What portion of the electromagnetic spectrum do cats see?

What portion of the electromagnetic spectrum do cats see?

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I have seen numerous articles and various information about how cats and dogs see into the ultraviolet spectrum with interesting artistic renderings such as this:

But I have been unable to find any specific parameters of what wavelength boundaries actually exist for cats.

We know that humans see from around 750 to 400 nm, but what would a cat's range be?

Short answer
Spectral sensitivity of cats indeed ventures into the UV, but not beyond ~320 nm. Their maximum is likely similar to ours, i.e., ~750 nm.

The spectral sensitivity of blue cones (photoreceptors detecting low wavelengths) of many species, including humans and cats, extends into the UV range (Fig. 1).

Fig. 1. Human cone absorption spectra. Source: University of Kentucky

However, the various structures in the eye, most notably the lens, filter out UV in humans (Fig. 2). Indeed, surgical removal of the lens in humans results in enhanced sensitivity to UV light below 420 nm (Griswold & Stark, 1992).

Fig. 2. Human transmission spectra. Source: Columbia University

In the cat, however, the lens transmits a large portion of the UV light in the range of 320 - 400 nm, while primates transmit virtually no light of these wavelengths. Figure 3 shows the lens transmission spectra of various species. At 50% transmission the second (dotted) line from the left is the cat (50% transmission at ~340 nm), while a primate (squirrel monkey, species representative for humans and other primates) in this graph is line number 7 from the left with (50% transmission at ~410 nm). Hence, cat lenses absorb less light in the UV region, but transmission is virtually nil at 320 nm (Fig. 3). Given that their cones, just like humans, are sensitive to UV, we can reasonably expect that cats can see in the UV region including wavelengths of 320 nm and up. Cats also have the 560 nm (red) cones, like we do, so their maximum wavelength is expectedly similar to ours (~750 nm).

Fig. 3. Lens transmission spectra of various species. Source: Douglas & Jeffery, 2014

- Douglas & Jeffery, Proc R Soc B (2014); 281: 20132995
- Griswold & Stark, Vis Res (1992); 32(9): 1739-43

What portion of the electromagnetic spectrum do cats see? - Biology

The eye is the major sensory organ involved in vision (Figure 1). Light waves are transmitted across the cornea and enter the eye through the pupil. The cornea is the transparent covering over the eye. It serves as a barrier between the inner eye and the outside world, and it is involved in focusing light waves that enter the eye. The pupil is the small opening in the eye through which light passes, and the size of the pupil can change as a function of light levels as well as emotional arousal. When light levels are low, the pupil will become dilated, or expanded, to allow more light to enter the eye. When light levels are high, the pupil will constrict, or become smaller, to reduce the amount of light that enters the eye. The pupil’s size is controlled by muscles that are connected to the iris, which is the colored portion of the eye.

Figure 1. The anatomy of the eye is illustrated in this diagram.

After passing through the pupil, light crosses the lens, a curved, transparent structure that serves to provide additional focus. The lens is attached to muscles that can change its shape to aid in focusing light that is reflected from near or far objects. In a normal-sighted individual, the lens will focus images perfectly on a small indentation in the back of the eye known as the fovea, which is part of the retina, the light-sensitive lining of the eye. The fovea contains densely packed specialized photoreceptor cells (Figure 2). These photoreceptor cells, known as cones, are light-detecting cells. The cones are specialized types of photoreceptors that work best in bright light conditions. Cones are very sensitive to acute detail and provide tremendous spatial resolution. They also are directly involved in our ability to perceive color.

While cones are concentrated in the fovea, where images tend to be focused, rods, another type of photoreceptor, are located throughout the remainder of the retina. Rods are specialized photoreceptors that work well in low light conditions, and while they lack the spatial resolution and color function of the cones, they are involved in our vision in dimly lit environments as well as in our perception of movement on the periphery of our visual field.

Figure 2. The two types of photoreceptors are shown in this image. Cones are colored green and rods are blue.

