The Celestial Frame and the Weighting of the Celestial Pole Offsets in the Computation of VLBI-Based Corrections for the Main Lunisolar Nutation Terms

Very long baseline interferometry (VLBI) is the only technique in space geodesy that can determine directly the celestial pole offsets (CPO). In this paper, we make use of the CPO derived from global VLBI solutions to estimate empirical corrections to the main lunisolar nutation terms included in the IAU 2006/2000A precession–nutation model. In particular, we pay attention to two factors that affect the estimation of such corrections: the celestial reference frame used in the production of the global VLBI solutions and the stochastic model employed in the least-squares adjustment of the corrections. In both cases, we have found that the choice of these aspects has an effect of a few μas in the estimated corrections.

Towards Understanding the Interconnection between Celestial Pole Motion and Earth’s Magnetic Field Using Space Geodetic Techniques

The understanding of forced temporal variations in celestial pole motion (CPM) could bring us significantly closer to meeting the accuracy goals pursued by the Global Geodetic Observing System (GGOS) of the International Association of Geodesy (IAG), i.e., 1 mm accuracy and 0.1 mm/year stability on global scales in terms of the Earth orientation parameters. Besides astronomical forcing, CPM excitation depends on the processes in the fluid core and the core–mantle boundary. The same processes are responsible for the variations in the geomagnetic field (GMF). Several investigations were conducted during the last decade to find a possible interconnection of GMF changes with the length of day (LOD) variations. However, less attention was paid to the interdependence of the GMF changes and the CPM variations. This study uses the celestial pole offsets (CPO) time series obtained from very long baseline interferometry (VLBI) observations and data such as spherical harmonic coefficients, geomagnetic jerk, and magnetic field dipole moment from a state-of-the-art geomagnetic field model to explore the correlation between them. In this study, we use wavelet coherence analysis to compute the correspondence between the two non-stationary time series in the time–frequency domain. Our preliminary results reveal interesting common features in the CPM and GMF variations, which show the potential to improve the understanding of the GMF’s contribution to the Earth’s rotation. Special attention is given to the corresponding signal between FCN and GMF and potential time lags between geomagnetic jerks and rotational variations.

A First Assessment of the interconnection between celestial pole offset and geomagnetic field variations

<p>The Global Geodetic Observing System (GGOS) of the International Association of Geodesy (IAG) provides the geodetic infrastructure needed to monitor the Earth system.. The understanding of forced temporal variations of celestial pole motion (CPM) could bring us significantly closer to meeting the GGOS goals (i.e. 1 mm accuracy and 0.1 mm/year stability on global scales in terms of the ITRF defining parameters). Besides astronomical forcing, CPM excitation depends on the processes in the fluid core and the core-mantle boundary. The same processes are responsible for the variations of the geomagnetic field (GMF). This study investigates the interconnection between the celestial pole offset (CPO) and effective geophysical processes that contribute to the Earth's rotational variation. We use the CPO time series obtained from very long baseline interferometry (VLBI) observations together with the latest GMF data such as geomagnetic jerk and magnetic dipole moment, and a state-of-the-art geomagnetic field model to explore the correlation between CPM and GMF. <br>Our results confirm the findings of previous studies, revealing that  substantial free core nutation (FCN) disturbance occurred at the epochs close to the GMJ events. The results also reveal some common features in the FCN and GMF variation, which show the potential to improve knowledge regarding the GMF's contribution to the Earth's rotation.</p>

Analysis of the Alignment of Non-Random Patterns of Spin Directions in Populations of Spiral Galaxies

Observations of non-random distribution of galaxies with opposite spin directions have recently attracted considerable attention. Here, a method for identifying cosine-dependence in a dataset of galaxies annotated by their spin directions is described in the light of different aspects that can impact the statistical analysis of the data. These aspects include the presence of duplicate objects in a dataset, errors in the galaxy annotation process, and non-random distribution of the asymmetry that does not necessarily form a dipole or quadrupole axes. The results show that duplicate objects in the dataset can artificially increase the likelihood of cosine dependence detected in the data, but a very high number of duplicate objects is required to lead to a false detection of an axis. Inaccuracy in galaxy annotations has relatively minor impact on the identification of cosine dependence when the error is randomly distributed between clockwise and counterclockwise galaxies. However, when the error is not random, even a small bias of 1% leads to a statistically significant cosine dependence that peaks at the celestial pole. Experiments with artificial datasets in which the distribution was not random showed strong cosine dependence even when the data did not form a full dipole axis alignment. The analysis when using the unmodified data shows asymmetry profile similar to the profile shown in multiple previous studies using several different telescopes.

