of Inga.

#2 Hurricane Ginger (1971) September 5-October 3 27.25 days (from formation to final extratropical transition)

Hurricane Ginger originated from a very large trough of low pressure spanning from the Gulf of Mexico, into the Bahamas, and through parts of the Caribbean. A total of four tropical cyclones, one depression, one tropical storm, and two hurricanes, could be traced back to this low-pressure area. The second of these to form from the trough was Ginger. The tropical depression that became Ginger was recognized as such on September 5, and drifted for much of the next four days. Heading southeast, and then northeast, the depression became Tropical Storm Ginger on September 10. Ginger started to accelerate east-north-east, and rapidly gained intensity before becoming a hurricane. On September 14, now a Category 2 hurricane, Ginger reached its peak intensity of 105 mph winds and a minimum sea level pressure of 959 millibars. Then, a strong high pressure system to the northeast of Ginger slowed its movement, turned it around, and weakened it to a Category 1 hurricane. It stalled for a few days, making a very tight loop on the 19th and 20th of September, before adopting a sluggish, but steady, westward movement. On September 23, Ginger passed its closest to Bermuda. Ginger stalled again a day later and drifted from the 24th to the 29th. During this time, Project Stormfury tried to weaken the storm on September 26 and September 28. Project Stormfury is a program that attempted to dissipate the clouds associated with tropical cyclones by "seeding" them, or dropping chemicals into the eyewall to weaken it. Ginger was the last hurricane to be used for this experiment due to lack of financial support and the fact that it simply didn't seem to work. The idea is sound in theory, but execution isn't feasible for two reasons. Firstly, it costs too much to carry a significant amount of chemicals to high altitudes, and second that the hurricanes quickly redevelop due to the abundance of moisture in ocean air. Soon after Ginger turned to the northwest, and became a Category 2 hurricane again, before weakening to a Category 1. On September 30, Ginger struck North Carolina, still a hurricane, but barely. It weakened inland and was nearly stationary for the first few days of October before becoming extratropical and moving off the coast the east on October 3, joining the Atlantic Ocean once more. Ginger caused some damage, $53 million adjusted for inflation ($10 million at the time), but no deaths resulted. Most of the damage came from the central coast of North Carolina, where a wide area had received over ten inches of rain from Ginger. Ginger had an ACE of 44.19.



Track of Hurricane Ginger, spanning nearly a month.

#1 Hurricane Three (1899) August 3-September 4 28 days (from formation to final extratropical transition)

The tropical storm destined to be named Hurricane San Ciriaco for the place it damaged formed on August 3, 1899. It quickly intensified in the favorable region and was a hurricane by August 5 and a major hurricane soon afterward. It brushed the easternmost islands of the Caribbean shortly before striking Puerto Rico, and its namesake, San Ciriaco, at its peak intensity as a Category 4 of 150 mph winds and an approximate pressure of 930 millibars. After devastating Puerto Rico, the system moved onward to the Dominican Republic, passing north of the island. Over the next four days or so, the hurricane passed through the Bahamas, still a Category 3, before striking North Carolina on August 17. It emerged off of North Carolina as a minimal Category 1 hurricane, and sped off eastward into open waters becoming extratropical on August 22. However, the system was pushed south for a time, and regained enough tropical characteristics to be a tropical storm again on August 26. The tropical storm slowly moved north, and then slowly east. The storm intensified and accelerated east, briefly becoming a Category 1 hurricane on October 3rd before losing its tropical features and becoming extratropical for the last time the next day. Although the damage caused by this storm cannot be calculated in dollars, it can be measured as one of the deadliest tropical cyclones in history, causing 3,433 fatalities, most of them (about 3,200 of them) occurring in Puerto Rico. Hurricane San Ciriaco also had the highest ACE of any Atlantic hurricane, at 73.57.



Track of Hurricane San Ciriaco, a long-lived and deadly hurricane.

