Meridian Circle Research Articles

What Happened to and in Detroit?

The paper describes the fiscal status of the City of Detroit, leading up to its filing for bankruptcy on July 18, 2013. Then the economic history of metropolitan Detroit and the city of Detroit from 1950 to the present is examined in an effort to answer these questions. Why did Detroit file for bankruptcy - and not some other major city? And why now and not earlier? The paper concludes that, while Detroit and several other cities in the northeastern region suffered major population and employment losses and went through a long period of urban crisis between roughly 1970 and 1990, the severity of Detroit's problems compared to other cities did not emerge until the most recent decade. Population and employment losses during the 2000-2010 decade were much worse in the city of Detroit than in the other major central cities in the Northeast. These problems produced collapse in real estate markets, a high poverty rate and a drastic decline in median family income, worsening social problems, and declining tax revenues for the City. Detroit suffered a vicious circle of decline in the most recent decade that exceeded the experiences of other cities.

첨성대 수치와 역할에 대한 연구

Chumsungdae is an ancient astronomical observatory whose main role was doing `chunmoon`. It was administrate by a royal advisory agency on state affairs. The observers observed the heaven on the observatory platform, recorded peculiar events, and watched and interpreted the signs displayed in the heaven. Chumsungdae is an stonemasonry which represents almanac principles with its peculiar shapes and the numbers of strata and stones. The numbers were thoroughly invented to match exactly the almanac constants. Chumsungdae is comprised largely of three main parts, namely the square base, the stratified cylindrical body, and the top #-shaped stonework, and the total number of stones is 404. The number of the strata (27) and the height of the cylindrical body (27 尺) stand for the days in a sidereal month (27.3 days), which implies that the motion of the Moon with respect to the stars was given more priority than to the Sun at that time of geocentricism. And the cylindrical body was thoroughly designed to consist of 365 stones, which is of course the number of days in a solar year. In addition, there are 12 strata each under and above the south entrance and this in sum makes the 24 divisions of the year. Also there is 182 stones below the 13th stratum and this represents the number of days in the winter ~ summer solstice period, and the rest 183 stones the vice versa. The #-shaped top stonework was aligned in such a way that one of the diagonals points the direction of sunrise on the winter solstice. The square base also layed with the same manner. The south entrance was built 16 degrees SE, and the upright direction of the right pillar stone coincides with the meridian circle. This was a kind of built-in standard meridian circle facilitating the observations. In a symbolic sense, Chumsungdae was thought as the tunnel reaching the heaven, where the observers wished to be enlightened with the signs and inspirations in need. With the craftsmanship and skill, the builder reinforced the stratified cylindrical body with two sets of #-shaped beam stones, piercing at a right angle at 19th ~ 20th and 25th ~ 26th strata. Likewise, by placing the double #-shaped stonework with 8 beam stones on the platform of the observatory, both the stability of the stonemasonry and a guard rail for the nightly observers were securely provided.

Astrometric binaries with invisible components in fields of the axial meridian circle of the Nikolaev Observatory

As a result of observations in 2008–2011 with the axial meridian circle of the Nikolaev Astronomical Observatory, we compiled two catalogs with a total of 284557 objects. We conducted a search for probable candidates for binary and multiple systems using the method checking differences between quasi-instantaneous and long-term proper motions for statistical significance. The resulting list of probable candidates for double and multiple systems with invisible companions contains 9379 objects.

Calculus and geometry

In this article we compute volume and surface area of the torus, volume of a slice of a 3-ball. Besides this we discuss some interesting facts like ‘derivative of the area of a circle with respect to its radius is its perimeter, derivative of the volume of the sphere with respect to its radius is its surface area and derivative of the volume of the torus with respect to the radius of its meridian circle is its surface area’.

