At a wavelength of 70 centimeters (432 MHz). All via the magic of extremely effective error correcting codes (and fairly rare atmospheric conditions).
Related, I'm amazed that my little $70 WSPR transmitter can push a 20m/14MHz signal from San Francisco to Georgia using only 0.2W, transmitting on a pretty lousy backyard dipole only 10 feet off the ground. True, it's only a beacon ("call sign Kxxxxx transmitting from SF at 200mW"), but still...
I got from central Switzerland to Japan on about 10W on 20m once using JT65 or JT9 (I can't remember which). The antenna was a random length of wire tied a rock and tossed out of my fourth-story apartment window into a field below.
I've done US east coast to Australia and New Zealand on 160m, with 5 watts and a vertical. Well, the vertical was 90' of tower and had 40,000 feet of wire underneath it and was feed with 1 5/8" hardline, but still.
But they are line of sight. That's what makes this so special.
Stars are many lightyears away, and radiate insane amounts of power the vast majority of which is lost. By the time it reaches here you may need a very long exposure to be able to see them at all. But it is line of sight. These waves were of the line-of-sight variety and somehow they were bent around the planet enough to register. That's a very hard to achieve thing.
