Gamma Rays

Gamma rays are the final type of radiation found on the electromagnetic spectrum. Gamma rays have the highest frequency and smallest wavelength of any radiation, and therefore also have the highest energy.

Gamma rays are powerful enough to penetrate most substances, and are powerful ionizers. The gamma ray spectrum involves wavelengths lower than one trillionth of a meter (less than .000000000001 meters).

This radiation is often produced as a byproduct of atomic decay, in which unstable atoms emit energy through gamma rays and other particles before settling to a stable state. Descriptions of some of these reactions can be found here.

Among the parts of the electromagnetic spectrum, gamma rays are comparatively rare. Few objects are powerful enough to give off high amounts of gamma ray energy. However, this radiation is very important on atomic scales, when atomic decay spontaneously converts mass into energetic photons, i.e. gamma rays. This is possible due to the well known mass-energy relation

E=mc^2

where E corresponds to energy, m to mass, and c a constant (the speed of light: 186282 miles per second). The meaning of this equation is that a certain amount of mass is equal to a certain amount of energy. During the early stages of the Universe, the temperature was sufficiently high that particles collided with their antiparticle counterparts. When they collide, they instantly annihilate each other, releasing energy. As energy, the reverse happened, with particles and antiparticles being spontaneously created. Now these reactions only take place in extreme conditions, such as on the edges of a black hole.

Despite this, astronomical gamma ray sources can still be found, and the closest is the Moon.



An image of the Moon taken by a gamma ray telescope. The gamma rays emitted from the Moon originate when other solar ionizing radiation, such as ultraviolet, hits the Moon and causes the excitation of heavy atoms, and this in turn, causes the emission of gamma rays. In contrast, the Sun is nearly invisible in the gamma ray spectrum, because it consists of very light atoms (mostly Hydrogen and Helium) that cannot be excited by ionizing radiation.

Other gamma ray sources include solar flares, the death of massive stars (through processes such as supernovae) and their remnants (neutron stars and black holes), as well as active galaxies. Galaxies are "active" if large amounts of infalling matter are feeding their central black hole, giving off enormous amounts of radiation. Most information on gamma ray bursts is theoretical, as little is actually known about their sources, and they usually are very distant.

Gamma ray bursts and their sources are some of the most fascinating areas of astronomy.

Sources: http://en.wikipedia.org/wiki/Gamma_ray, http://science.hq.nasa.gov/kids/imagers/ems/gamma.html, http://en.wikipedia.org/wiki/Timeline_of_the_Big_Bang, http://en.wikipedia.org/wiki/Mass–energy_equivalence

X-rays

X-rays are yet another type of electromagnetic radiation, which is radiation in the form of photons. X-rays are very high energy, and therefore have a very short wavelength and a very high frequency.

X-rays are the first portion of the electromagnetic spectrum to be ionizing, (high frequency ultraviolet rays also have this property) meaning that they have high enough energy to dislodge electrons from the outer shells of atoms, thus converting them into ions.

This part of the electromagnetic spectrum varies in wavelength from .01 nanometers to 10 nanometers, covering three orders of magnitude. X-rays are primarily used for medical purposes, although they can be carcinogens in larger doses. It is estimated that a common dental X-ray does not meaningfully increase cancer risk, but more invasive CAT scans may significantly increase the risk.



The first known instance of a medical X-ray, taken in 1895 by William Roentgen of his wife's hand. The X-rays penetrate skin but not bone, and the lack of X-rays passing through creates the image above. Note the ring present on the ring finger.

Sheets of lead are often used to contain this radiation, as it is the most cost efficient metal for doing so. Varied thicknesses are used, although 10 mm is sufficient for most X-rays.

In astronomy, X-ray telescopes are used to detect sources of radiation throughout the galaxy. The closest source of X-rays is our Sun, (these are often reflected off the moon) but the Sun predominantly emits light at higher wavelengths, and large sources of X-rays are relatively rare. The accretion disc of a black hole emits large amounts of X-rays as it is heated to extreme temperatures. These sources are particularly prominent when the black hole has a large source of material, e.g. a binary star companion.