We have all experienced the different sensitivities of rods and cones when making the transition from a brightly lit environment to a dimly lit environment. Imagine going to see a blockbuster movie on a clear summer day. As you walk from the brightly lit lobby into the dark theater, you notice that you immediately have difficulty seeing much of anything. After a few minutes, you begin to adjust to the darkness and can see the interior of the theater. In the bright environment, your vision was dominated primarily by cone activity. As you move to the dark environment, rod activity dominates, but there is a delay in transitioning between the phases. If your rods do not transform light into nerve impulses as easily and efficiently as they should, you will have difficulty seeing in dim light, a condition known as night blindness.

Rods and cones are connected (via several interneurons) to retinal ganglion cells. Axons from the retinal ganglion cells converge and exit through the back of the eye to form the optic nerve. The optic nerve carries visual information from the retina to the brain. There is a point in the visual field called the blind spot: Even when light from a small object is focused on the blind spot, we do not see it. We are not consciously aware of our blind spots for two reasons: First, each eye gets a slightly different view of the visual field therefore, the blind spots do not overlap. Second, our visual system fills in the blind spot so that although we cannot respond to visual information that occurs in that portion of the visual field, we are also not aware that information is missing.

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The optic nerve from each eye merges just below the brain at a point called the optic chiasm. As Figure 3 shows, the optic chiasm is an X-shaped structure that sits just below the cerebral cortex at the front of the brain. At the point of the optic chiasm, information from the right visual field (which comes from both eyes) is sent to the left side of the brain, and information from the left visual field is sent to the right side of the brain.

Figure 3. This illustration shows the optic chiasm at the front of the brain and the pathways to the occipital lobe at the back of the brain, where visual sensations are processed into meaningful perceptions.

Once inside the brain, visual information is sent via a number of structures to the occipital lobe at the back of the brain for processing. Visual information might be processed in parallel pathways which can generally be described as the “what pathway” (the ventral pathway) and the “where/how” pathway (the dorsal pathway). The “what pathway” is involved in object recognition and identification, while the “where/how pathway” is involved with location in space and how one might interact with a particular visual stimulus (Milner & Goodale, 2008 Ungerleider & Haxby, 1994). For example, when you see a ball rolling down the street, the “what pathway” identifies what the object is, and the “where/how pathway” identifies its location or movement in space.

Figure 4. Visual areas in the brain.

What do you think?

Astronomy Across the Electromagnetic Spectrum

While all light across the electromagnetic spectrum is fundamentally the same thing, the way that astronomers observe light depends on the portion of the spectrum they wish to study.

For example, different detectors are sensitive to different wavelengths of light. In addition, not all light can get through the Earth's atmosphere, so for some wavelengths we have to use telescopes aboard satellites. Even the way we collect the light can change depending on the wavelength. Astronomers must have a number of different telescopes and detectors to study the light from celestial objects across the electromagnetic spectrum.

A sample of telescopes (operating as of February 2013) operating at wavelengths across the electromagnetic spectrum. Observatories are placed above or below the portion of the EM spectrum that their primary instrument(s) observe.

The represented observatories are: HESS, Fermi and Swift for gamma-ray, NuSTAR and Chandra for X-ray, GALEX for ultraviolet, Kepler, Hubble, Keck (I and II), SALT, and Gemini (South) for visible, Spitzer, Herschel, and Sofia for infrared, Planck and CARMA for microwave, Spektr-R, Greenbank, and VLA for radio. Click here to see this image with the observatories labeled.

(Credit: Credit: Observatory images from NASA, ESA (Herschel and Planck), Lavochkin Association (Specktr-R), HESS Collaboration (HESS), Salt Foundation (SALT), Rick Peterson/WMKO (Keck), Germini Observatory/AURA (Gemini), CARMA team (CARMA), and NRAO/AUI (Greenbank and VLA) background image from NASA)

Can Dogs See in Ultraviolet?

Research suggests that your dog may be able to see things that are completely invisible to you.

