Search

To effectively eliminate optical end loss for small-scale linear solar concentrators, a fixed linear-focus Fresnel lens solar system (FLFS) with triangle cavity receiver is described and the principle is provided. The effects of the receiver parameters including receiver position f, solar declination angle δ , solar hour angle ω , internal surface absorptivity α a b and end plane reflectivity ρ r on the end loss ratio ( μ o e l ) and relative optical efficiency ( η r e − o p t ) of the proposed system have been studied by the control variable method and Monte Carlo ray tracing (MCRT) method which is implemented by software TracePro®. Significance tests of critical factors are conducted to assess the effect of receiver parameters. These results revealed that the FLFS could effectively solve the problem of optical end loss of linear solar concentrators. When f = 650 mm and δ = 0°, 8°, 16°, and 23°27 ′ , the corresponding average η r e − o p t at ω from 0° to 60° are 0.9459, 0.9422, 0.9145, and 0.8144, respectively. As δ increases, reducing f can ensure the system operates at a high-efficiency state. The η r e − o p t shows a positive relationship with α a b and no relationship with ρ r . δ occupies the greatest significant influence on η r e − o p t , which is followed by ω , α a b and f.

In this study, performance analysis of flat plate solar collector has been carried out analytically. A comprehensive mathematical modelling of thermal performance is modelled using Response Surface Methodology and optimal geometrical and thermodynamic parameters are predicted pertaining to optimum performance of the system. In this study a model was developed for evaluating and predicting the efficiency, outlet temperature and performance of a flat plate solar collector considering the hour angle, day and input temperature as input parameters. In the cause of the work it was found that the days and months close to the beginning of the year (January, February, March and April) yielded higher outlet temperature and solar radiation due to dry season, while the months at the middle of the year showed lower outlet temperature and solar radiation due to the rainy season. The months towards the ending of the year also showed higher outlet temperature and solar radiation respectively.

International audience; The Dark Energy Spectroscopic Instrument (DESI) is a Stage IV ground-based dark energy experiment that will measure the expansion history of the Universe using the Baryon Acoustic Oscillation technique. The spectra of 35 million galaxies and quasars over 14000 square degrees will be measured during the life of the experiment. We describe the installation of the major elements of the instrument at the Mayall 4m telescope, completed in late 2019. The previous prime focus corrector, spider vanes, and upper rings were removed from the Mayall’s Serrurier truss and replaced with the newlyconstructed DESI ring, vanes, cage, hexapod, and optical corrector. The new corrector was optically aligned with the primary mirror using a laser tracker system. The DESI focal plane system was integrated to the corrector, with each of its ten 500-fiber-positioner petal segments installed using custom installation hardware and the laser tracker. Ten DESI spectrographs with 30 cryostats were installed in a newly assembled clean room in the Large Coude Room. The ten cables carrying 5000 optical fibers from the positioners in the focal plane were routed down the telescope through cable wraps at the declination and hour angle axes, and their integral slitheads were integrated with the ten spectrographs. The fiber view camera assembly was installed to the Mayall’s primary mirror cell. Servers for the instrument control system replaced existing computer equipment. The fully integrated instrument has been commissioned and is ready to start its operations phase.

Precise determination of the astronomical azimuth using the local hour angle (LHA) of Polaris is only applicable in northern middle latitudes. Therefore, to achieve fast and precise astrono...

The Ultraviolet Forward Spectrometer is a new type of spectrometer for monitoring the vertical distribution of atmospheric trace gases in the global middle atmosphere. It is on the TianGong-2 space laboratory, which was launched on 15 September 2016. The spectrometer uses a solar calibration mode to modify its irradiance. Accurately calculating the solar orientation is a prerequisite of spectral calibration for the Ultraviolet Forward Spectrometer. In this paper, a method of calculating the solar orientation is proposed according to the imaging geometric characteristics of the spectrometer. Firstly, the solar orientation in the horizontal rectangular coordinate system is calculated based on the solar declination angle algorithm proposed by Bourges and the solar hour angle algorithm proposed by Lamm. Then, the solar orientation in the sensor coordinate system is achieved through several coordinate system transforms. Finally, we calculate the solar orientation in the sensor coordinate system and evaluate its calculation accuracy using actual orbital data of TianGong-2. The results show that the accuracy is close to the simulation method with STK (Satellite Tool Kit), and the error is not more than 2 %. The algorithm we present does not need a lot of astronomical knowledge, but only needs some observation parameters provided by TianGong-2.

This paper proposes a mobile sun-tracking system, which allows continuous tracking of the sun and effective harvesting of solar energy on mobile platforms. Based on the dynamic sun-tracking algorithm which we previously proposed, the system takes not only the date, time, and geographical information, but also the dynamic changes of coordinates of the mobile platforms into account to calculate the hour angle of sun relative to the ideal azimuth elevation axes in real time. The advantage of this design is that it can be easily duplicated for mass deployment on the land or ocean. Our results show that the accuracy of mobile tracking in stationary state is 8.085 mrad while the accuracy in mobile state is 127 mrad on average.

