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An aurora sometimes referred to as polar lights, northern lights (aurora borealis) or southern lights (aurora australis), is a natural light display in the Earth's sky, predominantly seen in the high-latitude regions (around the Arctic and Antarctic).
Auroras are produced when the magnetosphere is sufficiently disturbed by the solar wind that the trajectories of charged particles in both solar wind and magnetospheric plasma, mainly in the form of electrons and protons, precipitate them into the upper atmosphere (thermosphere/exosphere) due to Earth's magnetic field, where their energy is lost.
The resulting ionization and excitation of atmospheric constituents emits light of varying color and complexity. The form of the aurora, occurring within bands around both polar regions, is also dependent on the amount of acceleration imparted to the precipitating particles. Precipitating protons generally produce optical emissions as incident hydrogen atoms after gaining electrons from the atmosphere. Proton auroras are usually observed at lower latitudes.
Etymology
Aurora came from the Latin word for "dawn, morning light", since auroras were formerly thought to be the first light of dawn.
Occurrence of terrestrial auroras
Most auroras occur in a band known as the "auroral zone",[which is typically 3° to 6° wide in latitude and between 10° and 20° from the geomagnetic poles at all local times (or longitudes), most clearly seen at night against a dark sky. A region that currently displays an aurora is called the "auroral oval", a band displaced towards the night side of the Earth. Early evidence for a geomagnetic connection comes from the statistics of auroral observations. Elias Loomis (1860), and later Hermann Fritz (1881) and S. Tromholt (1882) in more detail, established that the aurora appeared mainly in the auroral zone. Day-to-day positions of the auroral ovals are posted on the internet.
In northern latitudes, the effect is known as the aurora borealis or the northern lights. The former term was coined by Galileo in 1619, from the Roman goddess of the dawn and the Greek name for the north wind. The southern counterpart, the aurora australis or the southern lights, has features almost identical to the aurora borealis and changes simultaneously with changes in the northern auroral zone. The Aurora Australis is visible from high southern latitudes in Antarctica, Chile, Argentina, New Zealand, and Australia.
A geomagnetic storm causes the auroral ovals (north and south) to expand, and bring the aurora to lower latitudes. It was hardly ever seen near the geographic pole, which is about 2000 km away from the magnetic pole. The instantaneous distribution of auroras ("auroral oval") is slightly different, being centered about 3–5° nightward of the magnetic pole, so that auroral arcs reach furthest toward the equator when the magnetic pole in question is in between the observer and the Sun. The aurora can be seen best at this time, which is called magnetic midnight.
Auroras seen within the auroral oval may be directly overhead, but from farther away, they illuminate the poleward horizon as a greenish glow, or sometimes a faint red, as if the Sun were rising from an unusual direction. Auroras also occur poleward of the auroral zone as either diffuse patches or arcs, which can be subvisual.
Auroras are occasionally seen in latitudes below the auroral zone, when a geomagnetic storm temporarily enlarges the auroral oval. Large geomagnetic storms are most common during the peak of the 11-year sunspot cycle or during the three years after the peak. An aurora may appear overhead as a "corona" of rays, radiating from a distant and apparent central location, which results from perspective. An electron spirals (gyrates) about a field line at an angle that is determined by its velocity vectors, parallel and perpendicular, respectively, to the local geomagnetic field vector B. This angle is known as the "pitch angle" of the particle. The distance, or radius, of the electron from the field line at any time is known as its Larmor radius. The pitch angle increases as the electron travels to a region of greater field strength nearer to the atmosphere. Thus, it is possible for some particles to return, or mirror, if the angle becomes 90° before entering the atmosphere to collide with the denser molecules there. Other particles that do not mirror enter the atmosphere and contribute to the auroral display over a range of altitudes. Other types of auroras have been observed from space, e.g."poleward arcs" stretching sunward across the polar cap, the related "theta aurora", and "dayside arcs" near noon. These are relatively infrequent and poorly understood. Other interesting effects occur such as flickering aurora, "black aurora" and subvisual red arcs. In addition to all these, a weak glow (often deep red) observed around the two polar cusps, the field lines separating the ones that close through the Earth from those that are swept into the tail and close remotely.
Visual forms and colors
Auroras frequently appear either as a diffuse glow or as "curtains" that extend approximately in the east–west direction. At some times, they form "quiet arcs"; at others, they evolve and change constantly. These are called "active aurora".
The most distinctive and brightest are the curtain-like auroral arcs. Each curtain consists of many parallel rays, each lined up with the local direction of the magnetic field, consistent with auroras being shaped by Earth's magnetic field. In situ particle measurements confirm that auroral electrons are guided by the geomagnetic field, and spiral around them while moving toward Earth. The similarity of an auroral display to curtains is often enhanced by folds within the arcs. Arcs can fragment or break up into separate, at times rapidly changing, often rayed features that may fill the whole sky. These are the discrete auroras, which are at times bright enough to read a newspaper by at night. and can display rapid subsecond variations in intensity. The diffuse aurora, though, is a relatively featureless glow sometimes close to the limit of visibility. It can be distinguished from moonlit clouds because stars can be seen undiminished through the glow. Diffuse auroras are often composed of patches whose brightness exhibits regular or near-regular pulsations. The pulsation period can be typically many seconds, so is not always obvious. Often there black aurora i.e. narrow regions in diffuse aurora with reduced luminosity. A typical auroral display consists of these forms appearing in the above order throughout the night.
Red: At the highest altitudes, excited atomic oxygen emits at 630 nm (red); low concentration of atoms and lower sensitivity of eyes at this wavelength make this color visible only under more intense solar activity. The low number of oxygen atoms and their gradually diminishing concentration is responsible for the faint appearance of the top parts of the "curtains". Scarlet, crimson, and carmine are the most often-seen hues of red for the auroras.