Through this and two other posts, the top ten Atlantic hurricanes it terms of longevity have been listed. However, one record remains, the longest lived tropical cyclone in the world. Hurricane San Ciriaco is still second in the world, behind only a remarkable cyclone that was both a hurricane and a typhoon in the Pacific Ocean, due to the fact that it crossed the International Date Line. A summary of the cyclone is shown below.

#1 (world) Hurricane/Typhoon John (1994) August 11-September 10 31 days (from formation to final extratropical transition)

Due to the advanced reanalysis that occurs for all tropical cyclones after (sometimes years after) they form, this particularly powerful hurricane that formed in the Pacific, can have its wave origins trace back to the Atlantic. On July 25, 1994, a tropical wave moved off Africa, and moved westward into unfavorable conditions for development. Therefore, the wave didn't become a low pressure system until it entered the East Pacific Ocean through Central America and became a tropical depression on August 11. It quickly became a tropical storm, but wind sheer was ripping at the system, and Tropical Storm John couldn't strengthen until August 19, when John had nearly passed out of the reach of the sheering system. Upon entering this favorable zone, John became a hurricane, and soon, a major hurricane. On August 20, John passed out of the East Pacific, into the Central Pacific. Unlike the Atlantic, whose boundaries are easily measured by land and the equator, the Pacific is split into three separate basins, the East, the Central, and the West. The East Pacific goes from the west coast of Mexico and the U.S. out to a line. In this area there is an alphabetic name list, similar to the Atlantic. A cyclone that passes from the East to the Central Pacific is still called a hurricane, and retains the same name. However, cyclones that form in this basin follow a different name list that does not go in any alphabetical order, because of the relative lack of cyclones in the region. Therefore, when Hurricane John entered the Central Pacific and switched basins, it was still was Hurricane John, and was still gaining intensity. By the time John was at its closest approach to the Hawaiian Islands it was a Category 5 hurricane, but, fortunately for the islands, John was 345 miles away. Despite this, John's outer rain bands caused a significant amount of damage. However, the system couldn't turn towards Hawaii because the usual high pressure system over the islands was blocking all cyclones from turning north. Later that same day of its closest approach, on August 22, John reached its peak intensity of 175 mph winds and a pressure of 929 millibars. However, the pressure was probably much lower than this, because the pressure had last been taken when John was not at its peak intensity. Now, John took a northwest turn, and steadily weakened to Category 1 hurricane strength. Over the next days, however, John regained some of its intensity and reached Category 4 status. It was at a secondary peak with 135 mph winds when it crossed the International Date Line and entered the West Pacific. The West Pacific had another name list still, with another major difference. The scale of intensity was also different. Instead of going tropical depression, tropical storm, hurricane, it went tropical depression, tropical storm, typhoon, super typhoon. Therefore, when John crossed the date line on August 27, it was still John, but a typhoon, not a hurricane. However, upon crossing the date line, John had nearly stopped moving and by September 1, John was a stationary tropical storm. John went through a slow loop, first east, and then back west, still a tropical storm. By the time this loop ended, a trough was moving in, forcing John quickly to the northeast. On September 8, John had crossed back into the Central Pacific and was still a tropical storm. John attained hurricane strength again and reached 90 mph winds before finally becoming extratropical on September 10. John hadn't caused much damage and the only damage was to Hawaii and to Johnston Atoll in the north-central Pacific. John's ACE was not accurate because it had crossed three basins, but it is estimated to be in the 50's.



Hurricane John at primary peak intensity as a strong Category 5 hurricane.



Track of John.

Some of the above cyclones are the most notable in the world, and many have some of the most erratic tracks of any cyclones ever.

The information on this post can be credited mostly to wikipedia, which, in turn, got its information from the National Hurricane Center that keeps records of Atlantic tropical cyclones dating back to 1850. Any cyclones before that time cannot be on the above list, due to lack of information.

Notable Hurricanes: Longevity; Part 2

This is the second part of a three part post. For the first part, see here.