An artist's conception of a binary star system in which one of the stars has become a black hole. The gravitational pull from the black hole pulls in material from its companion star, and this material rotates the black hole at extreme speeds, (often over a million miles per hour) causing it to emit X-rays. The most well-known example of a binary system containing a black hole is Cygnus X-1, named for being a strong X-ray source in the constellation Cygnus.



X-ray image of Cygnus X-1 (false-color). The blue supergiant companion star is not prominent in this part of the spectrum, and is therefore not visible.

Other astronomical sources of X-rays include very massive stars, and the supernovae they result in, as well as black holes at galaxy centers. In the former case, the massive stars are often very unstable, and shed material in terrific explosions periodically, culminating in a supernova, in which, huge amounts of X-rays are emitted in an extreme explosion. The latter case works on the same principle as stellar black holes: with accreted matter increasing in temperature and energy, and subsequently releasing X-rays before being sucked in to the black hole.

Sources: http://en.wikipedia.org/wiki/X-ray, http://science.hq.nasa.gov/kids/imagers/ems/xrays.html, http://en.wikipedia.org/wiki/Astrophysical_X-ray_source

Ultraviolet Rays

Ultraviolet Light is another type of electromagnetic radiation. It is known as ultraviolet because the frequency of ultraviolet rays are just larger than that of violet visible light (ultra=beyond).

This area of the spectrum has wavelengths as large as 400 nanometers (right on the cusp of visible light) and as small as 10 nanometers. This area is further subdivided into regions, the most well-known of them being UVA, UVB, and UVC, spanning 400-315, 315-280, and 280-100 nanometers, respectively. Unlike many of the former parts of the spectrum, ultraviolet light is primarily blocked from reaching the surface of the Earth. Of the ultraviolet light that does pass through the ozone layer, (perhaps 2% of the radiation that reaches the ozone layer from the Sun) most of it is UVA rays.

UVA rays are beneficial to health in small quantities, as they cause the production of vitamin D. In larger quantities, they cause tanning of the skin, and in excess, sunburn. UVA rays also are emitted from black lights, lights that are just on the edge of ultraviolet, making them partially visible. However, a majority of the light emitted is within the UVA region of the electromagnetic spectrum. and this radiation can cause chemical reactions, allowing a few substances to radiate a glow under UVA light.



An example of this is the security band on a typical U.S. $20 bill. This band is hard to duplicate, discouraging counterfeit.

UVB light (315-280 nm) is the next type (in increasing frequency) of ultraviolet light. It affects the skin in a more negative way, and is the rarer of the two types (UVA and UVB) that penetrate the atmosphere. Radiation in this part of the spectrum is more likely to cause cancer than UVA.

UVC light (280-100 nm) is blocked by the ozone layer, but is sometimes artificially produced on the earth's surface. This type of radiation serves as a disinfectant, as exposure of a microorganism to UVC rays damages its genetic material, resulting in mutations that cause infertility, and shortly after, death. In large exposure, these rays have harmful effects on humans as well. Despite their health hazard, they have practical applications in the disinfection of water and other materials.

The remainder of the ultraviolet spectrum (100-10 nm) is mainly used for astronomical purposes, although the Universe looks fundamentally different in ultraviolet than in visible. The most prominent feature, or, in this case, lack thereof, is the dimness of most stars in ultraviolet. Only stars with surfaces at higher temperatures (very young stars and stars in the final stages of their evolution) appear brightly in this part of the spectrum. The interstellar medium, or the sparse material occupying the space between stars, can be best seen and studied with ultraviolet telescopes. These telescopes must be mounted in space, however, due to the low amount of the radiation that reaches the surface of the Earth.



An image (false-color) of the galaxy Messier 81 seen in ultraviolet light. To obtain colorful images of other galaxies, these images are often combined with the images in visible light to detect more features.

Sources: http://en.wikipedia.org/wiki/Ultraviolet, http://science.hq.nasa.gov/kids/imagers/ems/uv.html, http://www.germsquad.com/home/faqs/6-what-are-uv-c-rays-and-how-can-they-benefit-us.html

Visible Light

Visible light is a type of electromagnetic radiation, and is the only type observable through the naked eye.

