Polycyclic aromatic hydrocarbon
Polycyclic aromatic hydrocarbons are hydrocarbons—organic compounds containing only carbon and hydrogen—that are composed of multiple aromatic rings. The simplest such chemicals are naphthalene, having two aromatic rings, the three-ring compounds anthracene and phenanthrene. PAHs are uncharged, non-polar molecules found in tar deposits, they are produced by the thermal decomposition of organic matter. PAHs are abundant in the universe, have been found to have formed as early as the first couple of billion years after the Big Bang, in association with formation of new stars and exoplanets; some studies suggest. Polycyclic aromatic hydrocarbons are discussed as possible starting materials for abiotic syntheses of materials required by the earliest forms of life. By definition, polycyclic aromatic hydrocarbons have multiple cycles, precluding benzene from being considered a PAH. Naphthalene is considered the simplest polycyclic aromatic hydrocarbon by the US EPA and US CDC for policy contexts. Other authors consider PAHs to start with the tricyclic species anthracene.
PAHs are not considered to contain heteroatoms or carry substituents. PAHs with five or six-membered rings are most common; those composed only of six-membered rings are called alternant PAHs. The following are examples of PAHs that vary in the number and arrangement of their rings: Principal PAH Compounds PAHs are nonpolar and lipophilic. Larger PAHs are insoluble in water, although some smaller PAHs are soluble and known contaminants in drinking water; the larger members are poorly soluble in organic solvents and in lipids. They are colorless; the aromaticity varies for PAHs. According to Clar's rule, the resonance structure of a PAH that has the largest number of disjoint aromatic pi sextets—i.e. Benzene-like moieties—is the most important for the characterization of the properties of that PAH. Benzene-substructure resonance analysis for Clar's rule For example, in phenanthrene one Clar structure has two sextets—the first and third rings—while the other resonance structure has just one central sextet.
In contrast, in anthracene the resonance structures have one sextet each, which can be at any of the three rings, the aromaticity spreads out more evenly across the whole molecule. This difference in number of sextets is reflected in the differing ultraviolet–visible spectra of these two isomers, as higher Clar pi-sextets are associated with larger HOMO-LUMO gaps. Three Clar structures with two sextets each are present in the four-ring chrysene structure: one having sextets in the first and third rings, one in the second and fourth rings, one in the first and fourth rings. Superposition of these structures reveals that the aromaticity in the outer rings is greater compared to the inner rings. Polycyclic aromatic compounds characteristically reduce to the radical anions; the redox potential correlates with the size of the PAH. Polycyclic aromatic hydrocarbons are found in natural sources such as creosote, they can result from the incomplete combustion of organic matter. PAHs can be produced geologically when organic sediments are chemically transformed into fossil fuels such as oil and coal.
PAHs are considered ubiquitous in the environment and can be formed from either natural or manmade combustion sources. The dominant sources of PAHs in the environment are thus from human activity: wood-burning and combustion of other biofuels such as dung or crop residues contribute more than half of annual global PAH emissions due to biofuel use in India and China; as of 2004, industrial processes and the extraction and use of fossil fuels made up more than one quarter of global PAH emissions, dominating outputs in industrial countries such as the United States. Wildfires are another notable source. Higher outdoor air and water concentrations of PAHs have been measured in Asia and Latin America than in Europe, the U. S. and Canada. PAHs are found as complex mixtures. Lower-temperature combustion, such as tobacco smoking or wood-burning, tends to generate low molecular weight PAHs, whereas high-temperature industrial processes generate PAHs with higher molecular weights. Most PAHs are insoluble in water, which limits their mobility in the environment, although PAHs sorb to fine-grained organic-rich sediments.