The brightness temperature (TB) data of the Moon acquired by the microwave radiometer (MRM) on-board the Chinese Chang’e-2 (CE-2) lunar probe are valuable and comprehensive data, which can be helpful in studying the physical properties of the lunar regolith, such as thickness, physical temperature, and dielectric constant. To construct the accurate and high-resolution lunar TB model with the TB data obtained by the MRM on-board CE-2, 2401 tracks of the original TB data are quantized by using the hour angle processing, and the hierarchical MK splines function (HMKSF) method is presented, which uses a hierarchy of coarse-to-fine control lattices to generate a sequence of TB model functions. The TB model constructor is the sum of the TB model functions derived at each level of the hierarchy. In addition, the lunar TB models with a resolution of $0.5 {^{\circ }} \times 0.5 {^{\circ }}$ in all four frequency channels are constructed for both the daytime and the nighttime. The obtained models show rich information, e.g., the global distribution of TB over the lunar surface, the effect of frequency on the TB model.

The purpose of this work is to develop a simple control law to implement stable orbits about a small rotating celestial body to achieve global coverage as well as fixed-body hovering on the equatorial plane. The celestial body is assumed to be rotating about a principal axis, with constant rotational velocity along the largest moment of inertia. A simple three dimensional closed-loop guidance law function of position and velocity is defined and analyzed, enabling the determination of the guidance constants to assure convergence to any desired circular orbit about the irregular celestial body, controlling independently five orbital parameters: inclination, right ascension of the ascending node, orbital radius, orbital rate and equatorial longitude. Representative numerical results are presented for an Eros type asteroid.

Estimation of global solar radiation using existing models becomes necessary in areas where measurements are not carried outdue to lack of technical knowledge, unavailability of measuring instrument and cost of getting such measurements if available.In this study, the possibility of estimating the global solar radiation for a particular location using another location's sunshine duration data is explored due to the closeness in the latitude of the two locations and to what extent is the estimation true. Ibadan's (latitude 7.37750N) sunshine duration data is used as Iwo's (latitude 7.62920N) sunshine duration data and employed in the Angstrom - Prescott's sunshine based model, while retaining the latitude of Iwo in the model, mean sunset/rise hour angle and extraterrestrial radiation. The sunshine duration data for Ibadan (2008 - 2012) was gotten from International Institute of Tropical Agriculture, Ibadan while the measured global solar radiation data for Iwo (2014 - 2015) was measured at Bowen University Iwo, Osun state in Nigeria. The estimated global solar radiation for Iwo is validated with measured global solar radiation at Iwo by carrying out some statistical analysis like mean bias error (-0.03), root mean square error (0.81), mean percentage error (-0.23), Nash-Sutcliffe error (r2) or coefficient of determination (0.88), coefficient of correlation (0.94). The estimated values when validated against the measured values performed excellently well. Hence it is possible to use the available sunshine duration data of another location as the sunshine duration data when estimating the global solar radiation available at the location of interest.

Demircan, Cihan/0000-0003-2094-0473 WOS: 000514838400011 The change of the solar radiation reaching the earth depending on specific conditions brings the execution of system planning meticulously and optimally by solar power researchers to the fore. For the estimation of the solar radiation, the most frequently used model is the Angtrom-Prescott model. In this model, sunshine ratio plays an important role. In the study, it is attempted to enhance the annual and semi-annual models developed for the city of Mugla, Turkey and to congregate the semi-annual models in a single model by using the Artificial Bee Colony (ABC) algorithm. The results obtained have revealed that in the multiple model relying on only the sunshine duration, the statistical error values were not reduced to very low levels. In order to cope with this problem, the multiple model relying on both the sunshine duration and the sunset-sunrise hour angle has been proposed. In this way, the statistical errors are found to be reduced by about 40% using the ABC algorithm and the multiple model. It was seen that the models recommended are superior to all the models especially in summer and spring months when there is plenty of sunshine.

New approaches for the computation of the sampling points for an annual simulation of a solar tower power plant are presented. The annual sun-path in azimuth and elevation and in ecliptic longitude and the hour angle are considered. Real measured weather data is considered in the computation of these sampling points.

Solar plate collectors are utilized to heat up water or a mixture of water and glycol by capturing solar radiation and transfer this heat to the collector fluid. In this study, the efficiency of solar plate collector during 19th, 20th and 21st of February, was investigated experimentally. The time of day, plate collector mean temperature, solar intensity and external air temperature can effect on the efficiency of solar collector. And the effect of incidence angle on solar irradiation has been studied; as a result, the solar irradiance will be decreased as the angle of incidence increased. A method presented can be used to calculate hour angle, diffuse solar radiation and total solar radiation at various temperatures in this paper its MATLAB programs.

