Celestial polesThe two points in the sky around which all stars seem to turn: the extension of the Earth’s axis. The north celestial pole lies very close to Polaris; the south pole has no bright star. The pole’s height above the horizon equals your latitude.
DeclinationThe celestial “latitude”: an object’s angle north (+) or south (−) of the celestial equator, from +90° to −90°. Vega is at +38.8°, Sirius at −16.7°. From a given latitude, declination tells you whether an object is always up, never up, or rises and sets.
CulminationAn object’s crossing of the meridian, at the highest point of its path; the best time to observe it. For an object south of the zenith, its altitude then is 90° − latitude + declination. From London (51.5°), the Orion Nebula (−5.4°) culminates at about 33°.