Ptolemy’s equant
E1025921
Ptolemy’s equant is a geometric device in his planetary theory that allows planets to move with uniform angular speed around an off-center point, introduced to better match observed non-uniform planetary motion.
All labels observed (1)
| Label | Occurrences |
|---|---|
| Ptolemy’s equant canonical | 1 |
How this entity was disambiguated
This entity first appeared as the object of triple T13132078 — resolving that mention is where its identity was fixed. The disambiguator weighed these candidate entities and picked the highlighted one (or “None”, minting a new entity). This is how homonymy is resolved: the same surface form can point to different entities.
NED1
Entity disambiguation (via context triple)
gpt-5-mini-2025-08-07
Target entity: Ptolemy’s equant Context triple: [Ibn al-Shatir planetary model, replaces, Ptolemy’s equant]
-
A.
Tychonic system
The Tychonic system is a historical hybrid model of the cosmos in which Earth is stationary at the center while the Sun orbits Earth and the other planets orbit the Sun, proposed as a compromise between geocentric and heliocentric theories.
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B.
Ibn al-Shatir planetary model
The Ibn al-Shatir planetary model is a 14th-century geocentric astronomical system that replaced Ptolemy’s equant with epicycles to more accurately predict planetary motions and anticipated key mathematical features of later heliocentric models.
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C.
Ptolemaic system
The Ptolemaic system is an ancient geocentric cosmological model that places Earth at the center of the universe with the Sun, Moon, and planets moving around it in complex circular paths.
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D.
Alfonsine Tables
The Alfonsine Tables are a set of medieval astronomical tables, compiled under the patronage of Alfonso X of Castile in the 13th century, that provided planetary positions and were widely used in Europe for centuries.
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E.
Tusi couple
The Tusi couple is a geometric device from medieval Islamic astronomy that generates linear motion from the sum of two circular motions, later influencing Copernican models of planetary motion.
- F. None of above. chosen
- G. Unsure - the case is ambiguous/there is not enough information to decide.
NED2
Entity disambiguation (via description)
gpt-5-mini-2025-08-07
Target entity: Ptolemy’s equant Target entity description: Ptolemy’s equant is a geometric device in his planetary theory that allows planets to move with uniform angular speed around an off-center point, introduced to better match observed non-uniform planetary motion.
-
A.
Tychonic system
The Tychonic system is a historical hybrid model of the cosmos in which Earth is stationary at the center while the Sun orbits Earth and the other planets orbit the Sun, proposed as a compromise between geocentric and heliocentric theories.
-
B.
Ibn al-Shatir planetary model
The Ibn al-Shatir planetary model is a 14th-century geocentric astronomical system that replaced Ptolemy’s equant with epicycles to more accurately predict planetary motions and anticipated key mathematical features of later heliocentric models.
-
C.
Ptolemaic system
The Ptolemaic system is an ancient geocentric cosmological model that places Earth at the center of the universe with the Sun, Moon, and planets moving around it in complex circular paths.
-
D.
Alfonsine Tables
The Alfonsine Tables are a set of medieval astronomical tables, compiled under the patronage of Alfonso X of Castile in the 13th century, that provided planetary positions and were widely used in Europe for centuries.
-
E.
Tusi couple
The Tusi couple is a geometric device from medieval Islamic astronomy that generates linear motion from the sum of two circular motions, later influencing Copernican models of planetary motion.
- F. None of above. chosen
Statements (44)
| Predicate | Object |
|---|---|
| instanceOf |
concept in astronomy
ⓘ
geometric device ⓘ mathematical construct ⓘ |
| addresses | non-uniform apparent speed of planets ⓘ |
| appliesTo |
Moon’s motion
ⓘ
Sun’s apparent motion ⓘ planetary motion ⓘ |
| assumes | Earth near but not at the center of planetary orbits ⓘ |
| category |
ancient Greek astronomy
ⓘ
history of science ⓘ |
| conceptualStatus | approximation to elliptical motion ⓘ |
| contrastsWith | uniform motion about the geometric center of the deferent ⓘ |
| criticizedBy |
Ibn al-Shatir
ⓘ
Nasir al-Din al-Tusi ⓘ medieval Islamic astronomers ⓘ |
| definesMotionAs | uniform angular speed around an off-center point ⓘ |
| describedIn | Almagest ⓘ |
| field |
ancient astronomy
ⓘ
celestial mechanics ⓘ |
| hasConsequence |
increased accuracy of Ptolemaic predictions
ⓘ
philosophical tension with uniform circular motion doctrine ⓘ |
| hasPurpose |
to model non-uniform planetary motion
ⓘ
to preserve uniform angular motion about a point ⓘ |
| historicalPeriod | 2nd century CE ⓘ |
| improves | fit to observed planetary positions ⓘ |
| influenced |
Copernican heliocentric theory
ⓘ
development of alternative planetary models in Islamic astronomy ⓘ |
| inspired | geometric devices such as the Tusi couple ⓘ |
| introducedBy |
Claudius Ptolemy
ⓘ
linked to:
Claudius Ptolemaeus
|
| locatedRelativeTo |
Earth
ⓘ
center of the deferent ⓘ |
| mathematicalRole | parameterization of orbital non-uniformity ⓘ |
| namedAfter |
Claudius Ptolemy
ⓘ
linked to:
Claudius Ptolemaeus
|
| partOf | Ptolemaic planetary theory ⓘ |
| relatedTo |
eccentric deferent
ⓘ
epicycle ⓘ |
| relativeTo | deferent circle ⓘ |
| replacedBy | elliptical orbits in Keplerian astronomy ⓘ |
| replacedIn | Copernican system ⓘ |
| represents | point from which angular motion appears uniform ⓘ |
| usedFor |
predicting planetary longitudes
ⓘ
refining astronomical tables ⓘ |
| usedIn |
Ptolemaic model of the Solar System
ⓘ
linked to:
Ptolemaic system
|
| violates | Aristotelian principle of uniform circular motion about the center ⓘ |
How these facts were elicited
The pipeline generated the facts above by prompting gpt-5.1 with this entity's name + description and the instruction below.
Instruction
You are a knowledge base construction expert. Given a subject entity and a description of it, return factual statements that you know for the subject as a JSON list of dictionaries(triples), where keys must be "subject", "predicate" and "object". The number of facts may be very high, between 25 to 50 or more, for very popular subjects. For less popular subjects, the number of facts can be very low, like 5 or 10. # Requirements - If you don't know the subject at all, return an empty list. - If the subject is not a named entity, return an empty list. - Include at least one triple where predicate is "instanceOf". - Do not get too wordy. - Separate several objects into multiple triples with one object.
Input
Subject: Ptolemy’s equant Description of subject: Ptolemy’s equant is a geometric device in his planetary theory that allows planets to move with uniform angular speed around an off-center point, introduced to better match observed non-uniform planetary motion.
Referenced by (1)
Full triples — surface form annotated when it differs from this entity's canonical label.