In this article, we report all results obtained with a fiber scrambler on the Hamilton spectrograph at Lick Observatory. We demonstrate an improvement in the stability of the instrumental profile using this fiber scrambler. Additionally, we present data obtained with a double scrambler that further improves the stability of the instrument by a factor 2. These results show that errors related to the coupling between the telescope and the spectrograph are the dominant source of instrumental profile variability at Lick Observatory. In particular, we show a strong correlation between instrumental profile variations and hour angle, most likely due to pointing-dependent illumination of the spectrograph optics.

This paper is mainly about using the length changes of the shadows to determine the location while the length of the object is unknown. Using the solar elevation as a bridge, we build function models between solar declination, geographic latitude of the observing place, hour angle and the length of shadow, and then use Stephenson accelerate iterative method to help solve latitude positioning model, finally realize the shadow positioning.

A systematic approach is presented for the sampling and interpolation over sun path. The annual sun path is described in terms of the ecliptic longitude and hour angle so that all possible positions of the sun are mapped on a rectangular domain. This enables the use of many efficient algorithms, and the bicubic interpolation with Catmull–Rom splines is proposed. It is shown that a sufficiently good accuracy can be achieved with as little as 32 sampling points for a year.

In this paper, we will establish practical and reliable mathematical model to determine the video filming locations and dates by analyzing the shadow variations of the object in the video. At first, we convert the video into image sequences which can been read by MATLAB at regular intervals. So we can analyze the image sequences to obtain coordinates of the end of the shadow in the video; in the second place, we adopt the method of data transformation based on three-dimensional reconstruction to obtain the actual coordinates of the end of the shadow; next,taking advantage of the parametric equations of the shadow and the actual coordinates of the end of the shadow, we establish goal programming model to make the sum of the error of the shadow length and deviation angle variance of the coordinate system minimum. And we can obtain solar hour angle、declination and angle latitude; Finally, we analyze the conversion relation of the solar hour angle with longitude and declination with dates to determine the video filming locations and dates.

When analyzing the data of photos and videos, it's very important to determine the shooting time and place. Usually, we can get the sun's shadow from the pictures and videos and establish different mathematical models to solve time and space positioning problems by the known parameters. Firstly, use basic amounts to establish Analemmatic sundial model; when obtaining a series of picture messages, you can get vertex coordinate data of a fixture's sun shadow on the level ground. Then to establish |y/x| scale model by Orthogonal multinomial fitting method, which can solve the latitude and longitude separately, and select 1 ‰ screening indicator as the error correction to get exact location; About shooting time, according to |y/x| scale model determining the position longitude, using MATLAB to enumerate solar declination, then develop Dynamic measurement error filter rule, select the appropriate latitude and solar declination values to calculate shooting date; when getting a video recording a fixture shadow changes, use MATLAB function of Videoreader frame image, then use Rgb2gray Function convert into gray image, finally use Ginput Function reads the image coordinates. Use those to establish a comprehensive model to get the time and location of the video shoot. Accomplish data analyzing work, which has important applications in the investigation, pointing prediction, spatial and temporal positioning and so on. Before establishing the model, there are some assumptions are as follows:  Assuming that the earth is a rule sphere, the entire radius are equal.  Assuming that the sun light is parallel to the Earth, and the communication process is unhindered.  Assuming that the number of days in a year is 365 days. After accessing to information, we can know that the sun irradiating to the Earth's surface projected shadow, whose length is related to ascension, hour angle and solar altitude, they represent the meridional coordinate of equatorial coordinate system, the difference between the right ascension (RA) and local the sidereal time (LST), the angle formed by the Earth's equatorial plane and the line between the center of the earth and sun and the angle formed by the sun's rays and earth surface tangent (1).

In recent decades, with the level of material life improves quickly, more and more people are on fire for outdoor adventure. They usually trek in desert and wasteland. However the case that compass or communication equipment is out of order happens frequently. For someone who lack direction, it is easy for them to be lost. So it is a meaningful work to research a way to find position with the help of the sun shadow. The sun shadow position is a huge project. Our paper aims to solve one link of the whole project. As the time and location change, the length of pole’s shadow change, which we make research on to get the exact function model. As is known to all, earth-sun distance is much higher than mean radius of the earth. So we can approximately think the sunlight shining on the earth is parallel light. If we believe pole length is constant. The shadow length only relates with solar elevation angle. So we can use solar declination angle, solar hour angle, geographical longitude and latitude to calculate solar elevation angle. In a word, we use parameters such as date, longitude, latitude and time to refer to above variable, with the help of geographical knowledge. And then we establish the model which describe the change of shadow length. At last we apply the model in practice. The result prove that our model is reasonable. KEYWORD: shadow positioning; solar elevation; shadow length change model 4th International Conference on Mechanical Materials and Manufacturing Engineering (MMME 2016) © 2016. The authors Published by Atlantis Press 343

