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Leap Year – In Other Countries

Posted by jase on July 27, 2009

The Gregorian calendar, used by most western countries, recognizes an extra day at the end of February every four years except centenary years not divisible by 400. However, some cultures use calendars that do not apply the same leap year rules as the Gregorian calendar.

Some calendars, such as the Iranian calendar, do not observe February 29 as a leap day. Other calendars, such as the Chinese calendar, recognize a leap month. A few calendars that do not follow the conventional leap year model are listed below.  

Chinese Leap Year

The Chinese leap year has 13 months. A leap month is added to the Chinese calendar about every three years. The name of a leap month is the same as previous lunar month. The leap month’s place in the Chinese calendar varies from year to year. Unlike the Gregorian calendar, 2006 was a leap year in the Chinese calendar.

To determine a leap year, calculate the number of new moons between the 11th month in one year and the 11th month in the following year. A leap month is inserted if there are 13 moons from the start of the 11th month in the first year to the start of the 11th month in the next year. The leap month does not contain a principal term (Zhongqi). The Chinese calendar has been used for centuries and observes the movement of the sun, moon and stars. 

Jewish Leap Year

Like the Chinese calendar, the Jewish calendar has 13 months in a leap year. There are 29 or 30 days in each month in a Jewish leap year, which has 383, 384, or 385 days. An extra month, Adar I, is added after the month of Shevat and before the month of Adar in a leap year. According to Jewish tradition, Adar is a lucky and happy month.

A leap year is referred to in Hebrew as Shanah Me’uberet, or a pregnant year. A Jewish leap year occurs seven times in a 19-year cycle. The 3rd, 6th, 8th, 11th, 14th, 17th, and 19th years are leap years in this cycle.  

Iranian Leap Year

There are about eight leap years in every 33-year cycle in the Iranian (or Persian) calendar. An extra day is added to the last month in a leap year. Leaps years occur when there are 366 days between two New Year’s days. However, it is not universally accepted that the calendar is solely based on observing the vernal equinox.

Leap years usually occur every four years. After every six or seven leap years, the Iranian calendar provides for a leap year that occurs on the fifth year instead of the fourth year. A period of 2820 years was the base for calculations to establish the frequency of a leap year occurring on the fifth year. At the start and the end of the 2820-year cycle, the vernal equinox takes place exactly at the same time of the tropical year.  

The Iranian calendar dates back to the 11th century, when a panel of scientists created a calendar that was more accurate than other calendars at the time. Although some changes have been made to the calendar, it is slightly more accurate than the Gregorian calendar. Compared with the Gregorian calendar, which errors by one day in about every 3226 years, the Iranian calendar needs a one-day correction in about every 141,000 years.  

Hindu Leap Year

The Hindu calendar inserts an extra month, often referred to as Adhika Maas, in a leap year. Adhika Maas typically occurs once every three years or four times in 11 years. Therefore the yearly lag of a lunar year is adjusted every three years. This adjustment allows for Hindu festivals tend to occur within a given span rather than on a set day.

The Indian National Calendar and the Revised Bangla Calendar of Bangladesh organize their leap years so their leap day is close to February 29 in the Gregorian calendar.  

Islamic Leap Year

In the Islamic Hijri calendar one extra day is added to the last month (making it 30 days instead of 29 days) in a leap year. This month, Dhu ‘l-Hidjdja, is also referred to as the month of the Hajj – the Muslim pilgrimage to Mecca. The Hijri calendar has a 30-year cycle with 11 leap years of 355 days and 19 years of 354 days. In the long term, it is accurate to about one day in 2500 years.

The leap year occurs in the 2nd, 5th, 7th, 10th, 13th, 16th, 18th, 21st, 24th, 26th and 29th years of the 30-year cycle. Leap months are forbidden by the Qur’an. The calendar is based on the Qur’an and its proper observance is a sacred duty for Muslims. It is a purely lunar calendar and contains 12 months that are based on the moon’s motion.  