Aqueous solubility of PAHs decreases logarithmically as molecular mass increases. Two-ringed PAHs, to a lesser extent three-ringed PAHs, dissolve in water, making them more available for biological uptake and degradation. Further, two- to four-ringed PAHs volatilize sufficiently to appear in the atmosphere predominantly in gaseous form, although the physical state of four-ring PAHs can depend on temperature. In contrast, compounds with five or more rings have low solubility in water and low volatility. In solid state, these compounds are less accessible for biological uptake or degradation, increasing their persistence in the environment. Spiral galaxy NGC 5529 has been
In astronomy, the interstellar medium is the matter and radiation that exists in the space between the star systems in a galaxy. This matter includes gas in ionic and molecular form, as well as dust and cosmic rays, it fills interstellar space and blends smoothly into the surrounding intergalactic space. The energy that occupies the same volume, in the form of electromagnetic radiation, is the interstellar radiation field; the interstellar medium is composed of multiple phases, distinguished by whether matter is ionic, atomic, or molecular, the temperature and density of the matter. The interstellar medium is composed of hydrogen followed by helium with trace amounts of carbon and nitrogen comparatively to hydrogen; the thermal pressures of these phases are in rough equilibrium with one another. Magnetic fields and turbulent motions provide pressure in the ISM, are more important dynamically than the thermal pressure is. In all phases, the interstellar medium is tenuous by terrestrial standards.
In cool, dense regions of the ISM, matter is in molecular form, reaches number densities of 106 molecules per cm3. In hot, diffuse regions of the ISM, matter is ionized, the density may be as low as 10−4 ions per cm3. Compare this with a number density of 1019 molecules per cm3 for air at sea level, 1010 molecules per cm3 for a laboratory high-vacuum chamber. By mass, 99% of the ISM is gas in any form, 1% is dust. Of the gas in the ISM, by number 91% of atoms are hydrogen and 8.9% are helium, with 0.1% being atoms of elements heavier than hydrogen or helium, known as "metals" in astronomical parlance. By mass this amounts to 70% hydrogen, 28% helium, 1.5% heavier elements. The hydrogen and helium are a result of primordial nucleosynthesis, while the heavier elements in the ISM are a result of enrichment in the process of stellar evolution; the ISM plays a crucial role in astrophysics because of its intermediate role between stellar and galactic scales. Stars form within the densest regions of the ISM, which contributes to molecular clouds and replenishes the ISM with matter and energy through planetary nebulae, stellar winds, supernovae.
This interplay between stars and the ISM helps determine the rate at which a galaxy depletes its gaseous content, therefore its lifespan of active star formation. Voyager 1 reached the ISM on August 25, 2012, making it the first artificial object from Earth to do so. Interstellar plasma and dust will be studied until the mission's end in 2025, its twin, Voyager 2 entered the ISM in November 2018. Table 1 shows a breakdown of the properties of the components of the ISM of the Milky Way. Field, Goldsmith & Habing put forward the static two phase equilibrium model to explain the observed properties of the ISM, their modeled ISM consisted of a cold dense phase, consisting of clouds of neutral and molecular hydrogen, a warm intercloud phase, consisting of rarefied neutral and ionized gas. McKee & Ostriker added a dynamic third phase that represented the hot gas, shock heated by supernovae and constituted most of the volume of the ISM; these phases are the temperatures where cooling can reach a stable equilibrium.
Their paper formed the basis for further study over the past three decades. However, the relative proportions of the phases and their subdivisions are still not well known; this model takes into account only atomic hydrogen: Temperature larger than 3000 K breaks molecules, lower than 50 000 K leaves atoms in their ground state. It is assumed. Pressure is assumed low, so that durations of free paths of atoms are larger than the ~ 1 nanosecond duration of light pulses which make ordinary, temporally incoherent light. In this collisionless gas, Einstein’s theory of coherent light-matter interactions applies, all gas-light interactions are spatially coherent. Suppose that a monochromatic light is pulsed scattered by molecules having a quadrupole resonance frequency. If “length of light pulses is shorter than all involved time constants”, an “impulsive stimulated Raman scattering ” works: While light generated by incoherent Raman at a shifted frequency has a phase independent on phase of exciting light, thus generates a new spectral line, coherence between incident and scattered light allows their interference into a single frequency, thus shifts incident frequency.
