Opening the Dome

Sunset at Paranal had the colour of a peach. The sky went red, then violet, then a deep cobalt that nothing else looks like.

At half past six, the dome of UT1 began to open.

Polly was perched on the catwalk above. The slit was twenty metres tall and six metres wide. It opened slowly. Through the gap, the inside of the dome was almost completely dark.

The shape inside was not what most people would call a telescope. It looked more like a vast hospital instrument the size of a house. The main mirror, eight point two metres across, was a curved disc at the bottom. It was polished to a tolerance of fifty nanometres across its entire surface. It was made of a glass-ceramic called Zerodur. It had been ground to its current shape in Germany over five years and brought here by ship and slow truck.

At the back of the dome, an astronomer was at a console with eight monitors. Her name was Camila Vargas. She was thirty-four, from Concepción. She had been a senior support astronomer at Paranal for four years.

Camila was running calibration. "First, we focus," she said. "The telescope's mirror gets warped a little every day by gravity and temperature. We adjust the mirror surface in real time using 150 actuators that push on the back of the glass. We can change its shape by less than the width of a sound wave. We do this every few minutes during the night."

The dome shifted with a hum, rotating to point at a different patch of sky. Twenty-five thousand tons of steel turned on smooth bearings. Polly felt the catwalk tilt.

The first stars came out. Then the Milky Way. The Atacama sky was not like the sky at Glacier Point. It was more. The dust lanes were clearer. The galactic core was a real visible structure with depth.

Camila looked up. "OK. We are open. We have our first target."