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reflection, refraction,diffractionand interference

Ptolemy measured the angle that a beam of light hits a boundary, the angle of incidence, and the angle at which it leaves, the angle of refraction, through different mediums. He discovered that the angle of incidence is proportional to the angle of refraction, but could not derive the full equation. Like Euclid, Ptolemy thought that light is emitted in rays from the eye.[3]

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Diffraction vs reflectionexamples

↑ Lindberg, D. C., The Beginnings of Western Science: The European Scientific Tradition in Philosophical, Religious, and Institutional Context, Prehistory to A.D. 1450, University of Chicago Press, 2010.

The Dutch mathematician Willebrord Snellius rediscovered the sine law of refraction in 1621. Snellius’ theory was not published in his lifetime and, in 1637, the French natural philosopher Rene Descartes rediscovered the law again, independently.[5]

reflection, refractiondiffractionexamples

Red dwarfs are the most common of all stars. They are much smaller than our Sun and are the coolest of the stars having a temperature of about 3000 K which means that these stars radiate most strongly in the near-infrared. Many of these stars are too faint in visible light to even be detected by optical telescopes, and have been discovered for the first time in the near-infrared. MID INFRARED: As we enter the mid-infrared region of the spectrum, the cool stars begin to fade out and cooler objects such as planets, comets and asteroids come into view. Planets absorb light from the sun and heat up. They then re-radiate this heat as infrared light. This is different from the visible light that we see from the planets which is reflected sunlight. The planets in our solar system have temperatures ranging from about 53 to 573 degrees Kelvin. Objects in this temperature range emit most of their light in the mid-infrared. For example, the Earth itself radiates most strongly at about 10 microns. Asteroids also emit most of their light in the mid-infrared making this wavelength band the most efficient for locating dark asteroids. Infrared data can help to determine the surface composition, and diameter of asteroids. An infrared view of the Earth IRAS mid-infrared view of Comet IRAS-Araki-Alcock Dust warmed by starlight is also very prominent in the mid-infrared. An example is the zodiacal dust which lies in the plane of our solar system. This dust is made up of silicates (like the rocks on Earth) and range in size from a tenth of a micron up to the size of large rocks. Silicates emit most of their radiation at about 10 microns. Mapping the distribution of this dust can provide clues about the formation of our own solar system. The dust from comets also has strong emission in the mid-infrared. Warm interstellar dust also starts to shine as we enter the mid-infrared region. The dust around stars which have ejected material shines most brightly in the mid-infrared. Sometimes this dust is so thick that the star hardly shines through at all and can only be detected in the infrared. Protoplanetary disks, the disks of material which surround newly forming stars, also shines brightly in the mid-infrared. These disks are where new planets are possibly being formed. FAR INFRARED: In the far-infrared, the stars have all vanished. Instead we now see very cold matter (140 Kelvin or less). Huge, cold clouds of gas and dust in our own galaxy, as well as in nearby galaxies, glow in far-infrared light. In some of these clouds, new stars are just beginning to form. Far-infrared observations can detect these protostars long before they "turn on" visibly by sensing the heat they radiate as they contract." IRAS view of infrared cirrus - dust heated by starlight Michael Hauser (Space Telescope Science Institute), the COBE/DIRBE Science Team, and NASA The center of our galaxy also shines brightly in the far-infrared because of the thick concentration of stars embedded in dense clouds of dust. These stars heat up the dust and cause it to glow brightly in the infrared. The image (at left) of our galaxy taken by the COBE satellite, is a composite of far-infrared wavelengths of 60, 100, and 240 microns. Except for the plane of our own Galaxy, the brightest far-infrared object in the sky is central region of a galaxy called M82. The nucleus of M82 radiates as much energy in the far-infrared as all of the stars in our Galaxy combined. This far-infrared energy comes from dust heated by a source that is hidden from view. The central regions of most galaxies shine very brightly in the far-infrared. Several galaxies have active nuclei hidden in dense regions of dust. Others, called starburst galaxies, have an extremely high number of newly forming stars heating interstellar dust clouds. These galaxies, far outshine all others galaxies in the far-infrared. IRAS infrared view of the Andromeda Galaxy (M31) - notice the bright central region. Discovery of Infrared | What is Infrared? | Infrared Astronomy Overview | Atmospheric Windows | Near, Mid & Far Infrared | The Infrared Universe | Spectroscopy | Timeline | Background | Future Missions | News & Discoveries | Images & Videos | Activities | Infrared Links | Educational Links | Getting into Astronomy HOME INFRARED PROCESSING AND ANALYSIS CENTER INDEX

The sine of 90° is 1 because the opposite length will also be the longest, the hypotenuse. In the triangle above, sin(C) would equal length c / length c, which equals 1.