Saharan mineral dust outbreaks observed over the North Atlantic island of La Palma in summertime between 1984 and 2012

AbstractWe estimate the frequency of Saharan mineral dust outbreak events observed over the North Atlantic island of La Palma based on in situ nightly atmospheric extinction measurements recorded almost continuously since 1984 by the Carlsberg Meridian Telescope at the Roque de los Muchachos observatory. The outbreak frequency shows a well‐defined seasonal peak in the months of July to September, during which time the occurrence of Saharan dust events (SDEs) is approximately 28 ± 6%. We find considerable year‐to‐year variability in the summertime SDE frequency, observing a steady reduction between 1984 and 1997, followed by a period of relative mean stability from 1999 to 2012. We investigated changes in the atmospheric extinction of the SDEs as an indicator of strength of the episodes and found that this parameter approximately follows the SDE frequency, however, instrumental limitations prevented us from deriving precise conclusions regarding their long‐term changes. A lagged correlation analysis between SDE properties and the El Niño–Southern Oscillation (ENSO), North Atlantic Oscillation (NAO) and Sahel rainfall index (SRI) was performed. We found that 55 ± 4% of the year‐to‐year variations in July–September SDE frequency may be reproduced by a lagged relationship to the NAO conditions during the preceding October–December period, and 45 ± 4% may be reproduced by a negative correlation to the SRI during the preceding February–April period. Based on these relationships it may be possible to obtain an approximate indication of the strength of the upcoming summertime dust season over the North Atlantic around half a year in advance.

The Thousand Star Magnitudes in the Catalogues of Ptolemy, Al Sufi, and Tycho are All Corrected for Atmospheric Extinction

1. PRE-TELESCOPIC CATALOGUESThree pre-telescopic star catalogues contain about a thousand star magnitudes each (with magnitudes 1 , 2, 3, 4, 5, and 6), with these reported brightnesses as the original basis for what has become the modern magnitude scale. These catalogues are those of Ptolemy (c. 1 37 A.D., from Alexandria at a latitude of 3 1 .2°), Al Sufi (c. 960, from Isfahan at a latitude of 32.6°), and Tycho Brahe (c. 1590, from the island of Hven at a latitude of 55.9°). Previously, extensive work has been made on the positions of the catalogued stars, but only scant attention has been paid to the magnitudes as reported.1 These magnitudes will be affected by a variety of processes, including the dimming of the light by our Earth's atmosphere (atmospheric extinction), the quantization of the brightnesses into magnitude bins, and copying or influence from prior catalogues. This paper provides a detailed examination of these effects. Indeed, I find all three catalogues to report magnitudes that have near-zero extinction effects, so the old observers in some way extinction corrected their observations.The ancient star catalogue of Ptolemy appears in Books 7 and 8 of the Almagest, with positions and magnitudes for 1028 stars. These magnitudes are in the nowtraditional system of 1, 2, 3, 4, 5, and 6, however with notations for stars that are somewhat brighter or fainter than the integral magnitude. Thus, the notations go, from the nominal brightest to faintest, 1, 2, 2, 3, 3, 4, 4, 5, 5, 6, and faint. A handful of stars are duplicates or marked as nebulous instead of being given a magnitude. I adopt the magnitudes and star identifications as given in the translation of G. J. Toomer.2 Ptolemy does tell us how to measure star positions using armillary spheres, but he does not give one word on how the magnitude scale was set nor how to measure magnitudes. There is a substantial long-running debate as to whether the Almagest star catalogue was primarily observed by Ptolemy or rather Hipparchus (c. 128 b.c. from Rhodes with a latitude of 36.4°).3 This debate has a wide variety of arguments running many levels deep, with neither side able to produce decisive evidence to convince the other side. The primary material for this debate is the star positions recorded in the catalogue, with scant use having been made of any of the concurrent magnitude information.4In the Western world, the next star catalogue came from the Persian astronomer 'Abd al-Rahman al-Sufi (903-86) observing from Isfahan (latitude 32.7°). In his Book of fixed stars, published in 964, Al Sufi's star list gives the same stars and star positions (updated for precession) as in the Almagest. However, Al Sufi observed his own magnitudes, and these are substantially different from those in the Almagest. I adopt the magnitudes and star identifications as given for Al Sufi by E. B. Knobel.5 Al Sufi gives magnitudes in the same basic system as the Almagest, with the notation for the brightness bins, nominally from brightest to faintest, being 1, 1-2, 2-1, 2, 2-3, 3-2, 3, 3-4, 4-3, 4, 4-5, 5-4, 5, 5-6, 6-5, 6, and 6-7. These are magnitude bins, with several extra when compared to the Almagest (5-6, 6-5, and 6-7). To say one-third magnitude bins is approximately correct, but it is really a schematic description for categories that are variable in size with ill-defined edges and imperfect measurements. Nothing survives which tells us the details of how Al Sufi measured his magnitudes.The next star catalogue is that of Ulugh Begh (1394-1449), the grandson of Tamerlane, who ruled a large region of central Asia from Samarkand. He noted errors in the positions of the stars from the Almagest, collected a group of scholars, and a star catalogue was made from observations in Samarkand (latitude ? = 39.7°) around the year 1437.6 His star catalogue contains the same stars as are in the Almagest. The positions of the stars were newly measured with large sextants, armillary spheres, and meridian circles. …