If you look at the size, shape, and general structure of a dog's eye it looks very much like the human eye. For that reason we have a tendency to guess that vision in dogs is much like that in humans. However science has been advancing and we are learning that dogs and humans don't always see the same thing and don't always have the same visual abilities. For example, although dogs do have some color vision (click here for more about that) their range of colors is much more limited in comparison to humans. Dogs tend to see the world in shades of yellow, blue, and gray and can't discriminate between the colors that we see as red and green. Humans also have better visual acuity, and can discriminate details that dogs cannot (click here to read more about that).

On the flip side, the dog's eye is specialized for night vision and canines can see more under dim lighting than we humans can. Furthermore, dogs can see motion better than people. However a study published in the Proceedings of the Royal Society B* suggests that dogs may also see a whole range of visual information that humans cannot.

Ronald Douglas, a professor of biology at City University London and Glenn Jeffrey, a professor of neuroscience at University College London, were interested in seeing whether mammals could see in the ultraviolet light range. The wave lengths of visible light are measured in nanometers (a nanometer is one millionth of one thousandth of a meter). The longer wave lengths, around 700 nm, are seen by humans as red, and the shorter wavelengths, around 400 nm, are seen as blue or violet. Wavelengths of light which are shorter than 400 nm are not seen by normal humans, and light in this range is called ultraviolet.

It is well known that some animals, such as insects, fish, and birds, can see in the ultraviolet. For bees this is a vital ability. When humans look at certain flowers they might see something which has a uniform color, however many species of flowers have adapted their coloration so that when viewed with ultraviolet sensitivity the center of the flower (which contains the pollen and nectar) is a readily visible target making it easier for a bee to find. You can see that in this figure.

In human beings the lens inside the eye has a yellowish tint which filters out the ultraviolet light. The British research team reasoned that certain other species of mammals might not have such yellowish components in their eyes and therefore might be sensitive to ultraviolet light. It is certainly the case that people who have had the lens of their eye removed surgically because of cataracts often report a change in their vision. With the removal of the yellowish lens such individuals can now see in the ultraviolet range. For example, some experts believe that it was because of such a cataract operation the artist Monet began to paint flowers with a blue tinge.

In the current study a broad range of animals including: dogs, cats, rats, reindeer, ferrets, pigs, hedgehogs and many others, were tested. The transparency of the optical components of their eyes was measured and it was found that a number of these species did allow a good deal of ultraviolet light into their eyes. When the eye of the dog was tested they found that it allowed over 61% of the UV light to pass through and reach the photosensitive receptors in the retina. Compare this to humans where virtually no UV light gets through. With this new data we can determine how a dog might see a visual spectrum (like a rainbow) in comparison to a human and that is simulated in this figure.

The obvious question to ask is what benefits the dog derives from its ability to see in the ultraviolet. It may have something to do with having an eye that is adapted so that it has good night vision, since it appears that those species who were at least partially nocturnal had lenses capable of transmitting ultraviolet, while those who functioned mostly in the daylight did not. However it is also the case that certain types of information can be processed if you have ultraviolet sensitivity. Anything that either absorbs the ultraviolet or reflects it differentially would thus become visible. For example in this figure we have an individual on whom we have painted a pattern using a sunscreen lotion (which blocks ultraviolet). The pattern is not visible under normal conditions, but when viewed in ultraviolet light it becomes quite clear.

In nature there are a number of significant things which might become visible if you can see in the ultraviolet. Of interest to dogs is the fact that urine trails become visible in ultraviolet. Since urine is used by dogs to learn something about other dogs in their environment, it may be useful to be able to spot patches of it easily. This might also be of assistance in wild canines as a method of spotting and trailing potential prey.

In certain specific environments sensitivity to the ultraviolet part of the spectrum can provide an advantage to an animal that hunts in order to survive, such as the ancestors of our dogs. Consider the figure below. You can see that the white coloration of an arctic hare provides good camouflage and makes the animal difficult to spot against a snowy background. However such camouflage is not as good when used against an animal with ultraviolet visual capacities. This is because the snow will reflect much of the ultraviolet light while white fur does not reflect the UV rays as well. Thus to the UV sensitive eye the arctic hare is now much more easily seen since it appears as if it is a lightly shadowed form, rather than white against white, as can be seen in the simulation below.