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Infrared is usually divided into 3 spectral regions: near, mid and far-infrared. The boundaries between the near, mid and far-infrared regions are not agreed upon and can vary. The main factor that determines which wavelengths are included in each of these three infrared regions is the type of detector technology used for gathering infrared light. Near-infrared observations have been made from ground based observatories since the 1960's. They are done in much the same way as visible light observations for wavelengths less than 1 micron, but require special infrared detectors beyond 1 micron. Mid and far-infrared observations can only be made by observatories which can get above our atmosphere. These observations require the use of special cooled detectors containing crystals like germanium whose electrical resistance is very sensitive to heat. Infrared radiation is emitted by any object that has a temperature (ie radiates heat). So, basically all celestial objects emit some infrared. The wavelength at which an object radiates most intensely depends on its temperature. In general, as the temperature of an object cools, it shows up more prominently at farther infrared wavelengths. This means that some infrared wavelengths are better suited for studying certain objects than others. Visible (courtesy of Howard McCallon), near-infrared (2MASS), and mid-infrared (ISO) view of the Horsehead Nebula. Image assembled by Robert Hurt. As we move from the near-infrared into mid and far-infrared regions of the spectrum, some celestial objects will appear while others will disappear from view. For example, in the above image you can see how more stars (generally cooler stars) appear as we go from the visible light image to the near-infrared image. In the near-infrared, the dust also becomes transparent, allowing us to see regions hidden by dust in the visible image. As we go to the mid-infrared image, the cooler dust itself glows. The table below highlights what we see in the different infrared spectral regions. SPECTRAL REGION WAVELENGTH RANGE (microns) TEMPERATURE RANGE (degrees Kelvin) WHAT WE SEE Near-Infrared (0.7-1) to 5 740 to (3,000-5,200) Cooler red stars Red giants Dust is transparent Mid-Infrared 5 to (25-40) (92.5-140) to 740 Planets, comets and asteroidsDust warmed by starlight Protoplanetary disks Far-Infrared (25-40) to (200-350) (10.6-18.5) to (92.5-140) Emission from cold dust Central regions of galaxies Very cold molecular clouds NEAR INFRARED: Between about 0.7 to 1.1 microns we can use the same observing methods as are use for visible light observations, except for observation by eye. The infrared light that we observe in this region is not thermal (not due to heat radiation). Many do not even consider this range as part of infrared astronomy. Beyond about 1.1 microns, infrared emission is primarily heat or thermal radiation. As we move away from visible light towards longer wavelengths of light, we enter the infrared region. As we enter the near-infrared region, the hot blue stars seen clearly in visible light fade out and cooler stars come into view. Large red giant stars and low mass red dwarfs dominate in the near-infrared. The near-infrared is also the region where interstellar dust is the most transparent to infrared light. Visible (left) and Near-Infrared View of the Galactic Center Visible image courtesy of Howard McCallon. The infrared image is from the 2 Micron All Sky Survey (2MASS) Notice in the above images how center of our galaxy, which is hidden by thick dust in visible light (left), becomes transparent in the near-infrared (right). Many of the hotter stars in the visible image have faded in the near-infrared image. The near-infrared image shows cooler, reddish stars which do not appear in the visible light view. These stars are primarily red dwarfs and red giants. Red giants are large reddish or orange stars which are running out of their nuclear fuel. They can swell up to 100 times their original size and have temperatures which range from 2000 to 3500 K. Red giants radiate most intensely in the near-infrared region. Red dwarfs are the most common of all stars. They are much smaller than our Sun and are the coolest of the stars having a temperature of about 3000 K which means that these stars radiate most strongly in the near-infrared. Many of these stars are too faint in visible light to even be detected by optical telescopes, and have been discovered for the first time in the near-infrared. MID INFRARED: As we enter the mid-infrared region of the spectrum, the cool stars begin to fade out and cooler objects such as planets, comets and asteroids come into view. Planets absorb light from the sun and heat up. They then re-radiate this heat as infrared light. This is different from the visible light that we see from the planets which is reflected sunlight. The planets in our solar system have temperatures ranging from about 53 to 573 degrees Kelvin. Objects in this temperature range emit most of their light in the mid-infrared. For example, the Earth itself radiates most strongly at about 10 microns. Asteroids also emit most of their light in the mid-infrared making this wavelength band the most efficient for locating dark asteroids. Infrared data can help to determine the surface composition, and diameter of asteroids. An infrared view of the Earth IRAS mid-infrared view of Comet IRAS-Araki-Alcock Dust warmed by starlight is also very prominent in the mid-infrared. An example is the zodiacal dust which lies in the plane of our solar system. This dust is made up of silicates (like the rocks on Earth) and range in size from a tenth of a micron up to the size of large rocks. Silicates emit most of their radiation at about 10 microns. Mapping the distribution of this dust can provide clues about the formation of our own solar system. The dust from comets also has strong emission in the mid-infrared. Warm interstellar dust also starts to shine as we enter the mid-infrared region. The dust around stars which have ejected material shines most brightly in the mid-infrared. Sometimes this dust is so thick that the star hardly shines through at all and can only be detected in the infrared. Protoplanetary disks, the disks of material which surround newly forming stars, also shines brightly in the mid-infrared. These disks are where new planets are possibly being formed. FAR INFRARED: In the far-infrared, the stars have all vanished. Instead we now see very cold matter (140 Kelvin or less). Huge, cold clouds of gas and dust in our own galaxy, as well as in nearby galaxies, glow in far-infrared light. In some of these clouds, new stars are just beginning to form. Far-infrared observations can detect these protostars long before they "turn on" visibly by sensing the heat they radiate as they contract." IRAS view of infrared cirrus - dust heated by starlight Michael Hauser (Space Telescope Science Institute), the COBE/DIRBE Science Team, and NASA The center of our galaxy also shines brightly in the far-infrared because of the thick concentration of stars embedded in dense clouds of dust. These stars heat up the dust and cause it to glow brightly in the infrared. The image (at left) of our galaxy taken by the COBE satellite, is a composite of far-infrared wavelengths of 60, 100, and 240 microns. Except for the plane of our own Galaxy, the brightest far-infrared object in the sky is central region of a galaxy called M82. The nucleus of M82 radiates as much energy in the far-infrared as all of the stars in our Galaxy combined. This far-infrared energy comes from dust heated by a source that is hidden from view. The central regions of most galaxies shine very brightly in the far-infrared. Several galaxies have active nuclei hidden in dense regions of dust. Others, called starburst galaxies, have an extremely high number of newly forming stars heating interstellar dust clouds. These galaxies, far outshine all others galaxies in the far-infrared. IRAS infrared view of the Andromeda Galaxy (M31) - notice the bright central region. Discovery of Infrared | What is Infrared? | Infrared Astronomy Overview | Atmospheric Windows | Near, Mid & Far Infrared | The Infrared Universe | Spectroscopy | Timeline | Background | Future Missions | News & Discoveries | Images & Videos | Activities | Infrared Links | Educational Links | Getting into Astronomy HOME INFRARED PROCESSING AND ANALYSIS CENTER INDEX

