About 70 years ago “André Danjon” a French astrophysicist showed that as elongation of the moon decreases the arc length of
crescent gets less too. By studying the recent observational data, he concluded that at 7 degree elongation, the length of
arc (cusp to cusp) will reach zero degree. Today, this value is named as Danjon limit, which points to the limit at which
the moon crescent is formed. Danjon believed that the effective factor for occurring this limit was the shadows of moon’s
mountains. Later researchers have obtained different values for this limit. In this research based on the new data, the decreasing
dependence of length of arc versus elongation was obtained. The results show that the Danjon limit is about 5 degrees. The
effective factors to form the Danjon limit are then given and discussed. By considering the effects of astronomical seeing
and shadows of lunar features, the values of the arc length were calculated and compared with the observational data curve.
The results of this study show good agreement with the observational data. The present research shows that the above-mentioned
effects can reduce the length of arc. The effect of libration and roughness of the lunar terrain of the moon in forming the
moon crescent were also considered, and the possibility of observing thinner crescents by photometric model and breaking the
Danjon limit were given. 相似文献
Hydrology cycle of river basins and available water resources in arid and semi-arid regions are highly affected by climate changes. In recent years, the increment of temperature due to excessive increased emission of greenhouse gases has led to an abnormality in the climate system of the earth. The main objective of this study is to survey the future climate changes in one of the biggest mountainous watersheds in northeast of Iran (i.e., Kashafrood). In this research, by considering the precipitation and temperature as two important climatic parameters in watersheds, 14 models evolved in the general circulation models (GCMs) of the newest generation in the Coupled Model Intercomparison Project Phase 5 (CMIP5) were used to forecast the future climate changes in the study area. For the historical period of 1992–2005, four evaluation criteria including Nash–Sutcliffe (NS), percent of bias (PBIAS), coefficient of determination (R2) and the ratio of the root-mean-square-error to the standard deviation of measured data (RSR) were used to compare the simulated observed data for assessing goodness-of-fit of the models. In the primary results, four climate models namely GFDL-ESM2G, IPSL-CM5A-MR, MIROC-ESM, and NorESM1-M were selected among the abovementioned 14 models due to their more prediction accuracies to the investigated evaluation criteria. Thereafter, climate changes of the future periods (near-century, 2006–2037; mid-century, 2037–2070; and late-century, 2070–2100) were investigated and compared by four representative concentration pathways (RCPs) of new emission scenarios of RCP2.6, RCP4.5, RCP6.0, and RCP8.5. In order to assess the trend of annual and seasonal changes of climatic components, Mann–Kendall non-parametric test (MK) was also employed. The results of Mann–Kendall test revealed that the precipitation has significant variable trends of both positive and negative alterations. Furthermore, the mean, maximum, and minimum temperature values had significant positive trends at 90, 99, and 99.9 % confidence level. On the other hand, in all parts of the Kashafrood Watershed (KW), the average temperature of watershed will be increased up to 0.56–3.3 °C and the mean precipitation will be decreased up to 10.7 % by the end of the twenty-first century comparing to the historical baselines. Also, in seasonal scale, the maximum and minimum precipitations will occur in spring and summer, respectively, and the mean temperature is higher than the historical baseline in all seasons. The maximum and minimum values of the mean temperature will occur in summer and winter, respectively, and the amount of seasonal precipitation in these seasons will be reduced.
Participatory mapping approaches have raised increasing interest in a variety of fields of research and practice during the past two decades. However, their use in modeling and studying individual mobility and activity spaces is rather recent and limited. This paper focuses on the use of public participation GIS (PPGIS) data in activity space modeling and analysis and aims to draw more scholarly attention to the existing research potentials in this area. While reviewing the pros of using PPGIS for activity space studies, this paper also discusses the existing limitations and outlines how they can be addressed in future research. PPGIS effectively enables collecting data from larger samples, making it possible to conduct more comprehensive geospatial and statistical analyses on the data. Additionally, the strong link between individuals and places in PPGIS data facilitates more person-based approaches in investigating person-environment relationships. However, use of PPGIS for activity space studies comes with analytical and data quality challenges that need to be thoroughly taken into consideration. Particularly, future research needs to seek new ways of including the temporal dimension in PPGIS and find new methods of using the data for activity space modeling and analysis.
Theoretical and Applied Climatology - This study examined the effect of different attributes on regionalization of potential evapotranspiration (ETp) in Urmia Lake Basin (ULB), Iran, using the... 相似文献
Researchers for long have hypothesized relationships between mobility, urban context, and health. Despite the ample amount of discussions, the empirical findings corroborating such associations remain to be marginal in the literature. It is growingly believed that the weakness of the observed associations can be largely explained by the common misspecification of the geographical context. Researchers coming from different fields have developed a wide range of methods for estimating the extents of these geographical contexts. In this article, we argue that no single approach yet has sufficiently been capable of capturing the complexity of human mobility patterns. Subsequently, we discuss that reaching a better understanding of individual activity spaces can be possible through a spatially sensitive estimation of place exposure. Following this discussion, we take an integrative person and place-based approach to create an individualized residential exposure model (IREM) to estimate the local activity spaces (LAS) of the individuals. This model is created using data collected through public participation GIS. Following a brief comparison of IREM with other commonly used LAS models, the article continues by presenting an empirical study of aging citizens in Helsinki area to demonstrate the usability of the proposed framework. In this study, we identify the main dimensions of LASs and seek their associations with socio-demographic characteristics of individuals and their location in the region. The promising results from comparisons and the interesting findings from the empirical part suggest both a methodological and conceptual improvement in capturing the complexity of local activity spaces. 相似文献
BV photometry of close binary star AB And in two observational seasons have been presented. Updated O-C diagram analysis by Kalimeris method yielded the values of 0.0188 day and 0.0065 day as amplitudes of orbital period modulation with Pmod1～61 yr and Pmod2～34 yr as the modulation periodicities. Light curve analysis was carried out by W-D method and geometric and physical parameters of the components. Finally, the consequences of period changes have been discussed on the basis of light-time effect due to third body in the system and Applegate mechanism. 相似文献
