Old instruments
Intercept Method
Direct answer
Intercept Method is a sight-reduction method that plots a position line from the difference between observed and computed altitude.
Intercept Method is an altitude-difference plotting method used in historical astronomy, timekeeping, or navigation.
$0 today, then $12/month after 7 days. Cancel anytime.
At a glance
- Found in
- Historical Almanacs & Instruments
- Related
- Lunar Distance Method, Sight Reduction, Marcq Saint-Hilaire Method, Line of Position
Intercept Method is an altitude-difference plotting method used in historical astronomy, timekeeping, or navigation.
An engraved functional orientation; the page explains the real instrument, method, or publication.
What does your own chart say about you?
Choose love, work or purpose. Your reading is written from your chart. Your reading uses your own birth details.
Walk through Alex’s whole example first
The Road of AgesSee the turning points of your whole life, from your birth date
See your road's shape
Prefer to explore first?
The Road of AgesThe turning points of your whole life, from your own chart
Walk my road
Free, by email
Your daily Almanac letter
One short letter at 7 each morning: the day’s theme read for your own chart, and one thing to do with it.
The story behind Intercept Method
The intercept approach became the dominant practical form of modern manual celestial sight reduction.
A one-minute story
The Book of the Sky
How people learned to read the sky, from Babylon to the day you were born.
Why Intercept Method matters
Intercept Method matters because it replaces a difficult full circle of equal altitude with a short local straight-line construction.
How to read Intercept Method
Read Intercept Method by measuring the intercept in nautical miles along the azimuth from an assumed-position plotting point.
Intercept Method in practice: an example
An observed altitude 6.2 minutes greater than computed gives a 6.2-nautical-mile intercept toward the body.
Where readings of Intercept Method go wrong
The toward-or-away rule and azimuth direction must be correct; reversing either displaces the line.
Sources and editorial method
Research references used for this entry include:
- National Geospatial-Intelligence Agency: The American Practical Navigator - Official modern reference for navigation principles, celestial observations, sight reduction, and navigational tables.
- Source
- The Great Almanac Dictionary
- Category
- Historical Almanacs & Instruments
- Last updated
- 2026-09-26
Explore Intercept Method
A definition tells you what it is; your own birth chart tells you what it means for you. The Oracle casts your real chart and answers for your love, your work, and your year ahead, in conversation. It opens with the 7-day Seeker trial.
Speak with the OracleRelated terms
More in Historical Almanacs & Instruments
- Marine Chronometer
- Observed Altitude
- Refraction Correction
- Star Catalogue
- Agricultural Almanac
- Astronomical Clock
- Clepsydra
- Equation of Time Table
From the reference page to your own chart
Every word here
is in your own chart.
- A personal reading about love, work or purpose, written from your chart
- A practical next step to consider
- It opens with 7 days free, with the AI Oracle and daily guidance
$0 today, then $12/month after 7 days. Cancel anytime.
Common questions
What is Intercept Method?
Intercept Method is a sight-reduction method that plots a position line from the difference between observed and computed altitude.
What do people get wrong about Intercept Method?
The toward-or-away rule and azimuth direction must be correct; reversing either displaces the line.
Free, by email
The Almanac, in your inbox at 7
One short letter at 7 each morning: the day’s theme read for your own chart, and one thing to do with it.