Most of the hurricanes so far on the longevity countdown have made a loop. This usually is a result of a blocking high pressure, which steers the system, but doesn't always weaken it. However, blocking low pressure systems steer storms and weaken them or are too weak to affect them, and are therefore are less common.

#7 (tied) Hurricane Inez (1966) September 21-October 11 20.75 days (from formation to last extratropical transition)

The tropical wave that was to become Hurricane Inez emerged off Africa on September 18. On September 21, the system became a tropical depression, and on the 24th, it became Tropical Storm Inez. Inez strengthened rapidly into a hurricane and slammed into the most eastern islands in the Caribbean. Strengthening still further, Inez reached its peak intensity of 150 mph winds and a pressure of 929 millibars before making landfall in the Dominican Republic on September 29. The system weakened and emerged over water shortly before striking Cuba. After traveling over Cuba, Inez was barely holding on to minimal hurricane strength and became a tropical storm upon entering the southwestern Bahamas on October 2. Over the Bahamas, Inez became a hurricane again and was forced to the southwest by a subtropical ridge on the 4th. Soon after, Inez crossed the Florida Keys, and began to intensify once again. By this time, Inez skimmed the northern Yucatan Peninsula on October 7, it was a Category 3 and still getting stronger. Then, on October 10, after briefly reaching Category 4 status, the system made landfall in Mexico as a Category 3. Inez weakened rapidly, and dissipated on the 11th of October. Over 1,000 people died form Inez and $222 million in damage resulted ($1.5 billion adjusted for inflation since 1966). Because of this, the name Inez was retired from the circulating name list. Inez had an ACE of 54.58.



Track of Inez.

#7 (tied) Hurricane Carrie (1957) September 2-24 20.75 days (from formation to last extratropical transition)

The tropical depression that eventually became Carrie formed near Africa on September 2. Moving slowly westward, the system gained intensity, first becoming a tropical storm, then a hurricane, and then a major hurricane. Soon after, on September 8, Carrie reached its peak intensity of 155 mph winds and a pressure of 945 millibars. The system turned north weakening to a Category 1, and then turned west strengthening to a Category 4. On September 16, the system passed Bermuda at distance of about 100 miles, not causing any damage. Soon after, the system turned east as a minimal hurricane and became extratropical on the 23rd. The only impact of Carrie was a sunken ship off the Azores on September 21. 86 were aboard the ship and only 6 survived, despite a rescue effort. Carrie had an ACE of 62.59.



Track of Carrie.

#5 Hurricane Nadine (2012) September 11-October 4 21.75 days (spent as a tropical cyclone)
A post on this hurricane is located elsewhere on this blog.

#4 Hurricane Kyle (2002) September 20-October 12 22 days (from formation to final extratropical transition)

The low pressure system that later became Kyle was originally part of a front that moved over the Atlantic Ocean on October 15. A low formed over the dissipating front on September 18 and gained some characteristics of a tropical cyclone. On September 20, the system was midway between tropical and non-tropical features, and was therefore classified as a subtropical depression. The depression, moving slowly northward in the Central Atlantic, was hindered in movement by a blocking trough to its north and another low to its south. Despite all these factors, the depression strengthened into Subtropical Storm Kyle on September 21. Then, getting close to the blocking force in the north, Kyle was forced to make a loop, first going east, then south, and then west. While making this loop, Kyle started to exhibit more tropical features, and Kyle was reclassified as Tropical Storm Kyle on September 22. The system continued generally west over the next few days, intensifying as it went, and soon becoming a hurricane. Soon after, Kyle reached its peak intensity of 85 mph winds and a pressure of 980 millibars on September 26. The next day, however, Kyle started to weaken due to wind sheer. Before long, Kyle was a tropical storm again. Kyle later weakened into a depression, although only briefly, and it regained tropical storm status on October 1. Kyle did not move for the next few days, but soon continued its trek to the west. On October 7, Kyle was stalled again, and was forced southwest, again becoming a depression. It followed a slow arc, curving southwest, then west, and finally northwest due to an approaching front, becoming a tropical storm yet again before striking the coast of South Carolina, and then North Carolina on October 11. The system emerged over water and became extratropical on October 12. The system caused minor damage and one fatality. Kyle had an ACE of 14.44.



