What does appulse mean?
An appulse is the closest approach of one object to another — a term used today almost exclusively by astronomers. When two celestial bodies, such as the Moon and a planet or two bright stars, appear to pass very near each other in the sky without one actually hiding the other, that moment of minimum separation is called an appulse. The word derives from Latin "appulsus", meaning a driving toward or striking against, and it entered English in the seventeenth century. Although it once had broader use for any physical impact or contact, modern usage is confined to observational astronomy, where an appulse offers skywatchers a striking visual pairing even when no true eclipse occurs. Its rarity outside scientific writing gives it a precise, specialized character, making it a useful term for describing near-misses among the heavenly bodies.
nounThe closest approach of one celestial body to another, especially in a conjunction, occultation, or transit; more generally, the act of driving toward or striking against something.
- In astronomy: the closest apparent approach of one celestial body to another, as seen from Earth, often just short of an occultation or eclipse.
- A physical striking against or collision with something; the act of driving toward and touching.
"The appulse of Venus and Jupiter brought the two planets within a quarter of a degree of each other in the evening sky."
"Observers gathered to watch the rare appulse of Mercury and Saturn low on the western horizon."
"The comet's appulse with the cluster of stars made for a striking photographic pairing."
The plural is regular and appears mainly in astronomical literature when discussing multiple events.
"Several lunar appulses were recorded throughout the year."
When the Moon grazes a planet without quite covering it, astronomers call that near-miss an 'appulse' — a word borrowed straight from Latin for 'a striking against'.
Reviewed by Deb Chak, Editor. AI-assisted content curated by RJS Tech Solutions LLP.
Etymology of appulse
Appulse comes from the Latin noun "appulsus", meaning a driving or thrusting toward, derived from the verb "appellere" (to drive to), itself formed from "ad-" (toward) plus "pellere" (to drive). This same root "pellere" produced such English words as impulse, propel, expel, and repel. The word entered English in the early seventeenth century, initially with the general sense of a striking against or collision, before settling into its specialized astronomical meaning of a close apparent approach between celestial bodies.
How appulse is actually used
"Appulse" is a technical term used almost exclusively by astronomers; it is formal and rare in everyday speech. In astronomy it specifically denotes the moment of minimum angular separation between two bodies, even if no actual covering (occultation) occurs.
Easily confused with appulse
An impulse is a sudden urge or driving force acting on something, whereas an appulse is an actual close approach or coming into contact of two objects, typically astronomical bodies.