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Browsing by department "Tähtitieteen laitos"

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  • Asteroid identification at discovery 
    Granvik, Mikael (Helsingin yliopistoUniversity of HelsinkiHelsingfors universitet, 2003)
  • Asteroid lightcurve inversion : methods for obtaining a unique and stable shape solution 
    Torppa, Johanna (Helsingin yliopistoUniversity of HelsinkiHelsingfors universitet, 1999)
  • Rayleigh-testi periodisuudesta : muinaisegyptiläinen ennustuskalenteri sarjana aikapisteitä 
    Porceddu, Sebastian (Helsingin yliopistoUniversity of HelsinkiHelsingfors universitet, 2007)
    This study presents an analysis of the calendars of lucky and unlucky days by the application of the Rayleigh Test. In these ancient Egyptian texts each day of the year is assigned a so-called prognosis, which can be 'good' or 'bad' for each part of the day. The purpose of the analysis is to find out, whether the lucky and unlucky days were randomly or periodically distributed within the year. The period of 29.5 days found in the prognoses with a considerably high significance, represents the effect of the synodic month to the calendars. The found periods of 7.5 and 30 days suggest that the ancient Egyptian civil calendar also had influence on determining the prognoses. Other significant periods are also found in the time series, possibly based on a numerological meaning. The period of 2.85 is possibly a sign of an ancient Egyptian observation of the star Algol, which is one of the best known eclipsing variable stars. If this were the case, it could be the oldest known determination of the period of a variable star in history.
  • What kind of data would ascertain real periodicity in the terrestrial impact crater record 
    Lyytinen, Joonas (Helsingin yliopistoUniversity of HelsinkiHelsingfors universitet, 2008)
    The possible presence of periodicity in the terrestrial impact crater data has been discussed in several papers since 1984. The authenticity of this detected periodicity data is controversial. It is possible, however, that real periodicity is present and could be detected from more accurate and complete data. In our study we created simulated different probability distributions for terrestrial impact crater record, that covered completely aperiodic and periodic impact cratering scenarios, as well as two specific combinations of these two cases, with four different impact crater age uncertainties. From these distributions we then generated simulated time series of impact craters with different numbers of craters and tested if the periodicity in the distribution could be detected using the Rayleigh method. Our analysis shows that if only one third of the terrestrial impact craters are caused by periodic cratering events, the detection of a real period in the data is very difficult and probably could not be detected even if better impact crater data became available. If two thirds of the craters are caused by periodic impacts, detection is possible, but would require substantially better data than which is currently available. We conclude that the periodicities reported so far in the impact crater data are not caused by real physical phenomena.

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