Green: At lower altitudes, the more frequent collisions suppress the 630-nm (red) mode: rather the 557.7 nm emission (green) dominates. Fairly high concentration of atomic oxygen and higher eye sensitivity in green make green auroras the most common. The excited molecular nitrogen (atomic nitrogen being rare due to high stability of the N2 molecule) plays a role here, as it can transfer energy by collision to an oxygen atom, which then radiates it away at the green wavelength. (Red and green can also mix together to produce pink or yellow hues.) The rapid decrease of concentration of atomic oxygen below about 100 km is responsible for the abrupt-looking end of the lower edges of the curtains. Both the 557.7 and 630.0 nm wavelengths correspond to forbidden transitions of atomic oxygen, slow mechanism that is responsible for the graduality (0.7 s and 107 s respectively) of flaring and fading.
Blue: At yet lower altitudes, atomic oxygen is uncommon, and molecular nitrogen and ionized molecular nitrogen take over in producing visible light emission, radiating at a large number of wavelengths in both red and blue parts of the spectrum, with 428 nm (blue) being dominant. Blue and purple emissions, typically at the lower edges of the "curtains", show up at the highest levels of solar activity. The molecular nitrogen transitions are much faster than the atomic oxygen ones.
Ultraviolet: Ultraviolet radiation from auroras (within the optical window but not visible to virtually all humans) has been observed with the requisite equipment. Ultraviolet auroras have also been seen on Mars, Jupiter and Saturn.
Infrared: Infrared radiation, in wavelengths that are within the optical window, is also part of many auroras.
Yellow and pink are a mix of red and green or blue. Other shades of red, as well as orange, may be seen on rare occasions; yellow-green is moderately common. As red, green, and blue are the primary colours of additive synthesis of colours, in theory, practically any colour might be possible, but the ones mentioned in this article comprise a virtually exhaustive list.
An aurora sometimes referred to as polar lights, northern lights (aurora borealis) or southern lights (aurora australis), is a natural light display in the Earth's sky, predominantly seen in the high-latitude regions (around the Arctic and Antarctic).
Auroras are produced when the magnetosphere is sufficiently disturbed by the solar wind that the trajectories of charged particles in both solar wind and magnetospheric plasma, mainly in the form of electrons and protons, precipitate them into the upper atmosphere (thermosphere/exosphere) due to Earth's magnetic field, where their energy is lost.
The resulting ionization and excitation of atmospheric constituents emits light of varying color and complexity. The form of the aurora, occurring within bands around both polar regions, is also dependent on the amount of acceleration imparted to the precipitating particles. Precipitating protons generally produce optical emissions as incident hydrogen atoms after gaining electrons from the atmosphere. Proton auroras are usually observed at lower latitudes.
Etymology
Aurora came from the Latin word for "dawn, morning light", since auroras were formerly thought to be the first light of dawn.
Occurrence of terrestrial auroras
Most auroras occur in a band known as the "auroral zone",[which is typically 3° to 6° wide in latitude and between 10° and 20° from the geomagnetic poles at all local times (or longitudes), most clearly seen at night against a dark sky. A region that currently displays an aurora is called the "auroral oval", a band displaced towards the night side of the Earth. Early evidence for a geomagnetic connection comes from the statistics of auroral observations. Elias Loomis (1860), and later Hermann Fritz (1881) and S. Tromholt (1882) in more detail, established that the aurora appeared mainly in the auroral zone. Day-to-day positions of the auroral ovals are posted on the internet.
In northern latitudes, the effect is known as the aurora borealis or the northern lights. The former term was coined by Galileo in 1619, from the Roman goddess of the dawn and the Greek name for the north wind. The southern counterpart, the aurora australis or the southern lights, has features almost identical to the aurora borealis and changes simultaneously with changes in the northern auroral zone. The Aurora Australis is visible from high southern latitudes in Antarctica, Chile, Argentina, New Zealand, and Australia.
A geomagnetic storm causes the auroral ovals (north and south) to expand, and bring the aurora to lower latitudes. It was hardly ever seen near the geographic pole, which is about 2000 km away from the magnetic pole. The instantaneous distribution of auroras ("auroral oval") is slightly different, being centered about 3–5° nightward of the magnetic pole, so that auroral arcs reach furthest toward the equator when the magnetic pole in question is in between the observer and the Sun. The aurora can be seen best at this time, which is called magnetic midnight.
Auroras seen within the auroral oval may be directly overhead, but from farther away, they illuminate the poleward horizon as a greenish glow, or sometimes a faint red, as if the Sun were rising from an unusual direction. Auroras also occur poleward of the auroral zone as either diffuse patches or arcs, which can be subvisual.
Auroras are occasionally seen in latitudes below the auroral zone, when a geomagnetic storm temporarily enlarges the auroral oval. Large geomagnetic storms are most common during the peak of the 11-year sunspot cycle or during the three years after the peak. An aurora may appear overhead as a "corona" of rays, radiating from a distant and apparent central location, which results from perspective. An electron spirals (gyrates) about a field line at an angle that is determined by its velocity vectors, parallel and perpendicular, respectively, to the local geomagnetic field vector B. This angle is known as the "pitch angle" of the particle. The distance, or radius, of the electron from the field line at any time is known as its Larmor radius. The pitch angle increases as the electron travels to a region of greater field strength nearer to the atmosphere. Thus, it is possible for some particles to return, or mirror, if the angle becomes 90° before entering the atmosphere to collide with the denser molecules there. Other particles that do not mirror enter the atmosphere and contribute to the auroral display over a range of altitudes. Other types of auroras have been observed from space, e.g."poleward arcs" stretching sunward across the polar cap, the related "theta aurora", and "dayside arcs" near noon. These are relatively infrequent and poorly understood. Other interesting effects occur such as flickering aurora, "black aurora" and subvisual red arcs. In addition to all these, a weak glow (often deep red) observed around the two polar cusps, the field lines separating the ones that close through the Earth from those that are swept into the tail and close remotely.
