Complex sentence: The southern polar site is an exceptional location for this sort of telescope because of the extremely favourable atmospheric conditions, high altitude, and because the sun is only visible for six months of the year negating the need to shield the telescope from it during that time.
Split into simpler sentences: The southern polar site is an exceptional location for this sort of telescope because of the extremely favourable atmospheric conditions. Also, the sun is only visible for six months of the year negating the need to shield the telescope from it during that time.