If visual sensitivity in the ultraviolet does provide certain advantages to an animal like a dog, then perhaps the question we should be asking is why other animals, like humans, would not benefit as well from having the ability to register ultraviolet light. The answer seems to come from the fact that there are always trade-offs in vision. You can have an eye that is sensitive in low levels of light, such as the dog's eye, but that sensitivity comes at a cost. It is the short wavelengths of light (those that we see as blue, and even more so, those shorter yet wavelengths that we call ultraviolet) which are most easily scattered as they enter the eye. This light scattering degrades the image and makes it blurry so you can't see details. So dogs who evolved from nocturnal hunters may have maintained their ability to see ultraviolet light because they need that sensitivity when there is little light around. Animals who function in the daylight, such as we humans, rely more on our visual acuity to effectively deal with the world. So we have eyes that screen out the ultraviolet in order to improve our ability to see fine visual details.

We have been talking about the first study which has dealt with this aspect of canine vision and its results were a surprise to many of us who never expected that dogs might have this added form of visual sensitivity. Obviously further research is needed to determine how dogs really benefit from this ability. I doubt that it was an evolutionary development which simply allows dogs to have greater appreciation for the psychedelic posters which became so popular in the 1970s — you know those posters that were created by using inks that fluoresced under a "black light" or ultraviolet light source. But only through future research will we know for sure.

Copyright SC Psychological Enterprises Ltd. May not be reprinted or reposted without permission

* Data from: R. H. Douglas, G. Jeffery (2014). The writer spectral transmission of ocular media suggest ultraviolet sensitivity is widespread among mammals. Proceedings of the Royal Society B, April, volume 281, issue 1780.

What animal can see the most on the electromagnetic spectrum?

We've all heard that dogs and cats are colorblind (This is partially untrue they can see blues and yellows. Also, bulls can't see red so they aren't actually angry by it.), but there must be animals that can see more colors than humans. Being able to see color is caused by the cones in our eyes that help us distinguish them. Humans for example have red/green, blue/yellow, and black/white cones. Most humans that are colorblind have issues with their red/green cones.

Animals that pollinate, such as butterflies and bees, have sight that lets them see ultraviolet which guides them into the flower.

What else determines what we can see is the wave lengths that our eyes respond to. Human eyes generally respond to wavelengths between 390-750 nm (visible light). Birds typically see ultraviolet which is below 390 nm. In my searching I couldn't seem to find which animal sees the most of the EM spectrum but I did find what animal is believed to see the most colors: the mantis shrimp

1. Spectral Range

The electromagnetic spectrum is a map of all the types of light that we can see and identify. The electromagnetic spectrum separates all the types of light by their wavelength that depends on how energetic a particular wave is. Waves that are more energetic have shorter wavelengths while waves that are less energetic have longer wavelengths. Human vision is restricted to a small portion of the electromagnetic spectrum there are many kinds of electromagnetic waves that we cannot see. Nocturnal animals, on the other hand, have access to the wider sections of the spectrum and can see the infrared or ultraviolet spectrum as well.


Optical spectrometers or Optical Emission Spectrometer Edit

Optical absorption spectrometers Edit

Optical spectrometers (often simply called "spectrometers"), in particular, show the intensity of light as a function of wavelength or of frequency. The different wavelengths of light are separated by refraction in a prism or by diffraction by a diffraction grating. Ultraviolet–visible spectroscopy is an example.

These spectrometers utilize the phenomenon of optical dispersion. The light from a source can consist of a continuous spectrum, an emission spectrum (bright lines), or an absorption spectrum (dark lines). Because each element leaves its spectral signature in the pattern of lines observed, a spectral analysis can reveal the composition of the object being analyzed. [1]

Optical emission spectrometers Edit

Optical emission spectrometers (often called "OES or spark discharge spectrometers"), is used to evaluate metals to determine the chemical composition with very high accuracy. A spark is applied through a high voltage on the surface which vaporizes particles into a plasma. The particles and ions then emit radiation that is measured by detectors (photomultiplier tubes) at different characteristic wavelengths.