We describe the motivation, design and implementation of the CORNISH survey, an arcsecond resolution radio continuum survey of the inner Galactic plane at 5 GHz using the Karl G. Jansky Very Large Array (VLA). It is a blind survey co-ordinated with the northern Spitzer GLIMPSE I region covering 10 deg < l < 65 deg and |b| < 1 deg at similar resolution. We discuss in detail the strategy that we employed to control the shape of the synthesised beam across this survey that covers a wide range of fairly low declinations. Two snapshots separated by 4 hours in hour angle kept the beam elongation to less that 1.5 over 75% of the survey area and less than 2 over 98% of the survey. The prime scientific motivation is to provide an unbiased survey for ultra-compact HII regions to study this key phase in massive star formation. A sensitivity around 2 mJy will allow the automatic distinction between radio loud and quiet mid-IR sources found in the Spitzer surveys. This survey has many legacy applications beyond star formation including evolved stars, active stars and binaries, and extragalactic sources. The CORNISH survey for compact ionized sources complements other Galactic plane surveys that target diffuse and non-thermal sources as well as atomic and molecular phases to build up a complete picture of the ISM in the Galaxy., 17 pages, 14 figures. Accepted for publication in PASP (16th-August-2012)

In this research work some mathematical models have been simulated to estimate the regression coefficients, which are also known as Angstrom coefficients, with monthly and daily average solar radiation on horizontal surface using bright sunshine hours. This study of solar energy, information on solar radiation and its components at a given location is very essential for scientists, engineers, architects, agriculturists and hydrologists for various applications such as measuring aerosol optical thickness, solar heating, cooking, drying and interior illumination of buildings. But, for developing countries like Bangladesh, we have limitation of sophisticated measuring instruments. So, we have used some latitude based empirical models to calculate an important solar radiation geometry parameter- Angstrom Coefficients for Bangladesh without any help of costly instruments. DOI: http://dx.doi.org/10.3329/ijns.v2i1.10882 International Journal of Natural Sciences (2012), 2(1): 38-42

Sun observations provide a robust way for determining the geodetic or true azimuth at a location. Azimuth is generally defined as the angle in the plane measured from the meridian’s north (or south) to the location of the line of interest. It is common to use the north azimuth; also referred to as “azimuth”, especially in civilian surveying applications. The astronomic meridian is obtained through astronomic observations of the Sun or North Star (Polaris) and it is important since it provides one instance of the geodetic or true meridian. There are two methods for determining the sun azimuth; the first is known as the hour angle method and the other is called the altitude method. The hour angle method requires the determination of accurate time while altitude method requires accurate vertical angle. The hour angle method is more popular because it is more accurate, can be performed at any time of day and is applicable to the sun, Polaris and other stars. In this article, an error modeling framework for the errors result in the process of determining the sun azimuth using the hour angle method; namely random errors, is presented. A Gauss-Markov model is used to represent the errors in the true azimuth estimation process. Six sets of sun observation for azimuth data; three with telescope direct and three reverse, including horizontal circle’s readings and time were collected and used in order to estimate the true azimuth of a line in a study area in central Orlando, Florida, United States.

In this work, a new sun-tracking concept was proposed, and the optical performance of solar panels with such sun-tracking system was theoretically investigated based on the developed mathematical method and monthly horizontal radiation. The mechanism of the proposed sun-tracking technique is that the azimuth angle of solar panels is daily adjusted three times at three fixed positions: eastward, southward and westward in the morning, noon, and afternoon, respectively, by rotating solar panels about the vertical axis (3A sun-tracking, in short). The analysis indicated that the tilt-angle of solar panels, β3A, azimuth angle of solar panels in the morning and afternoon from due south, ϕa, and solar hour angle when the azimuth angle adjustment was made in the morning and afternoon, ωa, were three key parameters affecting the optical performance of such tracked solar panels. Calculation results showed that, for 3A tracked solar panels with a yearly fixed tilt-angle, the maximum annual collectible radiation was above 92% of that on a solar panel with full 2-axis sun-tracking; whereas for those with the tilt-angle being seasonally adjusted, it was above 95%. Results also showed that yearly or seasonally optimal values of β3A, ϕa and ωa for maximizing annual solar gain were related to site latitudes, and empirical correlations for a quick estimation of optimal values of these parameters were proposed based on climatic data of 32 sites in China.

This paper presents a model for predicting hourly solar radiation data using daily solar radiation averages. The proposed model is a generalized regression artificial neural network. This model has three inputs, namely, mean daily solar radiation, hour angle, and sunset hour angle. The output layer has one node which is mean hourly solar radiation. The training and development of the proposed model are done using MATLAB and 43800 records of hourly global solar radiation. The results show that the proposed model has better prediction accuracy compared to some empirical and statistical models. Two error statistics are used in this research to evaluate the proposed model, namely, mean absolute percentage error and root mean square error. These values for the proposed model are 11.8% and −3.1%, respectively. Finally, the proposed model shows better ability in overcoming the sophistic nature of the solar radiation data.

