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48-662: The term planet was applied originally only to the five planets known (i.e., visible to the naked eye ) and excluded the Earth . The term was later generalized, particularly during the Middle Ages , to include the sun and the moon (sometimes referred to as "lights"), making a total of seven planets. The seven days of the week of the Hindu calendar also corresponds with the seven classical planets and related day names of European culture and are named accordingly in most languages of

96-514: A few thousand parsecs of the Earth, extinction in the visual band of frequencies ( photometric system ) is roughly 1.8  magnitudes per kiloparsec. For Earth-bound observers , extinction arises both from the interstellar medium and the Earth's atmosphere ; it may also arise from circumstellar dust around an observed object. Strong extinction in Earth's atmosphere of some wavelength regions (such as X-ray , ultraviolet , and infrared )

144-453: A new record as the farthest object that can be seen from Earth with the naked eye. It occurred about 7.5 billion years ago, the light taking that long to reach Earth. Many other things can be estimated without an instrument. If an arm is stretched the span of the hand corresponds to an angle of 18 to 20°. The distance of a person, just covered up by the outstretched thumbnail, is about 100 meters. The vertical can be estimated to about 2° and, in

192-406: A result, when computing cosmic distances it can be advantageous to move to star data from the near-infrared (of which the filter or passband Ks is quite standard) where the variations and amount of extinction are significantly less, and similar ratios as to R(Ks): 0.49±0.02 and 0.528±0.015 were found respectively by independent groups. Those two more modern findings differ substantially relative to

240-482: A viewing distance of 16" = ~ 400 mm, which is considered a normal reading distance in the US, the smallest object resolution will be ~ 0.116 mm. For inspection purposes laboratories use a viewing distance of 200–250 mm, which gives the smallest size of the object recognizable to the naked eye of ~0.058–0.072 mm (58–72 micrometers). The accuracy of a measurement ranges from 0.1 to 0.3 mm and depends on

288-448: Is a broad 'bump' at about 2175 Å , well into the ultraviolet region of the electromagnetic spectrum. This feature was first observed in the 1960s, but its origin is still not well understood. Several models have been presented to account for this bump which include graphitic grains with a mixture of PAH molecules. Investigations of interstellar grains embedded in interplanetary dust particles (IDP) observed this feature and identified

336-552: Is a difficult averted vision object and only visible at all if it is higher than 50° in the sky. The globular clusters M 3 in Canes Venatici and M 92 in Hercules are also visible with the naked eye under such conditions. Under really dark sky conditions, however, M33 is easy to see, even in direct vision. Many other Messier objects are also visible under such conditions. The most distant objects that have been seen by

384-569: Is absent, stars as faint as +8 might be visible. The angular resolution of the naked eye is about 1 ′ ; however, some people have sharper vision than that. There is anecdotal evidence that people had seen the Galilean moons of Jupiter before telescopes were invented. Uranus and Vesta had most probably been seen but could not be recognized as planets because they appear so faint even at maximum brightness; Uranus's magnitude varies from +5.3 to +5.9 , and Vesta's from +5.2 to +8.5 (so that it

432-412: Is calculated and deducted. The name of the four sub-indices (R minus I etc.) and order of the subtraction of recalibrated magnitudes is from right to immediate left within this sequence. Interstellar reddening occurs because interstellar dust absorbs and scatters blue light waves more than red light waves, making stars appear redder than they are. This is similar to the effect seen when dust particles in

480-413: Is lowest at the observer's zenith and highest near the horizon . A given star, preferably at solar opposition, reaches its greatest celestial altitude and optimal time for observation when the star is near the local meridian around solar midnight and if the star has a favorable declination ( i.e. , similar to the observer's latitude ); thus, the seasonal time due to axial tilt is key. Extinction

528-801: Is much more strongly affected by light pollution than is that of planets and stars. Under typical dark conditions only a few such objects are visible. These include the Pleiades , h/χ Persei , the Andromeda Galaxy , the Carina Nebula , the Orion Nebula , Omega Centauri , 47 Tucanae , the Ptolemy Cluster Messier 7 near the tail of Scorpius and the globular cluster M13 in Hercules . The Triangulum Galaxy (M33)

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576-413: Is only visible near its opposition dates). Uranus, when discovered in 1781, was the first planet discovered using technology (a telescope ) rather than being spotted by the naked eye. Theoretically, in a typical dark sky, the dark adapted human eye would see the about 5,600 stars brighter than +6 while in perfect dark sky conditions about 45,000 stars brighter than +8 might be visible. In practice,