Bahá’í Leap Year

The Bahá’í year begins on March 21 and is divided into 19 months of 19 days each, totaling 361 days. Four or five intercalary days are added to raise the number of days to 365, or 366 in leap years. The leap day is inserted in the days of Ayyam-i-ha , a period of intercalary days devoted to fasting preparations, hospitality, charity and gift-giving from February 26 to March 1.

Ethiopian Leap Year

The Ethiopian calendar is very similar to the Egyptian Coptic calendar, which has 13 months. Like the Coptic calendar, the Ethiopian calendar adds an extra day to the end of the year once every four years. The Ethiopian and Coptic calendars consist of 13 months, where the first 12 months each have 30 days and the 13th month has six days in a leap year instead of five days in a standard year.

Other Leap Years

Greece converted to the Gregorian calendar in 1924, although there is debate that the change may have occurred in 1920 or as early as 1916. There is discussion that some Orthodox Christians prefer to use a revised Julian calendar, where there is a discrepancy with the Gregorian calendar with regard to a leap year that will occur in 2800.

More information

Further reading

Source: TimeAndDate.com

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Global Dimming and Death of Our Sun

Posted by jase on July 10, 2009

by Brian Cox

The Sun is Dying

Sol, our sun, will not live forever. It has enough fuel left, if our current understanding is correct, for another 5 billion years, at which point it will die. But could it be possible for the Sun to die much sooner, within the next 100 years even? From a scientific perspective, it should be said that this is very unlikely. But, it is also true that there is a lot about the universe that we do not understand.

Over the last few years astronomers have observed that there is extra “stuff” in the universe that we can see only by its gravitational influence on stars and galaxies. This stuff goes by the name of Dark Matter, and there is five times as much Dark Matter in the universe as there is normal matter, the stuff that makes up you, me, and the stars and planets we can see with our telescopes. What is this mysterious stuff? It’s possible, some scientists would say likely even, that this stuff is made of particles known as supersymmetric particles, a new and exotic form of matter that is high on the list of potential discoveries at CERN’s giant Large Hadron Collider, a 27km in circumference machine which begins operations this year after almost a decade of construction.

Theoretical physicists have spent many years calculating the properties of these supersymmetric particles, and we have a reasonable theoretical understanding of how they might behave. One possibility is that they could clump together into giant balls known as Q-balls. If this is true, then these heavy and exotic objects could have been made billionths of a second after our Universe began, and still be roaming the Universe today. It is speculated that, if a Q-ball drifts into the heart of a super-dense object such as a neutron star, it could begin to eat away at it’s core like a cancer, until the star is no longer massive enough to maintain itself and explodes in a violent explosion. Such explosions, known as gamma ray bursts, are seen in the Universe, although their cause is as yet unknown.

Could such a dangerous, exotic object drift into the Sun’s core and cause it to stop shining? It is likely that the Sun is many times too diffuse to stop a Q-ball – it would power right through. But maybe, just maybe, some strange exotic form of matter from the earliest times in the universe could settle deep within the Sun’s core, and disrupt its function enough to cause the catastrophic scenario seen in Sunshine. It’s far-fetched, but we have a saying in physics that anything that isn’t explicitly ruled out is therefore possible, so in the final analysis, you never quite know.

Global Dimming 

It is now suspected that pollution in the Earth’s atmosphere, caused by industrialization and natural phenomena such as volcanic eruptions, may have significantly reduced that amount of sunlight reaching the Earth’s surface. It is estimated that this could have led to a cooling effect of over 1 degree overt he last 40 years, which would go some way to offsetting the effect of global warming. Global warming is caused primarily by increasing carbon dioxide levels in the atmosphere that prevent heat being radiated back out into space from the Earth’s surface.

The phenomenon of global dimming may therefore have saved us, so far, from the worst affects of climate change, although it has been noticed that as pollution levels have been reduced, particularly in Western Europe, the affects of global dimming seem to be reducing, leading to an accelerating temperature rise once again. We may therefore be in the paradoxical situation that reducing pollution might INCREASE the effects of global warming, leading us ever more quickly towards catastrophe.