Rather than being divided into different bands, visible light is divided into colors. The slight differences in the wavelengths of visible waves determine which color that the light is. Visible light is the "smallest" range of wavelengths of the seven main sections (logarithmically speaking) but it makes up everything we see.



Above: The division of visible light into a spectrum of colors. At the edges of the scale are near ultraviolet (the top) and near infrared (the bottom). The discovery of light as a composition of colors may have come in Isaac Newton's time (c. 1665), when the prism revealed sunlight as made up of light on many different wavelengths.



The prism is able to split visible light into its components because there are slight differences in the speeds of light through glass. Higher wavelengths are faster and have greater refraction angles, causing them to bend more and therefore appear at the bottom of the rainbow shown above. Red and other long wavelengths travel slower and refract at a smaller angle, causing them to be at the "top" of the rainbow above. Real rainbows work in a similar way, when water droplets disperse sunlight into the visible spectrum. This also proves that sunlight has many different wavelengths of light, by no means limited to visible light.

Visible, or optical astronomy, is by far the oldest type, and has been going on since antiquity. Only recently have observations in other parts of the spectrum expanded our knowledge of the heavens.

Sources: http://www.windows2universe.org/sun/spectrum/multispectral_sun_overview.html, http://www.juliantrubin.com/bigten/lightexperiments.html, http://en.wikipedia.org/wiki/Optical_astronomy

Infrared Rays

Infrared radiation is a type of radiation included in the electromagnetic spectrum. Infrared rays still have a longer wavelength than visible light, but one shorter than radio waves and microwaves.

Infrared is best known as being heat radiation. The shortest infrared rays are very close to being visible to humans, hence the name (Latin infra meaning below, "below red"). However, humans can sense this radiation as heat, and infrared makes up a majority of the radiation that the Earth receives at ground level. Animals absorb heat and emit it themselves, and these phenomena can be captured by thermographic images:



A thermographic image showing two people (false-color).

Infrared radiation is subdivided further into three zones, near-infrared (.7 to 5 microns, or .0000007 to .000005 meters), mid-infrared (5 microns to about 35 microns), and far-infrared (35 microns to about 300 microns). Each zone has separate uses, notably near-infrared for telecommunication, mid-infrared for heat-seeking missiles, and far-infrared for lasers.

The zones are labeled in this way because near-infrared is on the cusp of visible light, while far-infrared has a much longer wavelength. Some living things can naturally "see" into the infrared spectrum, such as some snakes that use a special heat-detecting sense to find live prey.

Infrared rays have many other uses, including night vision and the heating of objects. Infrared cameras are also a valuable resource in meteorology, as the surface of the earth emits more infrared radiation than that of clouds, creating an easy way to analyze cloud height and temperature.



An infrared image of the Atlantic Basin. Clouds of increasing height are brighter white. The image also shows Tropical Storm Richard in the Caribbean. Image taken 10/23/10 12:15 UTC.

Infrared astronomy was pioneered by the man who discovered infrared rays: William Herschel. He is also well known for discovering the planet Uranus, along with two of its moons. His discovery was made while studying the spectrum of visible light produced by a prism. He noted that there was a significant temperature increase outside the visible light spectrum, beyond the red. He performed more tests and concluded that it was indeed a new type of radiation, being absorbed and emitted just like visible light, and also being released in massive quantities from the Sun.

In modern times, near-infrared rays can usually be picked up with a normal optical telescope, as these telescopes often have larger visual ranges than the naked eye, seeing into both near-infrared and near-ultraviolet. As one progresses farther into the infrared spectrum, a vast majority of rays do not reach the surface of the earth. However, telescopes at high altitudes in dry environments can pick these rays up with good efficiency. Telescopes operating in infrared can detect objects behind interstellar dust clouds and within nebulas better than visible light, as they can see the heat emitted from the region.



A photo of the Orion constellation in visible (left) and infrared (right). Although the infrared provides little indication to the exact location of the stars, it detects gas clouds throughout the constellation and other features totally invisible in the optical spectrum.

