Friday, January 11, 2013
Stellar Evolution
http://chandra.harvard.edu/edu/formal/stellar_ev/stellar_ev_flash.html
http://www.unm.edu/~astro1/101lab/lab10/HRdiagram.html
Also, FYI:
http://phys.org/news/2013-01-astronomers-largest-universe.html
http://www.unm.edu/~astro1/101lab/lab10/HRdiagram.html
Also, FYI:
http://phys.org/news/2013-01-astronomers-largest-universe.html
Thursday, December 20, 2012
Solstice!
December solstice 2012: 21 Dec 11:12 (UTC)
Recall:
http://astro.unl.edu/naap/motion3/animations/sunmotions.swf
The December solstice occurs when the sun reaches its most southerly declination of -23.5 degrees. In other words, it is when the North Pole is tilted 23.5 degrees away from the sun. Depending on the Gregorian calendar, the December solstice occurs annually on a day between December 20 and December 23. On this date, all places above a latitude of 66.5 degrees north (Arctic Polar Circle) are now in darkness, while locations below a latitude of 66.5 degrees south (Antarctic Polar Circle) receive 24 hours of daylight.
The sun is directly overhead on the Tropic of Capricorn in the southern hemisphere during the December solstice. It also marks the longest day of the year in terms of daylight hours for those living south of the equator. Those living or traveling south from the Antarctic Circle towards the South Pole will see the midnight sun during this time of the year.
On the contrary, for an observer in the northern hemisphere, the December solstice marks the day of the year with the least hours of daylight. Those living or traveling north of the Arctic Circle towards the North Pole will not be able to see the sun during this time of the year.
The December solstice in the calendar
December 20 and December 23 solstices occur less frequently than December 21 or December 22 solstices in the Gregorian calendar. The last December 23 solstice occurred in 1903 and will not occur again until the year 2303. A December 20 solstice has occurred very rarely, with the next one occurring in the year 2080.
As with the June solstice, the December solstice’s varying dates are mainly due to the calendar system. The Gregorian calendar, which is used in most western countries, has 365 days in a common year and 366 days in a leap year. However, the tropical year, which is the length of time the sun takes to return to the same position in the seasons cycle (as seen from Earth), is different to the calendar year. The tropical year is approximately 365.242199 days but varies from year to year because of the influence of other planets. The exact orbital and daily rotational motion of the Earth, such as the “wobble” in the Earth's axis (precession), also contributes to the changing solstice dates.
Over the course of history, many different schemes have been devised to determine the start of the year. Some are astronomical, beginning at the September or March equinox, or at the June or December solstice. Solstices are more readily observable either by observing when the midday shadow of a gnomon is longest (winter solstice in the northern hemisphere) or shortest (summer solstice in the northern hemisphere). The solstices can also be observed by noting the point of time when the sun rises or sets as far south as it does during the course of the year (winter in the northern hemisphere) or maximally north (summer in the northern hemisphere).
(*) All dates refer to Coordinated Universal Time (UTC). Dates may vary depending on the time zone.
December solstice in relation to seasons
It is important to note that Earth does not move at a constant speed in its elliptical orbit. Therefore the seasons are not of equal length: the times taken for the sun to move from the vernal equinox to the summer solstice, to the autumnal equinox, to the winter solstice, and back to the vernal equinox are roughly 92.8, 93.6, 89.8 and 89.0 days respectively. The consolation in the northern hemisphere is that spring and summer last longer than autumn and winter (when the December solstice occurs).
The relative position of the Earth's axis to the sun changes during the cycle of seasons. This phenomenon is the reason why the sun’s height above the horizon changes throughout the year. It is also responsible for the seasons through controlling the intensity and duration of sunlight received at various locations around the planet.
Solstice’s influence on cultures
The December solstice has played an important role the lives of many people in ancient times. To this day, the world is still influenced by various traditions linked to the observance of the December solstice.
In modern times Christians all over the world celebrate the birth of Jesus Christ on Christmas, which falls on December 25. However, it is believed that this date was chosen to offset pagan celebrations of Saturnalia and Natalis Invicti. Some believe that celebrating the birth of the “true light of the world” was set in synchronization with the December solstice because from that point onwards, the days began to have more daylight in the northern hemisphere.
