|
|
|
|
| Table of
Contents View the Stars External Links
|
The Sun and
the Earth's orbit form a plane called the ecliptic. You can also think
of this as the path the Sun follows across the sky when viewed from
the Earth.
The ecliptic and the celestial equator intersect in only two points.
These two points are called equinoxes (from the Latin word meaning
equal), because when the Sun appears at either of these points, daytime
and nighttime are each 12 hours long at all locations on Earth. The Vernal Equinox marks the beginning of spring in the northern hemisphere and occurs about March 21. The autumnal equinox is when autumn starts in the northern hemisphere and is about September 21. Between the dates of the two equinoxes are two other important dates. These dates occur when the Sun reaches the lowest and highest points in the sky. On about June 21 the sun is reaches its highest position in the sky when viewed from the northern hemisphere. This point is called the summer solstice. When the sun reaches the lowest point in the sky when viewed from the northern hemisphere the winter solstice occurs. Note that the ecliptic is titled 23.5o relative to the celestial equator, why do think this is the case? Remember that the Celestial Sphere is a GEOCENTRIC view of the Earth, Sun and Stars. That is we are viewing the Universe as if the Earth was the center of the Universe. How do you think the picture above would change if you viewed the Earth from the Sun's point of view? |