Electron spectroscopy Edit

Some forms of spectroscopy involve analysis of electron energy rather than photon energy. X-ray photoelectron spectroscopy is an example.

Mass spectrometer Edit

A mass spectrometer is an analytical instrument that is used to identify the amount and type of chemicals present in a sample by measuring the mass-to-charge ratio and abundance of gas-phase ions. [2]

Time-of-flight spectrometer Edit

The energy spectrum of particles of known mass can also be measured by determining the time of flight between two detectors (and hence, the velocity) in a time-of-flight spectrometer. Alternatively, if the velocity is known, masses can be determined in a time-of-flight mass spectrometer.

Magnetic spectrometer Edit

When a fast charged particle (charge q, mass m) enters a constant magnetic field B at right angles, it is deflected into a circular path of radius r, due to the Lorentz force. The momentum p of the particle is then given by

where m and v are mass and velocity of the particle. The focusing principle of the oldest and simplest magnetic spectrometer, the semicircular spectrometer, [3] invented by J. K. Danisz, is shown on the left. A constant magnetic field is perpendicular to the page. Charged particles of momentum p that pass the slit are deflected into circular paths of radius r = p/qB. It turns out that they all hit the horizontal line at nearly the same place, the focus here a particle counter should be placed. Varying B, this makes possible to measure the energy spectrum of alpha particles in an alpha particle spectrometer, of beta particles in a beta particle spectrometer, [4] of particles (e.g., fast ions) in a particle spectrometer, or to measure the relative content of the various masses in a mass spectrometer.

Since Danysz' time, many types of magnetic spectrometers more complicated than the semicircular type have been devised. [4]

Generally, the resolution of an instrument tells us how well two close-lying energies (or wavelengths, or frequencies, or masses) can be resolved. Generally, for an instrument with mechanical slits, higher resolution will mean lower intensity.

Observatories Across the Electromagnetic Spectrum

Astronomers use a number of telescopes sensitive to different parts of the electromagnetic spectrum to study objects in space. Even though all light is fundamentally the same thing, the way that astronomers observe light depends on the portion of the spectrum they wish to study.

For example, different detectors are sensitive to different wavelengths of light. In addition, not all light can get through the Earth's atmosphere, so for some wavelengths we have to use telescopes aboard satellites. Even the way we collect the light can change depending on the wavelength. Here we briefly introduce observatories used for each band of the EM spectrum.

A sample of telescopes (operating as of February 2013) operating at wavelengths across the electromagnetic spectrum. Observatories are placed above or below the portion of the EM spectrum that their primary instrument(s) observe.

The represented observatories are: HESS, Fermi and Swift for gamma-ray, NuSTAR and Chandra for X-ray, GALEX for ultraviolet, Kepler, Hubble, Keck (I and II), SALT, and Gemini (South) for visible, Spitzer, Herschel, and Sofia for infrared, Planck and CARMA for microwave, Spektr-R, Greenbank, and VLA for radio. Click here to see this image with the observatories labeled.

(Credit: Observatory images from NASA, ESA (Herschel and Planck), Lavochkin Association (Specktr-R), HESS Collaboration (HESS), Salt Foundation (SALT), Rick Peterson/WMKO (Keck), Germini Observatory/AURA (Gemini), CARMA team (CARMA), and NRAO/AUI (Greenbank and VLA) background image from NASA)

Radio observatories

This artist's conception shows Earth and the Spektr-R spacecraft with an imagined radio antenna that is created by combining Spektr-R's data with that of Earth-bound radio telescopes. (Credit: Lavochkin Association)

Radio waves can make it through the Earth's atmosphere without significant obstacles. In fact, radio telescopes can observe even on cloudy days. In principle, then, we don't need to put radio telescopes in space. However, space-based radio observatories complement Earth-bound radio telescopes in some important ways.

A special technique used in radio astronomy is called "interferometry." Radio astronomers can combine data from two telescopes that are very far apart and create images that have the same resolution as if they had a single telescope as big as the distance between the two telescopes. This means radio telescope arrays can see incredibly small details. One example is the Very Large Baseline Array (VLBA), which consists of 10 radio observatories that reach from Hawaii to Puerto Rico, nearly a third of the way around the world.

