UFO widely seen in Middle East skies, linked to Russian missile test has an update from James Oberg, explaining that the spiral does not indicate a failed launch, but is a deliberate feature needed for the trajectory the Russians wanted.
Alessandra Celletti and Ettore Perozzi, Celestial Mechanics: The Waltz of the Planets. This is a semi-popular look at one of my old and persistent interests. Very little math, but a lot of graphs and terminology. It includes the traditional subjects, e.g. tidal forces, the discovery of Neptune, Delaunay’s lunar theory, and the stability of the solar system. but the emphasis is on modern developments, e.g.
- Modern dynamical systems theory and chaotic motion.
- Trojan satellites and Lagrange Points–L1 can actually be useful, even though it is unstable.
- Artificial satellites and space travel, including Hohmann transfer orbits.
- Planetary ring systems.
- The Kuiper belt, the outer solar system, and the demotion of Pluto from planetary status (correct, IMHO).
- Planets around other stars.
A unifying theme is the importance of resonant orbits. For example, Neptune makes three orbits around the Sun in about the same number of years as Pluto makes two. This is not a coincidence.
Recommended for those with some general knowledge of astronomy.