The Design and Simulation of an Astronomical Clock

This paper describes and explains the synthesis of an astronomical clock mechanism which displays the mean position of the Sun, the Moon, the lunar node and zodiac circle as well as the Moon phases and their motion during the year as seen from the Earth. The clock face represents the stereographic projection of the celestial equator, celestial tropics, zodiac circle (ecliptic) and horizon for the latitude of Belgrade from the north celestial pole to the equator plane. The observed motions of celestial objects are realized by a set of clock gear trains with properly calculated gear ratios. The method of continued fraction is applied in the computation of proper and practically applicable gear ratios of the clock gear trains. The fully operational 3D model of the astronomical clock is created and the motion study of its operation is accomplished by using the SolidWorks 2016 application. The simulation results are compared with the ephemeris data and the detected differences are used to evaluate the long-term accuracy of the astronomical clock operation. The presented methods of the clock mechanism synthesis can be useful for the design, maintenance and conservation of large-scale city astronomical clocks since these clocks represent a precious historical and cultural heritage of European civilization.

The M dwarf problem: Fe and Ti abundances in a volume-limited sample of M dwarf stars

ABSTRACT We report iron and titanium abundance measurements from high-resolution spectra in a volume-limited sample of 106 M0 and M0.5 dwarf stars. The sample includes stars north of the celestial equator and closer than 29 parsecs. The results imply that there is an M dwarf problem similar to the previously known G dwarf problem, in that the fraction of low-metallicity M dwarfs is not large enough to fit simple closed-box models of Galactic chemical evolution. This volume-limited sample avoids many of the statistical uncertainties present in a previous study using a brightness-limited sample of M dwarf stars.

Producing a BOSS CMASS sample with DES imaging

ABSTRACT We present a sample of galaxies with the Dark Energy Survey (DES) photometry that replicates the properties of the BOSS CMASS sample. The CMASS galaxy sample has been well characterized by the Sloan Digital Sky Survey (SDSS) collaboration and was used to obtain the most powerful redshift-space galaxy clustering measurements to date. A joint analysis of redshift-space distortions (such as those probed by CMASS from SDSS) and a galaxy–galaxy lensing measurement for an equivalent sample from DES can provide powerful cosmological constraints. Unfortunately, the DES and SDSS-BOSS footprints have only minimal overlap, primarily on the celestial equator near the SDSS Stripe 82 region. Using this overlap, we build a robust Bayesian model to select CMASS-like galaxies in the remainder of the DES footprint. The newly defined DES-CMASS (DMASS) sample consists of 117 293 effective galaxies covering $1244\,\deg ^2$. Through various validation tests, we show that the DMASS sample selected by this model matches well with the BOSS CMASS sample, specifically in the South Galactic cap (SGC) region that includes Stripe 82. Combining measurements of the angular correlation function and the clustering-z distribution of DMASS, we constrain the difference in mean galaxy bias and mean redshift between the BOSS CMASS and DMASS samples to be $\Delta b = 0.010^{+0.045}_{-0.052}$ and $\Delta z = \left(3.46^{+5.48}_{-5.55} \right) \times 10^{-3}$ for the SGC portion of CMASS, and $\Delta b = 0.044^{+0.044}_{-0.043}$ and $\Delta z= (3.51^{+4.93}_{-5.91}) \times 10^{-3}$ for the full CMASS sample. These values indicate that the mean bias of galaxies and mean redshift in the DMASS sample are consistent with both CMASS samples within 1σ.

PENENTUAN AWAL WAKTU SUBUH MENGGUNAKAN SKY QUALITY METER PADA VARIASI DEKLINASI MATAHARI

<p class="AbstractEnglish"><strong>Abstract:</strong> Determination of the beginning of the prayer time is very important for Muslims because it is one of the prayer pillars. However, the determination of beginning morning prayer is still difficult, because the sun is below the horizon. The determination of the beginning of dzuhur, ashr, and maghrib times are easier since the sun's shadow is still clearly visible. The sun position is determined by sun declination. The sun declination value is given a positive sign (+) when it is north of the sky equator and negative sign (-) when it is to the south of the celestial equator. This research method uses the experimental method. The determination of the subuh time has been done by measuring sky brightness level that was measured by SQM. There is a difference between the beginning of morning prayer time between the Accurate Times software calculation and the measurement. In the sun declination variation, difference data ranged from 21 - 36 minutes. From this study, it was concluded that the value of sun declination affected the beginning of dawn time.</p><p class="KeywordsEngish"><strong>Abstrak:</strong> Penentuan awal waktu salat yang tepat penting bagi umat muslim, karena merupakan salah satu rukun salat. Namun, penentuan awal waktu salat subuh masih sulit, karena matahari berada di bawah horizon. Penentuan awal waktu zuhur, asar, dan magrib lebih mudah karena bayangan matahari masih terlihat jelas. Posisi matahari ditentukan oleh deklinasi matahari, nilai deklinasi matahari diberi tanda positif (+) ketika berada di sebelah utara ekuator langit dan negatif (-) ketika berada di sebelah selatan ekuator langit. Metode penelitian ini menggunakan metode eksperimen. Penentuan awal waktu subuh dengan menggunakan pengukuran Tingkat Kecerahan Langit (TKL) ini diukur dengan <em>Sky Quality Meter (SQM)</em>. Terdapat selisih awal waktu salat subuh antara perhitungan <em>Software Accurate Times</em> dan pengukuran. Pada variasi deklinasi matahari diperoleh data selisih berkisar antara 21-36 menit. Dari penelitian ini disimpulkan bahwa nilai deklinasi matahari berpengaruh terhadap awal waktu subuh.</p>