Visual forms and colors
Auroras frequently appear either as a diffuse glow or as "curtains" that extend approximately in the east–west direction. At some times, they form "quiet arcs"; at others, they evolve and change constantly. These are called "active aurora".
The most distinctive and brightest are the curtain-like auroral arcs. Each curtain consists of many parallel rays, each lined up with the local direction of the magnetic field, consistent with auroras being shaped by Earth's magnetic field. In situ particle measurements confirm that auroral electrons are guided by the geomagnetic field, and spiral around them while moving toward Earth. The similarity of an auroral display to curtains is often enhanced by folds within the arcs. Arcs can fragment or break up into separate, at times rapidly changing, often rayed features that may fill the whole sky. These are the discrete auroras, which are at times bright enough to read a newspaper by at night. and can display rapid subsecond variations in intensity. The diffuse aurora, though, is a relatively featureless glow sometimes close to the limit of visibility. It can be distinguished from moonlit clouds because stars can be seen undiminished through the glow. Diffuse auroras are often composed of patches whose brightness exhibits regular or near-regular pulsations. The pulsation period can be typically many seconds, so is not always obvious. Often there black aurora i.e. narrow regions in diffuse aurora with reduced luminosity. A typical auroral display consists of these forms appearing in the above order throughout the night.
Red: At the highest altitudes, excited atomic oxygen emits at 630 nm (red); low concentration of atoms and lower sensitivity of eyes at this wavelength make this color visible only under more intense solar activity. The low number of oxygen atoms and their gradually diminishing concentration is responsible for the faint appearance of the top parts of the "curtains". Scarlet, crimson, and carmine are the most often-seen hues of red for the auroras.
Green: At lower altitudes, the more frequent collisions suppress the 630-nm (red) mode: rather the 557.7 nm emission (green) dominates. Fairly high concentration of atomic oxygen and higher eye sensitivity in green make green auroras the most common. The excited molecular nitrogen (atomic nitrogen being rare due to high stability of the N2 molecule) plays a role here, as it can transfer energy by collision to an oxygen atom, which then radiates it away at the green wavelength. (Red and green can also mix together to produce pink or yellow hues.) The rapid decrease of concentration of atomic oxygen below about 100 km is responsible for the abrupt-looking end of the lower edges of the curtains. Both the 557.7 and 630.0 nm wavelengths correspond to forbidden transitions of atomic oxygen, slow mechanism that is responsible for the graduality (0.7 s and 107 s respectively) of flaring and fading.
Blue: At yet lower altitudes, atomic oxygen is uncommon, and molecular nitrogen and ionized molecular nitrogen take over in producing visible light emission, radiating at a large number of wavelengths in both red and blue parts of the spectrum, with 428 nm (blue) being dominant. Blue and purple emissions, typically at the lower edges of the "curtains", show up at the highest levels of solar activity. The molecular nitrogen transitions are much faster than the atomic oxygen ones.
Ultraviolet: Ultraviolet radiation from auroras (within the optical window but not visible to virtually all humans) has been observed with the requisite equipment. Ultraviolet auroras have also been seen on Mars, Jupiter and Saturn.
Infrared: Infrared radiation, in wavelengths that are within the optical window, is also part of many auroras.
Yellow and pink are a mix of red and green or blue. Other shades of red, as well as orange, may be seen on rare occasions; yellow-green is moderately common. As red, green, and blue are the primary colours of additive synthesis of colours, in theory, practically any colour might be possible, but the ones mentioned in this article comprise a virtually exhaustive list.
An aurora sometimes referred to as polar lights, northern lights (aurora borealis) or southern lights (aurora australis), is a natural light display in the Earth's sky, predominantly seen in the high-latitude regions (around the Arctic and Antarctic).
Auroras are produced when the magnetosphere is sufficiently disturbed by the solar wind that the trajectories of charged particles in both solar wind and magnetospheric plasma, mainly in the form of electrons and protons, precipitate them into the upper atmosphere (thermosphere/exosphere) due to Earth's magnetic field, where their energy is lost.
The resulting ionization and excitation of atmospheric constituents emits light of varying color and complexity. The form of the aurora, occurring within bands around both polar regions, is also dependent on the amount of acceleration imparted to the precipitating particles. Precipitating protons generally produce optical emissions as incident hydrogen atoms after gaining electrons from the atmosphere. Proton auroras are usually observed at lower latitudes.
Etymology
Aurora came from the Latin word for "dawn, morning light", since auroras were formerly thought to be the first light of dawn.
Occurrence of terrestrial auroras
Most auroras occur in a band known as the "auroral zone",[which is typically 3° to 6° wide in latitude and between 10° and 20° from the geomagnetic poles at all local times (or longitudes), most clearly seen at night against a dark sky. A region that currently displays an aurora is called the "auroral oval", a band displaced towards the night side of the Earth. Early evidence for a geomagnetic connection comes from the statistics of auroral observations. Elias Loomis (1860), and later Hermann Fritz (1881) and S. Tromholt (1882) in more detail, established that the aurora appeared mainly in the auroral zone. Day-to-day positions of the auroral ovals are posted on the internet.
In northern latitudes, the effect is known as the aurora borealis or the northern lights. The former term was coined by Galileo in 1619, from the Roman goddess of the dawn and the Greek name for the north wind.[8] The southern counterpart, the aurora australis or the southern lights, has features almost identical to the aurora borealis and changes simultaneously with changes in the northern auroral zone. The Aurora Australis is visible from high southern latitudes in Antarctica, Chile, Argentina, New Zealand, and Australia.
A geomagnetic storm causes the auroral ovals (north and south) to expand, and bring the aurora to lower latitudes. It was hardly ever seen near the geographic pole, which is about 2000 km away from the magnetic pole. The instantaneous distribution of auroras ("auroral oval") is slightly different, being centered about 3–5° nightward of the magnetic pole, so that auroral arcs reach furthest toward the equator when the magnetic pole in question is in between the observer and the Sun. The aurora can be seen best at this time, which is called magnetic midnight.