Christmas is also referred to as Yule, which may have derived from the Norse word jól, referring to the pre-Christian winter solstice festival. Yule is also known as Alban Arthan and was one of the “Lesser Sabbats” of the Wiccan year in a time when ancient believers celebrated the rebirth of the Sun God and days with more light. This took place annually around the time of the December solstice and lasted for 12 days. The Lesser Sabbats fall on the solstices and equinoxes.
The Feast of Juul was a pre-Christian festival observed in Scandinavia at the time of the December solstice. Fires were lit to symbolize the heat, light and life-giving properties of the returning sun. A Yule or Juul log was brought in and burned on the hearth in honor of the Scandinavian god Thor.
A piece of the log was kept as both a token of good luck and as kindling for the following year’s log. In England, Germany, France and other European countries, the Yule log was burned until nothing but ash remained. The ashes were then collected and either strewn on the fields as fertilizer every night until Twelfth Night or kept as a charm and or as medicine.
French peasants believed that if the ashes were kept under the bed, they would protect the house against thunder and lightning. The present-day custom of lighting a Yule log at Christmas is believed to have originated in the bonfires associated with the feast of Juul.
Saturnalia in Ancient Rome
In Ancient Rome the winter (December) solstice festival Saturnalia began on December 17 and lasted for seven days. It was held to honor Saturn, the father of the gods and was characterized by the suspension of discipline and reversal of the usual order. Grudges and quarrels were forgotten while businesses, courts and schools were closed. Wars were interrupted or postponed and slaves were served by their masters. Masquerades often occurred during this time.
It was traditional to offer gifts of imitation fruit (a symbol of fertility), dolls (symbolic of the custom of human sacrifice), and candles (reminiscent of the bonfires traditionally associated with pagan solstice celebrations). A mock king was chosen, usually from a group of slaves or criminals, and although he was permitted to behave in an unrestrained manner for seven days of the festival, he was usually killed at the end. The Saturnalia eventually degenerated into a week-long spree of debauchery and crime – giving rise to the modern use of the tern saturnalia, meaning a period of unrestrained license and revelry.
Other Cultures and Modern Day Celebrations
In Poland the ancient December solstice observance prior to Christianity involved people showing forgiveness and sharing food. It was a tradition that can still be seen in what is known as Gody. In the northwestern corner of Pakistan, a festival called Chaomos, takes place among the Kalasha or Kalash Kafir people. It lasts for at least seven days, including the day of the December solstice. It involves ritual baths as part of a purification process, as well as singing and chanting, a torchlight procession, dancing, bonfires and festive eating.
Many Christians celebrate St Thomas’ Day in honor of St Thomas the Apostle on December 21. In Guatemala on this day, Mayan Indians honor the sun god they worshipped long before they became Christians with a dangerous ritual known as the polo voladore, or “flying pole dance”. Three men climb on top of a 50-foot pole. As one of them beats a drum and plays a flute, the other two men wind a rope attached to the pole around one foot and jump. If they land on their feet, it is believed that the sun god will be pleased and that the days will start getting longer. Some churches celebrate St Thomas’ Day on other days in the year.
The ancient Incas celebrated a special festival to honor the sun god at the time of the December solstice. In the 16th century ceremonies were banned by the Roman Catholics in their bid to convert the Inca people to Christianity. A local group of Quecia Indians in Cusco, Peru, revived the festival in the 1950s. It is now a major festival that begins in Cusco and proceeds to an ancient amphitheater a few miles away.
http://www.timeanddate.com/calendar/december-solstice.html
GREAT RESOURCE!
>
The winter solstice is the solstice that occurs in winter. It is the time at which the Sun is appearing at noon at its lowest altitude above the horizon. In the Northern Hemisphere this is the Southern solstice, the time at which the Sun is at its southernmost point in the sky, which usually occurs on December 21 to 22 each year.
In the Southern Hemisphere this is the Northern solstice, the time at which the Sun is at its northernmost point in the sky, which usually occurs on June 20 to 21 each year.
The axial tilt of Earth and gyroscopic effects of the planet's daily rotation keep the axis of rotation pointed at the same point in the sky. As the Earth follows its orbit around the Sun, the same hemisphere that faced away from the Sun, experiencing winter, will, in half a year, face towards the Sun and experience summer. Since the two hemispheres face opposite directions along the planetary pole, as one polar hemisphere experiences winter, the other experiences summer.