This discovery isn’t all bad, however, because it may suggest a short term solution to climate change. Why not intentionally put pollutants, which may be designed to be benign in other respects, into the atmosphere to accelerate global dimming, and therefore slow the climate change caused by carbon dioxide emissions. Several suggestions along these lines have been made, including adding small particles to airplane fuel, and therefore using one of the main contributors to climate change, aircraft, to slow its effects. It’s an intriguing possibility, and one that is the focus of significant research, although it should be said that we cannot at present predict the effects of such fine-tuning of the climate, so global dimming shouldn’t be seen as a means to allow us to continue to increase carbon dioxide emissions.

Posted in Astronomy, Climate, Earth, extinction, Global Warming, Science, Solar Energy, Space | Tagged: , , , , , , , , , , , | Leave a Comment »

Ever Heard of: Auroras

Posted by jase on July 7, 2009

Auroras, sometimes called the northern and southern (polar) lights or aurorae (singular: aurora), are natural light displays in the sky, usually observed at night, particularly in the polar regions. They typically occur in the ionosphere. They are also referred to as polar auroras. In northern latitudes, the effect is known as the aurora borealis, named after the Roman goddess of dawn, Aurora, and the Greek name for north wind, Boreas by Pierre Gassendi in 1621. The aurora borealis is also called the northern polar lights, as it is only visible in the sky from the Northern Hemisphere, the chance of visibility increasing with proximity to the North Magnetic Pole, which is currently in the arctic islands of northern Canada. Auroras seen near the magnetic pole may be high overhead, but from further away, they illuminate the northern horizon as a greenish glow or sometimes a faint red, as if the sun was rising from an unusual direction. The aurora borealis most often occurs from September to October and from March to April. The northern lights have had a number of names throughout history. The Cree people call this phenomenon the “Dance of the Spirits.” Auroras can be spotted throughout the world. It is most visible closer to the poles due to the longer periods of darkness and the magnetic field.

Its southern counterpart, the aurora australis or the southern polar lights, has similar properties, but is only visible from high southern latitudes in Antarctica, South America, or Australasia. Australis is the Latin word for “of the South.”

Benjamin Franklin first brought attention to the “mystery of the Northern Lights.” He theorized the shifting lights to a concentration of electrical charges in the polar regions intensified by the snow and other moisture.

The phenomenon of aurora is an interaction between the Earth’s magnetic field and solar wind.

Auroras are produced by the collision of charged particles from Earth’s magnetosphere, mostly electrons but also protons and heavier particles, with atoms and molecules of Earth’s upper atmosphere (at altitudes above 80 km (50 miles)). The particles have energies of 1 to 100 keV. They originate from the Sun and arrive at the vicinity of Earth in the relatively low-energy solar wind. When the trapped magnetic field of the solar wind is favorably oriented (principally southwards) it connects with Earth’s magnetic field, and solar particles enter the magnetosphere and are swept to the magnetotail. Further magnetic reconnection accelerates the particles towards Earth.

The collisions in the atmosphere electrically excite electrons to take quantum leaps (a mechanism in which the electron’s kinetic energy is converted to visible light); and molecules in the upper atmosphere. The excitation energy can be lost by light emission or collisions. Most auroras are green and red emissions from atomic oxygen. Molecular nitrogen and nitrogen ions produce some low level red (pink) and very high blue/violet auroras. The light blue and green colors are produced by ionic nitrogen and the neutral helium gives off the purple colour whereas neon is responsible for the rare orange flares with the rippled edges. Different gasses interacting with the upper atmosphere will produce different colors, caused by the different compounds of oxygen and nitrogen. The level of solar wind activity from the Sun can also influence the color and intensity of the auroras.

The Earth is constantly immersed in the solar wind, a rarefied flow of hot plasma (gas of free electrons and positive ions) emitted by the Sun in all directions, a result of the million-degree heat of the Sun’s outermost layer, the corona.