Kyle at minimal hurricane status.



The odd-looking track of Kyle.

For the last part of this post, see here.

Notable Hurricanes: Longevity; Hurricane ACE

Among the many Atlantic hurricanes that have formed in the past 150 years or so, most are notable because of their intensity or for their impact. In this post, starting with the 12th, the top twelve hurricanes in terms of longevity will be listed. But first, a little word about ACE, or Accumulated Cyclone Energy, which combines the intensity and longevity of a cyclone into one statistic.

ACE is a formula that adds together the intensities of a cyclone every six-hour period throughout the total history of the cyclone. For each period of six hours, the maximum sustained wind speed is estimated, squared, and divided by ten thousand. This is the ACE figure for that six hour interval. The sum of all the intervals determines the ACE of a storm. However, there are a few extra rules associated with ACE. For one, the ACE is only taken when a cyclone is tropical (tropical meaning that the cyclone has hurricane-like characteristics). When a cyclone is extratropical or subtropical (midway between extratropical and tropical, but there is no given line between these categories) ACE is not taken. Also, when the tropical cyclone has winds less than 40 mph, i.e. a tropical depression, the ACE figure drops to zero. Most long-lived hurricanes have high ACE's, but this isn't always true. Since the statistic applies to longevity and intensity, an intense long-lived storm will have the highest ACE.

#12: Hurricane Ivan (2004) September 2-24 18.75 days (as a tropical cyclone)

Hurricane Ivan was a Cape Verde hurricane that became a tropical depression on September 2, 2004. The system became a tropical depression and then a hurricane quickly. Ivan also set the record for most southerly Atlantic major hurricane when it became a Category 3 on September 5 at 10.6 N latitude. It continued west-north-westward and became a Category 5 hurricane on September 9. Hurricane Ivan, continuing through the Caribbean and fluctuating between Category 4 and 5 once or twice, devastated the Cayman Islands, Cuba, Jamaica, and Grenada. Billions of dollars in damage and over 50 deaths occurred during this rampage, despite the fact that Hurricane Ivan did not make landfall in any of these places, but passed by them. On September 13, the storm entered the Gulf of Mexico and approached the coast of Alabama. The storm made landfall in the United States at Category 3 intensity on September 16 and became a remnant low on the 18th. Causing 54 deaths in the region, the low continued northeastward The low was disregarded while it slowly turned to the south, and emerged back into the Gulf from Florida. On September 22, the system became a tropical depression again, and the National Hurricane Center, recognizing the depression as the remnants of Ivan, called it Tropical Depression Ivan. It strengthened into a tropical storm shortly before making its second landfall in Louisiana and causing minor damage. The system dissipated on the 24th. Although the storm was only the 10th most long lived, it had the second highest ACE of any storm in the Atlantic: 70.38.



Ivan as a Category 5 in the Caribbean.



Track of Ivan. The circles denote the storm as tropical with blue the weakest and red the strongest. The triangles show the remnants of Ivan when it was not tropical.

#11 Hurricane Nine (1893) September 25-October 15 19.25 days (as a tropical cyclone)

Due to the lack of radar and other tracking instruments in 1893, it is not known whether the storm actually originated on the 25th of September. However, it is known that a Cape Verde hurricane formed in late September of this year, and very slowly made its way westward. The system quickly strengthened into a hurricane and then a major hurricane. Since names weren't introduced until 1950, the system was simply called Hurricane Nine. It took a turn north and then once again followed a westerly path as a Category 3 hurricane through the Bahamas. On October 13, the hurricane struck Myrtle Beach, South Carolina, and accelerated northward, dissipating on the 15th. The system caused 28 deaths and had an ACE of 63.5.



