Investigating factors affecting students’ performance to PISA Science items

The present paper aims to investigate, on the one hand, the extent to which PISA Science items validly assess the knowledge and skills of 15 year-old Greek students, while, on the other hand, to examine the effect of the following factors: student’s gender, scientific processes and contexts (situations) on the students’ performance in these PISA items. The research used paper-and-pencil test with published PISA Science items, conducted individual semi-structured interviews with 15 year-old students and finally marked the students’ responses, according to the PISA marking guide. Τhe basic finding resulting from the data analysis is that the paper-and-pencil test with the PISA Science items does not tend, unlike the interview, to effectively record the Greek students’ Science knowledge and skills. Moreover, the analysis revealed that the performance of students in the PISA Science items (paper-and-pencil test and interview) tend to be independent of the student’s gender and depend on the context in which the knowledge and processes are assessed. Additionally, the possible correlation between the students’ performance and the factor of scientific processes seems to depend on the setting in which the students provide their responses (paper-and-pencil test or interview)

Observational detection of eight mutual eclipses and occultations between the satellites of Uranus

We carried out observations, with five different instruments ranging in aperture from 0.4m to 10m, of the satellites of Uranus during that planet's 2007 Equinox. Our observations covered specific intervals of time when mutual eclipses and occultations were predicted. The observations were carried out in the near-infrared part of the spectrum to mitigate the glare from the planet. Frames were acquired at rates > 1/min. Following modelling and subtraction of the planetary source from these frames, differential aperture photometry was carried out on the satellite pairs involved in the predicted events. In all cases but one, nearby bright satellites were used as reference sources. We have obtained fifteen individual lightcurves, eight of which show a clear drop in the flux from the satellite pair, indicating that a mutual event took place. Three of these involve the faint satellite Miranda. All eight lightcurves were model-fitted to yield best estimates of the time of maximum flux drop and the impact parameter. In three cases best-fit albedo ratios were also derived. We used these estimates to generate intersatellite astrometric positions with typical formal uncertainties of <0.01 arcsec, several times better than conventional astrometry of these satellites. The statistics of our estimated event midtimes show a systematic lag, with the observations later than predictions. In addition, lightcurves of two partial eclipses of Miranda show no statistically significant evidence of a light drop, at variance with the predictions. These indicate that new information about the Uranian satellite system is contained in observations of mutual events acquired here and by other groups.Comment: 8 pages, 3 figures, accepted for publication in Astronomy and Astrophysics Uses aa style packag