The IMF originates on the Sun, related to the field of sunspots, and its field lines (lines of force) are dragged out by the solar wind. That alone would tend to line them up in the Sun-Earth direction, but the rotation of the Sun skews them (at Earth) by about 45 degrees, so that field lines passing Earth may actually start near the western edge (“limb”) of the visible sun.[9]

Earth’s magnetosphere is the space region dominated by its magnetic field. It forms an obstacle in the path of the solar wind, causing it to be diverted around it, at a distance of about 70,000 km (before it reaches that boundary, typically 12,000–15,000 km upstream, a bow shock forms). The width of the magnetospheric obstacle, abreast of Earth, is typically 190,000 km, and on the night side a long “magnetotail” of stretched field lines extends to great distances.

When the solar wind is perturbed, it easily transfers energy and material into the magnetosphere. The electrons and ions in the magnetosphere that are thus energized move along the magnetic field lines to the polar regions of the atmosphere.

The aurora is a common occurrence in the Poles. It is occasionally seen in temperate latitudes, when a strong magnetic storm temporarily expands the auroral oval. Large magnetic storms are most common during the peak of the eleven-year sunspot cycle or during the three years after that peak. Geomagnetic storms that ignite auroras actually happen more often during the months around the equinoxes. It is not well understood why geomagnetic storms are tied to Earth’s seasons while polar activity is not.

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Massive Solar Plane Will Fly For Years on End

Posted by jase on June 26, 2009

From Popular Science:

Nine days: That’s the longest any airplane has stayed in the air. Burt and Dick Rutan’s Voyager set the record in 1986 by flying 24,986 miles around the world without refueling. But nine days of uninterrupted flight won’t cut it for Darpa, the Pentagon’s advanced-research organization. It’s challenged the aviation industry to come up with an unmanned surveillance and communications plane that can circle targets for half a decade — and do so on nothing but solar power.

The aircraft you see here, Odysseus, was the first entry in the Vulture program, the competition Darpa created to make its extreme-endurance dreams come true. If the plane’s designers at Aurora Flight Sciences beat rival entries by Boeing and Lockheed — Darpa could pick a winner as early as this year — it will have the opportunity to make this concept into the real thing: a 492-foot-wide folding aircraft that can cruise at 140 mph at 70,000 feet for five years straight, powered by the solar panels that cover the top of the plane.

In fact, Odysseus is three planes in one, a collection of 164-foot-long wing-shaped constituent aircraft that take off separately and dock in the stratosphere, where the air is calmer and less stressful on the massive structure. (Aurora CEO John Langford says the company hasn’t chosen a docking mechanism yet but that it’s considering something based on the system that connected NASA’s Apollo command and lunar modules.) Each piece is interchangeable and can be swapped out in midair for repairs or upgrades. The three-piece construction allows Odysseus to autonomously change shape throughout the day to trap as much solar energy as it can. It could pleat like an accordion into a “Z” to absorb sunlight at low angles — at dusk, for example — and flatten into a more aerodynamically efficient traditional wing at night.

Catching as much sun as possible is essential, because energy — specifically, energy storage — is one of the biggest obstacles to solar flight, particularly solar flight that must continue without fail for years on end. Langford says Aurora is exploring storage methods, including flywheels, fuel cells and an array of batteries embedded throughout the airframe. The plane also needs to be light, so Aurora’s design relies on featherweight carbon composites. The huge craft could weigh in at under 7,000 pounds — approximately 2,000 pounds less than a fully fueled Voyager, which was less than a quarter of Odysseus‘s size.

Although it’s designed to be a surveillance platform, the lanky Odysseus would probably appear to the naked eye as a starlike glint, so it could be used for less-covert missions, such as patrolling a border or watching over suspected nuclear-reactor sites. And it could have civilian applications: Langford imagines it as an atmospheric buoy, monitoring storm development, climate change or the health of the ozone layer. Either way, he says, it would demonstrate the potential of solar power and serve as a testbed for green aircraft technology. “If we can build an airplane that can stay up for five years with nothing but sunlight,” he says, “what else can we do?”

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