624-434: Is overcome by the use of space-based observatories . Since blue light is much more strongly attenuated than red light, extinction causes objects to appear redder than expected; this phenomenon is called interstellar reddening . Interstellar reddening is a phenomenon associated with interstellar extinction where the spectrum of electromagnetic radiation from a radiation source changes characteristics from that which

672-446: Is possible. This represents only 200 meters at the moon's distance of 385,000 km. Observing a nearby small object without a magnifying glass or a microscope , the size of the object depends on the viewing distance. Under normal lighting conditions (light source ~ 1000 lumens at height 600–700 mm, viewing angle ~ 35 degrees) the angular size recognized by naked eye will be round 1 arc minute = 1/60 degrees = 0.0003 radians. At

720-501: Is strongly affected by light pollution . Even a few hundred kilometers away from a metropolitan area where the sky can appear to be very dark, it is still the residual light pollution that sets the limit on the visibility of faint objects. For most people, these are likely to be the best observing conditions within their reach. Under such "typical" dark sky conditions, the naked eye can see stars with an apparent magnitude up to +6 . Under perfect dark sky conditions where all light pollution

768-416: Is supported by work in starburst galaxies (which are undergoing intense star formation episodes) which shows that their dust lacks the 2175 Å bump. Atmospheric extinction gives the rising or setting Sun an orange hue and varies with location and altitude . Astronomical observatories generally are able to characterise the local extinction curve very accurately, to allow observations to be corrected for

816-786: Is the theoretical value which it would have if unaffected by extinction. In the first system, the UBV photometric system devised in the 1950s and its most closely related successors, the object's color excess E B − V {\displaystyle E_{B-V}} is related to the object's B−V color (calibrated blue minus calibrated visible) by: E B − V = ( B − V ) observed − ( B − V ) intrinsic {\displaystyle E_{B-V}=(B-V)_{\textrm {observed}}-(B-V)_{\textrm {intrinsic}}\,} For an A0-type main sequence star (these have median wavelength and heat among

864-513: Is usually taken to be 0.7–1.0 mag/kpc−simply an average due to the clumpiness of interstellar dust. In general, however, this means that a star will have its brightness reduced by about a factor of 2 in the V-band viewed from a good night sky vantage point on earth for every kiloparsec (3,260 light years) it is farther away from us. The amount of extinction can be significantly higher than this in specific directions. For example, some regions of

912-493: The B and V filter bands. Another measure used in the literature is the absolute extinction A(λ)/A(V) at wavelength λ, comparing the total extinction at that wavelength to that at the V band. R(V) is known to be correlated with the average size of the dust grains causing the extinction. For the Milky Way Galaxy, the typical value for R(V) is 3.1, but is found to vary considerably across different lines of sight. As

960-604: The Galactic Center are awash with obvious intervening dark dust from our spiral arm (and perhaps others) and themselves in a bulge of dense matter, causing as much as more than 30 magnitudes of extinction in the optical, meaning that less than 1 optical photon in 10 passes through. This results in the zone of avoidance , where our view of the extra-galactic sky is severely hampered, and background galaxies, such as Dwingeloo 1 , were only discovered recently through observations in radio and infrared . The general shape of

1008-518: The Indian subcontinent . Most Hindu temples around the world have a designated place dedicated to the worship of the navagraha. Muthuswami Dikshitar (1776–1835), a Carnatic music composer from southern India, composed the Navagraha Kritis in praise of the nine grahas . Each song is a prayer to one of the nine planets. The Sahitya (lyrics) of the songs reflect a profound knowledge of

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1056-408: The mantra and jyotisha sastras . This mythology -related article is a stub . You can help Misplaced Pages by expanding it . Naked eye Naked eye , also called bare eye or unaided eye , is the practice of engaging in visual perception unaided by a magnifying , light-collecting optical instrument , such as a telescope or microscope , or eye protection . In astronomy ,

1104-470: The observer . Interstellar extinction was first documented as such in 1930 by Robert Julius Trumpler . However, its effects had been noted in 1847 by Friedrich Georg Wilhelm von Struve , and its effect on the colors of stars had been observed by a number of individuals who did not connect it with the general presence of galactic dust . For stars lying near the plane of the Milky Way which are within

1152-619: The phases of Venus , among other things. Meteor showers are better observed by naked eye than with binoculars. Such showers include the Perseids (10–12 August) and the December Geminids . Some 100 satellites per night, the International Space Station and the Milky Way are other popular objects visible to the naked eye. On 19 March 2008, a major gamma-ray burst (GRB) known as GRB 080319B , set