Star catalogue in the fields of axial meridian circle of the Nikolaev observatory

On the base of CCD-observations made with the axial meridian circle of the Nikolaev Observatory from 2008 to 2009, we compiled a catalogue for astrometric positions and proper motions for 140321 stars located in an ecliptic zone and around high proper motion stars. The root-meansquare error for a star position is 20–65 mas in right ascension and 30–70 mas in declination. The UCAC2 catalogue is used as a reference for astrometric reductions. To derive stars’ proper motion and to estimate systematic errors of the compiled catalogue, cross-identification of the obtained data with modern astronomic catalogues Tycho2, 2MASS, CMC14, LSPM, PPMX, USNO-A2, and XPM-1.0 is performed. In addition to star position and proper motion, our catalogue contains photometric values B, V, r’, J, H, and K taken from other catalogues.

The unseen population of F- to K-type companions to hot subdwarf stars

We present a method to select hot subdwarf stars with A to M-type companions using photometric selection criteria. We cover a wide range in wavelength by combining GALEX ultraviolet data, optical photometry from the SDSS and the Carlsberg Meridian telescope, near-infrared data from 2MASS and UKIDSS. We construct two complimentary samples, one by matching GALEX, CMC and 2MASS, as well as a smaller, but deeper, sample using GALEX, SDSS and UKIDSS. In both cases, a large number of composite subdwarf plus main-sequence star candidates were found. We fit their spectral energy distributions with a composite model in order to estimate the subdwarf and companion star effective temperatures along with the distance to each system. The distribution of subdwarf effective temperature was found to primarily lie in the 20,000 - 30,000 K regime, but we also find cooler subdwarf candidates, making up ~5-10 per cent. The most prevalent companion spectral types were seen to be main-sequence stars between F0 and K0, while subdwarfs with M-type companions appear much rarer. This is clear observational confirmation that a very efficient first stable Roche-lobe overflow channel appears to produce a large number of subdwarfs with F to K-type companions. Our samples thus support the importance of binary evolution for subdwarf formation.

