Unformatted text preview: let’s begin by thinking about the Sun’s changing position on the
Reminder: Over the course of a year the Sun moves around the celestial sphere, relative to the background stars on
a path called the ecliptic. This apparent motion is a reﬂection of the Earth's annual orbit around the Sun.
Because of Earth’s rotation axis tilt, the plane of Earth’s orbit around the Sun is at an angle to the plane of Earth’s
equator. If we draw this path onto the celestial sphere, we see that the ecliptic (in green) is at an angle of 23.5º to
the celestial equator (in red).
Therefore, the Sun will be north of the celestial equator for half the year, south of the celestial equator for half the
year, and crossing the celestial equator at twice per year Sols8ces and Equinoxes
(Sept 21) Summer
c E Winter
(Dec 21) 3.5º
2 CEq ~ Vernal
(Mar 21) SCP
Richard Pogge Monday, October 22, 12 We can identify four important points on the ecliptic that help us mark the passing of the seasons.
Solstices occur when the Sun is at its maximum north and south of the celestial equator. Solstices occur twice a
year in June and December:
• Summer (June) Solstice: Sun is at its maximum north of the celestial equator (occurs on or about June 21).
• Winter (December) Solstice: Sun is at its maximum south of the celestial equator (occurs on or about
Equinoxes occur when the Sun crosses the Celestial Equator....
View Full Document
- Fall '12