Auroras seen within the auroral oval may be directly overhead, but from farther away, they illuminate the poleward horizon as a greenish glow, or sometimes a faint red, as if the Sun were rising from an unusual direction. Auroras also occur poleward of the auroral zone as either diffuse patches or arcs, which can be subvisual.
Auroras are occasionally seen in latitudes below the auroral zone, when a geomagnetic storm temporarily enlarges the auroral oval. Large geomagnetic storms are most common during the peak of the 11-year sunspot cycle or during the three years after the peak. An aurora may appear overhead as a "corona" of rays, radiating from a distant and apparent central location, which results from perspective. An electron spirals (gyrates) about a field line at an angle that is determined by its velocity vectors, parallel and perpendicular, respectively, to the local geomagnetic field vector B. This angle is known as the "pitch angle" of the particle. The distance, or radius, of the electron from the field line at any time is known as its Larmor radius. The pitch angle increases as the electron travels to a region of greater field strength nearer to the atmosphere. Thus, it is possible for some particles to return, or mirror, if the angle becomes 90° before entering the atmosphere to collide with the denser molecules there. Other particles that do not mirror enter the atmosphere and contribute to the auroral display over a range of altitudes. Other types of auroras have been observed from space, e.g."poleward arcs" stretching sunward across the polar cap, the related "theta aurora", and "dayside arcs" near noon. These are relatively infrequent and poorly understood. Other interesting effects occur such as flickering aurora, "black aurora" and subvisual red arcs. In addition to all these, a weak glow (often deep red) observed around the two polar cusps, the field lines separating the ones that close through the Earth from those that are swept into the tail and close remotely.
Visual forms and colors
Auroras frequently appear either as a diffuse glow or as "curtains" that extend approximately in the east–west direction. At some times, they form "quiet arcs"; at others, they evolve and change constantly. These are called "active aurora".
The most distinctive and brightest are the curtain-like auroral arcs. Each curtain consists of many parallel rays, each lined up with the local direction of the magnetic field, consistent with auroras being shaped by Earth's magnetic field. In situ particle measurements confirm that auroral electrons are guided by the geomagnetic field, and spiral around them while moving toward Earth. The similarity of an auroral display to curtains is often enhanced by folds within the arcs. Arcs can fragment or break up into separate, at times rapidly changing, often rayed features that may fill the whole sky. These are the discrete auroras, which are at times bright enough to read a newspaper by at night. and can display rapid subsecond variations in intensity. The diffuse aurora, though, is a relatively featureless glow sometimes close to the limit of visibility. It can be distinguished from moonlit clouds because stars can be seen undiminished through the glow. Diffuse auroras are often composed of patches whose brightness exhibits regular or near-regular pulsations. The pulsation period can be typically many seconds, so is not always obvious. Often there black aurora i.e. narrow regions in diffuse aurora with reduced luminosity. A typical auroral display consists of these forms appearing in the above order throughout the night.
Red: At the highest altitudes, excited atomic oxygen emits at 630 nm (red); low concentration of atoms and lower sensitivity of eyes at this wavelength make this color visible only under more intense solar activity. The low number of oxygen atoms and their gradually diminishing concentration is responsible for the faint appearance of the top parts of the "curtains". Scarlet, crimson, and carmine are the most often-seen hues of red for the auroras.
Green: At lower altitudes, the more frequent collisions suppress the 630-nm (red) mode: rather the 557.7 nm emission (green) dominates. Fairly high concentration of atomic oxygen and higher eye sensitivity in green make green auroras the most common. The excited molecular nitrogen (atomic nitrogen being rare due to high stability of the N2 molecule) plays a role here, as it can transfer energy by collision to an oxygen atom, which then radiates it away at the green wavelength. (Red and green can also mix together to produce pink or yellow hues.) The rapid decrease of concentration of atomic oxygen below about 100 km is responsible for the abrupt-looking end of the lower edges of the curtains. Both the 557.7 and 630.0 nm wavelengths correspond to forbidden transitions of atomic oxygen, slow mechanism that is responsible for the graduality (0.7 s and 107 s respectively) of flaring and fading.
Blue: At yet lower altitudes, atomic oxygen is uncommon, and molecular nitrogen and ionized molecular nitrogen take over in producing visible light emission, radiating at a large number of wavelengths in both red and blue parts of the spectrum, with 428 nm (blue) being dominant. Blue and purple emissions, typically at the lower edges of the "curtains", show up at the highest levels of solar activity. The molecular nitrogen transitions are much faster than the atomic oxygen ones.
Ultraviolet: Ultraviolet radiation from auroras (within the optical window but not visible to virtually all humans) has been observed with the requisite equipment. Ultraviolet auroras have also been seen on Mars, Jupiter and Saturn.
Infrared: Infrared radiation, in wavelengths that are within the optical window, is also part of many auroras.
Yellow and pink are a mix of red and green or blue. Other shades of red, as well as orange, may be seen on rare occasions; yellow-green is moderately common. As red, green, and blue are the primary colours of additive synthesis of colours, in theory, practically any colour might be possible, but the ones mentioned in this article comprise a virtually exhaustive list.
...
Yet another shot of a wristwatch I showed before. Too cold here to take some new photos, folks... my finger would freeze up on the shutter... :D
...
First signs of patina on my new strap (deliberated).
Woohoo... ;)
Strap from www.uhrenbaender.de/.
An aurora sometimes referred to as polar lights, northern lights (aurora borealis) or southern lights (aurora australis), is a natural light display in the Earth's sky, predominantly seen in the high-latitude regions (around the Arctic and Antarctic).
