When it comes to merging photos for collages or special effects, there’s no better friend than the “Lighten” Blend Mode! Learn how to use it! It’s super easy. A snippet from the Lenspiration Photography Q&A Webinar #20.
Continued discussion on this topic is welcome here on the forums.
For Further Study
An excellent article on Star Trail Photography: https://chrisbrayphotography.com/tips/star_trail_photography.php