By putting a radio telescope in orbit around Earth, radio astronomers can make images as if they had a radio telescope the size of the entire planet. The first mission dedicated to space interferometry was the Japanese HALCA mission which ran from 1997 to 2005. The second dedicated mission is the Russian Spektr-R satellite, which launched in 2011.

Microwave observatories

Artist's conception of the European Space Agency's (ESA's) Planck observatory cruising to its orbit. (Credit: ESA/D. Ducros)

The Earth's atmosphere blocks much of the light in the microwave band, so astronomers use satellite-based telescopes to observe cosmic microwaves. The entire sky is a source of microwaves in every direction, most often referred to as the cosmic microwave background (or CMB for short). These microwaves are the remnant of the Big Bang, a term used to describe the early universe.

A very long time ago, all the matter in existence was scrunched together in a very small, hot ball. The ball expanded outward and became our universe as it cooled. Since the Big Bang, which is estimated to have taken place 13.8 billion years ago, it has cooled all the way to just three degrees above absolute zero. It is this "three degrees" that we measure as the microwave background.

The first precise measurements of the temperature of the microwave background across the entire sky was done by the Cosmic Background Explorer (COBE) satellite from 1989 to 1993. Since then, the Wilkinson Microwave Anisotropy Probe (WMAP) refined the COBE measurements, operating from 2001 to 2010. More recently, the Planck mission launched in 2009 and further improved astronomer's understanding of the CMB.

Infrared observatories

Artist's conception of SOFIA flying at sunset (Credit: NASA)

Photograph of the Keck I and II domes at dawn the Keck telescopes operate in visible and infrared wavelengths. (Credit: Rick Peterson/WMKO)

Infrared astronomy has to overcome a number of challenges. While some infrared radiation can make it through Earth's atmosphere, the longer wavelengths are blocked. But that's not the biggest challenge – everything that has heat emits infrared light. That means that the atmosphere, the telescope, and even the infrared detectors themselves all emit infrared light.

Ground-based infrared telescopes reside at high altitudes in dry climates in an effort to get above much of the water vapor in the atmosphere that absorbs infrared. However, ground-based infrared observatories must still account for the atmosphere in their measurements. To do this, the infrared emission from the atmosphere is measured at the same time as the measurement of the cosmic object being observed. Then, the emission from the atmosphere can be subtracted to get an accurate measurement of the cosmic object. The telescopes, for both ground-based and space/airborne observatories, are also designed to limit the spurious infrared radiation from reaching the detector, and the detectors are cooled to limit their infrared emissions.

In 2003, NASA launched the Spitzer Space Telescope into an earth-trailing, heliocentric orbit, where it did not have to contend with the comparatively warm environment in near-Earth space. Another major infrared facility is the Stratospheric Observatory for Infrared Astronomy (SOFIA). SOFIA carries a large telescope inside a 747 aircraft flying at an altitude sufficient to get it well above most of the Earth's infrared absorbing atmosphere.

Scheduled for launch in 2018, the James Webb Space Telescope is a large, space-based observatory, that is optimized for infrared wavelengths. Webb will be able to look further back in time to find the first galaxies that formed in the early Universe and to peer inside dust clouds where stars and planetary systems are forming today. Webb will also be in a heliocentric orbit at the second Lagrange point. To keep the mirror and instruments cold (and allow the telescope to detect the faintest of heat signals from distant objects), it has a giant sunshield, which will block the light and heat from the Earth, Sun, and Moon.

Visible spectrum observatories

The Hubble Space Telescope just after it was captures by the Space Shuttle Atlantis to be serviced in 2009. (Credit: NASA)

Visible light can pass right through our atmosphere, which is why astronomy is as old as humanity. Ancient humans could look up at the night sky and see the stars above them. Today, there is an army of ground-based telescope facilities for visible astronomy (also called "optical astronomy"). However, there are limits to ground-based optical astronomy. As light passes through the atmosphere, it is distorted by the turbulence within the air. Astronomers can improve their chances of a good image by putting observatories on mountain-tops (above some of the atmosphere), but there will still be limits to how crisp their images will be, especially for faint sources.

