Alignment types
Kinds of celestial alignment
The sky offers many ways for bodies to line up. Each type below is a distinct pattern you can search for, from a single planet passing a star to several worlds gathered along one arc.
Heliocentric
- Heliocentric conjunction — Planets (Sun-centred). Great-circle line fit of the planets as seen from the Sun.
- Heliocentric opposition — Planets (Sun-centred). Line fit with bodies on opposite sides of the Sun.
Apparent (from Earth)
- Apparent planetary alignment — Planets. Great-circle spread of the planets across the sky.
- Apparent alignment with stars — Planets and bright star(s). Great-circle spread including one or more bright stars.
Groupings
- Ecliptic clustering — Planets. Spread in ecliptic longitude of the cluster.
- Conjunction pairs and chains — Planets (Moon optional). Pairwise separations along a chain of close bodies.
- Horizon alignment — Planets (Moon optional). Spread in right ascension, a rise and set proxy refined by location.
Moon and Sun
- Planet and Moon alignment — Planets and the Moon. Great-circle spread including the Moon.
- Planet and Sun conjunction — Planet and the Sun. Angular separation of the planet from the Sun.
- Planet at opposition — Planet opposite the Sun. Angular separation of the planet from the anti-Sun point.
Grand configurations
- Grand trine — Planets (Moon optional). Fit to the 120 degree spaced triangle pattern.
- T-square — Planets (Moon optional). Fit to the 90 and 180 degree pattern.
- Grand cross — Planets (Moon optional). Fit to the four-way 90 degree cross pattern.
- Stellium — Planets (Moon optional). Tight grouping of bodies in ecliptic longitude.
Star appulses and occultations
- Star appulse — A planet or the Moon and a bright star. Closest angular approach to the star.
- Star occultation — A planet or the Moon and a bright star. Closest approach within the body's radius (geocentric).