Ok, so the main clause is
They call the phenomenon the “White Night” (Midnight Sun)
The modifying clause I think is translated as
“throughout the whole day the sun is bright whether it doesn’t descend or even if it descends”
So together,
They call the phenomenon, where throughout the whole day the sun is bright whether it doesn’t descend or even if it descends, the “White Night” (Midnight Sun).
Not very smooth but I think this is a possible rough translation.
The confusing part is the sun descending but still bright which I think means that during the White Night period even though the sun is moving around in the sky as usual and does descend, it’s not to the point where it goes below the horizon leading to darkness.
I thought there were 3 possible translations for か in this context. It could mean there was an embedded question, or mean “or” or “whether”. It didn’t seem like an embedded question so I thought “or” or “whether” made more sense.
Maybe someone can check the rules for it meaning “or”. I don’t know if it has to occur between two nouns or not.
To me, it made more sense for it to go with おひさま because of しずんでも which together meant “even if it does descend, ( おひさま) is bright”.
Yes, it was a little confusing to me as well but the modifying clause didn’t seem complete without it so that’s why I thought it went with おひさま. I could be totally wrong of course.
Edit: Remember the clause I was having trouble with before a few days ago on p56
よちよち 歩く すがたが とても あいらしい ペンギンは、どうぶつ園などでも 大人気ですね。
Here’s the adjective あいらしい that goes with すがた even though it’s right next ペンギン.
I was trying to find out if this ~か +てverb+も construction could be explained somewhere but I can’t find anything. I’m pretty sure there’s some better way to translate this part.
Maybe it’s time for a native speaker consult hint hint.