Track of Nine.

#10 Hurricane Four (1926) September 2-24 19.5 days (as a tropical cyclone)

A tropical storm formed on September 2 and moved northwest very slowly for the next two weeks. During this time, the system became a Category 4 hurricane, and its movement slowed even more. Then, it turned northeast and made a tight loop. It became extratropical shortly after and dissipated on the 24th. Although the system caused no damage to land, it had the third highest ACE of any Atlantic hurricane, at 67.59.



Track of Four.

#9 Hurricane Alberto (2000) August 3-23 19.75 days (as a tropical cyclone)

The tropical depression that was to become Hurricane Alberto formed very close to the African coast on August 3. The system moved generally westward, and strengthened into a tropical storm and then a hurricane. However, on August 9, the system experienced wind sheer, and weakened to a tropical storm, and turned northeast. After moving out of the influence of the wind sheer, the system strengthened to a hurricane and then reached its peak intensity of 125 mph and 950 millibars on August 12. Then, due to the influence of a subtropical ridge, Alberto began a large loop in the north-Central Atlantic, and once again weakened to a tropical storm on the 14th of August. Then, it began to turn south, and then west again, before becoming a hurricane for the third time on August 18. It became a Category 2 hurricane again, and reached a secondary peak intensity of 105 mph winds Then, Alberto finally turned northward once again, starting slow, and then accelerating, and finally becoming extratropical late on August 23. Although no damage resulted from Alberto, it was notable for its odd track, and it had an ACE of 36.9, which is fairly low for Alberto's longevity, but since it never went beyond Category 3, it wasn't intense for much of its lifetime.



Hurricane Alberto at its primary peak intensity as a major hurricane.



Track of Alberto.

The top ten is continued on Notable Hurricanes: Longevity; Part 2.

Lightning

Lightning and thunder are the easily observed (and heard) phenomena that are associated with storms, specifically thunderstorms. Although lightning is a very common and well known occurrence, the actual nature of lightning, and the variety of types, are relatively unknown.

The best known type of lightning, called cloud-to-ground lightning, originates when ionized particles in a cloud form an electric field. It is unknown from where the negatively charged particles come from, probably from space in the form of solar wind. These ionized particles form a substance called plasma. (see here) This plasma in the cloud is negatively charged for normal lightning, and forms a large electric field. This electric field is strong enough to attract positively charged particles to cluster on the ground. As the storm moves across the sky, a group of particles follows a similar path along the ground. Soon, enough particles have accumulated and the negatively charged particles flow from the cloud downward. During this process, the flow of particles can split into many different paths, causing the phenomenon we know as fork lightning. We cannot see this part of the lightning's development, because the voltage is relatively low in this stage. In fact, the process that brings streams of negative particles down from the cloud taking a "long" time, relative to the flash, sometimes lasting up to a second. As the particles approach the ground, the attraction becomes powerful enough that the positive particles on the ground start to defy gravity, and soar upward. Then, the particles meet. Suddenly, the positively charged particles can neutralize their counterparts in the cloud easily by moving along the path. A huge movement of positive particles follows, resulting in a flow of energy 500 times larger than previously, heating the surrounding air to a remarkable temperature of 60,000 degrees. This flow, the original stroke of which lasts only a few milliseconds, is the flash we see. Additional flows of particles can occur in the next few hundred milliseconds, which add more flashes to the first.

When this extreme temperature hits the air, the velocity of the air molecules increases hundredfold, causing them to bump into other molecules, creating more heat. All this sudden movement is similar to an explosion, the sound of which creates thunder. Roars of thunder are longer than lightning flashes because the sound comes from each part of the lightning bolt. The sound from the ground area reaches you first, and then the sound from the upper part of the bolt. Additional lightning strokes cause prolonged thunder.

