The Ecliptic

The ecliptic is the year-long path of the Sun against the background of fixed stars. Is it the same as the Celestial Equator, or different?

Different. The celestial equator is a projection of the earth's equator, and is inclined to the path of the sun (the ecliptic) by 23.5 degrees. The ecliptic is important because where the Sun travels, the planets follow. Constellations containing portions of the ecliptic are zodiac constellations, and bright stars in zodiac constellations that don't appear on star charts are probably visiting planets.

The Ecliptic and the motions of the Sun

  • The basic observation underlying the ecliptic: Heliacal Rising and Sidereal year
  • Which coordinate system is based on the ecliptic?
    • Celestial latitude = degrees measured above or below the ecliptic.
    • Celestial longitude = degrees measured along the ecliptic, starting from the March equinox (intersection of the ecliptic with the celestial equator).
    • Angular distances measured from the ecliptic were used in antiquity and in the early modern period, e.g., by Ptolemy and Copernicus.
  • Rising points of the Sun on the horizon
    • Equinoxes
    • Solstices
    • Tropical year
    • Does the sun always rise due east and set due west?
    • Is the altitude of the Sun on the meridian at noon always the same throughout the year?
      • On what day is the sun highest in the sky?
      • How close does the Sun come to directly overhead (the zenith) in Shawnee?
      • Diurnal Motion of the Sun
        • If the sun rises in the northeast on the summer solstice, will it set that evening in the southwest or in the northwest?
        • The Sun's annual motion is along the ecliptic, which is a great circle. Is the sun's daily motion along a great circle? Does it move parallel to a great circle?
  • Does the angle between the ecliptic and the horizon remain the same throughout the year?

Seasons

Zodiac Sign

Celestial Longitude

 Declination  

# Days Sun is in this sign

Season Sun is in each Sign
Aries 0 degrees 0 degrees 00' 30.5 Spring
Taurus 30 degrees 11 degrees 28.5' 31.0 92.8
Gemini 60 degrees 20 degrees 09.3' 31.3
Cancer 90 degrees 23 degrees  26.6' 31.5 Summer
Leo 120 degrees 20 degrees 09.3' 31.3 93.7 days
Virgo 150 degrees 11 degrees 28.5' 30.9
Libra 180 degrees 0 degrees 00' 30.4 Autumn
Scorpio 210 degrees -11 degrees 28.5' 29.9 89.8 days
Sagittarius 240 degrees -20 degrees 09.3' 29.5
Capricorn 270 degrees -23 degrees 26.6' 29.4 Winter
Aquarius 300 degrees -20 degrees 09.3'  29.6 89.0 days
Pisces 330 degrees -11degrees 28.5' 30.0 

  

  1. Do all of the zodiac constellations occupy equal lengths in celestial longitude?
  2. If the celestial longitude of the Sun is 190 degrees...
    • What season is it?
    • Which sign will contain the Sun?
  3. Declination is measured north and south above the... (check one):
    • ecliptic
    • celestial equator
  4. Which signs have the same declinations?
  5. Which signs have opposite declinations?
  6. Is the Sun north or south of the celestial equator...
    • When it is in Gemini?
    • When it is in Sagittarius?
  7. In which sign does the Sun move...
    • Fastest?
    • Slowest?
    • Does the Sun move faster at higher or lower declinations?
  8. For each pair, circle the time at which the Sun moves faster:
    • Equinoxes, Summer Solstice
    • Equinoxes, Winter Solstice
    • Summer Solstice, Winter Solstice
  9. Which season is the...
    • Longest?
    • Shortest?
Representations - Other
Ecliptic