Galactic centre
Point of the Milky Way where the center of rotation of the Milky Way is located, in the direction of the constellations of Sagittarius, Ophiucus and Scorpio. Very interesting for photographers as it is in appearance the brightest area. Wikipedia
GC
See Galactic Center.
GMT
An acronym for Greenwich Mean Time (GMT). It’s a time system that refers to solar time at the Royal Observatory in Greenwich, London. For a value of GMT -1 indicates that the time zone is 1 hours later than GMT, which is the time zone of Germany, France, part of Spain, … Wikipedia.
Golden hour
Time period of the day that by the qualities of sunlight is photographically appreciated. This type of light is more diffuse than that of the central hours of the day, it is softer and less contrasted and of a warmer tone. It is considered the golden hour, both dawn and dusk, when the sun is between 6º above and -4º below the horizon. Wikipedia.