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Mercury's year is 88 Earth days. One sunrise-to-sunrise day on Mercury lasts 176. The day is exactly twice the year — the planet completes two full orbits of the Sun between one dawn and the next.
September 16, 2026 at 12:00 PM
Mercury's year is 88 Earth days. One sunrise-to-sunrise day on Mercury lasts 176. The day is exactly twice the year — the planet completes two full orbits of the Sun between one dawn and the next.
Your latitude is also a radius. From 51° north, everything within 51° of the celestial pole never sets. A cap the same size behind the opposite pole never rises — which is why London cannot see the Southern Cross, and Sydney cannot see Polaris.
September 15, 2026 at 12:00 PM
Your latitude is also a radius. From 51° north, everything within 51° of the celestial pole never sets. A cap the same size behind the opposite pole never rises — which is why London cannot see the Southern Cross, and Sydney cannot see Polaris.
Laws and rules, raw resources, and the authority of age. Mundane astrology gives all three to a single planet. Which?
Saturn — who takes the constraints that come with them.
Saturn — who takes the constraints that come with them.
September 14, 2026 at 12:00 PM
Laws and rules, raw resources, and the authority of age. Mundane astrology gives all three to a single planet. Which?
Saturn — who takes the constraints that come with them.
Saturn — who takes the constraints that come with them.
The decans began as a clock. Painted inside Egyptian coffin lids by the 21st century BC, 36 star groups rose ten days apart, and each rising marked another hour of the night. The Greeks called them dekanoi — tenths. The same 36 are the ten-degree decans still in use.
September 13, 2026 at 12:00 PM
The decans began as a clock. Painted inside Egyptian coffin lids by the 21st century BC, 36 star groups rose ten days apart, and each rising marked another hour of the night. The Greeks called them dekanoi — tenths. The same 36 are the ten-degree decans still in use.
To forecast a planet's year, Babylonian scribes copied out observations from one goal-year period earlier — 8 years for Venus, 46 for Mercury, 59 for Saturn — and expected the same phenomena on the same dates. Prediction by looking up the past.
September 12, 2026 at 12:00 PM
To forecast a planet's year, Babylonian scribes copied out observations from one goal-year period earlier — 8 years for Venus, 46 for Mercury, 59 for Saturn — and expected the same phenomena on the same dates. Prediction by looking up the past.
Uraniborg, built on Hven between 1576 and 1580 and named for the muse of astronomy, was more than an observatory. Tycho Brahe gave it a printing office, a water mill for making paper, and an alchemical laboratory in the cellar. A second observatory followed in 1584.
September 11, 2026 at 12:00 PM
Uraniborg, built on Hven between 1576 and 1580 and named for the muse of astronomy, was more than an observatory. Tycho Brahe gave it a printing office, a water mill for making paper, and an alchemical laboratory in the cellar. A second observatory followed in 1584.
“According to some, there are but four winds.” Vitruvius says those more curious reckon eight — and names Andronicus of Kyrrhos, who built an octagonal marble tower in Athens, a wind carved on each face and a bronze Triton on the roof pointing to the one that blew.
September 10, 2026 at 12:00 PM
“According to some, there are but four winds.” Vitruvius says those more curious reckon eight — and names Andronicus of Kyrrhos, who built an octagonal marble tower in Athens, a wind carved on each face and a bronze Triton on the roof pointing to the one that blew.
Retrograde loops are a fact about where you are standing. The Earth overtakes an outer planet the way an outside lane passes an inside one, and it appears to slide backwards. Measure from the Sun instead and the loops are not reduced — they are absent.
September 9, 2026 at 12:00 PM
Retrograde loops are a fact about where you are standing. The Earth overtakes an outer planet the way an outside lane passes an inside one, and it appears to slide backwards. Measure from the Sun instead and the loops are not reduced — they are absent.
Leave a planet exactly where it is. Tilt the plane you measure it against by 23.4° and it reads a different degree — nothing moved but the reference. A body one degree above the crossing point shifts by four tenths of a degree. That factor is just sin 23.4°.
September 8, 2026 at 12:00 PM
Leave a planet exactly where it is. Tilt the plane you measure it against by 23.4° and it reads a different degree — nothing moved but the reference. A body one degree above the crossing point shifts by four tenths of a degree. That factor is just sin 23.4°.
Timocharis recorded Spica 8° west of the autumn equinox in the 280s BC. Some 150 years later Hipparchus measured 6° — and in 127 BC concluded it was the equinox that had moved, not the star. That 2° discrepancy is the discovery of precession.
September 7, 2026 at 12:00 PM
Timocharis recorded Spica 8° west of the autumn equinox in the 280s BC. Some 150 years later Hipparchus measured 6° — and in 127 BC concluded it was the equinox that had moved, not the star. That 2° discrepancy is the discovery of precession.
Communication, commerce, and short journeys. Mundane astrology gives all three to one planet. Which?
Mercury — who also takes transportation in every form, and the quick intelligence that goes with it.
Mercury — who also takes transportation in every form, and the quick intelligence that goes with it.
September 6, 2026 at 12:00 PM
Communication, commerce, and short journeys. Mundane astrology gives all three to one planet. Which?
Mercury — who also takes transportation in every form, and the quick intelligence that goes with it.
Mercury — who also takes transportation in every form, and the quick intelligence that goes with it.
In Hesiod's Theogony the winds are born to Eos and Astraios: Zephyros, Boreas, Notos. Three, not four — no east wind in the list. The next lines give the same mother the morning star and “the gleaming stars with which heaven is crowned.”