Diffraction vs reflection vsrefraction

In the case of a double rainbow, secondary bows are caused by double reflection inside the raindrop. This causes the colours to be reversed and produces visible light at about 52°-54°.

Red giants are large reddish or orange stars which are running out of their nuclear fuel. They can swell up to 100 times their original size and have temperatures which range from 2000 to 3500 K. Red giants radiate most intensely in the near-infrared region. Red dwarfs are the most common of all stars. They are much smaller than our Sun and are the coolest of the stars having a temperature of about 3000 K which means that these stars radiate most strongly in the near-infrared. Many of these stars are too faint in visible light to even be detected by optical telescopes, and have been discovered for the first time in the near-infrared. MID INFRARED: As we enter the mid-infrared region of the spectrum, the cool stars begin to fade out and cooler objects such as planets, comets and asteroids come into view. Planets absorb light from the sun and heat up. They then re-radiate this heat as infrared light. This is different from the visible light that we see from the planets which is reflected sunlight. The planets in our solar system have temperatures ranging from about 53 to 573 degrees Kelvin. Objects in this temperature range emit most of their light in the mid-infrared. For example, the Earth itself radiates most strongly at about 10 microns. Asteroids also emit most of their light in the mid-infrared making this wavelength band the most efficient for locating dark asteroids. Infrared data can help to determine the surface composition, and diameter of asteroids. An infrared view of the Earth IRAS mid-infrared view of Comet IRAS-Araki-Alcock Dust warmed by starlight is also very prominent in the mid-infrared. An example is the zodiacal dust which lies in the plane of our solar system. This dust is made up of silicates (like the rocks on Earth) and range in size from a tenth of a micron up to the size of large rocks. Silicates emit most of their radiation at about 10 microns. Mapping the distribution of this dust can provide clues about the formation of our own solar system. The dust from comets also has strong emission in the mid-infrared. Warm interstellar dust also starts to shine as we enter the mid-infrared region. The dust around stars which have ejected material shines most brightly in the mid-infrared. Sometimes this dust is so thick that the star hardly shines through at all and can only be detected in the infrared. Protoplanetary disks, the disks of material which surround newly forming stars, also shines brightly in the mid-infrared. These disks are where new planets are possibly being formed. FAR INFRARED: In the far-infrared, the stars have all vanished. Instead we now see very cold matter (140 Kelvin or less). Huge, cold clouds of gas and dust in our own galaxy, as well as in nearby galaxies, glow in far-infrared light. In some of these clouds, new stars are just beginning to form. Far-infrared observations can detect these protostars long before they "turn on" visibly by sensing the heat they radiate as they contract." IRAS view of infrared cirrus - dust heated by starlight Michael Hauser (Space Telescope Science Institute), the COBE/DIRBE Science Team, and NASA The center of our galaxy also shines brightly in the far-infrared because of the thick concentration of stars embedded in dense clouds of dust. These stars heat up the dust and cause it to glow brightly in the infrared. The image (at left) of our galaxy taken by the COBE satellite, is a composite of far-infrared wavelengths of 60, 100, and 240 microns. Except for the plane of our own Galaxy, the brightest far-infrared object in the sky is central region of a galaxy called M82. The nucleus of M82 radiates as much energy in the far-infrared as all of the stars in our Galaxy combined. This far-infrared energy comes from dust heated by a source that is hidden from view. The central regions of most galaxies shine very brightly in the far-infrared. Several galaxies have active nuclei hidden in dense regions of dust. Others, called starburst galaxies, have an extremely high number of newly forming stars heating interstellar dust clouds. These galaxies, far outshine all others galaxies in the far-infrared. IRAS infrared view of the Andromeda Galaxy (M31) - notice the bright central region. Discovery of Infrared | What is Infrared? | Infrared Astronomy Overview | Atmospheric Windows | Near, Mid & Far Infrared | The Infrared Universe | Spectroscopy | Timeline | Background | Future Missions | News & Discoveries | Images & Videos | Activities | Infrared Links | Educational Links | Getting into Astronomy HOME INFRARED PROCESSING AND ANALYSIS CENTER INDEX

