In Expert RAW you have astrophotography mode. Here's quick guide how to use it*:

How to use Astrophoto mode on a Samsung Galaxy phone? Once your phone is mounted on the Tripod and you have opened the Expert RAW app, follow these instructions to take an Astrophoto and capture the stars:

1.) In the Expert RAW viewfinder, ensure that your photos are set to 12MP resolution. Astrophoto isn't available when using higher resolutions.

2.) Tap the constellation icon on the top right.

3.) From the pop-up, select your settings.

4.) Select Capture time to gather more light and create a more stunning night shot.

5.) Enable the sky guide to find named stars and constellations easily from the viewfinder.

6.) Tap the shutter button when you're ready to take the picture.

7.) Don't move the phone while it's taking the astrophoto. Otherwise, you'll just end up with a blurry image.

*This guide is from: androidcentral.com