1200-422: The spectroscopic lines unchanged. In most photometric systems , filters (passbands) are used from which readings of magnitude of light may take account of latitude and humidity among terrestrial factors. Interstellar reddening equates to the "color excess", defined as the difference between an object's observed color index and its intrinsic color index (sometimes referred to as its normal color index). The latter

1248-457: The temperature and density in the nebula. For example, the ratio of hydrogen-alpha to hydrogen-beta emission is always around 2.85 under a wide range of conditions prevailing in nebulae. A ratio other than 2.85 must therefore be due to extinction, and the amount of extinction can thus be calculated. One prominent feature in measured extinction curves of many objects within the Milky Way

1296-637: The LMC and SMC which are similar to those found in the Milky Way and finding extinction curves in the Milky Way that look more like those found in the LMC2 supershell of the LMC and in the SMC Bar has given rise to a new interpretation. The variations in the curves seen in the Magellanic Clouds and Milky Way may instead be caused by processing of the dust grains by nearby star formation. This interpretation

1344-608: The Naked eye only if Neptune is at its maximum brightness (magnitude +7.8). The Sun and the Moon—the remaining noticeable naked-eye objects of the solar system—are sometimes added to make seven "planets". During daylight only the Moon and Sun are obvious naked eye objects, but in many cases Venus can be spotted in daylight and in rarer cases Jupiter . Close to sunset and sunrise, bright stars like Sirius or even Canopus can be spotted with

1392-476: The air. This is of importance in meteorology and for the " seeing " of astronomy. Light pollution is a significant problem for amateur astronomers but becomes less late at night when many lights are shut off. Air dust can be seen even far away from a city by its "light dome". Extinction (astronomy) In astronomy , extinction is the absorption and scattering of electromagnetic radiation by dust and gas between an emitting astronomical object and

1440-424: The atmosphere of Earth contribute to red sunsets . Broadly speaking, interstellar extinction is strongest at short wavelengths, generally observed by using techniques from spectroscopy. Extinction results in a change in the shape of an observed spectrum. Superimposed on this general shape are absorption features (wavelength bands where the intensity is lowered) that have a variety of origins and can give clues as to

1488-415: The atmospheric extinction and dust reduces this number somewhat. In the center of a city, where the naked-eye limiting magnitude due to extreme amounts of light pollution can be as low as 2 , as few as 50 stars are visible. Colors can be seen but this is limited by the fact that the eye uses rods instead of cones to view fainter stars. The visibility of diffuse objects such as star clusters and galaxies

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1536-666: The carrier with organic carbon and amorphous silicates present in the grains. The form of the standard extinction curve depends on the composition of the ISM, which varies from galaxy to galaxy. In the Local Group , the best-determined extinction curves are those of the Milky Way, the Small Magellanic Cloud (SMC) and the Large Magellanic Cloud (LMC). In the LMC, there is significant variation in

1584-472: The characteristics of the ultraviolet extinction with a weaker 2175 Å bump and stronger far-UV extinction in the region associated with the LMC2 supershell (near the 30 Doradus starbursting region) than seen elsewhere in the LMC and in the Milky Way. In the SMC, more extreme variation is seen with no 2175 Å bump and very strong far-UV extinction in the star forming Bar and fairly normal ultraviolet extinction seen in

1632-467: The chemical composition of the interstellar material, e.g. dust grains. Known absorption features include the 2175  Å bump, the diffuse interstellar bands , the 3.1  μm water ice feature, and the 10 and 18 μm silicate features. In the solar neighborhood , the rate of interstellar extinction in the Johnson–Cousins V-band (visual filter) averaged at a wavelength of 540 nm

1680-425: The commonly referenced historical value ≈0.7. The relationship between the total extinction, A(V) (measured in magnitudes ), and the column density of neutral hydrogen atoms column, N H (usually measured in cm ), shows how the gas and dust in the interstellar medium are related. From studies using ultraviolet spectroscopy of reddened stars and X-ray scattering halos in the Milky Way, Predehl and Schmitt found

1728-642: The effect. Nevertheless, the atmosphere is completely opaque to many wavelengths requiring the use of satellites to make observations. This extinction has three main components: Rayleigh scattering by air molecules, scattering by particulates , and molecular absorption . Molecular absorption is often referred to as telluric absorption , as it is caused by the Earth ( telluric is a synonym for terrestrial ). The most important sources of telluric absorption are molecular oxygen and ozone , which strongly absorb radiation near ultraviolet , and water , which strongly absorbs infrared . The amount of such extinction