Assume that a star radiates a continuous light spectrum up to X rays. Lyman frequencies are absorbed in this light and pump atoms to first excited state. In this state, hyperfine periods are longer than 1 ns, so that an ISRS “may” redshift light frequency, populating high hyperfine levels. An other ISRS “may” transfer energy from hyperfine levels to thermal electromagnetic waves, so that redshift is permanent. Temperature of a light beam is defined from spectral radiance by Planck's formula; as entropy must increase, “may” becomes “does”. However, where a absorbed line reaches Lyman alpha frequency, redshifting process stops and all hydrogen lines are absorbed, but the stop is not perfect if there is energy at frequency shifted to Lyman beta frequency, which produces a slow redshift. Successive redshifts separated by Lyman absorptions generate many absorption lines, frequencies of which, deduced from absorption process, obey a law more dependable than Karlsson’s formula; the previous process excites more and more atoms because a de-excitation obeys Einstein’s law of coherent interactions: Variation dI of radiance
Buckminsterfullerene is a type of fullerene with the formula C60. It has a cage-like fused-ring structure that resembles a football, made of twenty hexagons and twelve pentagons, with a carbon atom at each vertex of each polygon and a bond along each polygon edge, it was first generated in 1984 by Eric Rohlfing, Donald Cox and Andrew Kaldor using a laser to vaporize carbon in a supersonic helium beam. In 1985 their work was repeated by Harold Kroto, James R. Heath, Sean O'Brien, Robert Curl, Richard Smalley at Rice University, who recognized the structure of C60 as buckminsterfullerine. Kroto and Smalley were awarded the 1996 Nobel Prize in Chemistry for their roles in the discovery of buckminsterfullerene and the related class of molecules, the fullerenes. Buckminsterfullerene is the most common occurring fullerene, it can be found in small quantities in soot. The molecule has been detected in deep space; the discoverers of the allotrope named the newfound molecule after Buckminster Fuller, who designed many geodesic dome structures that look similar to C60.
This is misleading, however, as Fuller's geodesic domes are constructed only by further dividing hexagons or pentagons into triangles, which are deformed by moving vertices radially outward to fit the surface of a sphere. A common, shortened name for buckminsterfullerene is "buckyballs". Theoretical predictions of buckyball molecules appeared in the late 1960s and early 1970s, but these reports went unnoticed. In the early 1970s, the chemistry of unsaturated carbon configurations was studied by a group at the University of Sussex, led by Harry Kroto and David Walton. In the 1980s, Smalley and Curl at Rice University developed experimental technique to generate these substances, they used laser vaporization of a suitable target to produce clusters of atoms. Kroto realized. Concurrent but unconnected to the Kroto-Smalley work, astrophysicists were working with spectroscopists to study infrared emissions from giant red carbon stars. Smalley and team were able to use a laser vaporization technique to create carbon clusters which could emit infrared at the same wavelength as had been emitted by the red carbon star.
Hence, the inspiration came to Smalley and team to use the laser technique on graphite to generate fullerenes. C60 was discovered in 1985 by Robert Curl, Harold Kroto, Richard Smalley. Using laser evaporation of graphite they found Cn clusters of which the most common were C60 and C70. A solid rotating graphite disk was used as the surface from which carbon was vaporized using a laser beam creating hot plasma, passed through a stream of high-density helium gas; the carbon species were subsequently ionized resulting in the formation of clusters. Clusters ranged in molecular masses, but Kroto and Smalley found predominance in a C60 cluster that could be enhanced further by allowing the plasma to react longer, they discovered that the C60 molecule formed a cage-like structure, a regular truncated icosahedron. For this discovery Curl and Smalley were awarded the 1996 Nobel Prize in Chemistry; the experimental evidence, a strong peak at 720 atomic mass units, indicated that a carbon molecule with 60 carbon atoms was forming, but provided no structural information.
The research group concluded after reactivity experiments, that the most structure was a spheroidal molecule. The idea was rationalized as the basis of an icosahedral symmetry closed cage structure. Kroto mentioned geodesic dome structures of the noted futurist and inventor Buckminster Fuller as influences in the naming of this particular substance as buckminsterfullerene. In 1989 physicists Wolfgang Krätschmer, Konstantinos Fostiropoulos, Donald R. Huffman observed unusual optical absorptions in thin films of carbon dust; the soot had been generated by an arc-process between two graphite electrodes in a helium atmosphere where the electrode material evaporates and condenses forming soot in the quenching atmosphere. Among other features, the IR spectra of the soot showed four discrete bands in close agreement to those proposed for C60. Another paper on the characterization and verification of the molecular structure followed on in the same year from their thin film experiments, detailed the extraction of an evaporable as well as benzene soluble material from the arc-generated soot.
