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%
Plate GST at midnight (0h UT) on the A7 date
active lineRule read from the ephemeris row for A7
Why The plate's GST is the sky clock at Greenwich midnight on A7.
Carry ladder · regroup at 60 h m s 05 25 42 Read each column from right to left; carry or borrow one only when a column crosses sixty.
Your paper result05:25:42Reference answer05:25:42Tolerance · within 2 s- Residual
- 0 s
- Cause
- Sidereal-time rounding
Interval since 0h = A6
waitingAcceleration = B2 × 9.86 s per hour
waitingMagnitude check · always under 4 minutes
Greenwich sidereal time at birth = B1 + B2 + B3
waitingRule carry at 60
Longitude in time = longitude × 4 min per degree
waitingRule East add · West subtract
Local sidereal time = B4 + B5
waitingRule if 24h or more subtract 24h
Southern hemisphere?
waitingRule if Y add 12h to B6 and normalise · this is the table entry
Blank permanent A–F reduction form
Part ATime
| Line | Operation and rule | Working | Result |
|---|---|---|---|
| A1 | Birth date, civil | ||
| A2 | Clock time, 24-hour | ||
| A3 | Summer time in force?if Y subtract 1h · older war time may be 2h · stated on the bench | ||
| A4 | Standard time = A2 − A3 | ||
| A5 | Zone offset from GreenwichWest add · East subtract | ||
| A6 | Universal Time = A4 + A5if 24h or more subtract 24h and move A7 forward a day · if below 0 add 24h and move A7 back | ||
| A7 | UT datemay differ from A1 · every plate row is read on this date |
Part BSidereal time
| Line | Operation and rule | Working | Result |
|---|---|---|---|
| B1 | Plate GST at midnight (0h UT) on the A7 dateread from the ephemeris row for A7 | ||
| B2 | Interval since 0h = A6 | ||
| B3 | Acceleration = B2 × 9.86 s per hourCheck: always under 4 minutes | ||
| B4 | Greenwich sidereal time at birth = B1 + B2 + B3carry at 60 | ||
| B5 | Longitude in time = longitude × 4 min per degreeEast add · West subtract | ||
| B6 | Local sidereal time = B4 + B5if 24h or more subtract 24h | ||
| B7 | Southern hemisphere?if Y add 12h to B6 and normalise · this is the table entry |
Part CAngles and cusps
| Line | Operation and rule | Working | Result |
|---|---|---|---|
| C1 | Table rows bracketing B7: lower ST, upper STrows are 4 minutes apart | ||
| C2 | Fraction f = (B7 − lower) in seconds ÷ 240Check: always between 0 and 1 | ||
| C3 | MC: lower, upper, difference, × f, + lowerthe same for every latitude | ||
| C4 | Latitude rows bracketing the birth: lower, upper; fraction gtable rows are 1° apart | ||
| C5 | 11 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 | ||
| C10 | Southern? Reverse every sign on C3 and C5degrees and minutes unchanged | ||
| C11 | Opposites: IC = MC + 180, DSC = ASC + 180, 5 6 8 9 = 11 12 2 3 + 180same degree and minute, opposite sign |
Part DBodies
| Line | Operation and rule | Working | Result |
|---|---|---|---|
| D:sun | Sun: this midnight, next midnight, motion, × A6 ÷ 24, positionnegative motion is retrograde, write R · a negative travel subtracts | ||
| D:moon | Moon: this midnight, next midnight, motion, × A6 ÷ 24, positionnegative motion is retrograde, write R · a negative travel subtracts | ||
| D:mercury | Mercury: this midnight, next midnight, motion, × A6 ÷ 24, positionnegative motion is retrograde, write R · a negative travel subtracts | ||
| D:venus | Venus: this midnight, next midnight, motion, × A6 ÷ 24, positionnegative motion is retrograde, write R · a negative travel subtracts | ||
| D:mars | Mars: this midnight, next midnight, motion, × A6 ÷ 24, positionnegative motion is retrograde, write R · a negative travel subtracts | ||
| D:jupiter | Jupiter: this midnight, next midnight, motion, × A6 ÷ 24, positionnegative motion is retrograde, write R · a negative travel subtracts | ||
| D:saturn | Saturn: this midnight, next midnight, motion, × A6 ÷ 24, positionnegative motion is retrograde, write R · a negative travel subtracts | ||
| D:uranus | Uranus: this midnight, next midnight, motion, × A6 ÷ 24, positionnegative motion is retrograde, write R · a negative travel subtracts | ||
| D:neptune | Neptune: this midnight, next midnight, motion, × A6 ÷ 24, positionnegative motion is retrograde, write R · a negative travel subtracts | ||
| D:pluto | Pluto: this midnight, next midnight, motion, × A6 ÷ 24, positionnegative motion is retrograde, write R · a negative travel subtracts | ||
| D:trueNode | True Node: this midnight, next midnight, motion, × A6 ÷ 24, positionnegative motion is retrograde, write R · a negative travel subtracts |
Part EFigure and aspects
| Line | Operation and rule | Working | Result |
|---|---|---|---|
| E1 | Cusps on the wheel. ASC at the left, houses counterclockwise, C11 filled | ||
| E2 | Bodies into houses by comparing D5 with the cuspsnote any body within 1° of a cusp | ||
| E3 | Aspectarian: the five Ptolemaic aspects, applying or separating from motionorbs as on the free transits surface |
Part FReceipt
| Line | Operation and rule | Working | Result |
|---|---|---|---|
| F | Receipt: paper, Moira, Δ, cause for every computed line |
Part F · continuationPaper-to-Moira discrepancy account
| Line | Paper | Moira | Δ | Cause / 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