The project was to investigate the implications of the shape of the Sun upon the orbits of the planets in our solar system, and to expand the investigation to more general planetary systems.

Johannes Kepler found his three laws of planetary motion by studying the measurements of Mars, made by Tycho Brahe in the late 16th century. In the middle of the 19th century, the french physicist Urbain Le Verrier found that the perihelion of Mercury was in fact precessing with a rate of 42" per century. Perplexed physicists struggled to find an explanation of this phenomenon, until Albert Einstein could give an explanation using his general theory of relativity. However, it is possible that not the entire precession effect is explained by relativity, but by the shape of the Sun.

In the project, that spanned over 15 academic points, I investigated how sensitive the Tycho Brahe measurements were to the oblateness of the Sun.

Download © Andreas Johansson

**My masters thesis**

The project aims to investigates the properties of an accretion disk aound a neutron star. Millisecond pulsars have been studied that show a variation in the spin velocity and the torque excerted on star by the disk is thought to be able to explain this phenomenon. My tutor Ulf Torkelsson and a PhD-student of his, Solomon Tessema, has developed a model to describe a thin accretion disk around magnetised stars, using a kinetic dynamo. The velocity field that is needed to describe the dynamo is approximated with the Keplerian rotational velocity and turbulence according to the alpha description by Shakura and Sunyaev.

My first objective was to develope a general solution for the model for a stationary, since only special cases, when certain components of pressure and opacity could be neglected. The code I developed to solve the stationary disc solution is currently used by a collegue Addis Abeba.

The second step, which I am currently completing, is to investigate the properties of a time-dependent thin accretion after the same model. A code that can solve the disk in time has been developed in order to investigate how the dynamo is changing in time and if this model may explain the observed variations in spin.

The thesis is in completion now and will be availalbe soon.

**Matlab codes**

When I find myself with nothing to do, I like to write matlab codes with questionable usefulness. Some of the codes are listed below. Most of them are not tidied up enough to be displayed in public...

A function to plot the time of sunrise and sundown w.r.t. latitude

A code to plot the equipotential lines of the Roche potential

**Riddles**

Who owns the zebra and who drinks water?

**Useful links**

The Great, Big List of LaTeX Symbols

Stellarium, an open source planetarium for your computer.

Aktuellt på natthimlen at Populär astronomi (swedish)

Die Grundlage der allgemeinen Relativitätstheorie; von A. Einstein