More evident from high latitudes, a hemisphere's winter solstice occurs on the shortest day and longest night of the year, when the sun's daily maximum elevation in the sky is the lowest. Since the winter solstice lasts only a moment in time, other terms are often used for the day on which it occurs, such as "midwinter", "the longest night", "the shortest day" or "the first day of winter". The seasonal significance of the winter solstice is in the reversal of the gradual lengthening of nights and shortening of days.
Worldwide, interpretation of the event has varied from culture to culture, but most Northern Hemisphere cultures have held a recognition of rebirth, involving holidays, festivals, gatherings, rituals or other celebrations around that time.
History and cultural significance
The solstice itself may have been a special moment of the annual cycle of the year even during neolithic times. Astronomical events, which during ancient times controlled the mating of animals, sowing of crops and metering of winter reserves between harvests, show how various cultural mythologies and traditions have arisen. This is attested by physical remains in the layouts of late Neolithic and Bronze Age archaeological sites such as Stonehenge in Britain and Newgrange in Ireland. The primary axes of both of these monuments seem to have been carefully aligned on a sight-line pointing to the winter solstice sunrise (Newgrange) and the winter solstice sunset (Stonehenge). Significant in respect of Stonehenge is the fact that the Great Trilithon was erected outwards from the centre of the monument, i.e., its smooth flat face was turned towards the midwinter Sun.
The winter solstice may have been immensely important because communities were not certain of living through the winter, and had to be prepared during the previous nine months. Starvation was common in winter between January and April, also known as "the famine months". In temperate climates, the midwinter festival was the last feast celebration, before deep winter began. Most cattle were slaughtered so they would not have to be fed during the winter, so it was almost the only time of year when a supply of fresh meat was available. The majority of wine and beer made during the year was finally fermented and ready for drinking at this time. The concentration of the observances were not always on the day commencing at midnight or at dawn, but the beginning of the pre-Romanized day, which falls on the previous eve.
Since the event is seen as the reversal of the Sun's ebbing presence in the sky, concepts of the birth or rebirth of sun gods have been common and, in cultures using winter solstitially based cyclic calendars, the year as reborn has been celebrated with regard to life-death-rebirth deities or new beginnings such as Hogmanay's redding, a New Year cleaning tradition. Also reversal is yet another usual theme as in Saturnalia's slave and master reversals.
http://en.wikipedia.org/wiki/Winter_solstice
Recall:
http://astro.unl.edu/naap/motion3/animations/sunmotions.swf
The December solstice occurs when the sun reaches its most southerly declination of -23.5 degrees. In other words, it is when the North Pole is tilted 23.5 degrees away from the sun. Depending on the Gregorian calendar, the December solstice occurs annually on a day between December 20 and December 23. On this date, all places above a latitude of 66.5 degrees north (Arctic Polar Circle) are now in darkness, while locations below a latitude of 66.5 degrees south (Antarctic Polar Circle) receive 24 hours of daylight.
The sun is directly overhead on the Tropic of Capricorn in the southern hemisphere during the December solstice. It also marks the longest day of the year in terms of daylight hours for those living south of the equator. Those living or traveling south from the Antarctic Circle towards the South Pole will see the midnight sun during this time of the year.
On the contrary, for an observer in the northern hemisphere, the December solstice marks the day of the year with the least hours of daylight. Those living or traveling north of the Arctic Circle towards the North Pole will not be able to see the sun during this time of the year.
The December solstice in the calendar
December 20 and December 23 solstices occur less frequently than December 21 or December 22 solstices in the Gregorian calendar. The last December 23 solstice occurred in 1903 and will not occur again until the year 2303. A December 20 solstice has occurred very rarely, with the next one occurring in the year 2080.
As with the June solstice, the December solstice’s varying dates are mainly due to the calendar system. The Gregorian calendar, which is used in most western countries, has 365 days in a common year and 366 days in a leap year. However, the tropical year, which is the length of time the sun takes to return to the same position in the seasons cycle (as seen from Earth), is different to the calendar year. The tropical year is approximately 365.242199 days but varies from year to year because of the influence of other planets. The exact orbital and daily rotational motion of the Earth, such as the “wobble” in the Earth's axis (precession), also contributes to the changing solstice dates.
Over the course of history, many different schemes have been devised to determine the start of the year. Some are astronomical, beginning at the September or March equinox, or at the June or December solstice. Solstices are more readily observable either by observing when the midday shadow of a gnomon is longest (winter solstice in the northern hemisphere) or shortest (summer solstice in the northern hemisphere). The solstices can also be observed by noting the point of time when the sun rises or sets as far south as it does during the course of the year (winter in the northern hemisphere) or maximally north (summer in the northern hemisphere).
