Introduction To Masking For Astrophotography
Chapters 5-8
This is the first four of an eight chapter series of the introduction to masking in Photoshop by Ken Crawford. These tutorials will cover the basics to the advanced methods of creating and refining masks in Photoshop to selectively enhance your images. Learning these masking methods will benefit your image processing for years to come.

Here is the link to Chapters 1-4  
Chapter 5: This tutorial will continue covering blending high dynamic range areas with smooth transitions
Chapter 6: Tutorial for using star masks to correct and boost color and improve star profiles
Chapter 7: This tutorial demonstrates how to blend faint structures using background masks
Chapter 8: This final chapeter will cover masking image enhancements including more work with star masks