Diffraction vs reflectionphysics

The ancient Greek astronomer Hipparchus created the first documented table of sine functions before 125 BCE.[6] Hipparchus’ work was referenced by Ptolemy over 250 years later, and so it’s not known why he didn’t derive the sine law of refraction himself.[7][8]

The Iraqi mathematician Ibn Sahl discovered the full law of refraction in 984. Sahl showed that the angle of incidence is related to the angle of refraction using the law of sines.[4] Sahl couldn’t use this method to measure the actual speed of light, however, and could only determine the ratios.

Refractionvs reflection

The sine function shows how the angle inside a triangle changes as the lengths of its sides change. The sine of an angle (θ) equals the ratio of two lengths - the length opposite the angle, and the longest length, the hypotenuse.

To see sunlight that has passed through a raindrop, there needs to be an angle of about 40°-42° between you, the raindrop, and the Sun. The set of all the raindrops that can be seen from this angle at once forms a cone pointing towards the Sun. Coloured light is not visible from any other angle, and so when you move, the rainbow moves with you. This is why you will never be able to reach the end of a rainbow.

NEAR INFRARED: Between about 0.7 to 1.1 microns we can use the same observing methods as are use for visible light observations, except for observation by eye. The infrared light that we observe in this region is not thermal (not due to heat radiation). Many do not even consider this range as part of infrared astronomy. Beyond about 1.1 microns, infrared emission is primarily heat or thermal radiation. As we move away from visible light towards longer wavelengths of light, we enter the infrared region. As we enter the near-infrared region, the hot blue stars seen clearly in visible light fade out and cooler stars come into view. Large red giant stars and low mass red dwarfs dominate in the near-infrared. The near-infrared is also the region where interstellar dust is the most transparent to infrared light.

Near-infrared observations have been made from ground based observatories since the 1960's. They are done in much the same way as visible light observations for wavelengths less than 1 micron, but require special infrared detectors beyond 1 micron. Mid and far-infrared observations can only be made by observatories which can get above our atmosphere. These observations require the use of special cooled detectors containing crystals like germanium whose electrical resistance is very sensitive to heat. Infrared radiation is emitted by any object that has a temperature (ie radiates heat). So, basically all celestial objects emit some infrared. The wavelength at which an object radiates most intensely depends on its temperature. In general, as the temperature of an object cools, it shows up more prominently at farther infrared wavelengths. This means that some infrared wavelengths are better suited for studying certain objects than others.