Overall, infrared rays have important uses, such as telecommunication and lasers, as well as transmitting heat throughout the Universe.

Sources: National Hurricane Center, http://www.ipac.caltech.edu/Outreach/Edu/Regions/irregions.html, http://en.wikipedia.org/wiki/Infrared. http://www.nasa.gov/mission_pages/SOFIA/infrared.html

Microwaves

Microwaves are a type of wave in the electromagnetic spectrum (see here). Their wavelengths are longer than any type of wave except for radio waves (see here).

The wavelength of a microwave can range from 1 millimeter (.001 meter) to 1 meter. This range is actually within the broader term radio wave, but on some scales, they are separate. Accordingly, the frequency range of microwaves is 300 MHz to 300 GHz (300,000,000 to 300,000,000,000 Hz).

Microwaves are specifically used in areas such as communication, power, and radar. Before fiber-optic cables were adopted into the phone system, microwaves were used for the same purpose. Radar, or the ability to map objects by bouncing waves off them, lies predominantly within the microwave region, but perhaps the most famous of microwave uses is the microwave oven. Microwave ovens bombard non-radioactive radiation into food, installing energy into, and therefore heating, it.



The main component of the microwave oven is the magnetron. This is a cross-section of such a device which generates an electric field to produce microwaves. Magnetrons are generally for heating certain substances with microwaves, such as water, sugar, and fats in food, and sometimes, humans. Microwaves, however, are not specifically heat radiation.

Microwaves, just like all waves used for communication are divided into bands to organize their use. WIth microwaves, these bands are denoted by letter, (e.g. the L Band, ranging from 1 to 2 GHz) and each band has specific uses.

Yet another use of microwaves is in astronomy. There are many sources of microwaves in the heavens, but the most notable is the Cosmic Microwave Background Radiation. This radiation was emitted 379,000 years of the Big Bang, when the Universe became transparent due to the cessation of photon-plasma reactions. Plasma is ionized gas, and is therefore made of ionized atoms. When the temperature of the Universe had fallen enough to support complete atoms with electrons, the atoms became neutral, and the reactions stopped. The image of the Universe released at that moment was carried by gamma rays, but over time red shifting transferred these into microwaves, as they are today. More and less intense patches on the radiation indicate the density of different parts of the Universe. The differences were minute at the time, but gravity gradually increased the differences, and all of the structure in the large scale Universe was defined.



An image adjusted from the original Cosmic Microwave Background to show temperature differences in the early Universe.

Microwaves have a variety of uses, from communication to heating to discovering the origins of the Universe.

Sources: http://en.wikipedia.org/wiki/Microwave, http://www.gallawa.com/microtech/mwave.html, http://en.wikipedia.org/wiki/Cosmic_microwave_background_radiation, etc.

Radio Waves

Radio Waves are part of the electromagnetic spectrum (see here) and consist of photons in their wave form. Out of all of the electromagnetic waves, radio waves have the lowest frequency and highest wavelength.

The range of radio waves is approximately 3 Hz, meaning three wavelengths per second, to 300 GHz, or 300,000,000,000 Hz, although the boundary isn't clearly defined, and waves with frequencies even smaller than these exist. This range is equivalent to wavelengths from 1 millimeter (.001 meter) to 100,000 kilometers (100,000,000 meters).

Radio waves are both man-made, and occur from natural sources, and have many uses, due to the fact that most of the radio spectrum pass through Earth's atmosphere intact. The percentage of waves that pass through the atmosphere are shown on the picture below, along with the rest of the spectrum.



Since radio waves can pass through the atmosphere, they are invaluable for communication purposes and information propagation takes place mainly in the radio spectrum. This portion of the spectrum is further divided into powers of 10. For example, the area from 3-30 Hz is known as Extremely Low Frequency (ELF), the area from 30-300 Hz is known as Super Low Frequency (SLF), the area from 300-3,000 Hz (3 kHz) is known as Ultra Low Frequency (ULF) and so on. The chart of frequencies above ULF are shown below.



