Asgard holographic projection

From The Stargate Omnipedia

Asgardholographicprojection2.jpg

Device which delivers and maintains a holographic recording or image of a person or object potentially galaxies away. Interference is rare, as the technology is very nearly a perfect visual transmitter, but when it does occur it is typically in the form of a temporary shimmer or blur.

The Asgard install holographic projectors into their Halls on protected planets, as well as utilize them in communications with the High Council. One may step onto a holographic platform and be projected in real-time into another galaxy, such as Ida, where some Asgard reside.

KEY EPISODES

Thor's Hammer - O'Neill and Teal'c bear witness to a false image of Thor via a holographic projector.
Thor's Chariot - After passing the Cimmerian test, Carter, Jackson and Gairwyn see the true Thor for himself through a holographic projection.
Nemesis - O'Neill's image is holographically transmitted into the conference room of the S.G.C. with dire news for his team.
Red Sky - O'Neill's image is transmitted across galactic voids to the Asgard High Council chamber in an attempt to plead for their aid.
Revelations - Carter's holographic image is synthesized in a corridor aboard Osiris' mothership, allowing Teal'c and O'Neill the element of surprise.
Covenant - Thor transports himself to the Julia Donovan's Inside Access studio to show the people of Earth that he is artificial. The ruse succeeds.