This extract had TEM and X-ray crystal analysis consistent with arrays of spherical C60 molecules 1.0 nm in van der Waals diameter as well as the expected molecular mass of 720 u for C60 in their mass spectra. The method was simple and efficient to prepare the material in gram amounts per day which has boosted the fullerene research and is today applied for the commercial production of fullerenes; the discovery of practical routes to C60 led to the exploration of a new field of chemistry involving the study of fullerenes. Soot is produced by pyrolysis of aromatic hydrocarbons. Fullerenes are extracted from the soot with organic solvents using a Soxhlet extractor; this step yields a solution containing up to 75% of C60, as well as other fullerenes. These fractions are separated using chromatography; the fullerenes are dissolved in a hydrocarbon or halogenated hydrocarbon and separated using alumina columns. Buckminsterfullerene is a truncated icosahedron with 60 vertices and 32 faces with a carbon atom at the vertices of each polygon and a bond along each polygon edge.
The van der Waals diameter of a C60 molecule is about 1.01 nanometers. The nucleus to nucleus diameter of a
The Doppler effect is the change in frequency or wavelength of a wave in relation to an observer, moving relative to the wave source. It is named after the Austrian physicist Christian Doppler, who described the phenomenon in 1842. A common example of Doppler shift is the change of pitch heard when a vehicle sounding a horn approaches and recedes from an observer. Compared to the emitted frequency, the received frequency is higher during the approach, identical at the instant of passing by, lower during the recession; the reason for the Doppler effect is that when the source of the waves is moving towards the observer, each successive wave crest is emitted from a position closer to the observer than the crest of the previous wave. Therefore, each wave takes less time to reach the observer than the previous wave. Hence, the time between the arrival of successive wave crests at the observer is reduced, causing an increase in the frequency. While they are traveling, the distance between successive wave fronts is reduced, so the waves "bunch together".
Conversely, if the source of waves is moving away from the observer, each wave is emitted from a position farther from the observer than the previous wave, so the arrival time between successive waves is increased, reducing the frequency. The distance between successive wave fronts is increased, so the waves "spread out". For waves that propagate in a medium, such as sound waves, the velocity of the observer and of the source are relative to the medium in which the waves are transmitted; the total Doppler effect may therefore result from motion of the source, motion of the observer, or motion of the medium. Each of these effects is analyzed separately. For waves which do not require a medium, such as light or gravity in general relativity, only the relative difference in velocity between the observer and the source needs to be considered. Doppler first proposed this effect in 1842 in his treatise "Über das farbige Licht der Doppelsterne und einiger anderer Gestirne des Himmels"; the hypothesis was tested for sound waves by Buys Ballot in 1845.
He confirmed that the sound's pitch was higher than the emitted frequency when the sound source approached him, lower than the emitted frequency when the sound source receded from him. Hippolyte Fizeau discovered independently the same phenomenon on electromagnetic waves in 1848. In Britain, John Scott Russell made an experimental study of the Doppler effect. In classical physics, where the speeds of source and the receiver relative to the medium are lower than the velocity of waves in the medium, the relationship between observed frequency f and emitted frequency f 0 is given by: f = f 0 where c is the velocity of waves in the medium; the frequency is decreased. Equivalent formula, easier to remember: f v w r = f 0 v w s = 1 λ where v w r is the wave's velocity relative to the receiver; the above formula assumes that the source is either directly approaching or receding from the observer. If the source approaches the observer at an angle, the observed frequency, first heard is higher than the object's emitted frequency.
Thereafter, there is a monotonic decrease in the observed frequency as it gets closer to the observer, through equality when it is coming from a direction perpendicular to the relative motion, a continued monotonic decrease as it recedes from the observer. When the observer is close to the path of the object, the transition from high to low frequency is abrupt; when the observer is far from the path of the object, the transition from high to low frequency is gradual. If the speeds v s and v r are small compared to the speed of the wave, the relationship between observed frequency f and emitted frequency f 0 is where Δ f = f
Petrus Matheus Marie Jenniskens is a Dutch and American astronomer and a senior research scientist at the Carl Sagan Center of the SETI Institute and at NASA Ames Research Center. He is an expert on meteor showers. Jenniskens is the author of the 790 page book "Meteor Showers and their Parent Comets" published by Cambridge University Press in 2006. Jenniskens is president of Commission 22 of the International Astronomical Union and was chair of the Working Group on Meteor Shower Nomenclature after it was first established. Discovered at Ondřejov Observatory by Petr Pravec, asteroid "42981 Jenniskens" is named in his honor. In 2008, Jenniskens together with Muawia Shaddad, led a team from the University of Khartoum in Sudan that recovered fragments of asteroid 2008 TC3 in the Nubian Desert, marking the first time meteorite fragments had been found from an object, tracked in outer space before hitting Earth. Jenniskens is the principal investigator of NASA's Leonid Multi-Instrument Aircraft Campaign, a series of four airborne missions that fielded modern instrumental techniques to study the 1998 - 2002 Leonids meteor storms.
