Equinoxes

• Definition of Equinox

  • Common understanding: Days when, at every point on Earth, day and night are of equal length.

  • Misleading aspects:

  • Light appears before sunrise and continues after sunset, reducing actual night duration.

  • Determining equinoxes based on time between sunrise and sunset falsely assumes a flat horizon and neglects atmospheric effects, particularly refraction.

• Astronomical Perspective of Equinoxes

  • Clear definition: Equinoxes occur when the Earth's axis does not lean toward or away from the sun.

  • Positioning: Roughly a quarter of the way around from the two solstices due to Earth's elliptical orbit.

  • Celestial sphere view: The sun crosses the celestial equator when its declination is zero.

  • Occurrence:

  • Vernal (spring) equinox: March 20 or 21 (Gregorian calendar).

  • Autumnal equinox: September 22 or 23.

  • Note: Spring and autumn interchange in the southern hemisphere.

Historical Context of Equinox Understanding

• Hellenistic Astronomy

  • Natural thought process for ancient astronomers attempting to develop geometric models based on observational data.

  • Hipparchus (2nd century BCE): Developed a solar motion model where the sun orbits in a circle at a uniform speed while the Earth is displaced from the center.

  • Process to model solar motion:

    1. Draw a circle for the sun's orbit around Earth.

    2. Divide it into quarter-points (solstices and equinoxes).

    3. Observe the timing between these points.

    4. Adjust the model to fit the observations.

  • Importance of geometric approach illustrates how equinoxes emerge naturally within that context.

• Cultural Context of Equinox

  • Many cultures, especially in the prehistoric past, may have different inclinations towards understanding the cosmos geometrically.

  • Common misinterpretation of equinox in cultural settings:

  • Often understood as the halfway point between solstices, leading to ambiguities.

  • Halfway points can refer to space (sunrise positions) or time (days between solstices).

    • Spatial midway: Observed rising points of the sun between solstices.

    • Temporal midway: Count half the days between solstices.

  • Thom Equinox:

  • Alexander Thom suggested prehistoric Britain marked this event with monumental alignments.

  • Occurs 1-2 days later in March and earlier in September than true equinox when sun's declination is about +0.5 degrees.

Prehistoric Alignments and Equinoxes

• Monumental Alignments

  • Alignments found in structures like the passage tomb of Knowth in Ireland, often assumed to mark the equinoxes.

  • Pragmatic grounds support the idea of marking the halfway points as they could be directly observed, but precision poses questions.

• Cultural Significance

  • Inquiry into whether equinoxes held any significant meaning for early cultures raises doubts:

  • Evidence from history suggests

  • Most societies focused on significant local dates, often tied to agricultural events.

  • Ceremonial significance attached to solar events aligned with landscape features, e.g., sacred mountains (Ca caxtla in Mexico).

• Physical vs. Abstract Concepts of Time and Space

  • People typically do not perceive space and time in abstract, scientific ways but through physical markers and events in their environment.

  • Solstices marked by discernible longest/shortest days; equinoxes lack inherent observable significance, leading to modern biases in interpretation.

The Religious Context of Equinoxes

• Liturgical Importance

  • Equinox has gained prominence in Christian tradition for determining Easters timing.

  • Challenges in marking equinoxes during medieval times impacted church orientation processes, reflecting historical difficulties.

• Worldwide Evidence

  • Overall, scant evidence shows intentional interest in equinox positions or equinoctial alignments in earlier societies.

  • European prehistoric tombs aligned more with solstices than equinoxes, and in Mesoamerica, the significance of eastward alignments prevailed without equinoctial evidence.

Interpretation of Ancient Structures

• Toolkit for Alignments

  • Common practice to utilize a "toolkit" of astronomical targets for ancient structures, with equinoxes(equinox sunrise/sunset) often at the forefront.

  • Ambiguous definition of 'equinoctial' aligns with east-west orientations and is assumed meaningful across cultures, often inaccurately.

• Critical Understanding

  • It's essential to disentangle modern Western concepts from historical interpretations to understand diverse cultural meanings surrounding celestial observations.

  • The equinox illustrates the need for critical reflection on the significance assigned to astronomical events beyond one's cultural context.