(*) All dates refer to Coordinated Universal Time (UTC). Dates may vary depending on the time zone.
December solstice in relation to seasons
It is important to note that Earth does not move at a constant speed in its elliptical orbit. Therefore the seasons are not of equal length: the times taken for the sun to move from the vernal equinox to the summer solstice, to the autumnal equinox, to the winter solstice, and back to the vernal equinox are roughly 92.8, 93.6, 89.8 and 89.0 days respectively. The consolation in the northern hemisphere is that spring and summer last longer than autumn and winter (when the December solstice occurs).
The relative position of the Earth's axis to the sun changes during the cycle of seasons. This phenomenon is the reason why the sun’s height above the horizon changes throughout the year. It is also responsible for the seasons through controlling the intensity and duration of sunlight received at various locations around the planet.
Solstice’s influence on cultures
The December solstice has played an important role the lives of many people in ancient times. To this day, the world is still influenced by various traditions linked to the observance of the December solstice.
In modern times Christians all over the world celebrate the birth of Jesus Christ on Christmas, which falls on December 25. However, it is believed that this date was chosen to offset pagan celebrations of Saturnalia and Natalis Invicti. Some believe that celebrating the birth of the “true light of the world” was set in synchronization with the December solstice because from that point onwards, the days began to have more daylight in the northern hemisphere.
Christmas is also referred to as Yule, which may have derived from the Norse word jól, referring to the pre-Christian winter solstice festival. Yule is also known as Alban Arthan and was one of the “Lesser Sabbats” of the Wiccan year in a time when ancient believers celebrated the rebirth of the Sun God and days with more light. This took place annually around the time of the December solstice and lasted for 12 days. The Lesser Sabbats fall on the solstices and equinoxes.
The Feast of Juul was a pre-Christian festival observed in Scandinavia at the time of the December solstice. Fires were lit to symbolize the heat, light and life-giving properties of the returning sun. A Yule or Juul log was brought in and burned on the hearth in honor of the Scandinavian god Thor.
A piece of the log was kept as both a token of good luck and as kindling for the following year’s log. In England, Germany, France and other European countries, the Yule log was burned until nothing but ash remained. The ashes were then collected and either strewn on the fields as fertilizer every night until Twelfth Night or kept as a charm and or as medicine.
French peasants believed that if the ashes were kept under the bed, they would protect the house against thunder and lightning. The present-day custom of lighting a Yule log at Christmas is believed to have originated in the bonfires associated with the feast of Juul.
Saturnalia in Ancient Rome
In Ancient Rome the winter (December) solstice festival Saturnalia began on December 17 and lasted for seven days. It was held to honor Saturn, the father of the gods and was characterized by the suspension of discipline and reversal of the usual order. Grudges and quarrels were forgotten while businesses, courts and schools were closed. Wars were interrupted or postponed and slaves were served by their masters. Masquerades often occurred during this time.
It was traditional to offer gifts of imitation fruit (a symbol of fertility), dolls (symbolic of the custom of human sacrifice), and candles (reminiscent of the bonfires traditionally associated with pagan solstice celebrations). A mock king was chosen, usually from a group of slaves or criminals, and although he was permitted to behave in an unrestrained manner for seven days of the festival, he was usually killed at the end. The Saturnalia eventually degenerated into a week-long spree of debauchery and crime – giving rise to the modern use of the tern saturnalia, meaning a period of unrestrained license and revelry.
Other Cultures and Modern Day Celebrations
In Poland the ancient December solstice observance prior to Christianity involved people showing forgiveness and sharing food. It was a tradition that can still be seen in what is known as Gody. In the northwestern corner of Pakistan, a festival called Chaomos, takes place among the Kalasha or Kalash Kafir people. It lasts for at least seven days, including the day of the December solstice. It involves ritual baths as part of a purification process, as well as singing and chanting, a torchlight procession, dancing, bonfires and festive eating.
Many Christians celebrate St Thomas’ Day in honor of St Thomas the Apostle on December 21. In Guatemala on this day, Mayan Indians honor the sun god they worshipped long before they became Christians with a dangerous ritual known as the polo voladore, or “flying pole dance”. Three men climb on top of a 50-foot pole. As one of them beats a drum and plays a flute, the other two men wind a rope attached to the pole around one foot and jump. If they land on their feet, it is believed that the sun god will be pleased and that the days will start getting longer. Some churches celebrate St Thomas’ Day on other days in the year.