In the first part of this series, we discussed the celestial sphere and Aryabhata’s principle of axial rotation; in this part we shall discuss in detail the concept of sidereal day and then mention Aryabhata’s computations on the duration of sidereal day.

An investigation of the stability of the transfer function of the European Southern Observatory's Very Large Telescope Interferometer has been carried out through observations of Fomalhaut over a wide range in hour angle. No significant variation in the transfer function was found for the zenith angle range 5-70 degrees. The projected baseline varied between 139.7 m and 49.8 m during the observations and, as an integral part of the determination of the transfer function, a new accurate limb-darkened angular diameter for Fomalhaut has been established. This has led to improved values for the emergent flux, effective temperature, radius and luminosity., Comment: 6 pages, 4 figures, uses an.cls, accepted for publication in Astron. Nacht

Practical measurement of the passage of time requires the notion of a repeating phenomenon. The Earth's rotation has traditionally fulfilled this requirement. To cope with the impracticality of making precise measures of the Sun's hour angle or altitude, particularly in uncooperative weather conditions, various devices have been employed, but all have been calibrated with respect to astronomical phenomena related to the Earth's rotation, or to its orbital motion with respect to the Sun. Modern requirements for timing precision coupled with an increased understanding of the variability of the Earth's rotational speed are likely to bring about a change in the traditional relationship between precise timekeeping and astronomy. The historical background of this relationship and the current definitions are reviewed to show the development of timekeeping capabilities and the growing need for precise timekeeping. Possible future developments are outlined along with their advantages and disadvantages.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

(Abridged) Atmospheric dispersion and field differential refraction impose severe constraints on widefield MOS observations. Flux reduction and spectral distortions must be minimised by a careful planning of the observations -- which is especially true for instruments that use slits instead of fibres. This is the case of VIMOS at the VLT, where MOS observations have been restricted, since the start of operations, to a narrow two-hour range from the meridian to minimise slit losses. We revisit in detail the impact of atmospheric effects on the quality of VIMOS-MOS spectra. We model slit losses across the entire VIMOS FOV as a function of target declination. We explore two different slit orientations at the meridian: along the parallactic angle (North-South), and perpendicular to it (East-West). We show that, for fields culminating at zenith distances larger than 20 deg, slit losses are minimised with slits oriented along the parallactic angle at the meridian. The two-hour angle rule holds for these observations using N-S orientations. Conversely, for fields with zenith angles smaller than 20 deg at culmination, losses are minimised with slits oriented perpendicular to the parallactic angle at the meridian. MOS observations can be effectively extended to plus/minus three hours from the meridian in these cases. In general, night-long observations of a single field will benefit from using the E-W orientation. All-sky or service mode observations, however, require a more elaborate planning that depends on the target declination, and the hour angle of the observations. We establish general rules for the alignment of slits in MOS observations that will increase target observability, enhance the efficiency of operations, and speed up the completion of programmes -- a particularly relevant aspect for the forthcoming spectroscopic public surveys with VIMOS., Accepted to A&A. 11 pages, 15 figures. This paper presents the new recommendations for optimal slit alignment in VLT/VIMOS observations

We demonstrate the global secular rotation of the Celestial Ephemeris Origin (CEO), the nonrotating origin (NRO) for Earth's equator adopted recently by the IAU. The current speed of this global rotation is as high as -415 yr-1, where the minus sign indicates that the CEO rotates clockwise with respect to the inertial frame when viewed from the north celestial pole. Such secular rotation does not exist for some geometrically defined longitude origins. We think that the existence of a global secular rotation means that the CEO, and the NRO in general, is not appropriate to be specified as the x-axis of a celestial coordinate system.

Finding the direction of a line is done simply and accurately with a multiyear interactive computerized almanac (Mica), a theodolite, and a hand-held programmable calculator. Mica is the Multiyear Interactive Computer Almanac that is available from the U.S. Naval Observatory. An astronomic azimuth from station 081 to station 080 is measured with a set of six solar observations and the resulting average azimuth is compared to the value established by the Vermont Agency of Transportation (VAT), using the global positioning system. Each of the six sun shots is made by an independent observer, who in this study is represented by a first-year civil engineering student. Three readings were done with the telescope reversed and three were taken with the telescope direct. The local hour angle (LHA) method is used to calculate the astronomic azimuth. The solar constants for the equation of time (EOT), for declination (δ), and for semidiameter (SD) are found in Mica. The astronomic Azimuth 081–080 is 235° 15’ 50" from the student readings and is 235° 15’ 56" from VAT data.

