Solar Simulator 2
Carsten A. Arnholm, 20. October, 2008
The sun has an orbit!
Most people think the Sun rests at the centre of the solar system, and that the planets orbit it. This is almost correct, but not quite.
In reality, the Sun has an orbit like the planets. Both the Sun and the planets orbit the solar system's centre of mass (often referred to as the Barycentre). If you observe the solar system from far above the ecliptic plane (as in the
you may see the Sun wobble around a bit, it does not stand still at the centre of the solar system. What you see is the Sun's orbital movements, it is surprisingly complex.
The wobbling is due to the gravitational effects of the planets. Gravity works both ways: The Sun has a (large) effect on the planets, and the planets have a (relatively small) effect on the Sun. This is actually one of the ways one can detect planets around other stars, because a distant star wobbles in a similar manner if it has planets large enough orbiting it.
Ok, so how does the Sun move?
The complexity of the solar orbit is illustrated in the original Solar Orbit Simulator. As it is shown there, the Sun can wander up to ~2.2 solar radii away from the barycentre. The orbit has interesting periodicities which appear to be in synchronicity with, and maybe even have some effect on solar activity. This remains to be proven, though.
The original simulator used a Heliocentric view where the Sun was stationary and the barycentre moved in the view. It is perhaps more realistic to present things as they are perceived by an observer looking in a fixed direction. That is achieved by using a barycentric coordinate system, where the barycentre is at the centre of the view and the Sun moves around it. This is directly equivalent to the example with an observer far above the ecliptic plane.
The current simulator also introduces some features not seen on the original simulator:
- First, it allows the viewer to understand the gravitational effects better by adding pointers from the Sun to the actual positions of the planets. The lines drawn illustrate the direction of gravity between a pair of objects: The Sun and a planet. It is apparent that the giant gas planets Jupiter, Saturn, Uranus and Neptune are the most important in infuencing the Sun's orbit. But the other planets have some effect too.
- Second, the simulator can present information about solar activity in the form of Solar H-alpha Flares, as
ground based observations 1938-1979, and by the GOES satellite 1980-2008. The purpose of this feature is to investigate possible correlations with other phenomena. Obviously, the solar flares are correlated with the location of the Earth, since the solar flare data are observed from the GOES satellite, orbiting the Earth. The flares are drawn big for big events like the the 03 November 2003 X20+ flare, and small for small events. The red flares are north of the Solar equator, the blue ones are in the south. The actual time periods for flare visibility may be exaggerated by the user, since such events are very short lived (minutes) compared to the simulator time step (days). It is also possible to slow down simulation speed for high accuracy.
Third, the simulator can visualise the varying gravitational acceleration on the Sun, performed by the planet. It is shown that
the acceleration direction largely follows Jupiter, with some variation. The actual size of the gravitational force at any time is illustrated through the length of the acceleration vector.
The "Solar Simulator 2" program calculates solar system orbits based on the
theory presented in Astronomical Algorithms by Jean Meeus. The planetary
position algorithms in the book are implemented in the AA+ library by P.J. Naughter. Based on the planetary position data as well as solar and planetary masses, the solar system centre of mass is computed.
Solar Simulator 2 builds on the original Solar Simulator. The Solar flares idea came from Hugo Mildenberger, who also kindly provided a C++ library for reading the
H-alpha flares data. Hugos library was used to convert the original GOES files to a simpler format used in the simulator.