Auroras are produced when the magnetosphere is sufficiently disturbed by the solar wind that the trajectories of charged particles in both solar wind and magnetospheric plasma, mainly in the form of electrons and protons, precipitate them into the upper atmosphere (thermosphere/exosphere) due to Earth's magnetic field, where their energy is lost.
The resulting ionization and excitation of atmospheric constituents emits light of varying color and complexity. The form of the aurora, occurring within bands around both polar regions, is also dependent on the amount of acceleration imparted to the precipitating particles. Precipitating protons generally produce optical emissions as incident hydrogen atoms after gaining electrons from the atmosphere. Proton auroras are usually observed at lower latitudes.
Etymology
Aurora came from the Latin word for "dawn, morning light", since auroras were formerly thought to be the first light of dawn.
Occurrence of terrestrial auroras
Most auroras occur in a band known as the "auroral zone",[which is typically 3° to 6° wide in latitude and between 10° and 20° from the geomagnetic poles at all local times (or longitudes), most clearly seen at night against a dark sky. A region that currently displays an aurora is called the "auroral oval", a band displaced towards the night side of the Earth. Early evidence for a geomagnetic connection comes from the statistics of auroral observations. Elias Loomis (1860), and later Hermann Fritz (1881) and S. Tromholt (1882) in more detail, established that the aurora appeared mainly in the auroral zone. Day-to-day positions of the auroral ovals are posted on the internet.
In northern latitudes, the effect is known as the aurora borealis or the northern lights. The former term was coined by Galileo in 1619, from the Roman goddess of the dawn and the Greek name for the north wind. The southern counterpart, the aurora australis or the southern lights, has features almost identical to the aurora borealis and changes simultaneously with changes in the northern auroral zone. The Aurora Australis is visible from high southern latitudes in Antarctica, Chile, Argentina, New Zealand, and Australia.
A geomagnetic storm causes the auroral ovals (north and south) to expand, and bring the aurora to lower latitudes. It was hardly ever seen near the geographic pole, which is about 2000 km away from the magnetic pole. The instantaneous distribution of auroras ("auroral oval") is slightly different, being centered about 3–5° nightward of the magnetic pole, so that auroral arcs reach furthest toward the equator when the magnetic pole in question is in between the observer and the Sun. The aurora can be seen best at this time, which is called magnetic midnight.
Auroras seen within the auroral oval may be directly overhead, but from farther away, they illuminate the poleward horizon as a greenish glow, or sometimes a faint red, as if the Sun were rising from an unusual direction. Auroras also occur poleward of the auroral zone as either diffuse patches or arcs, which can be subvisual.
Auroras are occasionally seen in latitudes below the auroral zone, when a geomagnetic storm temporarily enlarges the auroral oval. Large geomagnetic storms are most common during the peak of the 11-year sunspot cycle or during the three years after the peak. An aurora may appear overhead as a "corona" of rays, radiating from a distant and apparent central location, which results from perspective. An electron spirals (gyrates) about a field line at an angle that is determined by its velocity vectors, parallel and perpendicular, respectively, to the local geomagnetic field vector B. This angle is known as the "pitch angle" of the particle. The distance, or radius, of the electron from the field line at any time is known as its Larmor radius. The pitch angle increases as the electron travels to a region of greater field strength nearer to the atmosphere. Thus, it is possible for some particles to return, or mirror, if the angle becomes 90° before entering the atmosphere to collide with the denser molecules there. Other particles that do not mirror enter the atmosphere and contribute to the auroral display over a range of altitudes. Other types of auroras have been observed from space, e.g."poleward arcs" stretching sunward across the polar cap, the related "theta aurora", and "dayside arcs" near noon. These are relatively infrequent and poorly understood. Other interesting effects occur such as flickering aurora, "black aurora" and subvisual red arcs. In addition to all these, a weak glow (often deep red) observed around the two polar cusps, the field lines separating the ones that close through the Earth from those that are swept into the tail and close remotely.
Visual forms and colors
Auroras frequently appear either as a diffuse glow or as "curtains" that extend approximately in the east–west direction. At some times, they form "quiet arcs"; at others, they evolve and change constantly. These are called "active aurora".
The most distinctive and brightest are the curtain-like auroral arcs. Each curtain consists of many parallel rays, each lined up with the local direction of the magnetic field, consistent with auroras being shaped by Earth's magnetic field. In situ particle measurements confirm that auroral electrons are guided by the geomagnetic field, and spiral around them while moving toward Earth. The similarity of an auroral display to curtains is often enhanced by folds within the arcs. Arcs can fragment or break up into separate, at times rapidly changing, often rayed features that may fill the whole sky. These are the discrete auroras, which are at times bright enough to read a newspaper by at night. and can display rapid subsecond variations in intensity. The diffuse aurora, though, is a relatively featureless glow sometimes close to the limit of visibility. It can be distinguished from moonlit clouds because stars can be seen undiminished through the glow. Diffuse auroras are often composed of patches whose brightness exhibits regular or near-regular pulsations. The pulsation period can be typically many seconds, so is not always obvious. Often there black aurora i.e. narrow regions in diffuse aurora with reduced luminosity. A typical auroral display consists of these forms appearing in the above order throughout the night.
Red: At the highest altitudes, excited atomic oxygen emits at 630 nm (red); low concentration of atoms and lower sensitivity of eyes at this wavelength make this color visible only under more intense solar activity. The low number of oxygen atoms and their gradually diminishing concentration is responsible for the faint appearance of the top parts of the "curtains". Scarlet, crimson, and carmine are the most often-seen hues of red for the auroras.
Green: At lower altitudes, the more frequent collisions suppress the 630-nm (red) mode: rather the 557.7 nm emission (green) dominates. Fairly high concentration of atomic oxygen and higher eye sensitivity in green make green auroras the most common. The excited molecular nitrogen (atomic nitrogen being rare due to high stability of the N2 molecule) plays a role here, as it can transfer energy by collision to an oxygen atom, which then radiates it away at the green wavelength. (Red and green can also mix together to produce pink or yellow hues.) The rapid decrease of concentration of atomic oxygen below about 100 km is responsible for the abrupt-looking end of the lower edges of the curtains. Both the 557.7 and 630.0 nm wavelengths correspond to forbidden transitions of atomic oxygen, slow mechanism that is responsible for the graduality (0.7 s and 107 s respectively) of flaring and fading.