Although cloud-to-ground lightning is the type we know best, there are many different types. Cloud-to-ground lightning causes many visual effects which include the appearance of a ribbon, when lightning strikes move in a direction with each stroke, blending together into a "ribbon". Other effects also occur, such as forked lightning. However, this is all under the category of cloud-to-ground. Dry lightning, or lightning striking the ground without any precipitation, is also under this category.



A bolt of lightning with many forks. The forks are negatively charged paths that never connected with the group of positive particles on the ground. Some positive particles defied gravity and illuminated these forks, but most followed the main path, which is the "easiest" way to reach the cloud.

The most common type of lightning is not cloud-to-ground, but cloud-to-cloud lightning. Most lightning of this type is hidden by clouds, and causes the visual effect called sheet lightning. Hidden by clouds, only a flash can be seen from the lightning, which brightens all the clouds around it. Heat lightning is also a type of cloud-to-cloud lightning that has nothing to do with heat at all, but refers to the occurrence of lightning without accompanying thunder, which is a result of the lightning being too far away to hear.

There is also another type of lightning that is not a visual phenomena, but the nature of the lightning itself is different from normal. In normal lightning negatively-charged cloud bottoms are the source of the electric field. However, in the cloud itself a group of positive particles must exist to even out the charge. Usually this is at the top or the anvil of the cumulonimbus thunderstorm cloud. If this positive group of particles is extremely strong, which is necessary for the event, the negative particles accumulate on the ground and a lightning bolt goes all the way from the top of the cloud to the ground, which can be up to a ten mile span. Also, this type of lightning often travels up to thirty miles to strike an area that is ahead of the thunderstorm. Therefore, this type of lightning can occur when it is sunny, a trait that has earned it the name "bolt from the blue". The voltage on this positive lightning is ten times that of normal lightning and lasts for ten times longer, making this type of a hundred times more powerful overall.



A bolt of positive lightning, from the top of the cloud 50,000 feet high to the ground.

Also, many miles above the cloud tops, upper-atmospheric, or megalightning occurs, often mirroring lightning down below. This is probably due to the mirrored electrical charges that correspond to the lightning below. However, they come in different types. Sprites, which occur less than a second after their companion lightning strokes, are huge, and can occur up to 60 miles from the surface and appear a dim red color. Another sometimes related event is an elve, or a halo that sometimes occurs alone, and sometimes with a sprite. They are the same color as sprites, and are very faint. A third type that occurs in the upper-atmosphere are so-called blue jets that start about 9 miles up, follow a blue arc through the sky stretching to about 30 miles above the surface. The cause of this phenomenon is unknown, and these mysterious blue jets are elusive and difficult to record. Little is known about the nature of these transient luminous events (the name given to them that doesn't strictly relate them to lightning and puts them in a more unique category, because they lack many characteristics of normal lightning) and many people are researching these odd events.



A table comparing the different types of transient luminous events or upper-atmospheric lightning.

Lightning also can occur on other planets, and definite occurrences have been recorded on Jupiter and Saturn. Venus has also had lightning recorded on it by early probes but recently there has been a debate whether the probes actually detected lightning. Hopefully, this mystery will be resolved by future spacecraft.

Before the nature of lightning was known, many different civilizations thought to be struck by lightning was a punishment from the gods. If this was true, the gods obviously had a problem with Roy Sullivan, a man who, between 1942-1977 was struck by lightning seven times. This is a world record according to the Guinness Book of Records, which has stood since.

Lightning is an amazing event, to witness and to study. There is still a lot that we don't know about it that will hopefully be revealed in the future.

Sources: http://upload.wikimedia.org/wikipedia/commons/8/86/Darwin_storms.jpg (image), http://geology.about.com/od/sprites/a/sprites.htm, http://upload.wikimedia.org/wikipedia/commons/thumb/c/c4/Upperatmoslight1.jpg/400px-Upperatmoslight1.jpg (image)

Hyperbolic and Other Geometries (Part III)

Note: This is the conclusion of a three part post. For the first part, see Hyperbolic and Other Geometries (Part I) and for the second part, see Hyperbolic and Other Geometries (Part II).

