A phenomenon that curtains of faint and shimmering light are visivle in the night sky can be seen around the North Pole.
The two sentences that are being joined by the conjunction 'that' are:
A phenomenon can be seen around the North Pole.
Curtains of faint and shimmering light are visible in the night sky.
Notice anything? Isn't this exactly what I was explaining at the beginning of my last post, when putting
He is a good teacher.
Effective strategies for classroom discipline are the envy and wish of every new teacher.
1. Curtains of faint and shimmering light are visible in the night sky.
2. The Aurora Borealis is a phenomenon.
...and why I couldn't use 'that'? Why I had to use 'whose'?
Perhaps I have not been able to explain it clearly enough, and someone else in the forum can come in at this point.