The ancient Incas celebrated a special festival to honor the sun god at the time of the December solstice. In the 16th century ceremonies were banned by the Roman Catholics in their bid to convert the Inca people to Christianity. A local group of Quecia Indians in Cusco, Peru, revived the festival in the 1950s. It is now a major festival that begins in Cusco and proceeds to an ancient amphitheater a few miles away.
http://www.timeanddate.com/calendar/december-solstice.html
GREAT RESOURCE!
>
The winter solstice is the solstice that occurs in winter. It is the time at which the Sun is appearing at noon at its lowest altitude above the horizon. In the Northern Hemisphere this is the Southern solstice, the time at which the Sun is at its southernmost point in the sky, which usually occurs on December 21 to 22 each year.
In the Southern Hemisphere this is the Northern solstice, the time at which the Sun is at its northernmost point in the sky, which usually occurs on June 20 to 21 each year.
The axial tilt of Earth and gyroscopic effects of the planet's daily rotation keep the axis of rotation pointed at the same point in the sky. As the Earth follows its orbit around the Sun, the same hemisphere that faced away from the Sun, experiencing winter, will, in half a year, face towards the Sun and experience summer. Since the two hemispheres face opposite directions along the planetary pole, as one polar hemisphere experiences winter, the other experiences summer.
More evident from high latitudes, a hemisphere's winter solstice occurs on the shortest day and longest night of the year, when the sun's daily maximum elevation in the sky is the lowest. Since the winter solstice lasts only a moment in time, other terms are often used for the day on which it occurs, such as "midwinter", "the longest night", "the shortest day" or "the first day of winter". The seasonal significance of the winter solstice is in the reversal of the gradual lengthening of nights and shortening of days.
Worldwide, interpretation of the event has varied from culture to culture, but most Northern Hemisphere cultures have held a recognition of rebirth, involving holidays, festivals, gatherings, rituals or other celebrations around that time.
History and cultural significance
The solstice itself may have been a special moment of the annual cycle of the year even during neolithic times. Astronomical events, which during ancient times controlled the mating of animals, sowing of crops and metering of winter reserves between harvests, show how various cultural mythologies and traditions have arisen. This is attested by physical remains in the layouts of late Neolithic and Bronze Age archaeological sites such as Stonehenge in Britain and Newgrange in Ireland. The primary axes of both of these monuments seem to have been carefully aligned on a sight-line pointing to the winter solstice sunrise (Newgrange) and the winter solstice sunset (Stonehenge). Significant in respect of Stonehenge is the fact that the Great Trilithon was erected outwards from the centre of the monument, i.e., its smooth flat face was turned towards the midwinter Sun.
The winter solstice may have been immensely important because communities were not certain of living through the winter, and had to be prepared during the previous nine months. Starvation was common in winter between January and April, also known as "the famine months". In temperate climates, the midwinter festival was the last feast celebration, before deep winter began. Most cattle were slaughtered so they would not have to be fed during the winter, so it was almost the only time of year when a supply of fresh meat was available. The majority of wine and beer made during the year was finally fermented and ready for drinking at this time. The concentration of the observances were not always on the day commencing at midnight or at dawn, but the beginning of the pre-Romanized day, which falls on the previous eve.
Since the event is seen as the reversal of the Sun's ebbing presence in the sky, concepts of the birth or rebirth of sun gods have been common and, in cultures using winter solstitially based cyclic calendars, the year as reborn has been celebrated with regard to life-death-rebirth deities or new beginnings such as Hogmanay's redding, a New Year cleaning tradition. Also reversal is yet another usual theme as in Saturnalia's slave and master reversals.
http://en.wikipedia.org/wiki/Winter_solstice
Tuesday, December 18, 2012
So far, so good.....
It's 6:05 PM and the clouds are sparse. Still, the weather is threatening rain or snow. I'll update again by 7:00 PM. Or contact me: 412-965-0805
Wednesday, December 12, 2012
The Geminids, peaking Dec 13.
http://www.skyandtelescope.com/observing/home/Geminid-Meteors-to-Peak-the-Night-of-Dec-13th-182385861.html
If it's clear, get outside!
See y'all on Friday.
If it's clear, get outside!
See y'all on Friday.
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