The first radio waves to be used for communication are AM radio waves, which extend from 148.5 kHz (148,500 Hz) to 30 MHz (30,000,000 Hz). These waves are in the Low, Medium, and High Frequency ranges. However, waves of these frequencies are produced naturally by the ionosphere and magnetic storms, causing interference. As a result, FM radio, falling entirely under the Very High Frequency range, is now used for long distance broad casts. This area of the spectrum is the busiest of all, as television, FM radio and mobile communications all resides within 30-300 MHz.

The very low frequencies, (VLF and lower) are used for military (submarine) communications as they are useful in subaquatic environments.

The higher frequencies also have uses. Super High Frequency (3-30 GHz, or 3,000,000,000-30,000,000,000 Hz) is used for radar, and Extremely High Frequency (30-300 GHz) is used for radio astronomy.



The Very Large Array, located in New Mexico, USA, is used for radio astronomy. Large, parabolic satellite dishes concentrate the signals on a specific sources in the center of each individual telescope. Since many radio waves picked up from space have very long wavelengths, a very large apparatus is needed to capture a reasonable image. The Very Large Area has 27 radio telescope receivers, each 82 feet in diameter, and the images produced by each are compiled into a single one in the center.



This is an optical (visible light) image of the M87 elliptical galaxy. The active center and jet of radiation from it are visible, but in visible light, most of the galaxy is a haze of stars.



However, by use of radio astronomy, a much more specific picture can be taken. Unlike visible light, radio waves are not produced to a great extent by any part of the galaxy except the active center, and it can therefore be identified better in radio astronomy. The above image is taken by the Very Large Array (VLA). However, the bottom image, which is magnified tens of thousands of times more than the above one, is taken by the Very Long Baseline Array (VLBA). Since M87 is over 50 million light years away, a resolution of this magnitude can only be created by use of a planet sized radio telescope, which is essentially what VLBA is. Satellite dishes all over the world are synced together by a central computer in Europe, and therefore at least a small number of radio waves coming in over a Earth-sized area can be put together to get a very precise view, even if all the incoming waves aren't picked up.

Notable sources of radio waves from space include the Sun (only due to its proximity to Earth, because stars do not emit a majority of their energy in radio waves), galactic centers, such as the Milky Way itself, and active ones like M87, neutron stars, and very distant powerfully emitted objects such as quasars. The redshift effect of the quasars' movement away from us causes the waves to lengthen in wavelength as they approach Earth. As a result, many waves that start higher in frequency are radio waves when they reach Earth. This effect is most notable at very long distances, billions of light years away. Among objects at this distance, only quasars are bright enough to be visible, and are therefore excellent subjects of radio astronomy.

Sources: http://www.google.com/imgres?imgurl=http://www.electronics-radio.com/, http://en.wikipedia.org/wiki/Radio_astronomy, etc.

Electromagnetic Spectrum

The Electromagnetic Spectrum, technically speaking, is the range of frequencies that a photon wave can assume. The photon is essentially the particle of light, and this particle has many interesting properties.

First, a photon has no mass, which means it can travel at a speed unlimited by its mass. The speed at which the light particle can travel in a vacuum defines the fastest known speed in the Universe, namely the speed of light, or 186,292 miles per second. Second, the photon can have properties of both a particle and a wave. But when dealing with the electromagnetic spectrum, the wave form of a photon is most important.

The electromagnetic spectrum deals with all possible photon waves, each of which are composed of the same particle, but have different energies. Along with energy, the three properties of a specific electromagnetic wave are amplitude, wavelength and frequency.



Electromagnetic waves are in a sinusoid form, meaning that they are shaped like the red line above. The distance, A, from the sinusoid axis to the peak of the curve is known as the amplitude of the wave, and the distance between peaks is known as the wavelength, while the distance between crossings of the sinusoid axis are half of a wavelength. The remaining element, frequency, is how many wavelengths the wave goes through over a certain period of time. The horizontal axis (x) on the graph above is the passage of time, and over this time, the wave modulates, or moves from peak to peak, in a cyclic manner.



