Nānā ao: Maunakea Observatories’ New Instrument
Among its many natural wonders, Maunakea is remarkable for its pristine, clear skies. Although Maunakea towers above the most active weather layers of the earth’s atmosphere, its summit still sees its share of clouds which poses a challenge for astronomical observations on occasion. Named by CFHT staff member Alexis Acohido, Nānā ao, literally “watcher of clouds” in ʻōlelo Hawaiʻi (Hawaiian), is a new instrument that will be shared by the Maunakea Observatories to facilitate the detection of oncoming banks of clouds by nighttime observers.
Nānā ao undergoing tests in the Canada-France-Hawaiʻi Telescope courtyard
Nānā ao improves on the former ASIVA instrument by providing higher sensitivity and spatial resolution in the visible (the colors our eyes are sensitive to) and long wave infrared (LWIR) bands (invisible, “thermal” light). The LWIR band camera is sensitive to light in the 8-14 micron wavelength range, which is the band in which room-temperature objects (~300 K or 27°C) predominantly emit thermal light. The background sky above the atmosphere is significantly cooler than this, sitting only a few Kelvin degrees above absolute zero, and the atmospheric gases are poor thermal emitters in comparison to most liquids and solids. Consequently, clouds – which are a suspension of liquid or solid water droplets/crystals – contrast strongly against the deep cool of outer space when imaged with an LWIR camera. Observers will use Nānā ao’s combined LWIR and visible, 180-degree “fisheye” field of view images, to distinguish both thick and thin clouds approaching Maunakea. This will provide them with advance warning to avoid the observation of targets that are sensitive to the blockage of light by clouds.
Ice buildup on ASIVA
An easily overlooked aspect of Nānā ao is that like any other outdoor-mounted optical device on Maunakea, it needs to be prepared to survive some impressively bad weather. Winds on Maunakea frequently reach hurricane strength, and ice buildup on structures can extend out horizontally by several feet! Nānā ao has a rotating cover that is designed to avoid damage from mechanical lock-ups due to ice build-up while affording it a full view of the horizon in all directions when it is open.
