https://wccftech.com/google-camera-mod-enables-manual-astrophotography-mode-on-pixels/

Pixel 4's Astrophotography mode has now officially made its way to older Pixel devices via an update to the Google Camera app. While it makes for excellent shots of the night sky under the right conditions, there is no way to trigger it manually. One has to point the camera at the sky and hope for it to trigger automatically. A Google Camera mod now makes it possible to trigger the Astrophotography mode manually, and it can make for some interesting photos.

Astrophotography mode works by exposing the camera lens to the light sky for extended periods of time. The technique can also be used to create a 'light painting' effect that creates trails of light. The mode is available in Camera PX, a GCam mod for Google Pixel devices. Three senior XDA Developers members worked on the app, which also enables a host of other features on Pixel devices listed below: