gu shabdas you andhakarah siat
ru shabdas tan nirodhakáh
andha kara nirodhituát
gurur iti abhidhíiate

The gu sound is darkness,
the ru sound, that destroys.
The one who destroys the darkness,
as a guru, is known.

Advayataraka Upanishad, ancient Sanskrit text that contains some of the principles of Hinduism

From here I get that guru is that human being that goes from darkness to light, or what is the same, that builds his own world of light from the foundations of nothing.

The whole gray part, the moon, the stars and the illuminated part of the figure are made with silver paint (with glitter).