Editing 4769 Castalia (section)

==General information==

On 25 August 1989 Castalia passed {{convert|0.0269378|AU|km mi|abbr=on|lk=on}}<ref name=jpl-close/> (within eleven [[Lunar distance (astronomy)|lunar distance]]s) of Earth, allowing it to be observed with [[Radar astronomy|radar]] from the [[Arecibo Observatory]] by [[Scott Hudson (electrical engineer)|Scott Hudson]] ([[Washington State University]]) and [[Steven J. Ostro]] ([[Jet Propulsion Laboratory|JPL]]). The data allowed Hudson et al. to produce a three-dimensional [[Mathematical model|model]] of the object. During the 1989 passage Castalia peaked at an [[apparent magnitude]] of 12.<ref name="NEODyS1989"/>

Castalia has a peanut shape, suggesting two approximately 800-meter-diameter pieces held together by their weak mutual gravity. Since then radar observations of other asteroids have found other [[contact binary (asteroid)|contact binaries]].<ref name="Binary"/>

Castalia is a [[potentially hazardous asteroid]] (PHA) because its [[minimum orbit intersection distance]] (MOID) is less than 0.05&nbsp;AU and its diameter is greater than 150 meters. The Earth-MOID is {{convert|0.0204|AU|km mi|abbr=on|lk=on}}.<ref name=jpldata/> Its orbit is well-determined for the next several hundred years.

{| class="wikitable" style="font-size: 0.9em;"
|+Earth Approach on 22 August 2023<ref name=jpldata/>
! Date
! [[JPL Horizons]]<br />[[Curve fitting|nominal]] geocentric<br />distance ([[astronomical unit|AU]])
! uncertainty<br />region<br />([[3-sigma]])
|-
|2023-Aug-22 09:21 ||{{Convert|0.11003|AU|e6km|abbr=unit|lk=on}}<ref name="jpldata"/> || ±{{val|6|u=km}}<ref name="CA2023"/>
|}