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Notice in the above images how center of our galaxy, which is hidden by thick dust in visible light (left), becomes transparent in the near-infrared (right). Many of the hotter stars in the visible image have faded in the near-infrared image. The near-infrared image shows cooler, reddish stars which do not appear in the visible light view. These stars are primarily red dwarfs and red giants. Red giants are large reddish or orange stars which are running out of their nuclear fuel. They can swell up to 100 times their original size and have temperatures which range from 2000 to 3500 K. Red giants radiate most intensely in the near-infrared region. Red dwarfs are the most common of all stars. They are much smaller than our Sun and are the coolest of the stars having a temperature of about 3000 K which means that these stars radiate most strongly in the near-infrared. Many of these stars are too faint in visible light to even be detected by optical telescopes, and have been discovered for the first time in the near-infrared. MID INFRARED: As we enter the mid-infrared region of the spectrum, the cool stars begin to fade out and cooler objects such as planets, comets and asteroids come into view. Planets absorb light from the sun and heat up. They then re-radiate this heat as infrared light. This is different from the visible light that we see from the planets which is reflected sunlight. The planets in our solar system have temperatures ranging from about 53 to 573 degrees Kelvin. Objects in this temperature range emit most of their light in the mid-infrared. For example, the Earth itself radiates most strongly at about 10 microns. Asteroids also emit most of their light in the mid-infrared making this wavelength band the most efficient for locating dark asteroids. Infrared data can help to determine the surface composition, and diameter of asteroids. An infrared view of the Earth IRAS mid-infrared view of Comet IRAS-Araki-Alcock Dust warmed by starlight is also very prominent in the mid-infrared. An example is the zodiacal dust which lies in the plane of our solar system. This dust is made up of silicates (like the rocks on Earth) and range in size from a tenth of a micron up to the size of large rocks. Silicates emit most of their radiation at about 10 microns. Mapping the distribution of this dust can provide clues about the formation of our own solar system. The dust from comets also has strong emission in the mid-infrared. Warm interstellar dust also starts to shine as we enter the mid-infrared region. The dust around stars which have ejected material shines most brightly in the mid-infrared. Sometimes this dust is so thick that the star hardly shines through at all and can only be detected in the infrared. Protoplanetary disks, the disks of material which surround newly forming stars, also shines brightly in the mid-infrared. These disks are where new planets are possibly being formed. FAR INFRARED: In the far-infrared, the stars have all vanished. Instead we now see very cold matter (140 Kelvin or less). Huge, cold clouds of gas and dust in our own galaxy, as well as in nearby galaxies, glow in far-infrared light. In some of these clouds, new stars are just beginning to form. Far-infrared observations can detect these protostars long before they "turn on" visibly by sensing the heat they radiate as they contract." IRAS view of infrared cirrus - dust heated by starlight Michael Hauser (Space Telescope Science Institute), the COBE/DIRBE Science Team, and NASA The center of our galaxy also shines brightly in the far-infrared because of the thick concentration of stars embedded in dense clouds of dust. These stars heat up the dust and cause it to glow brightly in the infrared. The image (at left) of our galaxy taken by the COBE satellite, is a composite of far-infrared wavelengths of 60, 100, and 240 microns. Except for the plane of our own Galaxy, the brightest far-infrared object in the sky is central region of a galaxy called M82. The nucleus of M82 radiates as much energy in the far-infrared as all of the stars in our Galaxy combined. This far-infrared energy comes from dust heated by a source that is hidden from view. The central regions of most galaxies shine very brightly in the far-infrared. Several galaxies have active nuclei hidden in dense regions of dust. Others, called starburst galaxies, have an extremely high number of newly forming stars heating interstellar dust clouds. These galaxies, far outshine all others galaxies in the far-infrared. IRAS infrared view of the Andromeda Galaxy (M31) - notice the bright central region. Discovery of Infrared | What is Infrared? | Infrared Astronomy Overview | Atmospheric Windows | Near, Mid & Far Infrared | The Infrared Universe | Spectroscopy | Timeline | Background | Future Missions | News & Discoveries | Images & Videos | Activities | Infrared Links | Educational Links | Getting into Astronomy HOME INFRARED PROCESSING AND ANALYSIS CENTER INDEX

SPECTRAL REGION WAVELENGTH RANGE (microns) TEMPERATURE RANGE (degrees Kelvin) WHAT WE SEE Near-Infrared (0.7-1) to 5 740 to (3,000-5,200) Cooler red stars Red giants Dust is transparent Mid-Infrared 5 to (25-40) (92.5-140) to 740 Planets, comets and asteroidsDust warmed by starlight Protoplanetary disks Far-Infrared (25-40) to (200-350) (10.6-18.5) to (92.5-140) Emission from cold dust Central regions of galaxies Very cold molecular clouds NEAR INFRARED: Between about 0.7 to 1.1 microns we can use the same observing methods as are use for visible light observations, except for observation by eye. The infrared light that we observe in this region is not thermal (not due to heat radiation). Many do not even consider this range as part of infrared astronomy. Beyond about 1.1 microns, infrared emission is primarily heat or thermal radiation. As we move away from visible light towards longer wavelengths of light, we enter the infrared region. As we enter the near-infrared region, the hot blue stars seen clearly in visible light fade out and cooler stars come into view. Large red giant stars and low mass red dwarfs dominate in the near-infrared. The near-infrared is also the region where interstellar dust is the most transparent to infrared light.

