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Craft · lessons, benches & plates
Lesson 02 · The sky's clock

2 The sky's clock

Carry the midnight Greenwich sidereal time to the birth instant and then to the birthplace.

Bench G1Stage 1 of 4 · Demonstration
Demonstration

G1 · Royal Observatory, Greenwich

Follow the source and working. Advance one numbered line at a time.

0 of 7 lines checked0%
The local sky clock · B1

Midnight at Greenwich

Sky clock, method & paper
  2. B2Elapsed UTwithheld
  3. B3Small accelerationwithheld
  4. B4Raw Greenwich sumwithheld
  5. B5Signed longitudewithheld
  6. B6Wrap to 24 hourswithheld
  7. B7Southern table entrywithheld
Source frame · Royal Observatory, Greenwich0h UT · Dec 13, 2023
Admitted reference · 24-hour sidereal clock
0006121805:25:42SIDEREAL HOURS

05:25:42

Read GST at 0h UT on A7. This is the Greenwich midnight reference, not the birth clock.

B1 · admitted reference
05:25:42
Read the admitted working

Read the source and the admitted result above.

The ephemeris source cells below belong to A7. Use their midnight GST, rounded to a whole second.

24-hour sidereal wrapping changes the clock reading, never the civil date or A7. The later C10 horizon reversal is not performed here.

A method diagram from checked or revealed lines. It makes no new engine request. Read exact retained seconds above; the dial is schematic.

All source cells for B1
Permanent reduction formParts A–F

  1. Plate GST at midnight (0h UT) on the A7 date

    active line

    Rule read from the ephemeris row for A7

    The local sky clock · B1

    Midnight at Greenwich

    Sky clock, method & paper
    2. B2Elapsed UTwithheld
    3. B3Small accelerationwithheld
    4. B4Raw Greenwich sumwithheld
    5. B5Signed longitudewithheld
    6. B6Wrap to 24 hourswithheld
    7. B7Southern table entrywithheld
    Source frame · Royal Observatory, Greenwich0h UT · Dec 13, 2023
    Admitted reference · 24-hour sidereal clock
    0006121805:25:42SIDEREAL HOURS

    05:25:42

    Read GST at 0h UT on A7. This is the Greenwich midnight reference, not the birth clock.

    B1 · admitted reference
    05:25:42
    Read the admitted working

    Read the source and the admitted result above.

    The ephemeris source cells below belong to A7. Use their midnight GST, rounded to a whole second.

    24-hour sidereal wrapping changes the clock reading, never the civil date or A7. The later C10 horizon reversal is not performed here.

    A method diagram from checked or revealed lines. It makes no new engine request. Read exact retained seconds above; the dial is schematic.

    All source cells for B1

    Why The plate's GST is the sky clock at Greenwich midnight on A7.

    Your paper result05:25:42
    Reference answer05:25:42
    Tolerance · within 2 s

  2. Interval since 0h = A6

    waiting

  3. Acceleration = B2 × 9.86 s per hour

    waiting

    Magnitude check · always under 4 minutes

  4. Greenwich sidereal time at birth = B1 + B2 + B3

    waiting

    Rule carry at 60

  5. Longitude in time = longitude × 4 min per degree

    waiting

    Rule East add · West subtract

  6. Local sidereal time = B4 + B5

    waiting

    Rule if 24h or more subtract 24h

  7. Southern hemisphere?

    waiting

    Rule if Y add 12h to B6 and normalise · this is the table entry

Moira Craft School

Blank permanent A–F reduction form

Part ATime

LineOperation and ruleWorkingResult
A1Birth date, civil
A2Clock time, 24-hour
A3Summer time in force?if Y subtract 1h · older war time may be 2h · stated on the bench
A4Standard time = A2 − A3
A5Zone offset from GreenwichWest add · East subtract
A6Universal Time = A4 + A5if 24h or more subtract 24h and move A7 forward a day · if below 0 add 24h and move A7 back
A7UT datemay differ from A1 · every plate row is read on this date

