The goal of this work is two-fold. In the first part of this paper we regard classical Plebanski's action as a BF action supplemented by constraints. We introduce a spin foam model for Riemannian general relativity by systematically implementing these constraints as restrictions on paths in the state-sum of the BF theory. The spin foam model

Amateur astronomers have always represented an important observing group in cometary astronomy. Much of our knowledge of cometary light curves has come from amateur data, initially in the form of total visual magnitude estimates and now increasingly in the form of CCD observations. The increasingly widespread use by amateur astronomers of CCD

We have observed the spectrum of Procyon A (F5 IV) from 4559 to 5780 Å with a signal-to-noise ratio of ~103 and a resolving power of 2×105. We have measured the line bisectors and relative line shifts of a large number of Fe I and Fe II lines, comparing them to those found in the solar spectrum. A three-dimensional hydrodynamical model atmosphere

Within the framework of the European Space Agency (ESA) SILEX project, aimed at experimentally demonstrating the feasibility of inter-satellite optical communications links, an Optical Ground Station (OGS) has been built by ESA in the premises of the Instituto de Astrofisica de Canarias (IAC, Institute of Astrophysics of the Canary Islands)

For a complete understanding of the physical processes causing the photometric variability of pre-main sequence systems, simultaneous optical and near-IR observations are required to disentangle the emission from the stars and that from their associated circumstellar disks. Data of this sort are extremely rare and little systematic work has been

The nucleus of 51P/Harrington suffered a major splitting event in Autumn 2001 discovered by amateur José Manteca. The light curve and separation of the fragments is examined based on data from the observers collaborating in the Spanish language ``Cometas_Obs'' mailing list, including a number of pre-announcement observations. There is some