Series
Computed sky
The astronomy and arithmetic underneath every chart, worked in the open. One full computation per essay, redoable on paper. Written by Meghnad Chitnis.
computed-sky
Why your moon sign changes between apps
Two apps agree about the sky and disagree about where zero is. What an ayanamsha does, why the named ones differ, and why software must state its zero.
computed-sky
The arithmetic of Vimshottari
The whole dasha algorithm worked by hand: 120 years, nine weights, a starting point read off the Moon, and sub-periods by simple proportion.
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The tilt that sets the seasons
The obliquity is 23° 26′ 09″ and falling. What owns that number, where it enters a chart, and one birth recomputed under three different tilts.
computed-sky
Everyone in India is on Allahabad time
One clock, one meridian near Allahabad, every other town's sky early or late. The longitude correction computed, and the lagna that skipping it costs.
computed-sky
Four house systems, one birth moment
Equal, Sripati, Placidus and KP cusps computed for one moment at Ujjain: twelve numbers under each rule, and the disagreement measured to the arcsecond.
computed-sky
The equation of centre
A mean moon can sit 8 degrees from the real one. The correction that closes most of that gap, worked for one morning and checked against an ephemeris.
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Sunrise is a decision, not an observation
Four defensible sunrises for one August morning at Ujjain, spread across 3 minutes 42 seconds, each worked to the second.
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Ten minutes of doubt
A birth time rounded to the nearest ten minutes, priced number by number: how far the lagna, the midheaven, the Moon and the dasha ledger really move.
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Navamsha as a division problem
The ninth part of a sign, computed from longitude alone: two divisions, three worked positions, and why the classical three-case rule is one running count.
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The slow clock of precession
The 26,000-year wobble under every chart: its rate, how Hipparchus caught it with two old numbers, and why the nakshatras and the seasons drift apart.
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What a birth chart actually computes
A chart is ten numbers and a set of stated conventions. The pipeline from clock time to signs and houses, sorted into what is fixed, chosen, and read.
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Making a planet go backwards
Retrograde motion built from two circles: Mars's 2020 loop computed month by month, its turning points located, and the error the model carries.
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The day number that every ephemeris agrees on
Every astronomy program turns your date into one running count of days. The Julian Day built from scratch, worked forward to a number and back to a date.
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Why the sundial and the clock disagree
A sundial and a clock drift apart and back again through the year. The equation of time worked by hand, its two causes separated and then added.
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Sidereal time, or what the sky reads on your clock
The earth turns in 23h 56m 4s, not 24. One birth moment carried from a wall clock to local sidereal time, step by step, checkable on paper.
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Raising the ascendant by hand
One rising degree computed for a real moment at Ujjain: the spherical trigonometry said in plain words first, then worked digit by digit and checked twice.
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Counting days since the beginning
The classical Indian day count worked from the Surya Siddhanta's own totals, then checked against the Julian Day, the weekday, and two printed calendars.
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Finding the exact moment a tithi turns
Two ephemeris rows an hour apart, a lunar day ending between them, and the crossing located by interpolation, then checked against printed almanac times.
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The eighteen-year wobble
The Moon's nodes retreat 19.355 degrees a year. That one rate sets the August 2026 eclipse pair and walks the eclipse seasons backwards.