Orbital Properties of the Solar System

The positions of the Inner planets on June 14, 2002

Orbital Properites of the Solar System

Summary From Before:

Overview of Solar System Orbits:

The problem of the orbit of Mercury Einstein to the rescue:

Moving Towards General Relativity

In the late 19th century, precision observations of the position of Mercury showed that it did not agree with the predictions from Newtonian theory

This is similar to the case of Mars, where Kepler used positional discrepancies to show that planetary orbits had to be elliptical in shape.

The resolution of the positional discrepancy of Mercury requires that space be "curved" in the vicinity of Mercury so that Mercury orbits inside this curvature. Such an orbit will differ slightly from an orbit in purely flat space.

Newton had implicitly assumed that space was flat.

General Theory of Relativity

Space communicates with matter and instructs it how to move and, in turn, matter communicates with space and instructs it how to curve.

Mercury orbits in Curved Space because it is a near a very large mass (the Sun).

The Visibility of the Planets:

Depends on the the planet-earth-sun angle. For the Outer Planets:

  • When this angle is 180 degrees , planet is overhead at midnight
  • When this angle is 0 degrees , the planet is up in the day time
  • When this angle is 90 degrees the planet is overhead at sunset
  • When this angle is 270 degrees the planet is overhead at sunrise

    For the Inner Planets the situation is much different as they are always relatively near the Sun. There is a time in the orbit of Mercury and Venus called greatest elongation in which Venus appears at its maximum angular separation from the Sun. This is illustrated below. Note that since there are 15 degrees in one hour of time, then the angle of 46 degrees shown below corresponds to about 3 hours of time. When Venus is at the position in its orbit shown below, it will appear in the sky either 3 hours before or after sunrise. At any other position in its orbit, Venus will appear closer in time and angular separation to the sun.

    For further experimentation please us Real Examples from the System Orbital Simulator