The Bombay Case: Astronomers, Instrument Makers and the East India Company

There are Observatories of all kinds from rough hovels of stone and mud, costing one hundred rupees with trap door at top and slits in direction of Meridian and Prime Vertical to hold Zenith Sector, Clock, Transit, Chronometers, Thermometers etc., up to Greenwich Observatory, Cambridge Observatory, Cape of Good Hope Observatory, etc. These are filled with most costly instruments on scale of magnificence and splendour which quite dazzle minds of those who only look at surface.George Everest, 18291The Case Is OpenedThe Bombay case arrived in London at end of 1827. This was no ordinary package from India. Its contents were not raw silk, indigo nor cotton, but pair of Londonmade astronomical instruments, 46-inch achromatic telescope and 5 -ft focal length transit instrument wrapped in oilcloth and paper. Also crammed inside were pair of mountain barometers and half dozen thermometers. The case was then brought to East India Company's baggage warehouse on edge of City. On 22 January 1828 was opened in front of select witnesses. These were as remarkable as case: Company's Hydrographer, its Librarian, its official Mathematical Instrument Maker, and local stockbroker. The hydrographer was veteran navigator James Horsburgh, who had mapped Bombay harbour and in 1822 lobbied for Bombay observatory. The librarian was Sanskrit scholar Charles Wilkins, responsible for commissioning this observatory's instruments in 1824. The instrument maker was William Gilbert, from whose Leadenhall Street shop at Navigation Warehouse, just opposite entrance to East India House, Wilkins obtained both transit instrument and telescope in 1 826. Wilkins wanted Gilbert to be present at case's opening: it would not be proper that they should be opened but in presence of their Maker. The fourth witness, canny stockbroker Francis Baily, was one of managers of new Astronomical Society of London and familiar with ways along which these instruments had travelled to and from Bombay.2The Bombay case became notorious as an episode of costly controversy about construction of an observatory and its instruments in early nineteenth-century colonial world and epoch of political and administrative reform. Its career is analysed here for evidence of how astronomers, instrumentation and utility were all assessed in these critical years, period when something like modern astronomy networks were forged. This is also, principally, story about territories in which such personnel and hardware functioned, with themes of social and geographical proximity and distance providing stuff of ferocious dispute and earnest scrutiny. In 1815 government of Bombay presidency had accepted that was a national reflexion that the chief naval port and greatest mart in British India should not possess place for making astronomical observations. In 1818 land grant was made to Bombay Literary Society to construct such an observatory but its manager, local clockmaker, soon died.3 Support came from orientalist Henry Colebrooke, Company servant and one of Baily's colleagues amongst founders of Astronomical Society. The Company hired Colebrooke's client thirty-year-old John Curnin, then resident in Spitalfields, reportedly well versed both in Astronomy and in natural philosophy. Curnin was subsequently elected Fellow of Astronomical Society with backing of Baily and actuary Benjamin Gompertz.4 Curnin reached Bombay in early 1 823. With governor Mountstuart Elphinstone's backing, he demanded new site and equipment, including transit instrument, mural circle and an achromatic telescope all to be produced by eminent makers Edward Troughton and George Dollond. 'They will be lasting testimony of liberality and disposition of Honourable Court to promote science which has already so extensively benefited mankind and has at same time shewn us in part magnificence of Creation and permitted us as were to understand some of Councils [sic] of Almighty. …

‘Senses and Hands to the Same Degree as Thought’-Ole Rømer's Mechanical Astronomy

The astronomer Ole Romer emphasized the mechanical nature of the practice of astronomy and this paper attempts to unravel what Romer meant by the close association between mechanics and astronomy. The point of departure is Romer's work with Tycho Brahe's observations and his stay at the Royal Academy of the Sciences in Paris. Analyses of Romer's letters and treatises show that he not only focused on direct presentations of observations and instruments, but demanded an independence of his results that went beyond the rhetoric of first-hand knowledge. Romer wanted his observations and instruments to demonstrate the physical theories themselves, rather than asking for theories to be accepted on his authority. His invention of the meridian circle with its facility for cross-checking measurements is seen in connection with this drive to make what is observed ‘deserve credit in its own right rather than because of the observer.’

Technique of ECM Deburring for Intersecting Holes of Pump

Most recently automobile pumps contain intersecting holes. However, there has been no efficient method for burr at intersecting holes. The theory of electrochemical deburring for high pressure pump body is firstly introduced. Then math model of ECM deburring and cathode model are built. Experiment results indicate that the technique can effectively remove the burrs of the hole and regulate the corner radius of injection holes. The smooth transition circle could be obtained around the conjunction of the hole, thus ECM deburring method can effiectively increase cleanliness of injector body and make the whole injector more stable.

Proper motion and densification of the International Celestial Reference Frame in the direction of the Galactic bulge

Context. The definition, construction and realization of a reference system is one of the oldest and most fundamental tasks of astronomy. Currently, the International Celestial Reference System (ICRS), realized by the International Celestial Reference Frame (ICRF) or ICRF2, is the reference system adopted by the IAU. It is based on the very precise VLBI positions of a few hundred compact extragalactic radio sources. Despite its excellent precision, the ICRF is far from providing a reference system that is available for the entire sky and accessible to all observers. The ICRF has to be densified and extended to other wavelengths, mainly to the optical domain where the astronomical activities are more intense. For this reason, the IAU has recommended and encouraged works in this direction over the years. Many of them were developed to give sometimes good positions and proper motions, but they are very limited in magnitude, while others are extremely dense and deep in magnitude but have low accuracy, mainly for the proper motions. Nevertheless, all these contributions are very important because they are complementary. Aims. We present a homogeneous and precise optical astrometric catalog that extends the ICRF in the direction of 12 low-extinction windows of the Galactic bulge and provides at the same time a useful database for kinematic studies. Methods. The catalog was constructed on a total of 9 observational epochs spread over 15 years of observations with the CCD meridian circle of the Abrahao de Moraes Observatory (Valinhos – Brazil). The Galactic Bulge Valinhos Observatory Catalog (GBVOC) contains only those stars with at least 6 observational epochs and a time base of 10 years or more. We also imposed a minimum of 3 observations per star in each observational epoch and 20 observations in total. Results. The catalog provides positions and proper motions for about 11 600 stars with a mean internal precision of about 22 mas and 4.0 mas/yr, which ensures a high quality and reliable extension of the ICRF in this direction. The GBVOC is extremely dense with more than 3500 stars per square degree. Comparison of the GBVOC with other densification works allows us to estimate the external precision of the GBVOC to be better than 42.0 mas and 5.5 mas/yr in position and proper motion.

‘Stargazers at the world's end’: telescopes, observatories and ‘views’ of empire in the nineteenth-century British Empire

AbstractThis article argues that the study of astronomical observing instruments, their transportation around the globe and the personal and professional networks created by such exchanges are useful conceptual tools in exploring the role of science in the nineteenth-century British Empire. The shipping of scientific instruments highlights the physical and material connections that bound the empire together. Large, heavy and fragile objects, such as transit circles, were difficult to transport and repair. As such, the logistical difficulties associated with their movement illustrate the limitations of colonial scientific enterprises and their reliance on European centres. The discussion also examines the impact of the circulation of such objects on observatories and astronomers working in southern Africa, India and St Helena by tracing the connections between these places and British scientific institutions, London-based instrument-makers, and staff at the Royal Observatory, Greenwich. It explores the ways in which astronomy generally, and the use of observing instruments in particular, relate to broader themes about the applications of science, the development of colonial identities, and the consolidation of empire in the first half of the nineteenth century. In considering these issues, the article illustrates the symbiotic relationship between science and empire in the period, demonstrating the overlap between political and strategic considerations and purely scientific endeavours. Almost paradoxically, as they trained their sights and their telescopes on the heavens, astronomers and observers helped to draw diverse regions of the earth beneath closer together. By tracing the movement of instruments and the arcs of patronage, cooperation and power that these trajectories inscribe, the role of science and scientific objects in forging global links and influencing the dynamics of the nineteenth-century British Empire is brought into greater focus.

Kyiv meridian axial circle with a new CCD camera

Specifications of a new Apogee Alta U47 CCD camera mounted at the Kyiv meridian axial circle (MAC) are presented. The camera is based on the 1024 × 1024 pxl e2v CCD47-10 with pixel sizes of 13 × 13 μm. Observations are carried out in the scan-drift mode with an effective exposure time of 77 s for equatorial stars. The MAC photometric system answers the standard Johnson V band, the MAC limiting magnitude V is 17m. The test MAC observations of 2009 give positional accuracy and V magnitude errors equal to approximately 0.1″ and 0.09m, respectively, for Tycho-2 stars. The telescope is used for observations of equatorial stars with the purpose of detecting their positions, proper motion, and brightness.