These missions helped develop meteor storm prediction models, detected the signature of organic matter in the wake of meteors as a potential precursor to origin-of-life chemistry, discovered many new aspects of meteor radiation. More recent meteor shower missions include the Aurigid Multi-Instrument Aircraft Campaign, which studied a rare September 1, 2007, outburst of Aurigids from long-period comet C/1911 N1, the Quadrantid Multi-Instrument Aircraft Campaign, which studied the January 3, 2008, Quadrantids. Jenniskens identified several important mechanisms of. Since 2003, Jenniskens identified the Quadrantids parent body 2003 EH1, several others, as new examples of how fragmenting comets are the dominant source of meteor showers; these objects are now recognized as the main source of our zodiacal dust cloud. Before that, he predicted and observed the 1995 Alpha Monocerotids meteor outburst, proving that "stars fell like rain at midnight" because the dust trails of long-period comets wander on occasion in Earth's path.
His research includes artificial meteors. An overview of ongoing missions can be found at:. Jenniskens is the principal investigator of NASA's Genesis and Stardust Entry Observing Campaigns to study the fiery return from interplanetary space of the Genesis and Hayabusa sample return capsules; the beautiful reentry of JAXA's Hayabusa probe over Australia on 13 June 2010 included the disintegrating main spacecraft. These airborne missions studied what physical conditions the protective heat shield endured during the reentry before being recovered. More Jenniskens led a mission to study the destructive entry of ESA's Automated Transfer Vehicle "Jules Verne" on 29 September 2008, Orbital ATK's Cygnus OA6 reentry on 22 June 2016, the spectacular daytime re-entry of space debris object WT1190F near Sri-Lanka to practice a future observation of an impacting asteroid; the recovery of fragments of asteroid 2008 TC3 marked the first time fragments had been found from an object, tracked in outer space before hitting Earth.
This search was led by Peter Jenniskens and Muawia Shaddad of the University of Khartoum in Sudan, carried out with help from students and staff of the University of Khartoum. The search of the impact zone began on December 6, 2008 and turned up 24 pounds of rocks in about 600 fragments; the next biggest impact over land occurred in California's gold country on April 22, 2012. One of the fragments landed at Sutter's Mill, the site where gold was first discovered in 1848 that led to the California Gold Rush. Jenniskens found one of three fragments of this CM chondrite on April 24; the rapid recovery was made possible. A consortium study led by Jenniskens traced these meteorites back to a source region in the asteroid belt: a family of asteroids that move at low inclination and are close to the 3:1 mean-motion resonance with Jupiter; these were the first CM chondrites to be recovered from near the surface of the original parent body before it broke up, creating the asteroid family. Half a year in the evening of October 17, 2012, a bright fireball was seen near San Francisco.
The first Novato meteorite, a L6 type chondrite fragmental breccia, was found by Novato resident Lisa Webber following Jenniskens' publication of the trajectory of the fireball from video recorded by stations of his Cameras for Allsky Meteor Surveillance project. Three weeks after the February 15, 2013, Chelyabinsk meteor, Jenniskens participated in a Russian Academy of Sciences fact finding mission to Chelyabinsk Oblast. Over 50 villages were visited to map the extent of the glass damage. Traffic video records were collected to map the shock wave arrival times. In order to determine the meteoroid entry speed and angle, star background calibration images were taken and shadow obstacle dimensions were measured at sites where video cameras recorded the fireball and its shadows. Eyewitnesses were interviewed to learn about injuries, heat sensations, sunburn and where meteorites were found. Meteorites found shortly after the fall by Chelyabinsk State University colleagues were analyzed and the results from this consortium study were published in Science.
