The Seba library treats Trine in 6 passages, across 3 authors (including Donna Cunningham, Richard Tarnas, Liz Greene, Howard Sasportas).
When two planets form a trine, they are usually in the same element—e.g., from water sign to water sign or from air sign to air sign.
Cunningham provides the canonical definition of the trine as a 120-degree aspect linking planets of the same elemental quality, establishing its fundamental character as one of elemental consonance.
, An Astrological Guide to Self-Awareness, 1982thesis
Transiting Uranus was at the second trine position of its cycle in Locke's life during the years 1688–91.
Tarnas deploys the trine as a precise biographical marker within the Uranus cycle, correlating the 'second trine position' with the mature publication of Locke's major philosophical works and thereby demonstrating the trine's role in the unfolding of creative culmination.
, Prometheus the Awakener: An Essay on the Archetypal Meaning of the Planet Uranus, 1995thesis
Cyclical alignments having a different character, such as the trine and sextile, were not included. I mentioned only briefly such significant planetary cycles as the Neptune-Pluto and Saturn-Uranus cycles.
Tarnas explicitly distinguishes the trine and sextile from the quadrature aspects (conjunction, opposition, square), positioning them as a categorically distinct mode of archetypal alignment that his primary historical research chose to bracket rather than foreground.
, Cosmos and Psyche: Intimations of a New World View, 2006thesis
What sort of subpersonality might form around the Sun in Capricorn trine Saturn in Virgo? … a subpersonality which reflects stability as its core … or it could be a subpersonality which is tight, rigid and very anal.
Sasportas applies the trine to the generation of subpersonalities, demonstrating that same-element trines produce coherent but potentially over-consolidated archetypal clusters that manifest anywhere from structural stability to rigid constriction.
, The Development of Personality: Seminars in Psychological Astrology, Volume 1, 1987supporting
Stanley Kubrick 4°06′ †Uranus trine Sun … Timothy Leary 3°01″ Uranus trine Sun … Igor Stravinsky 6°08′ ††Uranus trine Saturn
Tarnas's natal aspect table documents multiple instances of Uranus trine Sun and Uranus trine Saturn in the charts of creative and revolutionary figures, supporting the argument that the trine aspect, while distinct from the conjunction, carries traceable archetypal signatures in biographical outcomes.
, Prometheus the Awakener: An Essay on the Archetypal Meaning of the Planet Uranus, 1995supporting
Basic Meanings of the Major Aspects … Conjunctions powerfully modify the qualities of planets in signs, because they merge the two planets' energies to work together as a unit.
Cunningham's survey of major aspects provides essential comparative context within which the trine is subsequently defined, establishing the broader taxonomy of astrological aspect interpretation from which trine-specific meaning emerges.
, An Astrological Guide to Self-Awareness, 1982aside