McMath-Pierce telescope. Top of the tower of the McMath-Pierce solar telescope at the Kitt Peak observatory in Arizona, USA. This is the world's largest solar telescope. It has a 2.1-metre Sun- tracking mirror (heliostat, upper centre) at the top of a 30-metre tower. The mirror reflects sunlight down a 152-metre long diagonal optical tunnel. Deep underground is a 1.5 metre focus mirror; this reflects the light half way back up the tunnel to a further mirror which directs the light down into an underground observing room. The vertical bars seen here are a wind shield.