Space impacts retrieved to Earth, such as those on LDEF and EuReCa, have led to an unprecedentedly high definition of the impact environment in Earth orbit. This leads to (1) a penetration flux distribution (2) angular dependence of the flux (3) physical signatures of the penetration through thin films and (4) chemical evidence of impact residues. At micron dimensions, space retrieved surfaces show an “excess” flux, mainly when exposed to the leading (ram) direction, attributable to space debris or to micrometeoroids captured in Earth orbit. We present results of studies to determine the capture efficiency of the Earth to interplanetary dust and the dwell time of microparticles in eccentric orbits. Effects of the solar hour angle of the initial argument of perigee at capture are critical and, especially, the increase or decrease of atmospheric density at subsequent perigee passages due to solar heating cycles. Results will be presented of interest to the relative importance of space debris and of astrophysical sources.

This paper proposes an algorithm to calculate the optimum tilt angle of solar panels by means of global horizontal solar radiation data, provided from Earth-based meteorological stations. This mathematical modeling is based on the maximization of the theoretical expression of the global solar irradiation impinging on an inclined surface, with respect to the slope and orientation of the panel and to the solar hour angle. A set of transcendent equations resulted, whose solutions give the optimum tilt and orientation of a solar panel. A simulation was carried out using global horizontal solar radiation data from the European Solar Radiation Atlas and some empirical models of diffuse solar radiation. The optimum tilt angle resulted was related to latitude by a linear regression with significant correlation coefficients. The standard error of the mean values resulted increased significantly with latitude, suggesting that unreliable values can be provided at high latitudes.

This paper deals with the distributive characteristics of the occurrence time of earthquakes with respect to the aftershock sequences of strong earthquakes. The distribution of lunar and solar local hour angles at the time of commencement of moderate and strong aftershocks indicates that the time of commencement of moderate and strong aftershocks is modulated by the positions of the sun and moon and then the earthquake restrained time zones exists also. In this paper the differences of earthquake restrained time zones between the preshock sequences and the aftershock sequences are compared, and the possible mechanism is analyzed preliminarily. And the possible maximum scope of accuracy in predicting the occurrence time of an earthquake is determined as well.

This paper deals with the distributive characteristics of the occurrence time of earthquakes with respect to the aftershock sequences of strong earthquakes. The distribution of lunar and solar local hour angles at the time of commencement of moderate and strong aftershocks indicates that the time of commencement of moderate and strong aftershocks is modulated by the positions of the sun and moon and then the earthquake-restrained time zones exists also. In this paper the differences of earthquake-restrained time zones between the preshock sequences and the aftershock sequences are compared, and the possible mechanism is analyzed preliminarily. And the possible maximum scope of accuracy in predicting the occurrence time of an earthquake is determined as well.

A Microsoft Excel application has been developed to utilize eclipsing binary elements to calculate binary ephemerides that are useful in a program of observing binary systems. Binary star systems consist of two stars orbiting a common center of mass. Consistent monitoring of eclipsing binary stars is important for establishing fundamental astronomical parameters, such as mass and composition of the stellar system. The application that was developed supports effective use of resources in such monitoring applications. The main quantities computed by the application at the time of the eclipse include: local time, Julian date, starting Epoch, altitude of the system, phase of the moon, Local Mean Sidereal Time, and Local Hour Angle. Other quantities computed by the application include current Universal Time (UT), UT/Local Time correction, Julian Date, and current moon phase/percent illuminated. The observing application has been demonstrated to be effective in practical application to obtain differential photometry data for SV Camelopardalis, a system of interest because of variability in its period caused by a third body. The application can be easily modified for use with other highly periodic astronomical systems, for instance transits of extrasolar planets.

In this paper, an overview of the production and consumption of Kuwait electrical energy, installed capacity and peak loads are presented. The results show that Kuwait has a serious situation because of the electrical energy lacking and load peaking. Based on the fact that Kuwait has enough budgets to transform all the power station powered by oil with renewable energy sources turning to greener Kuwait. The paper also is identifying and analyzing the geographical and temporal variability of solar energy inside Kuwait. The fundamental solar models are modified to estimate and identify daily and hourly solar radiation on horizontal surfaces on the basis of the more readily available meteorological data. The presented results prove that Kuwait has an abundance of solar energy capability in terms of almost cloudless atmosphere for nine months and twelve hours solar time a day over the year. The daily global and monthly averaged solar intensity on horizontal surface at Kuwait area is ranging from 3 Wh/m2 in winter to 8 kWh/m2 in summer. Monthly averaged clear sky solar radiation on horizontal surfaces at Kuwait area is ranging from 500W/m2/day to 1042W/m2/day.

