This is the quickest way from Marrakech to a really dark desert sky. You ride a camel into the dunes at sunset, eat dinner at camp and then have the evening under the stars. There is no telescope and no guided session; on a clear night you need neither, as the Milky Way, the bright planets and the constellations are all visible to the naked eye.
Erg Chebbi works because it is so far from anything lit. There is no glow from a city on any side, so on a clear night the Milky Way is not a faint haze but a band you can follow across the sky. Few places that dark are left within reach of most travellers.
The cost is the driving. Erg Chebbi is about 560 km and roughly eight hours from Marrakech each way, and the trip lasts two days: a long drive, a night at camp and a long drive back. The first day reaches the dunes for the camel ride and dinner; the second starts with sunrise and heads home. If you would rather break up the road, look at a 3 or 4-day desert trip.
Prices are per person: €518 travelling alone, €260 each for two, €191 for three, €160 for four, €139 for five and €121 for six. That covers return transport from Marrakech, the sunset camel ride, the night at camp, and dinner and breakfast. Lunch on the road is not included, though we stop for it, and travel insurance and tips are extra.
Two things are worth knowing. The moon matters more than the season, because a full moon washes out the faint stars, so if the Milky Way is why you are going, travel close to a new moon. And from autumn to spring the desert is cold at night, colder than most people pack for; the sky is best seen sitting still outside long after dark, so bring a warmer layer than you think you need. The trip is private, for one to ten people.