Sin, cos, and tan waves could not be represented graphically until after the invention of the Cartesian coordinate system by Descartes and the French mathematician Pierre de Fermat in 1637.[9]

Al-Haytham experimented with the laws of reflection and refraction using different shaped mirrors and lenses, and he accurately described how the eye functions as an optical instrument. He likened it to a camera obscura, a pinhole camera, and so suggested that images must also be inverted in the eye. This led him to suggest that vision occurs in the brain, rather than the eyes and that it is, therefore, subjective.[11]

Light is reflected in the same way that a ball would bounce off of a frictionless surface, and so Euclid claimed that light travels in rays that are discrete, like atoms, not continuous, like waves. This may mean that some of the objects in our visual field will always remain unilluminated, and therefore undetected. Unlike Aristotle, Euclid thought that light is emitted in rays from the eye.[1]

Laser power unit of measure is watts. Measurements are made with a laser power meter. Laser power meter has a detector that absorbs a laser ...

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↑ Pontrjagin, L. S., Learning Higher Mathematics: Part I: The Method of Coordinates Part II: Analysis of the Infinitely Small, Springer Science & Business Media, 2013.

The German philosopher Theodoric of Freiberg (also known as Dietrich of Freiberg) explained how rainbows are formed in about 1307.

MID INFRARED: As we enter the mid-infrared region of the spectrum, the cool stars begin to fade out and cooler objects such as planets, comets and asteroids come into view. Planets absorb light from the sun and heat up. They then re-radiate this heat as infrared light. This is different from the visible light that we see from the planets which is reflected sunlight. The planets in our solar system have temperatures ranging from about 53 to 573 degrees Kelvin. Objects in this temperature range emit most of their light in the mid-infrared. For example, the Earth itself radiates most strongly at about 10 microns. Asteroids also emit most of their light in the mid-infrared making this wavelength band the most efficient for locating dark asteroids. Infrared data can help to determine the surface composition, and diameter of asteroids. An infrared view of the Earth IRAS mid-infrared view of Comet IRAS-Araki-Alcock Dust warmed by starlight is also very prominent in the mid-infrared. An example is the zodiacal dust which lies in the plane of our solar system. This dust is made up of silicates (like the rocks on Earth) and range in size from a tenth of a micron up to the size of large rocks. Silicates emit most of their radiation at about 10 microns. Mapping the distribution of this dust can provide clues about the formation of our own solar system. The dust from comets also has strong emission in the mid-infrared. Warm interstellar dust also starts to shine as we enter the mid-infrared region. The dust around stars which have ejected material shines most brightly in the mid-infrared. Sometimes this dust is so thick that the star hardly shines through at all and can only be detected in the infrared. Protoplanetary disks, the disks of material which surround newly forming stars, also shines brightly in the mid-infrared. These disks are where new planets are possibly being formed. FAR INFRARED: In the far-infrared, the stars have all vanished. Instead we now see very cold matter (140 Kelvin or less). Huge, cold clouds of gas and dust in our own galaxy, as well as in nearby galaxies, glow in far-infrared light. In some of these clouds, new stars are just beginning to form. Far-infrared observations can detect these protostars long before they "turn on" visibly by sensing the heat they radiate as they contract." IRAS view of infrared cirrus - dust heated by starlight Michael Hauser (Space Telescope Science Institute), the COBE/DIRBE Science Team, and NASA The center of our galaxy also shines brightly in the far-infrared because of the thick concentration of stars embedded in dense clouds of dust. These stars heat up the dust and cause it to glow brightly in the infrared. The image (at left) of our galaxy taken by the COBE satellite, is a composite of far-infrared wavelengths of 60, 100, and 240 microns. Except for the plane of our own Galaxy, the brightest far-infrared object in the sky is central region of a galaxy called M82. The nucleus of M82 radiates as much energy in the far-infrared as all of the stars in our Galaxy combined. This far-infrared energy comes from dust heated by a source that is hidden from view. The central regions of most galaxies shine very brightly in the far-infrared. Several galaxies have active nuclei hidden in dense regions of dust. Others, called starburst galaxies, have an extremely high number of newly forming stars heating interstellar dust clouds. These galaxies, far outshine all others galaxies in the far-infrared. IRAS infrared view of the Andromeda Galaxy (M31) - notice the bright central region. Discovery of Infrared | What is Infrared? | Infrared Astronomy Overview | Atmospheric Windows | Near, Mid & Far Infrared | The Infrared Universe | Spectroscopy | Timeline | Background | Future Missions | News & Discoveries | Images & Videos | Activities | Infrared Links | Educational Links | Getting into Astronomy HOME INFRARED PROCESSING AND ANALYSIS CENTER INDEX

As we move away from visible light towards longer wavelengths of light, we enter the infrared region. As we enter the near-infrared region, the hot blue stars seen clearly in visible light fade out and cooler stars come into view. Large red giant stars and low mass red dwarfs dominate in the near-infrared. The near-infrared is also the region where interstellar dust is the most transparent to infrared light.