The different electromagnetic waves are separated by varying amplitude and wavelength. The above chart shows five different wave types. The horizontal axis represents time, as before. On the top of the chart is the wave with the highest wavelength, but lowest frequency, and as one goes down the chart, the wavelength decreases and the frequency increases. The two properties are inversely proportional because an electromagnetic wave is traveling at a constant speed through a vacuum, the speed of light, and therefore the wavelength determines a length of time between wave peaks, namely frequency. Wavelength is measured in meters, while frequency is measured in a unit called a Hertz (Hz), with 1 Hz meaning one wavelength per second.



The entire electromagnetic spectrum (click to enlarge), including names given to specific areas of the spectrum, some uses of particular wavelengths, and the corresponding wavelength and frequency axes. The plot is a log scale of base 10, meaning that instead of counting up 1, 2, 3... the graph counts 10^1, 10^2, 10^3... The frequency increases from the bottom to the top, starting at 10^6, and ending at 10^19, and the wavelength counts in meters (m), using symbols like cm to represent increments of meters.

The waves are as follows, from lowest to highest frequency are: radio waves, microwaves, infrared rays, visible light, ultraviolet rays, X-rays, and gamma rays. Each of these have their own individual posts. Click on one to enter and begin exploring the electromagnetic spectrum.

The Tachyon

One well-known exotic particle is the tachyon.  A tachyon is a hypothetical particle that travels faster than the speed of light.  This odd particle seems to defy detection, and many scientists think it might not exist.  If the tachyon did exist it would defy many logical paradoxes.  The tachyon would be able to travel backwards in time, an action that is impossible by the theory of relativity.  But the theory could stay intact if the tachyon couldn't transmit information.  So the tachyon alters the physics of the Universe by itself, proposing three possibilities.  One is the easy way out, just saying that tachyons do not exist.  The second is that, although particles can, information cannot travel faster than the speed of light.  Three, the horrifying choice, is the possibility that the general theory of relativity, even approximately at an larger-than-quantum scale, is false. Scientists have proposed this particle real mass, also defying many previously believed theories, such as the fact that anything with real mass travels at subliminal (below light) speeds. Quantum physics have yet to explain this mysterious particle.

Antiparticles

For most particles, there is an antiparticle.  An antiparticle has the opposite charge and the same mass as its particle partner.  Since particles and antiparticles annihilate each other, it is well-known that there are many more particles than antiparticles.  Antiparticle played apart in the creation of matter in the early Universe.  They also are the cause of Black Hole Evaporation. Because of these unbalanced amounts, antiparticles are not found naturally.  They are engineered in a lab by destroying another particle.  Particles with a quark composition have an antiparticle that contains antiquarks.  Also, two antiprotons, two antineutrons, and two antielectrons (also called the positron) would produce an antihelium atom.  Antiparticles mirror most particles, and they are very similiar with most properties.

The Electron

The Electron is an elementary particle found in the atom.  It is a lepton, and is stable, although it is possible that an electron may decay in 10^26 years (average).  The electron is the basis for the study of orbitals and atomic bonding.  Electrons are so small that their exact location is never determined and, like other particles have a wave form.  The electron has a negative charge (note 4). 

The Neutron

The Neutron is an elementary particle found in the nucleus of the atom with the proton.  Its neutral charge is caused by the quark composition (udd or up, down, down) because the charges of the quarks add (up=2/3 + down=-1/3 + down=-1/3 = 0) to zero.  Bound inside the nucleus neutrons are stable, but the free neutron (synthetic) is unstable, having a half-life of about 885 seconds (approx. 15 minutes).  It interacts with all four forces and through beta decay, it becomes a proton.  The neutron is the heaviest particle in the atom.

The Proton

The proton is an elementary particle found in the nucleus of an atom. Its quark composition is uud or up, up, down. The charges of these quarks add (up=+2/3 up=+2/3 and down=-1/3) to +1, which is why the proton is positively charged. After the discovery of the electron, a positively charged particle was theorized to balance the atom. It interacts with all four forces (gravity, electromagnetism, weak nuclear force, and the strong nuclear force) and it is the second-heaviest particle in the atom (just short of the neutron). The proton is the only member of the Hydrogen nucleus and the number of protons in an atom determines atomic number. Protons are very well-known particles.