Covering the celestial sphere at ultra-high energies: Full-sky cosmic-ray maps beyond the ankle and the flux suppression

Despite deflections by Galactic and extragalactic magnetic fields, the distribution of ultra-high energy cosmic rays (UHECRs) over the celestial sphere remains a most promising observable for the identification of their sources. Thanks to a large number of detected events over the past years, a large-scale anisotropy at energies above 8 EeV has been identified, and there are also indications from the Telescope Array and Pierre Auger Collaborations of deviations from isotropy at intermediate angular scales (about 20 degrees) at the highest energies. In this contribution, we map the flux of UHECRs over the full sky at energies beyond each of two major features in the UHECR spectrum – the ankle and the flux suppression -, and we derive limits for anisotropy on different angular scales in the two energy regimes. In particular, full-sky coverage enables constraints on low-order multipole moments without assumptions about the strength of higher-order multipoles. Following previous efforts from the two Collaborations, we build full-sky maps accounting for the relative exposure of the arrays and differences in the energy normalizations. The procedure relies on cross-calibrating the UHECR fluxes reconstructed in the declination band around the celestial equator covered by both observatories. We present full-sky maps at energies above ~ 10 EeV and ~ 50 EeV, using the largest datasets shared across UHECR collaborations to date. We report on anisotropy searches exploiting full-sky coverage and discuss possible constraints on the distribution of UHECR sources.

The Atacama Cosmology Telescope: two-season ACTPol extragalactic point sources and their polarization properties

ABSTRACT We report on measurements of the polarization of extragalactic sources at 148 GHz made during the first two seasons of the Atacama Cosmology Telescope Polarization (ACTPol) survey. The survey covered 680 deg2 of the sky on the celestial equator. Polarization measurements of 169 intensity-selected sources brighter than 30 mJy, that are predominantly active galactic nuclei, are presented. Above a total flux of 215 mJy where the noise bias removal in the polarization measurement is reliable, we detect 26 sources, 14 of which have a detection of linear polarization at greater than 3σ significance. The distribution of the fractional polarization as a function of total source intensity is analysed. Our result is consistent with the scenario that the fractional polarization of our measured radio source population is independent of total intensity down to the limits of our measurements and well described by a Gaussian distribution with a mean fractional polarization pm = 0.028 ± 0.005 and standard deviation $\sigma _{\mathrm{p_{m}}}$ = 0.054, truncated at p = 0. Extrapolating this model for the distribution of source polarization below the ACTPol detection threshold, we predict that one could get a clean measure of the E-mode polarization power spectrum of the microwave background out to $\ell \approx 6000$ with 1 $\mu$K-arcminute maps over ${10\!{\ \rm \%}}$ of the sky from a future survey. We also study the spectral energy distribution of the total and polarized source flux densities by cross-matching with low radio frequency catalogues. We do not find any correlation between the spectral indices for total flux and polarized flux.

PERHITUNGAN DATA EPHEMERIS KOORDINAT MATAHARI MENGGUNAKAN ALGORITMA JEAN MEEUS HIGHER ACCURACY DAN KETERKAITANNYA DENGAN PENGEMBANGAN ILMU FALAK

Data of solar coordinate such as longitude and latitude of the ecliptic, declination, and right ascension are the data that are often involved in astronomical reckoning and practical islamic astronomy. These data are often found in ephemeris tables such as the ephemeris of Hisab Rukyat by Ministry of Religious Affairs of the Republic of Indonesia, Nautica Almanac and others. One of the algorithms used in the preparation of ephemeris data tables is the Jean Meeus Higher Accuracy algorithm. Calculation of ephemeris data of solar coordinates using these algorithms starts with counting Julian Day (JD) and Julian Day Ephemeris (JDE). By using advanced algorithms based on VSOP87 theory, we can then calculate the longitude and latitude of the solar ecliptic, the distance of the earth to the Sun, the true obliquity (angle between the celestial equator and the ecliptic), the right ascension and declination, the equation of time and the Sun's semi diameter. The calculation of the solar coordinate in this paper is for June 7, 2017 at 19.00 WIB or 12.00 GMT. The results will then be compared with the data of solar coordinate in Ephemeris Hisab Rukyat 2017 at the same time.