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As you suggested, the Sagittarius constellation is a direction, not a place, as the stars and other components we see could be at vastly different distances from Earth.
Sagittarius A* is the name of what current cosmological theory interprets as a massive black hole at the center of the Milky Way galaxy, and which appears from our (radio-telescope) point of view to be in the vicinity of the Sagittarius constellation (hence the name).
In other words, that signal coming from Trantor (for those who recognize the reference).
Azimov and the “Foundation” trilogy.
The string 6EQUJ5, commonly misinterpreted as a message encoded in the radio signal, represents in fact the signal's intensity variation over time, expressed in the particular measuring system adopted for the experiment. The signal itself appeared to be an unmodulated continuous wave, although any modulation with a period of less than 10 seconds or longer than 72 seconds would not have been detectable.
Trantor was the home world of the seat of the Galatic Empire
I read your Books Asimov!