For this achievement, you have to find every stone circle and match their pattern to the stars. This achievement can be unlocked after the quest "May Amun Walk Beside You". Note that some stone circles are found in high-level areas, so low-level players might be attacked on the way. It's still completely do-able at all levels though, just keep an eye out for random enemies when heading to the stone circles.
Also, in regards to solving the star constellation, Segendary Ty points out
Alligning the constellations can be more easily done if you find the star that is shining orange.
Here's all the stone circle locations, along with their nearest FT (Fast travel). I've also put a video showing all the locations at the bottom of the page.
1. Amun Stone Circle. Area: Siwa, found south of Siwa. FT: Siwa fast travel
2. Osiris Stone Circle. Area: Qattara Depression, found alongside the mountainwall west of the open desert-area. FT: Southmost Sync. point in Paraitonion, north of the Stone Circle
3. Serqet Stone Circle. Area: Iment Nome, found north in the area. FT: Temple of Sekhmet in Yamu, located in Lake Mareotis
4. Divine Lion Stone Circle. Area: Iment Nome, found southeast of Eremos Hideout, East in Iment nome. FT: The only Sync. point found in Iment Nome,
5. Goat Fish Stone Circle. Area: Isolated Desert northwest in Isolated Desert, next to Tomb of the Nomads. FT: Western Sync. point in Isolated Desert, north of Pissa Oros Citadel
6. Apis Stone Circle. Area: Isolated Desert, found southeast in Isolated Desert, southeast of Burial Delving. FT: Remetch Ra fast travel found east in Isolated Desert.
7. Taweret Stone Circle. Area: Faiyum, western part of the lake, southwest of Abandoned Fishing Village. FT: Sync. Point found west in Faiyum, northwest of Dionysias Caravanserai
8. Pisces Stone Circle. Area: Faiyum, northeast part of the lake in Faiyum, southeast of Ketket Cove Hideout. FT: Sync. Point found in Kerke, Northwest in Atef-Pehu Nome
9. The Great Twins Stone Circle. Area: White Desert Oasis, found west of lake right by Sync. Point. FT: The only Sync. Point found in White Desert Oasis
10. Horus Stone Circle. Area: Uab Nome, right northwest of the Sync. Point. FT: Only Sync. Point found in Uab Nome
11. The Scales Stone Circle. Area: Uab Nome, almost directly east of Sync. Point and Senehem Depths. FT: Only Sync. Point. found in Uab Nome
12. Hathor Stone Circle. Area: Ka-Khem Nome, southeast of the Sync. Point. FT: Only Sync. Point found in Ka-Khem Nome
The achievement will unlock after the last stone circle, but I also suggest going back to the stone circle in Siwa to finish the side quest "Bayek's Promise", and get some nice xp.
I also found a great youtube video showing all the locations. All credits to PowerPyx for making the video.
Here are all the timestamps for each location in the video:
00.07 - Amin Stone Circle, Siwa
01.41 - Goat Fish Stone Circle, Isolated Desert
02.46 - Apis Stone Circle, Isolated Desert
03.36 - Osiris Stone Circle, Qattara Depression
04.17 - Divine Lion Stone Circle, Iment Nome
05.02 - Serqet Stone Circle, Intent Nome
06.00 - Hathor Stone Circle, Ka-khem None
06.43 - Pisces Stone Circle, Faiyum
07.24 - Taweret Stone Circle, Faiyum
08.10 - The Great Twins Stone Circle, White Desert Oasis
08.59 - Horus Stone Circle, Usb None
09.45 - The Scales Stone Circle, UAB Nome