We present a way of handling and interpreting stellar proper motions, in which the idea of substituting them by great circles, proposed by Herschel in 1783, allows us to take the entire celestial sphere as a field of application, making possible the study of dense and extensive stellar zones. A suitable mathematical processing of data together with

We obtained deep optical imaging of the Alpha Per open cluster using the KPNO 4-m CCD mosaic camera, MOSA, on November 19-22 1998. All of the images were obtained with the facility R and I filters. In addition to the KPNO/MOSA observations, we undertook several infrared observing campaigns at the Hispano-German Calar Alto Observatory in order to

The optical design for the proposed Euro50 extremely large telescope with integrated adaptive optics (AO) is presented. For atmospheric turbulence correction, we propose using single and dual-conjugate AO systems working with natural and laser guide stars. The corrective shape of the deformable mirrors (DMs) is derived from an analytical algorithm

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