It may seem that hyperbolic and elliptic geometry have no relevant meaning in the physical world, because everything here is purely, and simply, Euclidean. However, the surface of the Universe itself has a basis in the other types of geometry. In fact, there isn't any perfect Euclidean geometry in the physical world at all!

The geometry of the surface of space is not actually the shape of the Universe as a whole. Even if the geometry of the surface of the Universe was hyperbolic, the Universe could still be finite. This is because the surface of space isn't really a physical thing. In essence, it is what all the objects in the Universe "rest on". The gravitationally heavier objects, such as stars, make a dent in this surface and cause nearby objects to roll towards it. For example, the Sun creates a small depression in the center of the solar system, and all the planets roll toward it. However, the planets don't go hurtling into the Sun because each of them has a forward velocity. The closer you get to the Sun, the faster the forward velocity is needed to not roll into the Sun, because the depression is "steeper" in this area. Some objects are theorized to be so "heavy" on this surface, that they actually create a "hole" in space, with a steep well surrounding it. These objects are black holes. The hole in space could actually open a path to a parallel plane of space, an alternate universe!

With all these dents and holes, the Universe clearly isn't homogeneous or isotropic. Therefore, the crucial part is finding what the overall curvature of the Universe's surface is, i.e. what it would be without any of the inhomogeneities. As odd as it seems, the density of the Universe determines its geometry. It is known that there is a specified value in the Universe called the critical density of it. The critical density is the density of the Universe at which the curvature is zero and the surface of the Universe is Euclidean. If the the actual density is smaller than the critical density, the surface of the Universe is hyperbolic. If the density is higher than the critical density, the surface of space is elliptic.



In this image, the omega symbol represents the quotient of the actual density and the critical density of the Universe. For example, if the critical density equals the actual density, the omega would equal 1.

To calculate the density of the Universe, one must take into account not only density from the matter. One must also consider the mass contributed by energy. There is energy in empty space, called dark energy. The famous equation E=mc^2 shows that energy, E is equivalent to a certain amount of mass, m. Therefore, dark energy also adds density to the Universe. Regular matter and dark matter are attracted to each other gravitationally, but, oddly enough, dark energy seems to exert antigravity, or a force that pushes matter apart. The result of this is the creation of more space in the Universe, which in turn creates more dark energy, which accelerates the expansion even further. Despite the fact that the expansion of the Universe lowers the density of matter, the production of dark energy keeps the overall density constant throughout the lifetime of the Universe.

Using the Cosmic Background Radiation, one can easily infer how much matter existed at the beginning of the Universe. Using the speed at which different galaxies are receding from us, one can infer how much dark energy there is. Therefore, the densities of both dark energy and matter have been calculated. They do indeed add up to the critical density. To be exact, matter and dark matter makes up 27% of the actual density and dark energy makes up 73%. At the beginning of the Universe, the density of matter was minutely close to 100% of the critical density, and there was almost no dark energy. Since the amount of matter and dark matter hasn't changed for billions of years (since matter stopped spontaneously annihilating and turning into energy 380,000 years after the Big Bang) its density has steadily decreased. To varies with this change, the density of dark energy has increased. Therefore, the surface of the Universe is indeed flat. What does this tell us? It tells us that the Universe will never stop expanding. A value for the actual density that is the critical density or less dooms us to a fate of an infinitely expanding Universe. Only if the actual density is greater than the critical density will matter dominate. If this was the case, gravitational forces between matter would eventually cause the Universe to contract. Therefore, the Universe will continue to expand, at an ever increasing rate, until the Universe is infinitely large and infinitely old.

Overall, the fallacy of Euclid's parallel postulate has lead to to not only discover other geometries and theorems in mathematics, but has also determined the fate of our Universe.

This post and the others in this series were inspired by the following books: The Road to Reality by Roger Penrose Chapter 2, and Origins by Neil De Grasse Tyson and Donald Goldsmith Chapter 5.