Cerro Paranal European Southern Observatory

Situated in the Atacama desert at an altitude of 2635 m (8645 ft) Cerro Paranal is home to the Very Large Telescope (VLT) as well as several other instruments.

When the observatory was being planned, extensive research was carried out to find a site with the best possible attributes such as remoteness from artificial lights and steady seeing. Cerro Paranal was measured to be the best, enjoying better seeing than even Mauna Kea on Hawaii.

Approaching the Summit

This is the view of the observatory from the entrance gate. The coach that would take us the last thousand feet to the summit can be seen in the parking lot (external coaches are not allowed through for security).

The wind was at or above the maximum allowed for visits, but as we were a group of astronomers they bent the rules a little and let us in.

Four Giants

The VLT consists of four 8.2 m (320 in) telescope domes standing adjacent to each other on the flattened summit of the mountain. Together with their auxiliary telescopes and other instruments this makes Paranal the largest optical observatory in the southern hemisphere (by total light-collecting area) and the second only to Mauna Kea worldwide.

The four giant scopes of the VLT are named Antu, Kueyan, Melipal and Yeppen (meaning Sun, Moon, Southern Cross and Evening Star respectively in the local Mappuche language).

We visited Antu, the furthest away in the photo.

Everything about this site is huge: the buildings, the telescopes, the facilities – all are on a scale that dwarfs most other observatories.

Antu

This is the lower part of the 8.2 m scope, showing the mirror support structure which also controls the shape of the relatively thin mirror using 150 active optics actuators.

All four scopes are of the same basic Ritchey-Chretien design, with the 8.2 m  primary mirror having a focal ration f/1.75, making the optical tubes very squat. However, light is reflected from a secondary mirror at the top end, after which it either exits through a hole in the centre of the primary to the Cassegrain focus, or is diverted by a third mirror to either side (Nasmyth foci).

If the four scopes are being used as an interferometer, additional mirrors divert the light beam through tunnels to the VLTI beam combiners.

This image shows the upper part of Antu’s optical tube, including the 1.1 m secondary mirror (made of beryllium for lightness).

The mounting is alt-azimuth: presumably an equatorial mount that could carry the weight of the telescope would itself be prohibitively massive.

Notes on the Gallery images

The tunnels linking each VLT scope with the control center are normally off-limits to visitors – our kind guides allowed us to use them because of the high winds that day.

The smaller domes house 1.8m scopes that work with the four giants when configured as an interferometer. This can give incredible resolution but is only viable with bright objects such as Betelgeuse.

The final two images show the Residence for visiting astronomers. External shots were used in the Bond film Quantum of Solace and the internal shot with its swimming pool demonstrates that having to stay at a remote mountaintop location can have its compensations!