Visible-light observatories in space avoid the turbulence of the Earth's atmosphere. In addition, they can observe a somewhat wider portion of the electromagnetic spectrum, in particular ultraviolet light that is absorbed by the Earth's atmosphere. The Hubble Space Telescope is perhaps the most famous optical telescope in orbit. Also in orbit is the Kepler observatory. Kepler is using visible light to survey a portion of the Milky Way galaxy to discover planetary systems. The Swift satellite also carries an UltraViolet and Optical Telescope (the UVOT) to perform observations of gamma-ray bursts.

Ultraviolet observatories

Artist's concept of the GALEX satellite in orbit. (Credit: NASA/JPL-Caltech)

The Earth's atmosphere absorbs ultraviolet light, so ultraviolet astronomy must be done using telescopes in space. Other than carefully-select materials for filters, a ultraviolet telescope is much like a regular visible light telescope. The primary difference being that the ultraviolet telescope must be above Earth's atmosphere to observe cosmic sources.

The GALEX observatory was the most recent dedicated ultraviolet observatory. It was launched in 2003 and shut down operations in 2013. Its goal was to observe the history of star formation in our Universe in ultraviolet wavelengths, and it observed over a half-billion galaxies going back to when our Universe was just about 3 billion years old.

The Hubble Space Telescope and the UltraViolet and Optical Telescope on Swift can both perform a great deal of observing at ultraviolet wavelengths, but they only cover a portion of the spectrum that GALEX observes.

X-ray observatories

Artist's concept of the NuSTAR satellite. (Credit: NASA/JPL-Caltech)

X-ray wavelengths are another portion of the electromagnetic spectrum that are blocked by Earth's atmosphere. X-rays also pose a particular challenge because they are so small and energetic that they don't bounce off mirrors like lower-energy forms of light. Instead, they pass right through. Unless they just barely graze the surface of the mirror. (Read more about how X-rays are focused on the X-ray Telescope Introduction page.)

Focusing X-ray telescope require long focal lengths. In other words, the mirrors where light enters the telescope must be separated from the X-ray detectors by several meters. However. launching such a large observatory is costly and limits the launch vehicles to only the most powerful rockets (the Space Shuttle in the case of the Chandra X-ray Observatory).

In 2012, the Nuclear Spectroscopic Telescope Array (or NuSTAR for short), solved this problem by designing an observatory with a deployable mast. In other words, NuSTAR was designed with its mirror module and detector module on a mast, or boom, that could be extended once it was in orbit. By doing that, NuSTAR could be launched on a low-cost rocket.

Gamma-ray observatories

Artist's concept of the Fermi satellite. (Credit: NASA)

One of the HESS telescopes. (Credit: HESS Collaboration)

Not only are gamma-rays blocked by Earth's atmosphere, but they are even harder than X-rays to focus. In fact, so far, there have been no focusing gamma-ray telescopes. Instead, astronomers rely on alternate ways to determine where in the sky gamma-rays are produced. This can be properties of the detector or using special "masks" that cast gamma-ray shadows on the detector.

The Swift satellite was launched in 2004 to help solve the mystery of gamma-ray bursts. Swift has a gamma-ray detector that can observe half the sky at a time, and if it detects a gamma-ray burst, the satellite can quickly point its X-ray and optical telescopes in the direction of the burst. The Fermi Space Telescope was launched in 2008 and is designed to study energetic phenomena from a variety of cosmic sources, including pulsars, black holes, active galaxies, diffuse gamma-ray emission and gamma-ray bursts.

It might be surprising to know that astronomers can use ground-based astronomy to detect the highest energy gamma-rays. For these gamma-rays, the telescopes don't detect the gamma-rays directly. Instead, they use the atmosphere itself as a detector. The HESS array has been in operation for over 10 years. The array began with four telescopes arranged in a square, and recently added the HESS II telescope to its ranks.

