Solar and Lunar Eclipses

General Description

This simulation models the occurrences of solar and lunar eclipses. Moon's orbital inclination of 5.145 degrees with respect to the ecliptic (the Earth-Sun orbital plane) is what is responsible for solar and lunar eclipses not occurring every month. In addition, the orbital plane of Moon precesses every 8.85 years, the so-called precession of the apsides. The inclination, precession, and the motion of Moon and Earth are depicted (the size of Sun, Earth, and Moon and the size of Moon's orbit are not shown to scale). The illuminated sides of Earth and Moon and the regions of possible eclipses (in orange and red) are also depicted. In the Sky View, the motion of Sun and Moon across the sky (+/- 7 degrees from the ecliptic) are shown. Moon's phase is shown and solar and lunar eclipses can occur on the ecliptic when Earth, Sun, and Moon line up properly.

Additional simulations can be found on the OSP ComPADRE site.

Displays

• Display Options
  • Trace Sun shows and hides the Sun's path in the Sky View.
  • Trace Moon shows and hides the Moon's path in the Sky View.
  • Ecliptic shows and hides the ecliptic plane and Moon orbit plane in the 3D View.
  • Extra Options displays extra controls to change the visualisation and to adjust the tilt of Moon's orbit.
• Extra Options
  • Fill Ecliptic fills the ecliptic plane in the 3D View.
  • Stars shows and hides the background stars in the Sky View.
  • Labels shows and hides labels in the Sky View.
  • Moon Incline shows the moon inline slider to change the orbital incline of Moon.
• Sky View
  • Yellow circle: Sun.
  • White dots: stars. The simulation shows the 300 brightest stars, with positions taken from the Bright Star Catalog.
  • Green trail: Path of Moon as seen from Earth.
  • Blue trail: Path of Sun (the Ecliptic) as seen from Earth.
• 3D View
  • Yellow circle: Sun.
  • Blue polar grid: Earth orbit plane.
  • White polar grid: Moon orbit plane.
  • Yellow arrow: Line of sight from Earth to Sun.
  • Green arrow: Line of sight from Earth to Moon.
  • Orange rays: Arc where a partial eclipse can occur at 5.145 degrees moon-orbit tilt.
  • Red rays: Arc where a total eclipse can occur at 5.145 degrees moon-orbit tilt.

Controls

• Play/Pause: Start and stop the simulation.
• Step Forward: Advance the simulation forward by one time step.
• Step Back: Advance the simulation backward by one time step.
• Reset: Reset simulation to original state.
• Speed radio buttons: sets simulation’s the evolution speed.
  • Slow: Δt ~ 2 hours
  • Medium: Δt ~ 12 hours
  • Fast: Δt ~ 3 day