Complex sentence: A similar technique is used in liquid mirror telescopes which have mirrors, consisting of a liquid metal such as mercury or a low-melting alloy of gallium, that do not solidify, but are used while still liquid and rotating.
Split into simpler sentences: A similar technique is used in liquid mirror telescopes that have rotating mirrors consisting of a liquid metal such as mercury or a low-melting alloy of gallium. The mirrors do not solidify, but are used while still liquid and rotating.