In earlier collaborations, he discovered that an unusual viscous form of liquid water can be a common form of amorphous ice in comets and icy satellites
Astronomical spectroscopy is the study of astronomy using the techniques of spectroscopy to measure the spectrum of electromagnetic radiation, including visible light and radio, which radiates from stars and other celestial objects. A stellar spectrum can reveal many properties of stars, such as their chemical composition, density, distance and relative motion using Doppler shift measurements. Spectroscopy is used to study the physical properties of many other types of celestial objects such as planets, nebulae and active galactic nuclei. Astronomical spectroscopy is used to measure three major bands of radiation: visible spectrum, X-ray. While all spectroscopy looks at specific areas of the spectrum, different methods are required to acquire the signal depending on the frequency. Ozone and molecular oxygen absorb light with wavelengths under 300 nm, meaning that X-ray and ultraviolet spectroscopy require the use of a satellite telescope or rocket mounted detectors. Radio signals have much longer wavelengths than optical signals, require the use of antennas or radio dishes.
Infrared light is absorbed by atmospheric water and carbon dioxide, so while the equipment is similar to that used in optical spectroscopy, satellites are required to record much of the infrared spectrum. Physicists have been looking at the solar spectrum since Isaac Newton first used a simple prism to observe the refractive properties of light. In the early 1800s Joseph von Fraunhofer used his skills as a glass maker to create pure prisms, which allowed him to observe 574 dark lines in a continuous spectrum. Soon after this, he combined telescope and prism to observe the spectrum of Venus, the Moon and various stars such as Betelgeuse; the resolution of a prism is limited by its size. This issue was resolved in the early 1900s with the development of high-quality reflection gratings by J. S. Plaskett at the Dominion Observatory in Ottawa, Canada. Light striking a mirror will reflect at the same angle, however a small portion of the light will be refracted at a different angle. By creating a "blazed" grating which utilizes a large number of parallel mirrors, the small portion of light can be focused and visualized.
These new spectroscopes were more detailed than a prism, required less light, could be focused on a specific region of the spectrum by tilting the grating. The limitation to a blazed grating is the width of the mirrors, which can only be ground a finite amount before focus is lost. In order to overcome this limitation holographic gratings were developed. Volume phase holographic gratings use a thin film of dichromated gelatin on a glass surface, subsequently exposed to a wave pattern created by an interferometer; this wave pattern sets up a reflection pattern similar to the blazed gratings but utilizing Bragg diffraction, a process where the angle of reflection is dependent on the arrangement of the atoms in the gelatin. The holographic gratings can have up to 6000 lines/mm and can be up to twice as efficient in collecting light as blazed gratings; because they are sealed between two sheets of glass, the holographic gratings are versatile lasting decades before needing replacement. Light dispersed by the grating or prism in a spectrograph can be recorded by a detector.
Photographic plates were used to record spectra until electronic detectors were developed, today optical spectrographs most employ charge-coupled devices. The wavelength scale of a spectrum can be calibrated by observing the spectrum of emission lines of known wavelength from a gas-discharge lamp; the flux scale of a spectrum can be calibrated as a function of wavelength by comparison with an observation of a standard star with corrections for atmospheric absorption of light. Radio astronomy was founded with the work of Karl Jansky in the early 1930s, while working for Bell Labs, he built a radio antenna to look at potential sources of interference for transatlantic radio transmissions. One of the sources of noise discovered came not from Earth, but from the center of the Milky Way, in the constellation Sagittarius. In 1942, JS Hey captured the sun's radio frequency using military radar receivers. Radio spectroscopy started with the discovery of the 21-centimeter H I line in 1951. Radio interferometry was pioneered in 1946, when Joseph Lade Pawsey, Ruby Payne-Scott and Lindsay McCready used a single antenna atop a sea cliff to observe 200 MHz solar radiation.
Two incident beams, one directly from the sun and the other reflected from the sea surface, generated the necessary interference. The first multi-receiver interferometer was built in the same year by Martin Vonberg. In 1960, Ryle and Antony Hewish published the technique of aperture synthesis to analyze interferometer data; the aperture synthesis process, which involves autocorrelating and discrete Fourier transforming the incoming signal, recovers both the spatial and frequency variation in flux. The result is a 3D image. For this work and Hewish were jointly awarded the 1974 Nobel Prize in Physics. Newton used a prism to split white light into a spectrum of color, Fraunhofer's high-quality prisms allowed scientists to see dark lines of an unknown origin. In the 1850s, Gustav Kirchhoff and Robert Bunsen described the phenomena behind these dark lines
The Lick Observatory is an astronomical observatory and operated by the University of California. It is situated on the summit of Mount Hamilton, in the Diablo Range just east of San Jose, California, US; the observatory is managed by the University of California Observatories, with headquarters on the University of California, Santa Cruz campus, where its scientific staff moved in the mid-1960s. It is named after James Lick. Lick Observatory is the world's first permanently occupied mountain-top observatory; the observatory, in a Classical Revival style structure, was constructed between 1876 and 1887, from a bequest from James Lick of $700,000. Lick a carpenter and piano maker, chose the site atop Mount Hamilton and was buried there in 1887 under the future site of the telescope, with a brass tablet bearing the inscription, "Here lies the body of James Lick". Lick additionally requested that Santa Clara County construct a "first-class road" to the summit, completed in 1876. Lick chose John Wright, of San Francisco's Wright & Sanders firm of architects, to design both the Observatory and the Astronomer's House.