Blue: At yet lower altitudes, atomic oxygen is uncommon, and molecular nitrogen and ionized molecular nitrogen take over in producing visible light emission, radiating at a large number of wavelengths in both red and blue parts of the spectrum, with 428 nm (blue) being dominant. Blue and purple emissions, typically at the lower edges of the "curtains", show up at the highest levels of solar activity. The molecular nitrogen transitions are much faster than the atomic oxygen ones.
Ultraviolet: Ultraviolet radiation from auroras (within the optical window but not visible to virtually all humans) has been observed with the requisite equipment. Ultraviolet auroras have also been seen on Mars, Jupiter and Saturn.
Infrared: Infrared radiation, in wavelengths that are within the optical window, is also part of many auroras.
Yellow and pink are a mix of red and green or blue. Other shades of red, as well as orange, may be seen on rare occasions; yellow-green is moderately common. As red, green, and blue are the primary colours of additive synthesis of colours, in theory, practically any colour might be possible, but the ones mentioned in this article comprise a virtually exhaustive list.
The Rodina R005 is a bauhaus style watch equipped with a Sea-Gull ST17 movement.
This particular model is the smaller 34.5mm version which utilizes the removal of the rotor mechanism to provide a smaller, slimmer profile. The watch still maintains a mechanical movement but needs to be hand-wound daily.
I was up at the Renaissance Hotel in the Arboretum today taking photos for a charity event and grabbed this HDR on the way out. It would have been sharper if I had brought a remote release but I guess this will have to do for now...
BTW, the EXIF information on this image is completely bogus. It was taken using a 10mm lens and the shutter speed was subsecond for all 3 exposures. Photomatix beta bug?
Limited edition of 60 pieces. Custom stainless steel case with a separately constructed Tungsten bezel and Tungsten crown cap. Black plated case, screwdown pushers and screwdown crown . Crystal window in case back to reveal the Swiss automatic movement. Swiss made Valjoux 7750 automatic chronograph movement. 25 jewels movement. Black genuine crocodile leather band with custom black plated stainless steel deployment buckle. Hardened mineral crystal. Clean, classic dial with crisp contrast and attention to detail. Black CD texture dial. Black radial brushed concave ring. Applied white index with white super lum. Black hour and minute white super lum seconds hand and subdial hands. 6 hand chronograph with chrono hours, minutes, and sweeping subseconds hand. Water resistant up to 20ATM
Limited edition of 60 pieces. Custom stainless steel case with a separately constructed Tungsten bezel and Tungsten crown cap. Black plated case, screwdown pushers and screwdown crown . Crystal window in case back to reveal the Swiss automatic movement. Swiss made Valjoux 7750 automatic chronograph movement. 25 jewels movement. Black genuine crocodile leather band with custom black plated stainless steel deployment buckle. Hardened mineral crystal. Clean, classic dial with crisp contrast and attention to detail. Black CD texture dial. Black radial brushed concave ring. Applied white index with white super lum. Black hour and minute white super lum seconds hand and subdial hands. 6 hand chronograph with chrono hours, minutes, and sweeping subseconds hand. Water resistant up to 20ATM
Limited edition of 60 pieces. Custom stainless steel case with a separately constructed Tungsten bezel and Tungsten crown cap. Black plated case, screwdown pushers and screwdown crown . Crystal window in case back to reveal the Swiss automatic movement. Swiss made Valjoux 7750 automatic chronograph movement. 25 jewels movement. Black genuine crocodile leather band with custom black plated stainless steel deployment buckle. Hardened mineral crystal. Clean, classic dial with crisp contrast and attention to detail. Black CD texture dial. Black radial brushed concave ring. Applied white index with white super lum. Black hour and minute white super lum seconds hand and subdial hands. 6 hand chronograph with chrono hours, minutes, and sweeping subseconds hand. Water resistant up to 20ATM
This is an Audemars Piguet Tourbillon Chronograph in 18k pink gold on a leather strap. It has an automatic movement with subseconds, chronograph and tourbillon.
Go to www.grayandsons.com to view this and other fine watches available for purchase. We specialize in fine pre-owned watches and estate jewelry.
Tried and adjusted Gigapan to match Nikon S6's nodal point, and it generates less distorted image. Not perfect still since S6 doesn't have exposure lock and I have to set Gigapan to wait 7 seconds between shots since S6 is pretty slow in low light.
GigaPan Stitcher version 0.4.2735 (Windows)
Panorama size: 106 megapixels (13430 x 7926 pixels)
Input images: 42 (7 columns by 6 rows)
Field of view: 94.6 degrees wide by 55.9 degrees high (top=38.0, bottom=-17.8)
Settings:
All default settings
Original image properties:
Camera make: NIKON
Camera model: COOLPIX S6
Image size: 2816x2112 (5.9 megapixels)
Aperture: f/5.4
Exposure time: 0.0847458 - 2
ISO: 400
Focal length (35mm equiv.): 105.0 mm
Digital zoom: off
White balance: Fixed
Exposure mode: Automatic
Has subsecond timestamp: no
Horizontal overlap: 38.6 to 48.5 percent
Vertical overlap: 43.4 to 44.9 percent
Computer stats: 2014.22 MB RAM, 2 CPUs
Total time 39:23 (0:56 per picture)
Alignment: 2:16, Projection: 3:45, Blending: 33:21
First try with Gigapan.
It can fit Nikon S6 without problem and it seems working to a degree. As you can see, because of the lens module is different from other types of cameras, I really think the nodal point is quite off for close objects.
