1,721,096 research outputs found

    Analysis of the fraction of clear sky at the La Palma and Mt Graham sites

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    The amount of available telescope time is one of the most important requirements when selecting astronomical sites, as it affects the performance of ground-based telescopes. We present a quantitative survey of cloud coverage at La Palma and Mt Graham using both ground- and satellite-based data. The aim of this work is to derive clear nights for the satellite infrared channels and to verify the results using ground-based observations. At La Palma, we found a mean percentage of clear nights of 62.6 per cent from ground-based data and 71.9 per cent from satellite-based data. Taking into account the fraction of common nights, we found a concordance of 80.7 per cent of clear nights for ground- and satellite-based data. At Mt Graham, we found a 97 per cent agreement between the Columbine heliograph and the night-time observing log. From the Columbine heliograph and the Total Ozone Mapping Spectrometer-Ozone Monitoring Instrument (TOMS-OMI) satellite, we found that about 45 per cent of nights were clear, while satellite data (GOES, TOMS) are much more dispersed than those of La Palma. Setting a statistical threshold, we retried a comparable seasonal trend between the heliograph and satellite

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    “A WARNING FROM MARS”. Climate risk assessment in the Museo della Specola

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    Museum microclimate plays a key role in the conservation of scientific instruments on display. Finding appropriate values of temperature and relative humidity to guarantee the entire collections safeguard is a difficult task. Each object responses peculiarly to the environment depending on its composition, conservative history, and adaptations to the environment variability over years. Sometimes, the different materials coexisting in a scientific instrument may develop pathologies not yet fully known. The question becomes even more challenging if one considers that microclimate management is not easy, especially in buildings not originally designed for conservation purposes.The Museo della Specola in Palermo has recently face these critical issues. The museum is in the ancient Observatory, built in 1790, on the top of the 12ndcentury Royal Palace. Although efforts have been made to protect the collection over the years, there is still much to be done. An exhibited object had clearly evidenced that the environmental conditions need to be urgently improved. It is a 19th-century painted wooden globe reproducing the surface of Mars: in less than two years, damages of its pictorial layers occurred at a slow but progressive rate. Conservation measures have been adopted to stop the serious deteriorating processes, but the risk of further deterioration phenomena involving other objects is expected to increase substantially if no actions are taken. This contribution intends to present the results of the preliminary study concerning the thermo-hygrometric records taken in the museum over recent years to control the environmental conditions and assess if the collection is exposed to microclimate risks. Specific actions to improve climate conditions will be proposed
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