Part BSidereal time

LineOperation and ruleWorkingResult
B1Plate GST at midnight (0h UT) on the A7 dateread from the ephemeris row for A7
B2Interval since 0h = A6
B3Acceleration = B2 × 9.86 s per hourCheck: always under 4 minutes
B4Greenwich sidereal time at birth = B1 + B2 + B3carry at 60
B5Longitude in time = longitude × 4 min per degreeEast add · West subtract
B6Local sidereal time = B4 + B5if 24h or more subtract 24h
B7Southern hemisphere?if Y add 12h to B6 and normalise · this is the table entry

Part CAngles and cusps

LineOperation and ruleWorkingResult
C1Table rows bracketing B7: lower ST, upper STrows are 4 minutes apart
C2Fraction f = (B7 − lower) in seconds ÷ 240Check: always between 0 and 1
C3MC: lower, upper, difference, × f, + lowerthe same for every latitude
C4Latitude rows bracketing the birth: lower, upper; fraction gtable rows are 1° apart
C511 12 ASC 2 3 as columns: at the lower latitude, at the upper latitude, then by ga column that looks unlike its neighbours is the column with the mistake
C10Southern? Reverse every sign on C3 and C5degrees and minutes unchanged
C11Opposites: IC = MC + 180, DSC = ASC + 180, 5 6 8 9 = 11 12 2 3 + 180same degree and minute, opposite sign

Part DBodies

LineOperation and ruleWorkingResult
D:sunSun: this midnight, next midnight, motion, × A6 ÷ 24, positionnegative motion is retrograde, write R · a negative travel subtracts
D:moonMoon: this midnight, next midnight, motion, × A6 ÷ 24, positionnegative motion is retrograde, write R · a negative travel subtracts
D:mercuryMercury: this midnight, next midnight, motion, × A6 ÷ 24, positionnegative motion is retrograde, write R · a negative travel subtracts
D:venusVenus: this midnight, next midnight, motion, × A6 ÷ 24, positionnegative motion is retrograde, write R · a negative travel subtracts
D:marsMars: this midnight, next midnight, motion, × A6 ÷ 24, positionnegative motion is retrograde, write R · a negative travel subtracts
D:jupiterJupiter: this midnight, next midnight, motion, × A6 ÷ 24, positionnegative motion is retrograde, write R · a negative travel subtracts
D:saturnSaturn: this midnight, next midnight, motion, × A6 ÷ 24, positionnegative motion is retrograde, write R · a negative travel subtracts
D:uranusUranus: this midnight, next midnight, motion, × A6 ÷ 24, positionnegative motion is retrograde, write R · a negative travel subtracts
D:neptuneNeptune: this midnight, next midnight, motion, × A6 ÷ 24, positionnegative motion is retrograde, write R · a negative travel subtracts
D:plutoPluto: this midnight, next midnight, motion, × A6 ÷ 24, positionnegative motion is retrograde, write R · a negative travel subtracts
D:trueNodeTrue Node: this midnight, next midnight, motion, × A6 ÷ 24, positionnegative motion is retrograde, write R · a negative travel subtracts

Part EFigure and aspects

LineOperation and ruleWorkingResult
E1Cusps on the wheel. ASC at the left, houses counterclockwise, C11 filled
E2Bodies into houses by comparing D5 with the cuspsnote any body within 1° of a cusp
E3Aspectarian: the five Ptolemaic aspects, applying or separating from motionorbs as on the free transits surface

Part FReceipt

LineOperation and ruleWorkingResult
FReceipt: paper, Moira, Δ, cause for every computed line

Part F · continuationPaper-to-Moira discrepancy account

Retain the paper value; record Moira, the signed delta, and one cause from the fixed vocabulary.
LinePaperMoiraΔCause / notes
A4
A5
A6
A7
B1
B2
B3
B4
B5
B6
B7
C1
C2
C3
C4
C5
C10
C11
D:sun
D:moon
D:mercury
D:venus
D:mars
D:jupiter
D:saturn
D:uranus
D:neptune
D:pluto
D:trueNode
E2
E3

Blank permanent A–F reduction form · tropical zodiac · Placidus houses