In 2009 we started an intense radial-velocity monitoring of a few nearby, slowly-rotating and quiet solar-type stars within the dedicated HARPS-Upgrade GTO program. The goal of this campaign is to gather very-precise radial-velocity data with high cadence and continuity to detect tiny signatures of very-low-mass stars that are potentially present in the habitable zone of their parent stars. Ten stars were selected among the most stable stars of the original HARPS high-precision program that are uniformly spread in hour angle, such that three to four of them are observable at any time of the year. For each star we recorded 50 data points spread over the observing season. The data points consist of three nightly observations with a total integration time of 10 minutes each and are separated by two hours. This is an observational strategy adopted to minimize stellar pulsation and granulation noise. We present the first results of this ambitious program. The radial-velocity data and the orbital parameters of five new and one confirmed low-mass planets around the stars HD20794, HD85512, and HD192310 are reported and discussed, among which is a system of three super-Earths and one that harbors a 3.6 Earth-mass planet at the inner edge of the habitable zone. This result already confirms previous indications that low-mass planets seem to be very frequent around solar-type stars and that this may occur with a frequency higher than 30%, 18 pages, 22 figures, accepted by A&A on 15/08/2011 with reference AA/2011/17055. Radial velocity data will be available through CDS

MaNGA (Mapping Nearby Galaxies at Apache Point Observatory) is an integral-field spectroscopic survey that is one of three core programs in the fourth-generation Sloan Digital Sky Survey (SDSS-IV). MaNGA’s 17 pluggable optical fiber-bundle integral field units (IFUs) will observe a sample of 10,000 nearby galaxies distributed throughout the SDSS imaging footprint (focusing particularly on the North Galactic Cap). In each pointing these IFUs are deployed across a 3◦ field; they yield spectral coverage 3600-10,300 Å at a typical resolution R 2000, and sample the sky with 2” diameter fiber apertures with a total bundle fill factor of 56%. Observing over such a large field and range of wavelengths is particularly challenging for obtaining uniform and integral spatial coverage and resolution at all wavelengths and across each entire fiber array. Data quality is affected by the IFU construction technique, chromatic and field differential refraction, the adopted dithering strategy, and many other effects. We use numerical simulations to constrain the hardware design and observing strategy for the survey with the aim of ensuring consistent data quality that meets the survey science requirements while permitting maximum observational flexibility. We find that MaNGA science goals are best achieved with IFUs composed of a regular hexagonal grid of optical fibers with rms displacement of 5 μm or less from their nominal packing position; this goal is met by the MaNGA hardware, which achieves 3 μm rms fiber placement. We further show that MaNGA observations are best obtained in sets of three 15-minute exposures dithered along the vertices of a 1.44 arcsec equilateral triangle; these sets form the minimum observational unit, and are repeated as needed to achieve a combined signal-to-noise ratio of 5 °A−1 per fiber in the r-band continuum at a surface brightness of 23 AB arcsec−2. In order to ensure uniform coverage and delivered image quality, we require that the exposures in a given set be obtained within a 60 minute interval of each other in hour angle, and that all exposures be obtained at airmass less than or similar to 1.2 (i.e., within 1-3 hours of transit depending on the declination of a given field). Publisher PDF

International audience; Aims.We present the first lab and sky validation of spectro-polarimetric equipment put at the combined focus of an optical long-baseline interferometer. We tested the polarimetric mode designed for the visible GI2T Interferometer to offer spectropolarimetric diagnosis at the milliarcsecond scale. Methods.We first checked the whole instrumental polarization in the lab with a fringe simulator, and then we observed α Cep and α Lyr as stellar calibrators of different declinations to tabulate the polarization effects throughout the GI2T declination range. Results.The difference between both linear polarizations is within the error bars and the visibilities recorded in natural light (i.e. without the polarimeter) for calibration purposes are the same order of magnitude as the polarized ones. We followed the α Cep visibility for 2 h after the transit and α Lyr for 1.5 h and detected no decrease with hour angle due to the fringe pattern smearing by instrumental polarization. Conclusions.Differential celestial rotation due to the dissymetric Coudé trains of the GI2T is well-compensated by the field rotators, so the instrumental polarization is controlled over a relatively wide hour angle range (±2 h around the transit at least). Such a polarimetric mode opens new opportunities especially for studies of circumstellar environments and significantly enhances both the potential of an optical array and its ability for accurate calibration.

where /is is the hour angle of the Sun (angular distance from the meridian of a site in radians) at sunset. Sunrise and sunset are not exactly symmetrical about the time that the Sun reaches a local meridian, but for biological simulation purposes the symmetry implicit in equation (1) is acceptable. The geometric equation for sin a (where a is solar elevation) can be rearranged to find hs as follows

A microcomputer controlled all sky scanning radiometer covering the short wave (0.3–3.0 μm) and long wave (3.0–80.0 μm) regions and using a pyroelectric detector has been constructed for continuous automatic measurement of sky radiance. Angular distributions of short, long, and total wave sky radiance are recorded and plotted at each solar hour angle from which irradiances of tilted surfaces are computer calculated. Measurement of the local earth surface radiance facilitates estimation of short wave earth surface albedo and net income of radiation to variously oriented black surfaces. Total scanning, computation, and plotting time for each hour angle observation is 8 min.

