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The Ecliptic Plane of the Solar System

The ecliptic plane is an imaginary plane in our solar system formed by the earth's orbit around the sun. Nearly all of the objects in our solar system that orbit the sun do so at an angle very near to the ecliptic plane, usually within 10 degrees. This fact is evidence that our solar system was formed out of a disk-like formation of matter that eventually became the sun and planets.

Solar and Lunar Eclipses
- The ecliptic plane derives its name from its relation to eclipses of the moon and sun. Any object that passes the ecliptic plane in between the sun and the earth will block the path of light to earth. Any object that passes the ecliptic plane on the other side of the earth will be temporarily in earth's shadow. An eclipse occurs when the moon's orbit intersects the ecliptic plane (its orbit is about 5 degrees titled from the ecliptic). A solar eclipse occurs when the moon passes the ecliptic plane in front of the earth, casting a shadow on a circular portion of the earth's surface. A lunar eclipse occurs when the moon passes behind the earth, falling into its shadow temporarily.
The Four Seasons
- The ecliptic plane is also related to earth's seasonal changes. Earth's axis of rotation is 23.5 degrees tilted from perpendicular to the ecliptic plane, meaning one hemisphere is always tilted closer to the sun and one hemisphere is always tilted farther away. The hemisphere that is tilted closer to the sun receives more direct rays of sunlight, and therefore experiences hotter temperatures: the summer season. The hemisphere that is tilted farther from the sun receives fewer direct rays and lower temperatures: the winter season. If the axis of rotation were parallel or perpendicular to the ecliptic plane, the earth would not experience seasons.
The Signs of the Zodiac
- The 12 signs of the zodiac are derived from the constellations that are found on the ecliptic plane. As the earth orbits the sun, the position of the sun in the night sky relative to the stars changes. The 12 signs of the zodiac correspond to the major constellations or "houses" that the sun passes through each month of the year. For example, the month of March corresponds to the Pisces symbol because the sun was found in the house of Pisces in March, when the zodiac was developed.
The Planets of the Solar System
- An interesting feature of our solar system is that although it inhabits a three-dimensional vacuum of space, it is actually nearly flat: all of the planets' orbits make an angle of no more than 7 degrees with the ecliptic plane. Pluto's orbit, however, makes an angle of 17 degrees with the ecliptic plane, one of many traits that separate it from the other eight planets, which led to its recent demotion from planetary status to that of a "dwarf planet."

Astronomy