Despite all the new data, the nature of planetary rings is stíII
controversial. We don't know why each planetary ring is so different from the others and we have no idea of the nature of a single partícle ring, The large number of structures observed in planetary rings seems to indicate that many different physícal mechanisms are simultaneously at work. We are not yet able to include all of them in a single model. Resonances with nearby satellites play an ímportant role, but through complex mechanisms. Appropriate observations and more sophísticated models are needed to improve our understanding of rings and to identify the main physícal mechanisms involved.
Kosmické aktivity mají v Česku dlouhou tradici od samého počátku kosmického vědeckého výzkumu, kdy bylo tehdejší Československo zapojeno do projektů Interkosmos a Magion. Od roku 2008 je Česká republika členskou zemí Evropské kosmické agentury ESA. Toto členství umožňuje českým vědcům a inženýrům zapojovat se do technologicky nejšpičkovějších kosmických projektů. Tento článek je stručným přehledem hlavních vědeckých projektů ESA, do kterých je Česká republika zapojená. and Jiří Svoboda, Ondřej Santolík, Ivana Kolmašová, Jan Souček, Petr Heinzel.
Radial velocities of H2 - H9 abd Ca II K lines on 27 high dispersion (0.27 nm/mm) spectrograms of the HgMn-star Alpha Andromedae were measured, While radial velocities of Balmer lines show no significant changes, radial velocities of Ca II K line vary in the limits from 5 to 13 km/s. A frequency analysis of the Ca II K RV values leads to two different frequencies of 27.86 and 35.20 c/d. Their superposition results is a 196 min beat-phenomenon period. Halfwidth of the calcium line varies in the way which could be explained by nonradial oscillations.
The formation of giant regions of star formation by gravitational instabilities in spiral arms ard discussed, The importance of the spiral arms strength for triggering new star formation is emphasized.