September 5, 2026 at 12:00 PM
In Hesiod's Theogony the winds are born to Eos and Astraios: Zephyros, Boreas, Notos. Three, not four — no east wind in the list. The next lines give the same mother the morning star and “the gleaming stars with which heaven is crowned.”
In 1649 Nicholas Culpeper published an unauthorized English translation of the College of Physicians' Latin pharmacopoeia, dosages and all. The College was outraged: anyone who could buy the book could now be their own doctor.
September 4, 2026 at 12:00 PM
In 1649 Nicholas Culpeper published an unauthorized English translation of the College of Physicians' Latin pharmacopoeia, dosages and all. The College was outraged: anyone who could buy the book could now be their own doctor.
Saturn returns to the same star in 29.46 years (sidereal). The Moon returns to the same phase in 29.53 days (synodic). The slowest of the seven classical bodies and the most familiar cycle in the sky land on the same number — one in years, the other in days.
September 3, 2026 at 12:00 PM
Saturn returns to the same star in 29.46 years (sidereal). The Moon returns to the same phase in 29.53 days (synodic). The slowest of the seven classical bodies and the most familiar cycle in the sky land on the same number — one in years, the other in days.
Disaster came into English from the Italian disastro — dis- plus astro, an ill-starred thing. A calamity was once understood quite literally as the fault of a badly placed planet. The grammar of that belief survives in the word.
September 2, 2026 at 12:00 PM
Disaster came into English from the Italian disastro — dis- plus astro, an ill-starred thing. A calamity was once understood quite literally as the fault of a badly placed planet. The grammar of that belief survives in the word.
When William Herschel found a seventh planet in 1781 he named it Georgium Sidus, the Georgian Star, after his king. Britain used that name for nearly seventy years. The Nautical Almanac Office finally switched to Uranus in 1850.
September 1, 2026 at 12:46 PM
When William Herschel found a seventh planet in 1781 he named it Georgium Sidus, the Georgian Star, after his king. Britain used that name for nearly seventy years. The Nautical Almanac Office finally switched to Uranus in 1850.
Vettius Valens worked as an astrologer in the 2nd century and put over a hundred charts from his own case files into his Anthology. It is the best surviving evidence of what ancient practice actually looked like, rather than what it theorised.
August 31, 2026 at 12:00 PM
Vettius Valens worked as an astrologer in the 2nd century and put over a hundred charts from his own case files into his Anthology. It is the best surviving evidence of what ancient practice actually looked like, rather than what it theorised.
In Tertius Interveniens (1610) Kepler called astrology the foolish daughter of astronomy — then added that a mathematician's pay was so poor the mother would starve if the daughter earned nothing. Popular almanacs were funding the new astronomy.
August 30, 2026 at 12:00 PM
In Tertius Interveniens (1610) Kepler called astrology the foolish daughter of astronomy — then added that a mathematician's pay was so poor the mother would starve if the daughter earned nothing. Popular almanacs were funding the new astronomy.
In October 1582 ten days were removed from the calendar: Thursday the 4th was followed by Friday the 15th. Britain held out until 1752 and had to drop eleven. Casting a chart for a historical birth means knowing which calendar it used.
August 29, 2026 at 12:00 PM
In October 1582 ten days were removed from the calendar: Thursday the 4th was followed by Friday the 15th. Britain held out until 1752 and had to drop eleven. Casting a chart for a historical birth means knowing which calendar it used.
The Antikythera mechanism, a bronze geared device from the 2nd century BC raised from a shipwreck in 1901, is the oldest known analogue computer. Its front dial carries the Greek zodiac signs, divided in degrees. Joyofmuseums / CC BY-SA 4.0
August 28, 2026 at 12:00 PM
The Antikythera mechanism, a bronze geared device from the 2nd century BC raised from a shipwreck in 1901, is the oldest known analogue computer. Its front dial carries the Greek zodiac signs, divided in degrees. Joyofmuseums / CC BY-SA 4.0
Abu Ma'shar wrote his introduction to astrology around 848; John of Seville put it into Latin in 1133. Scholars have argued it was the most important single route by which Aristotle reached Europe — ahead of Aristotle's own books. Wellcome Collection / CC BY 4.0
August 27, 2026 at 12:00 PM
Abu Ma'shar wrote his introduction to astrology around 848; John of Seville put it into Latin in 1133. Scholars have argued it was the most important single route by which Aristotle reached Europe — ahead of Aristotle's own books. Wellcome Collection / CC BY 4.0
Partial lunar eclipse 28 Aug: 93% of the Moon's diameter in umbra at 4°51′ Pisces, greatest 04:13 UT, umbral phase 3h 18m. Ptolemy timed the darkening in equinoctial hours — reckoning as many years for a solar eclipse, months for a lunar one. Tetrabiblos II.6.
August 27, 2026 at 7:17 AM
Partial lunar eclipse 28 Aug: 93% of the Moon's diameter in umbra at 4°51′ Pisces, greatest 04:13 UT, umbral phase 3h 18m. Ptolemy timed the darkening in equinoctial hours — reckoning as many years for a solar eclipse, months for a lunar one. Tetrabiblos II.6.
Regiomontanus published his Ephemerides in 1474: planetary positions and eclipse times worked out decades ahead. Navigators took it to sea. Columbus and Vespucci both used it to reckon longitude in the Americas.
August 25, 2026 at 1:05 PM
Regiomontanus published his Ephemerides in 1474: planetary positions and eclipse times worked out decades ahead. Navigators took it to sea. Columbus and Vespucci both used it to reckon longitude in the Americas.