Science began to progress again in Europe after the Renaissance of the 12th century. This was mainly due to increased contact with the Islamic world.[12] The English philosopher Roger Bacon, who was one of the earliest European advocates of experimental science, reviewed Al-Haytham’s Book of Optics in 1267, and it was translated into Latin shortly after.[13]

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The Roman astronomer Ptolemy first tried to experimentally derive the law of refraction in the 2nd century CE.[2] Refraction explains how a ray of light changes direction when it travels between different mediums. This is either because it slows down or because it speeds up. Refraction occurs when light hits the surface of water or travels through the atmosphere, and it’s atmospheric refraction that causes the stars to ‘twinkle’.

The Italian natural philosopher Francesco Grimaldi discovered and coined the term ‘diffraction’ in 1660.[14] Grimaldi showed that a single beam of light spreads out, creating an interference pattern, if it’s shone through very small slits. Water and sound waves act the same way, and so this was an important finding for those that advocated for a wave theory of light. Before this, people had argued that the sharp boundaries created by shadows meant that light could not bend around corners in the same way that water or sound waves can.

Diffraction vsrefraction

As we move from the near-infrared into mid and far-infrared regions of the spectrum, some celestial objects will appear while others will disappear from view. For example, in the above image you can see how more stars (generally cooler stars) appear as we go from the visible light image to the near-infrared image. In the near-infrared, the dust also becomes transparent, allowing us to see regions hidden by dust in the visible image. As we go to the mid-infrared image, the cooler dust itself glows. The table below highlights what we see in the different infrared spectral regions. SPECTRAL REGION WAVELENGTH RANGE (microns) TEMPERATURE RANGE (degrees Kelvin) WHAT WE SEE Near-Infrared (0.7-1) to 5 740 to (3,000-5,200) Cooler red stars Red giants Dust is transparent Mid-Infrared 5 to (25-40) (92.5-140) to 740 Planets, comets and asteroidsDust warmed by starlight Protoplanetary disks Far-Infrared (25-40) to (200-350) (10.6-18.5) to (92.5-140) Emission from cold dust Central regions of galaxies Very cold molecular clouds NEAR INFRARED: Between about 0.7 to 1.1 microns we can use the same observing methods as are use for visible light observations, except for observation by eye. The infrared light that we observe in this region is not thermal (not due to heat radiation). Many do not even consider this range as part of infrared astronomy. Beyond about 1.1 microns, infrared emission is primarily heat or thermal radiation. As we move away from visible light towards longer wavelengths of light, we enter the infrared region. As we enter the near-infrared region, the hot blue stars seen clearly in visible light fade out and cooler stars come into view. Large red giant stars and low mass red dwarfs dominate in the near-infrared. The near-infrared is also the region where interstellar dust is the most transparent to infrared light.

Theodoric did this by experimenting with spherical flasks, which he filled with water to represent raindrops. Theodoric showed that the light of the Sun is refracted, and then internally reflected, inside each drop.[7]

The Ancient Greek mathematician Euclid described the law of reflection in about 300 BCE. This states that light travels in straight lines and reflects from a surface at the same angle at which it hit it.

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Usually, the microscope objective produces an intermediate image in the microscope, which is then further magnified with an eyepiece (ocular lens). Particularly ...

In the far-infrared, the stars have all vanished. Instead we now see very cold matter (140 Kelvin or less). Huge, cold clouds of gas and dust in our own galaxy, as well as in nearby galaxies, glow in far-infrared light. In some of these clouds, new stars are just beginning to form. Far-infrared observations can detect these protostars long before they "turn on" visibly by sensing the heat they radiate as they contract."

↑ Cloud, R. R., Aristotle’s journey to Europe: A synthetic history of the role played by the Islamic Empire in the transmission of Western educational philosophy sources from the fall of Rome through the medieval period, ProQuest, 2007.

↑ Yurkin, A. V., “New view on the diffraction discovered by Grimaldi and Gaussian beams”, arXiv preprint arXiv:1302.6287, 2013.

Between about 0.7 to 1.1 microns we can use the same observing methods as are use for visible light observations, except for observation by eye. The infrared light that we observe in this region is not thermal (not due to heat radiation). Many do not even consider this range as part of infrared astronomy. Beyond about 1.1 microns, infrared emission is primarily heat or thermal radiation. As we move away from visible light towards longer wavelengths of light, we enter the infrared region. As we enter the near-infrared region, the hot blue stars seen clearly in visible light fade out and cooler stars come into view. Large red giant stars and low mass red dwarfs dominate in the near-infrared. The near-infrared is also the region where interstellar dust is the most transparent to infrared light.

Infrared radiation is emitted by any object that has a temperature (ie radiates heat). So, basically all celestial objects emit some infrared. The wavelength at which an object radiates most intensely depends on its temperature. In general, as the temperature of an object cools, it shows up more prominently at farther infrared wavelengths. This means that some infrared wavelengths are better suited for studying certain objects than others.

