There's constellations in every chapter except chapters 1 & 9.
Chapter 2 - 1 ConstellationDining TableIn the room directly after the room where you need to form an exit door from slanted paintwork, you'll go into a sort of back room where there's some yellow metal stairs going up on the right. Below the metal stairs (you'll have to jump across some random objects) is a hidden black corridor leading to the constellation room. In this room, the constellation is a large circular table on its side. It takes a while to get the right angle, but it's there.
Chapter 3 - 1 ConstellationCoffee MugAs soon as you exit the yellow hall from the start, do a hairpin right turn to see the constellation room. The constellation in this room is a coffee mug on its side with the handle at the bottom. It takes a while to find the right spot, but it's there.
Chapter 4 - 1 ConstellationCheese WheelAt the start in the reception area on the right when entering, the side of the filing cabinet.
Thanks to Diquarks for this! Chapter 5 - 1 ConstellationVending MachineAfter the room with the duplicating sign with 'SomnaSculpt
Sleep Clinic Gallery' on it, you will come to a room with a table with flowers on it with a vending machine to the left of it. To the left of the vending machine is the route to the constellation room.
Thanks to Diquarks for this! Chapter 6 - 1 ConstellationChairFrom the start, enter the relaxation room, and then enter the theatre. Behind the right door of the set of double doors where you can exit from the theatre is the black pathway to the constellation room.
Thanks to Diquarks for this! Chapter 7 - 1 ConstellationLight ProjectorAfter you grab a dice and are transported to an all white room. In this room there is a white square outlining the floor, part of this is staircase leading down to the constellation room.
Thanks to Diquarks for this! Chapter 8 - 1 ConstellationKeyboardIn the large area with giant water coolers and other objects. Walk towards the exit, on the right are some rocks follow them to the right and down a hill. The entrance is at the bottom of the hill.
Thanks to Diquarks for this!