Een passie voor precisie: Frederik Kaiser en het instrumentarium van de Leidse Sterrewacht

Passion for precision. Frederik Kaiser and the instrumentation of Leiden Observatory Frederik Kaiser (1808-1872) was one of the most inspiring directors of the Leiden astronomical observatory. In Dutch astronomy he introduced a systematic observing and research program. Furthermore he succeeded in founding a new observatory after years of struggle. This paper describes how Kaiser's urge for precision led the way in his research, in his selection of instruments and in the design of the new observatory. Kaiser was educated in astronomy by his uncle, the Amsterdam mathematician and astronomer Jan Frederik Keijser. He introduced young Frederik also into the world of instruments, theory and influential persons. At the age of eighteen Frederik succeeded in getting appointed as an observer at Leiden Observatory. However, the bad relationship with its director and the lousy state of the instruments at this observatory made observing almost impossible. Instead, Frederik took up a study in physics and mathematics at Leiden University. In 1835 Kaiser's chances turned with the predicted return of Halley's comet. With borrowed equipment, Kaiser observed the comet at home. More important, Kaiser had rightfully predicted the perihelium-passage of the comet (the closest approach to the sun). His calculation differed only two hours with the actual moment. This exact computation enhanced Kaiser's reputation as a scholar and led in 1837 to his appointment as director of the Leiden Observatory. From the very outset Kaiser tried to incorporate 'statistal astronomy' in his research, imitating German scientists as Gauss, Bessel, Encke and Hansen. He therefore applied for a new observatory and instruments, but in first instance only some money for new instruments was granted. For his research on double stars and the trajectories of comets Kaiser bought some new instruments, like a Fraunhofer refractor with a precision micrometer and two transit instruments. In his publications Kaiser not only described his observations, but also meticulously investigated instrumental and personal errors. These errors brought Kaiser to improve and design instruments by himself. Kaiser's precision talents were noticed by the Dutch Naval Minister. He appointed Kaiser as 'Verificator of the National Maritime Instruments'. In this capacity Kaiser used his talent to reorganize naval research and redesign instruments used by the navy. Although his astronomical work brought Kaiser and the Leiden Observatory international prestige, he strived for more: a new building. Finally, in 1860, after numerous pleas, a new observatory was built.The most important instrument in this building was a large meridian circle, not surprisingly a very precise instrument. Together with the most accurate astronomical clock of that time, Kaiser started ambitiously with his 'absolute measurements'. Within the European zone program he was able to pinpoint the positions of some 10,000 stars. In 35 years Kaiser managed to bring the Leiden Observatory at the top of the international astronomical league, with his precise observation, critical analyses and lobby work. Kaiser therefore has been of enormous importance to Leiden Observatory.

Construction of 3D Triangles on Dupin Cyclides

This paper considers the conversion of the parametric Bézier surfaces, classically used in CAD-CAM, into patched of a class of non-spherical degree 4 algebraic surfaces called Dupin cyclides, and the definition of 3D triangle with circular edges on Dupin cyclides. Dupin cyclides was discovered by the French mathematician Pierre-Charles Dupin at the beginning of the 19th century. A Dupin cyclide has one parametric equation, two implicit equations, and a set of circular lines of curvature. The authors use the properties of these surfaces to prove that three families of circles (meridian arcs, parallel arcs, and Villarceau circles) can be computed on every Dupin cyclide. A geometric algorithm to compute these circles so that they define the edges of a 3D triangle on the Dupin cyclide is presented. Examples of conversions and 3D triangles are also presented to illustrate the proposed algorithms.

Type III 1 equilibrium states of the Toeplitz algebra of the affine semigroup over the natural numbers

We complete the analysis of KMS-states of the Toeplitz algebra T ( N ⋊ N × ) of the affine semigroup over the natural numbers, recently studied by Raeburn and the first author, by showing that for every inverse temperature β in the critical interval 1 ⩽ β ⩽ 2 , the unique KMS β -state is of type III 1. We prove this by reducing the type classification from T ( N ⋊ N × ) to that of the symmetric part of the Bost–Connes system, with a shift in inverse temperature. To carry out this reduction we first obtain a parametrization of the Nica spectrum of N ⋊ N × in terms of an adelic space. Combining a characterization of traces on crossed products due to the second author with an analysis of the action of N ⋊ N × on the Nica spectrum, we can also recover all the KMS-states of T ( N ⋊ N × ) originally computed by Raeburn and the first author. Our computation sheds light on why there is a free transitive circle action on the extremal KMS β -states for β > 2 that does not ostensibly come from an action of T on the C ⁎-algebra.