BTW, Gigapan unit took several minutes and mingling with the battery module to power up, at first I am nervous that I got a DoA unit. I don't know if it's battery module connection related or condensation related.
GigaPan Stitcher version 0.4.2735 (Windows)
Panorama size: 20 megapixels (6161 x 3337 pixels)
Input images: 6 (3 columns by 2 rows)
Field of view: 42.2 degrees wide by 22.9 degrees high (top=43.6, bottom=20.7)
Settings:
All default settings
Original image properties:
Camera make: NIKON
Camera model: COOLPIX S6
Image size: 2816x2112 (5.9 megapixels)
Aperture: f/5.4
Exposure time: 0.131579 - 0.344828
ISO: 50
Focal length (35mm equiv.): 105.0 mm
Digital zoom: off
White balance: Fixed
Exposure mode: Automatic
Has subsecond timestamp: no
Horizontal overlap: 20.6 to 64.2 percent
Vertical overlap: 41.7 to 42.1 percent
Computer stats: 2014.22 MB RAM, 2 CPUs
Total time 2:19 (0:23 per picture)
Alignment: 0:13, Projection: 0:25, Blending: 1:40
This is a Rolex Daytona in 18k white gold and has the famous Rolex meteorite face. It has an automatic movement with subseconds, sweep seconds, and date. The model number for this watch is 116519.
Go to www.grayandsons.com to view this and other fine watches available for purchase. We specialize in fine pre-owned watches and estate jewelry.
www.dpbolvw.net/ml105tenkem19532B541334B6464?sid=fllu.
Limited edition of 60 pieces. Custom stainless steel case with a separately constructed Tungsten bezel and Tungsten crown cap. Black plated case, screwdown pushers and screwdown crown . Crystal window in case back to reveal the Swiss automatic movement. Swiss made Valjoux 7750 automatic chronograph movement. 25 jewels movement. Black genuine crocodile leather band with custom black plated stainless steel deployment buckle. Hardened mineral crystal. Clean, classic dial with crisp contrast and attention to detail. Black CD texture dial. Black radial brushed concave ring. Applied white index with white super lum. Black hour and minute white super lum seconds hand and subdial hands. 6 hand chronograph with chrono hours, minutes, and sweeping subseconds hand. Water resistant up to 20ATM
This is the first try with Nikon D40x + 18-70DX, we can definitely see problems with the motor not powerful enough to position the camera to the first row, other than that it's kinda work.
GigaPan Stitcher version 0.4.2735 (Windows)
Panorama size: 65 megapixels (9997 x 6526 pixels)
Input images: 16 (4 columns by 4 rows)
Field of view: 47.7 degrees wide by 31.1 degrees high (top=19.2, bottom=-12.0)
Settings:
All default settings
Original image properties:
Camera make: NIKON CORPORATION
Camera model: NIKON D40X
Image size: 3872x2592 (10.0 megapixels)
Aperture: f/5.6
Exposure time: 2
ISO: 400
Focal length (35mm equiv.): 105.0 mm
Digital zoom: off
White balance: Automatic
Exposure mode: Manual
Has subsecond timestamp: no
Horizontal overlap: 47.4 to 50.7 percent
Vertical overlap: 50.2 to 53.6 percent
Computer stats: 2014.22 MB RAM, 2 CPUs
Total time 13:33 (0:50 per picture)
Alignment: 0:45, Projection: 1:32, Blending: 11:16
Femke Herregraven : Subsecond Flocks – When you startle awake at four in the morning it’s not because you’re feeling happy (2016)
Visite au STUK (Leuven) : The Act of Magic, 9 mars 2017.
www.artefact-festival.be/en/program/artefact-expo-act-magic
—
Erg (École de Recherche Graphique), Arts Numériques-Atelier, 2016-2017.
Professor : Marc Wathieu.
GigaPan Stitcher version 0.4.2735 (Windows)
Panorama size: 34 megapixels (7696 x 4541 pixels)
Input images: 20 (5 columns by 4 rows)
Field of view: 6.9 degrees wide by 4.1 degrees high (top=10.6, bottom=6.5)
Settings:
All default settings
Original image properties:
Camera make: NIKON CORPORATION
Camera model: NIKON D40X
Image size: 3872x2592 (10.0 megapixels)
Aperture: f/5.6
Exposure time: 0.769231
ISO: 400
Focal length (35mm equiv.): 450.0 mm
Digital zoom: off
White balance: Automatic
Exposure mode: Manual
Has subsecond timestamp: no
Horizontal overlap: 1.8 to 76.8 percent
Vertical overlap: 74.0 to 75.4 percent
Computer stats: 2014.22 MB RAM, 2 CPUs
Total time 40:48 (2:02 per picture)
Alignment: 2:01, Projection: 2:06, Blending: 36:40
my little dog!
--- EXIF DATA ---
File Name:_DSC0353.NEF
File Size:12.090.351 Bytes
File Type:Nikon NEF
Exif Byte Order:Big Endian (Motorola)
Image width:160
Image height:120
Bits Per Sample:8
Compression:uncompressed
PhotoMetric Interp:RGB
Manufacturer:NIKON CORPORATION
Model number:NIKON D300
Image orientation:Top, left
Resolution (width):300 pixels per inch
Resolution (height):300 pixels per inch
Software used:Ver.1.00
File date and time:2007:12:13 14:20:19
Date time of image:2007:12:13 14:20:19
Exposure time:0,0200 seconds
f number:5,6
Exposure program:Aperture priority
ISO speed rating:800
Date time of image:2007:12:13 14:20:19
Date time digitized:2007:12:13 14:20:19
Exposure bias:0,0 stops
Maximum lens aperture:f/5,7
Metering mode:Pattern
Light source:unknown
Flash:Flash did not fire
Lens focal length:200,0 mm
Date time subseconds:
Original subseconds:
Digitized subseconds:
Sensing method:One-chip color area sensor
Scene type:Directly photographed image
Custom rendered:Normal process
Exposure mode:Auto exposure
White balance:Auto white balance
Digital zoom ratio:1,0
35mm film focal length:300 mm
Scene capture type:Standard
www.purehorloge.com/audemars-piguet-unworn-jules-audemars... Model Number: 77238OR.OO.A088CR.01 Age: 2014 Case Size: 33mm Box & Papers: Box,Manuals&Guarantee Movement: Mechanical Manual Wind Case: 18k Rose Gold Dial: Silver guilloche with subseconds&Diamond hour Markers Bracelet: Brown Crocodile Leather Strap Length: Adjustable up to18cm Strap Width: At Case-18mm/AtBuckle-16mm Buckle: 18k Rose Gold Deployment Glass: Sapphire Crystal
This is a Zenith Chronomaster XXT Open in 18k pink gold on a leather strap. It has an automatic movement with subseconds, chronograph and power reserve.
