Tartarus: one of three places the dead went after being judged. Evil doers went to Tartarus below Hades; heroes went to the Elysian Fields; the remaining saints and sinners went to Hades. Tar-tarus was a stormy pit beneath the earth to which the Titans were exiled after their defeat by Zeus, and released at the end of the Age of Heroes.

Tetrarchy: In 293 AD the Emperor Diocletian divided the Roman Empire into four prefectures, the Tetrarchy, each ruled by a senior emperor or Augustus and seconded by a junior emperor and designated successor, a Caesar ruling part of their Augustus’ prefecture. This ended the Crisis of the Third Century (235-284 AD) and marked a recovery of the Roman Empire. The Tetrarchy lasted until 313 when mutually destructive conflict eliminated most claimants to power except Licinius in the East and Constantine in the West.

Thales of Miletus (c. 624 BC-c. 546 BC): one of the Seven Sages of Greece and the first well-known philosopher and mathematician. His advice "Know thyself" was engraved on the front façade of the Oracle of Apollo in Delphi. Thales tried to explain natural events without using mythology, which became a basic idea in the scientific revolution. The first to define general principles and set forth hypotheses, he is known as the Father of Science.

Terra: a primeval Roman goddess equivalent to the Greek Gaia, also called Tellus or Tellus Mater, and thus the Latin name for our planet. "Mater" means mother in Latin, so "Tellus Mater" is mother earth.

Terrestrial: an inhabitant of Terra, thus, an earthling in the interplanetary scheme of things.

Theogony: a 1022-line narrative epic poem written about 700 BC by Hesiod. It describes the origins and genealogy of the ancient Greek gods and syn-thesizes many existing myths and local traditions.

tidal locking: occurs when one side of an orbiting body always faces another. True of our Moon and most known moons in the Solar System, it occurs because the gravity of the parent causes a tidal bulge in the smaller body stabilizing towards the parent and locking in that orientation. Pluto and Charon are both tidally locked to each other.

Titans: Gaia, Uranus, and their children Kronos, Rhea, Oceanus, Tethys, Hyperion, Mnemosyne, Themis, Iapetus, Coeus, Crius, Phoebe, Thea, Prometheus, Epimetheus, Atlas and Metis (see genealogy, page 73). The Golden age of Man took place during the rule of Kronos and the Titans. The elder race or second generation of gods, the Titans refused to give up power to the next generation. A 10-year war ensued between the Titans and the Olympians led by Zeus, resulting in the Titans being exiled to Tartarus, a stormy pit beneath the Earth. At the end of the Age of Heroes Zeus released the Titans, making Kronos king of the Elysian Isles to rule over the shades of Heroes.

TNO: an initialism for Trans-Neptunian Object.

trans-Neptunian object (TNO): the name given to any solar system object that orbits the Sun on the average at a greater distance than Neptune. The volume of space populated by TNOs can be further subdivided into the Kuiper belt, the Oort cloud, and the scattered disk. As of Sep. 2011 Eris, Pluto, Makemake, Haumea, Sedna, Orcus, 2007 OR10, Quaoar and Charon are the nine largest TNOs in that order—but there are trillions of them.

translation of light: if planet A aspects planet B and planet B aspects planet C, then A may aspect C even if the orb between A and C is otherwise too wide. This is because their mutual aspect to planet B strengthens the aspect between A and C. This is particularly noticeable in harmonic syndromes of more than 3 planets like a grand cross or sextile.

transit(ing): a moving planet at some time after birth, usually significant insofar as it aspects some planetary birth position; also, the crossing of the local meridian by a celestial body.

trine: the 120° aspect; one third of the circle, denoting harmony, ease, gifts, stability and creativity; orb 6°-8°. Planets in trine are usually (but not necessarily) in the same element. For example, the Moon at 28° Cancer is trine (with a 4° orb) to the Sun at 2° Sagittarius, but they are not in the same element. Not conducive to change like the square; and, because of the inertia of the trine, the principal "use it or lose it" becomes relevant.

triplicity (see elements and page 52): any one of four groups of three signs apiece with the characteristic that all planets in any one triplicity relate harmoniously (are in trine or sextile) to each other. The ancient name for these four groups as a whole is elements, and the names of the elements are earth (Taurus, Virgo and Capricorn), air (Gemini, Libra and Aquarius), fire (Aries, Leo and Sagittarius), and water (Cancer, Scorpio and Pisces). Two or more planets in the same element usually relate harmoniously to each other, although what it means for planets to be "in aspect" must be understood and taken into account (see page 53).

Trojan: an asteroid or moon that shares its orbit with a larger planet or moon without colliding because it inhabits (or orbits about) one of the planet’s two stable Lagrangian points L4 or L5.

Trojan asteroid: asteroids that orbit stably about Jupiter’s Lagrangian points. The Trojan asteroids are colored green in the diagram on page 145.

tropical: referring to the northerly or southerly turning of the Sun twice a year at the solstices. This marks the seasonal cycle of light and dark on Earth bringing about the 12 signs. Tropical astrologers believe the signs are 12 equal divisions of the interval between successive vernal equinoxes, and that these 12 stages in Earth’s light and dark cycle, not the constellations from which they derived their names, are interpretively significant. Sidereal astrologers believe the more fixed, non-precessing constellations are interpretively significant.

tropical month: the interval between two successive lunar transits of the vernal equinox (27.321582 days). Because the vernal equinox moves slowly backwards along the ecliptic (precession), this is a little shorter than a sidereal month (27.321661 days), or a month with respect to the stars.

tropical year (aka "solar year"): the interval between two successive returns of the Sun to the same place in the cycle of seasons; e.g., between two vernal equinoxes or summer solstices. Because the equinoctial points precess backwards relative to the Sun’s motion and the stars, the tropical year is 20 minutes 24½ seconds shorter than the sidereal year. In the second century BC Hipparchos measured the tropical year to be 365 days 5 hours 55 minutes and 12 seconds, very close to its current 365 days 5 hours 49 minutes and 19 seconds.

T-square: an opposition with a third planet square to both ends. Although similar in energy to the grand cross, this structure is said to lack its balance, and therefore to focus one’s attention on the "missing leg." A heavy transiting planet filling in the open end often initiates a crisis.