Atmosphere Extinction at the ORM on La Palma: A 20 yr Statistical Database Gathered at the Carlsberg Meridian Telescope

ABSTRACTThe Observatorio del Roque de los Muchachos (ORM), in the Canary Islands (Spain), was one of the candidates to host the future European Extremely Large Telescope (E-ELT) and is the site of the Gran Telescopio Canarias (GTC), the largest optical infrared facility to date. Sky transparency is a key parameter as it defines the quality of the photometry to be acquired in the astronomical observations. We present a study of the atmosphere extinction at the ORM, carried out after analysis of a database spanning more than 20 yr, to our knowledge, the longest and most complete and homogeneous in situ database available for any observatory. It is based on photometric measurements in the V band and r′ band (transformed to the V-band extinction coefficient kV) using the Carlsberg Meridian Telescope (CMT). Clear seasonal variations that repeat yearly are observed. The median value of kV is 0.13 mag airmass-1; the mean value has a maximum in the summer months (June-September), corresponding to the season with maximum frequency of nights affected by dust or cirrus (∼29% in summer, but only ∼13% during the rest of the year). Two volcanic eruptions took place during the database baseline, which has enabled the study of the impact of volcanoes on the global atmosphere extinction. For the 5 yr of available information, we have estimated the average monthly weather downtime from the CMT data log, obtaining a result (20.7%) in reasonable agreement with earlier studies. The main conclusion of our study is that there is no significant evidence from the CMT data for any secular changes in kV over the 20 yr database baseline.

Results of site testing using an aerosol, backscatter lidar at the Roque de los Muchachos Observatory

Because of the high quality of its sky, the Roque de los Muchachos Observatory (ORM), located on the island of La Palma in the Canary Islands, is home to many astronomical facilities. In the context of the Extremely Large Telescope Design Study, two intensive lidar campaigns were performed at the ORM near the Jacobus Kapteyn Telescope between 2007 July 9 and 11 and between 2008 May 26 and June 14. The goal of the campaign was to characterize the atmosphere in terms of the height of the planetary boundary layer (PBL) and the aerosol stratification versus synoptic conditions. Three typical synoptic situations were found, which supported the intrusion of aerosols from marine/oceanic, anthropogenic and Saharan origins, respectively. All measurements revealed a multilayer stratification with a mean PBL height of 546 ± 198 m agl and top layers as high as ∼8400 m asl. As a by-product, an estimate of the aerosol optical thickness was also obtained and compared to the total atmospheric extinction coefficient measured by the Carlsberg Meridian Telescope. Except in the presence of Saharan dust, the aerosol optical thickness is very low; the average values are 0.0405 at 532 nm and 0.0055 at 1064 nm. In the presence of Saharan dust, values of 0.233 and 0.157 were found at 532 and 1064 nm, respectively. The proportion of aerosol optical thickness contained in the layers above the PBL against that contained in the PBL is in all cases greater or equal to 50 per cent. This emphasizes the importance of the upper layers in the scattering and absorption of astronomical signals. Additionally, for the first time, spaceborne lidar measurements were also compared to those of a ground lidar, in order to evaluate the use of a spaceborne active instrument for aerosol content monitoring at an astronomical site.

L A Sukharev Pulkovo Meridional Automatic Horizontal Instrument (MAGIS)

This paper describes the design features of the MAGIS horizontal-type meridional telescope of the Pulkovo Observatory and its operating principle. Questions are considered of the technological and metrological basis for choosing the materials for its subassemblies. The transit circle of MAGIS is intended for differential determinations of the coordinates (right ascensions and declinations) of objects to 17th stellar magnitude on the celestial sphere in the B, V, and R bands of the Johnson photometric system and in the integral sensitivity band of the detector.