Go to www.grayandsons.com to view this and other fine watches available for purchase. We specialize in fine pre-owned watches and estate jewelry.
A scratch-resistant sapphire crystal face protects the textured dial of a demure round watch detailed with a chic subseconds dial, date window and smooth leather strap. - See more at: www.shoppersfeed.com/20030-burberry-textured-dial-watch-40mm
A scratch-resistant sapphire crystal face protects the textured dial of a demure round watch detailed with a chic subseconds dial, date window and smooth leather strap. 40mm case; 18mm band width. Buckle closure. Sapphire crystal face. Stainless steel or stainless steel with gold ionic plating/PVC-coated leather. By Burberry; Swiss made. - See more at: www.shoppersfeed.com/20153-burberry-textured-dial-watch-4...
Femke Herregraven : Subsecond Flocks – When you startle awake at four in the morning it’s not because you’re feeling happy (2016)
Visite au STUK (Leuven) : The Act of Magic, 9 mars 2017.
www.artefact-festival.be/en/program/artefact-expo-act-magic
—
Erg (École de Recherche Graphique), Arts Numériques-Atelier, 2016-2017.
Professor : Marc Wathieu.
www.mndjet.com/item/1944/skagen-black-chrome-gmt-dual-tim....
This Swiss Movement timepiece is perfectly structured for professionals on the move. A luxurious black genuine Italian leather strap meets a polished stainless steel round case in silver. Silver dial features a multifunctional GMT dualtime zone date window and small subsecond hand. Super harden mineral crystal. Case 38mm. Water resistant to 50 meters.
Ferris Wheel; 5secs, f/9
# Exposure Time (1 / Shutter Speed) = 5/1 second ===> 5 second
# Lens F-Number / F-Stop = 9/1 ===> ƒ/9
# Exposure Program = manual control (1)
# ISO Speed Ratings = 100
# Exif Version = 0221
# Original Date/Time = 2009:10:22 18:28:22
# Digitization Date/Time = 2009:10:22 18:28:22
# Shutter Speed Value (APEX) = -2321928/1000000
Shutter Speed (Exposure Time) = 1/0.2 second
# Aperture Value (APEX) = 633985/100000
Aperture = ƒ/9
# Exposure Bias (EV) = 0/1 ===> 0
# Max Aperture Value (APEX) = 4/1 ===> 4
Max Aperture = ƒ/4
# Metering Mode = pattern / multi-segment (5)
# Flash = Flash did not fire, compulsory flash mode
# Focal Length = 24/1 mm ===> 24 mm
# Original Subsecond Time = 77
# Digitized Subsecond Time = 77
# Colour Space = 65535
# Image Width = 651 pixels
# Image Height = 522 pixels
# Focal Plane X-Resolution = 4272000/878 ===> 4865.6
# Focal Plane Y-Resolution = 2848000/584 ===> 4876.71
# Focal Plane X/Y-Resolution Unit = inch (2)
# Custom Rendered = normal process (0)
# Exposure Mode = manual exposure (1)
# White Balance = auto (0)
# Scene Capture Type = standard (0)
This is a Breitling Bently in stainless steel on a leather strap. It has an automatic movement with subseconds, date and chronograph. Model number is A25362.
Go to www.grayandsons.com to view this and other fine watches available for purchase. We specialize in fine pre-owned watches and estate jewelry.
An Iridium flare. Luckly this one passed in Ursa Minor
Here is the original version.
The thick track is the Sun reflecting onto an Iridium satellite antenna. Each Iridium has three big antennas which are almost specular.
Iridium's orbit is tightly controlled and it is possible to predict when and where they passes over our heads and when the satellite is in sunlight and where the reflected beam reach ground.
A web site is avaiable to predict Iridium flares in any world location. You must enter your coordinates with 4 decimals at least because an iriudium flare has only a 7km diameter.
Predictions have subsecond precision!!!
I was used to stun my friends and collegues callin'em out, start count down, point a finger toward the sky, and... "WHOOA", "WTH", "What is that?", "How do you know", "that's incredible"
total funny :)
If you took Iridium flare photos please post them to Iridium Flares group
An Iridium flare. Luckly this one passed in Ursa Minor
Here is an annotated version.
The thick track is the Sun reflecting onto an Iridium satellite antenna. Each Iridium has three big antennas which are almost specular.
Iridium's orbit is tightly controlled and it is possible to predict when and where they passes over our heads and when the satellite is in sunlight and where the reflected beam reach ground.
A web site is avaiable to predict Iridium flares in any world location. You must enter your coordinates with 4 decimals at least because an iriudium flare has only a 7km diameter.
Predictions have subsecond precision!!!
I was used to stun my friends and collegues callin'em out, start count down, point a finger toward the sky, and... "WHOOA", "WTH", "What is that?", "How do you know", "that's incredible"
total funny :)
If you took Iridium flare photos please post them to Iridium Flares group