Diffraction vs reflectionwavelength

Grimaldi’s findings were published in 1665, two years after his death.[15] Diffraction is now understood in terms of the superposition principle (discussed in Chapter 5).

Here v is velocity and n is the refractive index. n=c/v, where c is the speed of light in a vacuum, which is very close to its speed in air.

The Iraqi mathematician Ibn al-Haytham (also known as Alhazen) was the first person to correctly describe how perception occurs in about 1021 when he proved that light enters, but is not emitted by, the eye.[10] Al-Haytham stated that light consists of tiny particles of energy that travel in straight lines and emanate from the Sun at a large but finite velocity. Vision occurs when the Sun’s rays are reflected from objects and into our eyes.

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FAR INFRARED: In the far-infrared, the stars have all vanished. Instead we now see very cold matter (140 Kelvin or less). Huge, cold clouds of gas and dust in our own galaxy, as well as in nearby galaxies, glow in far-infrared light. In some of these clouds, new stars are just beginning to form. Far-infrared observations can detect these protostars long before they "turn on" visibly by sensing the heat they radiate as they contract." IRAS view of infrared cirrus - dust heated by starlight Michael Hauser (Space Telescope Science Institute), the COBE/DIRBE Science Team, and NASA The center of our galaxy also shines brightly in the far-infrared because of the thick concentration of stars embedded in dense clouds of dust. These stars heat up the dust and cause it to glow brightly in the infrared. The image (at left) of our galaxy taken by the COBE satellite, is a composite of far-infrared wavelengths of 60, 100, and 240 microns. Except for the plane of our own Galaxy, the brightest far-infrared object in the sky is central region of a galaxy called M82. The nucleus of M82 radiates as much energy in the far-infrared as all of the stars in our Galaxy combined. This far-infrared energy comes from dust heated by a source that is hidden from view. The central regions of most galaxies shine very brightly in the far-infrared. Several galaxies have active nuclei hidden in dense regions of dust. Others, called starburst galaxies, have an extremely high number of newly forming stars heating interstellar dust clouds. These galaxies, far outshine all others galaxies in the far-infrared. IRAS infrared view of the Andromeda Galaxy (M31) - notice the bright central region. Discovery of Infrared | What is Infrared? | Infrared Astronomy Overview | Atmospheric Windows | Near, Mid & Far Infrared | The Infrared Universe | Spectroscopy | Timeline | Background | Future Missions | News & Discoveries | Images & Videos | Activities | Infrared Links | Educational Links | Getting into Astronomy HOME INFRARED PROCESSING AND ANALYSIS CENTER INDEX

Warm interstellar dust also starts to shine as we enter the mid-infrared region. The dust around stars which have ejected material shines most brightly in the mid-infrared. Sometimes this dust is so thick that the star hardly shines through at all and can only be detected in the infrared. Protoplanetary disks, the disks of material which surround newly forming stars, also shines brightly in the mid-infrared. These disks are where new planets are possibly being formed. FAR INFRARED: In the far-infrared, the stars have all vanished. Instead we now see very cold matter (140 Kelvin or less). Huge, cold clouds of gas and dust in our own galaxy, as well as in nearby galaxies, glow in far-infrared light. In some of these clouds, new stars are just beginning to form. Far-infrared observations can detect these protostars long before they "turn on" visibly by sensing the heat they radiate as they contract." IRAS view of infrared cirrus - dust heated by starlight Michael Hauser (Space Telescope Science Institute), the COBE/DIRBE Science Team, and NASA The center of our galaxy also shines brightly in the far-infrared because of the thick concentration of stars embedded in dense clouds of dust. These stars heat up the dust and cause it to glow brightly in the infrared. The image (at left) of our galaxy taken by the COBE satellite, is a composite of far-infrared wavelengths of 60, 100, and 240 microns. Except for the plane of our own Galaxy, the brightest far-infrared object in the sky is central region of a galaxy called M82. The nucleus of M82 radiates as much energy in the far-infrared as all of the stars in our Galaxy combined. This far-infrared energy comes from dust heated by a source that is hidden from view. The central regions of most galaxies shine very brightly in the far-infrared. Several galaxies have active nuclei hidden in dense regions of dust. Others, called starburst galaxies, have an extremely high number of newly forming stars heating interstellar dust clouds. These galaxies, far outshine all others galaxies in the far-infrared. IRAS infrared view of the Andromeda Galaxy (M31) - notice the bright central region. Discovery of Infrared | What is Infrared? | Infrared Astronomy Overview | Atmospheric Windows | Near, Mid & Far Infrared | The Infrared Universe | Spectroscopy | Timeline | Background | Future Missions | News & Discoveries | Images & Videos | Activities | Infrared Links | Educational Links | Getting into Astronomy HOME INFRARED PROCESSING AND ANALYSIS CENTER INDEX