All of the construction materials had to be brought to the site by horse and mule-drawn wagons, which could not negotiate a steep grade. To keep the grade below 6.5%, the road had to take a winding and sinuous path, which the modern-day road still follows. Tradition maintains that this road has 365 turns; the road is closed. The first telescope installed at the observatory was a 12-inch refractor made by Alvan Clark. Astronomer E. E. Barnard used the telescope to make "exquisite photographs of comets and nebulae", according to D. J. Warner of Warner & Swasey Company; the 36-inch refracting telescope on Mt. Hamilton was Earth's largest refracting telescope during the period from when it saw first light on January 3, 1888, until the construction of Yerkes Observatory in 1897. Warner & Swasey designed and built the telescope mounting, with the 36-inch lens manufactured by one of the Clark sons, Alvan Graham. E. E. Barnard used the telescope in 1892 to discover a fifth moon of Amalthea; this was the first addition to Jupiter's known moons since Galileo observed the planet through his parchment tube and spectacle lens.
The telescope provided spectra for W. W. Campbell's work on the radial velocities of stars. In May 1888, the observatory was turned over to the Regents of the University of California, it became the first permanently occupied mountain-top observatory in the world. Edward Singleton Holden was the first director; the location provided excellent viewing performance because of lack of ambient pollution. When low cloud cover is present below the peak, light pollution is cut to nothing. On May 21, 1939, during a nighttime fog that engulfed the summit, a U. S. Army Air Force Northrop A-17 two-seater attack plane crashed into the main building; because a scientific meeting was being held elsewhere, the only staff member present was Nicholas Mayall. Nothing caught the two individuals in the building were unharmed; the pilot of the plane, Lt. Richard F. Lorenz, passenger Private W. E. Scott were killed instantly; the telephone line was broken by the crash, so no help could be called for at first. Help arrived together with numerous reporters and photographers, who kept arriving all night long.
Evidence of their numbers could be seen the next day by the litter of flash bulbs carpeting the parking lot. The press covered the accident and many reports emphasized the luck in not losing a large cabinet of spectrograms, knocked over by the crash coming through an astronomer's office window. More notable was the lack of fire or damage to a telescope dome. In 1950, the California state legislature appropriated funds for a 120-inch reflector telescope, completed in 1959; the observatory additionally has a 24-inch Cassegrain reflector dedicated to photoelectric measurements of star brightness, received a pair of 20-inch astrographs from the Carnegie Corporation. In 1886, Lick Observatory begins supplying Railroad Standard Time to the Southern Pacific Railroad, to other businesses, over telegraph lines; the signal was generated by a clock manufactured by E. Howard & Co. for the Observatory, which included an electric apparatus for transmitting the time signal over telegraph lines. While most of the nation's railroads received their time signal from the U.
S. Naval Observatory time signal via Western Union's telegraph lines, the Lick Observatory Time-Signal was used by railroads from the West coast all the way to Colorado. With the growth of San Jose, the rest of Silicon Valley, light pollution became a problem for the observatory. In the 1970s, a site in the Santa Lucia Mountains at Junípero Serra Peak, southeast of Monterey, was evaluated for possible relocation of many of the telescopes. However, funding for the move was not available, in 1980 San Jose began a program to reduce the effects of lighting, most notably replacing all streetlamps with low pressure sodium lamps; the result is that the Mount Hamilton site remains a viable location for a major working observatory. The International Astronomical Union named Asteroid 6216 San Jose to honor the city's efforts toward reducing light pollution. In 2006, there were 23 f