# Celestial Mechanics

Celestial mechanics is a branch of mathematics and astronomy that deals with the motions of celestial objects. The field applies principles of physics, gravitation, historically classical mechanics, to astronomical objects such as stars and planets to produce ephemeris data. Orbital mechanics (astrodynamics) is a subfield which focuses on the orbits of artificial satellites. Lunar theory is another subfield focusing on the orbit of the Moon.

For our latest developments/activities in this area, please see the listing at the end of this article.

Modern analytic celestial mechanics started over 300 years ago with Isaac Newton's Principia of 1687. The name "celestial mechanics" is more recent than that. Newton wrote that the field should be called "rational mechanics." The term "dynamics" came in a little later with Gottfried Leibniz, and over a century after Newton, Pierre-Simon Laplace introduced the term "celestial mechanics." Prior to Kepler there was little connection between exact, quantitative prediction of planetary positions, using geometrical or arithmetical techniques, and contemporary discussions of the physical causes of the planets' motion.

**Solar system dynamics**

The gravity force acting over eons has provided the solar system with an intricate dynamical structure, much of it revealed by recent space missions. Mathematical tools and physical models are needed for a complete understanding of the subject.

This is a multi-disciplinary subject that combines expertises from Geophysics, Dynamical Systems, and Numerical Simulations. We study the geophysical effects that modify the spin and the orbits of planets and satellites, in particular tidal effects and core-mantle friction.

See here a movie made by the NASA Science "Understanding orbits and Kepler's laws", for a brief historical review on the dynamics of the solar system.

## Latest Celestial Mechanics News & Events

## COST Workshop - "Exoplanets in the era of Gaia"

## 100 years of light bending

On May 29th 1919 Eddington and Cottingham measured the position of stars near the sun during a total eclipse observed at the island of Príncipe, off the west African coast. Their results, together with the ones of another expedition undertaken by Crommelin and Davidson to Sobral (Brazil), were announced on November 6th 1919 and confirmed the General Theory of Relativity. This openned a new era in our understanding of gravity, space, time and matter... and made Einstein world famous.

## Visit to University of Concepcion in Chile

Gr@v member Tjarda Boekholt recently travelled to the University of Concepcion in Chile. He was invited by the Theory and Starformation Group (TSG), which is led by a team of professors including Mike Fellhauer, Dominik Schleicher, Amelia Stutz and Stefano Bovino. In the first week Tjarda lectured students on the Astrophysical Multi-purpose Software Environment (AMUSE). In particular, they discussed the coupling between N-body and hydrodynamics.

## Tjarda Boekholt wins CIDMA Young Doctor Award

The CIDMA Young Doctor Award is a prize for a researcher within 5 years after the PhD, who has made important contributions to his or her research field. The 2018 award is granted to Gr@v member Tjarda Boekholt for his recent achievements in the field of dynamical chaos in astronomical systems. During the annual meeting of CIDMA 2018, Tjarda presented his new numerical N-body code and the ability to obtain reversible solutions to highly chaotic systems.