1776-403: The experience of the observer. The latter figure is the usual positional accuracy of faint details in maps and technical plans. A clean atmosphere is indicated by the fact that the Milky Way is visible. Comparing the zenith with the horizon shows how the "blue quality" is degraded depending on the amount of air pollution and dust. The twinkling of a star is an indication of the turbulence of

1824-417: The extinction curve for a star , the star's spectrum is compared to the observed spectrum of a similar star known not to be affected by extinction (unreddened). It is also possible to use a theoretical spectrum instead of the observed spectrum for the comparison, but this is less common. In the case of emission nebulae , it is common to look at the ratio of two emission lines which should not be affected by

1872-407: The extinction law into the mid-infrared wavelength range is difficult due to the lack of suitable targets and various contributions by absorption features. R(V) compares aggregate and particular extinctions. It is A(V)/E(B−V) . Restated, it is the total extinction, A(V) divided by the selective total extinction (A(B)−A(V)) of those two wavelengths (bands). A(B) and A(V) are the total extinction at

1920-401: The main sequence) the color indices are calibrated at 0 based on an intrinsic reading of such a star (± exactly 0.02 depending on which spectral point, i.e. precise passband within the abbreviated color name is in question, see color index ). At least two and up to five measured passbands in magnitude are then compared by subtraction: U, B, V, I, or R during which the color excess from extinction

1968-400: The more quiescent Wing. This gives clues as to the composition of the ISM in the various galaxies. Previously, the different average extinction curves in the Milky Way, LMC, and SMC were thought to be the result of the different metallicities of the three galaxies: the LMC's metallicity is about 40% of that of the Milky Way , while the SMC's is about 10%. Finding extinction curves in both

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2016-465: The naked eye are nearby bright galaxies such as Centaurus A , Bode's Galaxy , Sculptor Galaxy , and Messier 83 . Five planets can be recognized as planets from Earth with the naked eye: Mercury, Venus, Mars, Jupiter, and Saturn. Under typical dark sky conditions Uranus (magnitude +5.8) can be seen as well with averted vision, as can the asteroid Vesta at its brighter oppositions. Under perfect dark sky conditions Neptune may be visible to

2064-402: The naked eye as long as one knows the exact position in which to look. Historically, the zenith of naked-eye astronomy was the work of Tycho Brahe (1546–1601). He built an extensive observatory to make precise measurements of the heavens without any instruments for magnification. In 1610, Galileo Galilei pointed a telescope towards the sky. He immediately discovered the moons of Jupiter and

2112-482: The naked eye may be used to observe celestial events and objects visible without equipment, such as conjunctions , passing comets , meteor showers , and the brightest asteroids , including 4 Vesta . Sky lore and various tests demonstrate an impressive variety of phenomena visible to the unaided eye. Some basic properties of the human eye are: Visual perception allows a person to gain much information about their surroundings: The visibility of astronomical objects

2160-497: The northern hemisphere, observing the Pole Star and using a protractor can give the observer's geographic latitude , up to 1 degree of accuracy. The Babylonians , Mayans , ancient Egyptians , ancient Indians , and Chinese measured all the basics of their respective time and calendar systems by naked eye: In a similar manner star occultations by the moon can be observed. By using a digital clock an accuracy of 0.2 second

2208-426: The object originally emitted . Reddening occurs due to the light scattering off dust and other matter in the interstellar medium . Interstellar reddening is a different phenomenon from redshift , which is the proportional frequency shifts of spectra without distortion. Reddening preferentially removes shorter wavelength photons from a radiated spectrum while leaving behind the longer wavelength photons, leaving

2256-417: The relationship between N H and A(V) to be approximately: (see also: ). Astronomers have determined the three-dimensional distribution of extinction in the "solar circle" (our region of our galaxy), using visible and near-infrared stellar observations and a model of distribution of stars. The dust causing extinction mainly lies along the spiral arms , as observed in other spiral galaxies. To measure

2304-445: The ultraviolet through near-infrared (0.125 to 3.5 μm) extinction curve (plotting extinction in magnitude against wavelength, often inverted) looking from our vantage point at other objects in the Milky Way , is fairly well characterized by the stand-alone parameter of relative visibility (of such visible light) R(V) (which is different along different lines of sight), but there are known deviations from this characterization. Extending

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