Predators, prey, pollinators, and plants

Ultraviolet vision and reflectance play roles not only in interactions among birds but also in interactions between birds and their environments. Just as UV patterns on flower petals attract bees, for instance, pollinating hummingbirds may also use such information.

Fruit-eating birds may use UV cues in foraging. Many fruits whose seeds are dispersed by birds are covered with a waxy substance that reflects UV light. Although some studies have found no preference among birds for such berries, one recent study showed that Redwings (Turdus iliacus) preferred UV-reflecting bilberries under UV light but not under UV-deprived conditions. This preference was apparent only in older birds, suggesting that it is learned and that fruit reflectance may indicate ripeness.

Bird–insect interactions may be widely influenced by UV, but few studies have addressed this. Many insects, such as butterflies, are UV-reflectant and could catch the attention of avian predators if seen against a nonreflectant background. Take the peppered moth (Biston betularia)—that textbook case of natural selection in which dark moths became more abundant than light moths as trees in industrial England lost their light-colored lichens and became covered in soot, enabling the dark moths to escape bird predation. Consideration of UV reflectance throws a monkey wrench into the classic story, Michael Majerus, of the University of Cambridge, and his colleagues have found. One type of lichen absorbs UV light, as do dark moths, whereas light moths reflect UV and are conspicuous against this lichen. (However, the two morphs' tendencies to alight on different parts of trees where different lichen species grow helps compensate for the UV complication.)

Most caterpillars match their leaf or twig backgrounds cryptically in the UV as well as in visible spectra, Stuart Church, of the University of Bristol group has found. Church has come across one species, however, that stands out conspicuously against its host plant, and he speculates this may be a case of ultraviolet warning coloration.

Perhaps the most surprising predator–prey story yet revealed is that some raptors use UV cues to hunt rodent prey. Eurasian kestrels (Falco tinnunculus) and rough-legged hawks (Buteo lagopus) have been shown to detect UV cues that divulge the trails of voles through grass. Male voles produce urine and feces containing chemicals that absorb UV, and mark their trails with urine. The hawks identify areas of high vole density and adjust their behavior to focus on these regions, according to work by Jussi Viitala, of the University of Turku, Finland.

Minna Koivula, now also at the University of Turku, wondered if such behavior would also occur in nocturnal raptors that likely do not use such visual cues. Tengmalm's Owls (Aegolius funereus), she found, do not respond to UV-visible vole trails, suggesting that the response evolves or is retained only in those species that can exploit it.

What portion of the electromagnetic spectrum do cats see? - Biology

The question: "What percentage of the electromagnetic spectrum is visible light? I've read that visible light makes up a very tiny portion of EM radiation or frequency. I am curious if there is a more precise known percentage of visible light in relation to the whole (the other six wavelengths of the spectrum)."

Let's examine the available information. The electromagnetic spectrum is usually considered to extend from radio waves to gamma rays, with frequencies from about 10000 Hz to 10 19 Hz, respectively, while visible light goes from red to violet with frequencies from about 4x10 14 Hz to about 7.5x10 14 Hz, respectively.

So, if the entire spectrum is taken to span 15 orders of magnitude (log10(10 19 ) = 19, log10(10 4 ) = 4, and 19 - 4 = 15) while the visible spectrum spans only 0.35 of an order of magnitude, then we can say that the visible spectrum is 100%*0.35/15 of the entire electromagnetic spectrum, which works out to about 2.3%. But that is on a logarithmic scale, so let's do the calculation again on a linear scale:

The entire spectrum has the range 10 19 Hz - 10 4 Hz, which is 0.999999999999999x10 19 Hz. The visible spectrum has the range 3.5x10 14 Hz. So 100%*3.5x10 14 /0.999999999999999x10 19 = 0.0035%.

So, on a logarithmic scale of frequency, visible light is 2.3% of the whole electromagnetic spectrum, while on a linear scale it is 0.0035%.

If you would rather do the calculation using wavelengths I think there is enough information here for you to able to do so.


  1. Minninnewah

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  2. Orran

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  3. Danh

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  4. Ashraf

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  5. Jorah

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  6. Tygocage

    Interesting note

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