Culmination

6.13 - Understand, in relation to astronomical observations, the terms:
b) culmination

6.16 - Understand the apparent motion of circumpolar stars, including upper transit (culmination) and lower transit

Culmination is when a star (or other body) reaches the observer's meridian.

A star will do this twice each day.

  • Upper Culmination is at its the highest point.
  • Lower Culmination is at its the highest point.

These will mean different views depending on the location of the observer.

  • A circumpolar star will be reach upper and lower culmination in the sky.
  • A seasonal star will reach upper culmination in the sky and lower transit below the horizon.
  • A star never visibile from a location will technically culminate but both types will be beneath the horizon.

The word transit is sometimes used instead of culmination. In the specification upper culmination is called upper transit or just culmination so if you are asked 'when a star culminates...' it means upper culmination.

Maths Time

Co-declination (Distance between NCP and Star) = 90° - Declination

An object's altitude (A) in degrees at its upper culmination is equal to 90 subtracted by the observer's latitude (L) and added by the object's declination (δ): A = 90° − L + δ.

Upper Culmination takes place when Right Ascension = LST

 

Transit

There are two similar meanings of transit: A transit is one body moving in front of another
It is sometimes used instead of culmination when a body moves across a meridian line

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