Lycurgus, the Celestial Patron of Sparta

The ancient authors knew nothing certain about Spartan lawgiver Lycurgus save that he lost his eye (allegedly because of the opposition to his reforms). This small detail provides the best indication to the original character of Lycurgus. Greek, Indian, Iranian and other texts repeatedly mention the eye of a highest god, and there were Sumerian precedents for that. The idea of the eye of god was initially connected with the notion of the celestial pole and its symbolic representation. An important and characteristic function of the all-seeing Eye was to oversee justice and right order, just as ‘the eye of Zeus’ does in Hes. Op. 267. Spartan one-eyed Lycurgus was a god of that type. Conscious efforts of fifth century’s Spartan politicians who were able to influence contemporary poets and writers turned Lycurgus into a lawgiver of a kind of Athenian Solon.

Analyses of celestial pole offsets with VLBI, LLR, and optical observations

Aims. This work aims to explore the possibilities of determining the long-period part of the precession-nutation of the Earth with techniques other than very long baseline interferometry (VLBI). Lunar laser ranging (LLR) is chosen for its relatively high accuracy and long period. Results of previous studies could be updated using the latest data with generally higher quality, which would also add ten years to the total time span. Historical optical data are also analyzed for their rather long time-coverage to determine whether it is possible to improve the current Earth precession-nutation model. Methods. Celestial pole offsets (CPO) series were obtained from LLR and optical observations and were analyzed separately by weighted least-square fits of three empirical models, including a quadratic model, a linear term plus an 18.6-year nutation term, and a linear term plus two nutation terms with 18.6-year and 9.3-year periods. Joint analyses of VLBI and LLR data is also presented for further discussion. Results. We improved th determination of the nutation terms with both VLBI and LLR data. The VLBI data present a most reliable feature of the CPO series with the highest accuracy, and they are most important for determining the precession-nutation of the Earth. The standard errors of CPO obtained from the LLR technique have reached a level of several tens of microarcseconds after 2007, but they are probably underestimated because the models used in the calculation procedure are not perfect. Nevertheless, the poor time resolution of LLR CPO series is also a disadvantage. However, this indicates that LLR has the potential to determine celestial pole offsets with a comparably high accuracy with VLBI in the future and to serve as an independent check for the VLBI results. The current situation of LLR observations is also analyzed to provide suggestions of future improvement. The typical standard error of CPO series from historic optical observations is about two hundred times larger than that of the VLBI series and can therefore hardly contribute to the contemporary precession-nutation theory.

The C-Band All-Sky Survey (C-BASS): constraining diffuse Galactic radio emission in the North Celestial Pole region

ABSTRACT The C-Band All-Sky Survey (C-BASS) is a high sensitivity all-sky radio survey at an angular resolution of 45 arcmin and a frequency of 4.7 GHz. We present a total intensity map of the North Celestial Pole (NCP) region of sky, above declination >+80°, which is limited by source confusion at a level of ≈0.6 mK rms. We apply the template-fitting (cross-correlation) technique to WMAP and Planck data, using the C-BASS map as the synchrotron template, to investigate the contribution of diffuse foreground emission at frequencies ∼20–40 GHz. We quantify the anomalous microwave emission (AME) that is correlated with far-infrared dust emission. The AME amplitude does not change significantly (${\lt }10\, {{\ \rm per\ cent}}$) when using the higher frequency C-BASS 4.7 GHz template instead of the traditional Haslam 408 MHz map as a tracer of synchrotron radiation. We measure template coefficients of 9.93 ± 0.35 and $9.52\pm 0.34\,$ K per unit τ353 when using the Haslam and C-BASS synchrotron templates, respectively. The AME contributes $55\pm 2\, \mu$K rms at 22.8 GHz and accounts for ${\approx } 60{{\ \rm per\ cent}}$ of the total foreground emission. Our results show that a harder (flatter spectrum) component of synchrotron emission is not dominant at frequencies ≳5 GHz; the best-fitting synchrotron temperature spectral index is β = −2.91 ± 0.04 from 4.7 to 22.8 GHz and β = −2.85 ± 0.14 from 22.8 to 44.1 GHz. Free–free emission is weak, contributing ${\approx } 7\, \mu$K rms (${\approx } 7{{\ \rm per\ cent}}$) at 22.8 GHz. The best explanation for the AME is still electric dipole emission from small spinning dust grains.

Tritogeneia, Poseidon’s Trident and Early Sacred Trinity

The name Tritogeneia likely means ‘born of the Third’, this Third one being the supreme god, the Most High. Poseidon (at least Poseidon Helikonios) was once such a god. He was the lord of the water that descended from heaven and a deity closely associated with the celestial pole. His trident is the symbol that indicates his celestial nature, and this symbol developed from a previous one – a raised hand with three fingers. This number of fingers signified the similarity with the dwellers of the sky – the birds, with their three toes in front.