Monthly means of measured daily radiation data from a defined horizontal site are used to estimate the prevailing atmospheric attenuation parameter. The estimation method uses the properties of the Fourier structure of attenuation, as a function of the hour angle, at that site, for a range of attenuation parameters. The Fourier structure of the parameter estimate is then used to calculate the global daily radiation of a “nearby” site, of any orientation, by direct formula substitution.

The parallactic refraction correction should be applied to the photographic observations of the light signals carried either by artificial satellites or by meteorological balloons. The correction to the right ascension and declination are made with the equations where ϕ is the latitude of the observation station, z the zenith distance, α the right ascension, δ the declination and h the hour angle of the light signal. Parallactic refraction is denoted by Δζ.

A. Digby (The Paddocks, Eastcombe, Stroud, Gloucestershire) I think the most striking difference between Old World and New World calendrical systems which has emerged from the papers today is the use in America of a 260-day period combining the 20 day names with the numerals 1 to 13. There is a possibility that the number thirteen may have been determined by the characteristics and shortcomings of a peculiar sundial which could be used to determine annual as well as diurnal time by showing the declination as well as the hour angle of the sun. The evidence for the existence of this instrument lies in examples of the year glyph which can be shown to be a drawing of two trapezes set at right angles on a ring. One lying north to south would cast a shadow which would move from west to east across the base of the instrument between the hours of about 7 a.m. and 5 p.m., while the other, a taller trapeze would cast a shadow that travels across the instrument in a direction from south to north and back reflecting the declination of the Sun. There is some evidence to show that the instrument was tilted with the base parallel to the axis of the Earth like a ‘polar sundial’ (paper read to a symposium on recent Mesoamerican research, Cambridge 1972). Under these conditions, the shadow would make four traverses of equal length in the course of the year: from the centre of the instrument to the northern extremity (autumnal equinox to winter solstice); north extremity to centre (winter solstice to vernal equinox); centre to south extremity (vernal equinox to summer solstice); south extremity to centre (summer solstice to autumnal equinox), each of 91J days duration.

Attenuation of solar radiation as a function of hour angle is expressed as a Fourier cosine series. A simple procedure is derived for calculating total direct daily radiation at a site with known latitude and orientation.

The discovery by Dr. Lamont of a "decennial” period in the range of the solar diurnal variation of magnetic declination, naturally leads to the question whether a similar law may not exist for the lunar diurnal variation; the question is also of importance in connexion with the theory of the cause of these variations.

A simple calculator for solving the equation of a spherical triangle is described. This was designed for use in celestial navigation by amateur yachtsmen. It is much more rapid to use than the tables commonly employed. It can be made to be accurate to ± 1/2´of arc in calculating zenith distance, and so is suitable for any navigation to the usual standards of accuracy. Computation is based on Ohm’s law and effected by two potentiometers, each having two moving contacts. These are set by dials marked in angle to make resistances represent the appropriate derivations of latitude, declination, hour angle and zenith distance. When one of these is unknown, if the potentiometers are balanced the fourth resistance gives the solution. Sources of error and their avoidance in practical construction are discussed. It can solve any spherical triangle for a body above the observer’s horizon for declinations and latitudes up to about 80°, but for zenith distances less than 30° its accuracy is limited. The instrument is robust, portable and about the same weight as a book of nautical fivefigure tables.

1. While the observational study of terrestrial magnetism is receiving ever more and more attention, and being rewarded with success by the acquisition of new and important data, the theoretical side of the subject shows a much less rapid advance. The search for a physical theory of the earth’s magnetism and its changes is fascinating but elusive. Perhaps in one case only—that of Schuster’s important theory of the diurnal variations of the magnetic state of the earth—has there been put forward a clearly outlined theory which promises to explain the real mechanism of any magnetic phenomenon. On this theory, the solar diurnal variations are attributed to the action of electromotive forces produced in masses of conducting air in the upper atmosphere, by their motion across the permanent magnetic field of the earth. The magnetic field of the resulting electric currents is identified with that which produces the observed diurnal changes. Schuster has shown that if the motion of the air is taken to he substantially that which is indicated by the barometric variations, the atmosphere being supposed to oscillate as a whole, the conductivity required by the theory is not unreasonable, considering the ionization of the tenuous upper atmosphere by ultra-violet radiation from the sun. The fundamental assumptions are in accordance with Schuster’s demonstration! that the magnetic variations are principally due to a system of currents above the earth’s surface. In order to explain the relative magnitudes of the diurnal and semi-diurnal terms in the magnetic potential, it is necessary to suppose that the conductivity of the atmosphere varies with the solar hour angle, which is certainly à priori probable: the great excess of the summer variation over the winter variation is unexplained, however, as the usual rapid rate of recombination of ions makes it difficult to believe that the solar ionization is slowly cumulative.