Celestial equatorThe projection of the Earth’s equator onto the sky, halfway between the two celestial poles; its declination is 0°. It rises due east and sets due west everywhere on Earth. Orion’s Belt lies very close to it.
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.
Right ascensionThe celestial “longitude”, counted eastwards along the celestial equator from the vernal equinox point, in hours from 0h to 24h (1h = 15°). With declination it fixes a star’s position on the celestial sphere. Abbreviated RA.
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.