Station 00 · Sea level · 0 m AMSL
0m
You cannot
see anything.
Twenty millimetres of precipitable water vapour stand over this spot — not cloud, the whole column. The boundary layer under the inversion stays convective until well after dark, and the nearest town is forty kilometres upwind.
No mirror figure, no detector and no integration time recovers a wavefront that arrived broken. At sea level the limiting instrument is not the optics. It is the air.
Measured at the road head, 0 m
- Precipitable water vapour
- 20.4 mm
- Seeing, DIMM at 500 nm
- 2.8″
- V-band extinction
- 0.42 mag airmass⁻¹
- Zenith sky brightness
- 18.1 mag arcsec⁻²
Scroll to climb
Fig. 1 — What altitude actually removes
Ninety per cent of the water is below 2,600 metres.
Precipitable water vapour and V-band extinction against elevation, from the site survey. The curve is steep and then it is flat: almost all of the gain is bought in the first two and a half kilometres, and there is very little left to buy above them. This is the entire reason the facility is where it is.
- Precipitable water vapour mm
- V-band extinction mag airmass⁻¹
Station 01 · The inversion layer · 1,400 m AMSL
1,400m
The lid.
A subtropical marine inversion sits on this coast for two hundred and eighty nights a year. Below it, moist air is trapped and stirred. Above it, the temperature rises with height instead of falling, and convection simply stops. The lid is roughly two hundred metres thick and it is the most important geological feature on the site — more than the rock, more than the road.
The observatory is built four hundred metres above the top of it. Everything you were looking through a minute ago is now a floor.
- Deck top, median
- 1,180 m
- Inversion thickness
- ~200 m
- Nights capped / yr
- 281
Station 02 · The instrument · 2,635 m AMSL
2,635m
Now the mirror
is the limit.
With the air out of the way, everything the design does becomes visible. The dome is not a shed with a hole in it — it is a thermal machine whose only job is to be exactly the temperature of the night outside it. Click it to open the shutter.
Median delivered seeing · DIMM, 500 nm, 2019–2025
0.62″
Better than 1.0″ on 78% of usable nights. Hover for the seven-night range.
- Precipitable water vapour
- 1.9 mm
- Zenith sky brightness, V
- 21.9 mag arcsec⁻²
- Photometric nights per year
- 198
- Coherence time τ₀
- 5.8 ms
- Isoplanatic angle θ₀
- 2.1″
- Shutter closes above
- 15 m s⁻¹
Telescope
3.6m
- Optical design
- Ritchey–Chrétien
- Nasmyth f-ratio
- f/8
- Mount
- Altazimuth, direct drive
- Primary blank
- Zerodur, 178 mm
- Active support
- 150 axial actuators
- Pointing rms
- 1.2″ all-sky
Enclosure
22.0m
- Shutter aperture
- 4.5 m
- Rotation rate
- 2.0° s⁻¹ on 32 bogies
- Ventilation
- 18 louvres, 44 m² open
- Flushing target
- ΔT < 0.5 K
- Cladding
- Anodised aluminium panel
- Survival wind
- 55 m s⁻¹
Fig. 2 — Nasmyth path. Hover any element.
Permanently mounted instruments
- VRISVisible integral-field spectrograph · R = 4,000 – 18,000 · 0.36–1.02 μm
- CIRCEInfrared imager and long-slit · 0.9–2.5 μm · 8.5′ field
- ECHO-115Vacuum echelle · R = 115,000 · 0.4 m s⁻¹ stability over 12 months
- AO-340×40 Shack–Hartmann · 1,170-actuator DM · 62% Strehl in H
Station 03 · 2,635 m · 03:00 local
First light,
every night.
Nothing was added on the way up. The field you are looking at now is the same six thousand points that blinded you at the road head — same buffer, same count, same draw. The only variable that changed was how much air stood in front of it. That subtraction is the whole product, and it is the only thing this facility sells.
Drag horizontally to rotate the dome on its bogie rail Az 000.0°
Apply for observing time