top of page
Image of the Month
A Visit to the NASA Infra Red Telescope Facility (IRTF)
By the fime we had finished our lunch, we were starting to tire, definitely feeling the effects of the 14,000 foot elevation. We decided to just take a drive around the lower ridge that is shown in the photo above, and get a closer look at the Keck telescopes through the glass windows in their visitors gallery, and then drive back down the mountain. But as we drove toward the two Keck domes and were passing the NASA InfraRed Telescope dome, I noticed that the big overhead door at the loading dock was wide open, and the telescope could be seen, just inside. Just on an impulse, I pulled into the IRTF parking lot. Two gentlemen were standing on the dock just outside the open door. I got out, approached them, and asked if it would be alright if I went just inside the door to snap a photo of the telescope. They both said that they were waiting for a forklift to move a large instrument crate inside the door, and that it would be fine for me to snap a few photos, since everyone was just standing around! I jumped at the chance, rushed back to the car, grabbed my camera and went back to shoot a few photos! What a bonus! One of the photos is shown below.
This is a very unusual telescope. For those not familiar with Infrared telescopes, a bit of explanation helps. The infrared portion of the spectrum is below the visible wavelengths, lying between ultraviolet and the longer radio wavelengths. An infrared scope is actually observing heat, not light! Two of the main areas where an infra red scope is useful is to penetrate clouds of interstellar dust and observe any hot objects that are hidden by them. The other area is to probe below the surface clouds of gas giant planets like Jupiter or satellites with dense atmospheres like Saturns moon Titan. While some scopes which detect visible light can be used for some observations in the "near infrared" portion of the spectrum, just below ultraviolet,
observation in the "mid" and "far" infrared portion of the spectrum requires dedicated scopes such as the NASA IRTF.
In order to produce good infrared data, the telescopes themselves, as well as the detector instruments must be kept cooled with liquid nitrogen. The entire truss system of this telescope is cooled with refrigerant that circulates through the truss tubes! Another problem with infrared observation is that infrared radiation is absorbed by the water vapor in the Earth's atmosphere. For that reason, the best IR observations are made from the highest elevations on Earth, or from the Hubble Space Telescope. At 14,000 feet elevation, Mauna Kea offers the very best infrared observing conditions for a GROUND BASED telescope!
The NASA InfraRed Telescope is the most effective infrared telescope in the world, because of its optimal location and its outstanding design & construction. The physical construction of the tube assembly was designed to be the lightest possible and still have the greatest rigidity. The tube is supported by an extremely massive and rigid English yoke-type equatorial mount, which offers the most structural rigidity and resistance to deflection. These design features, along with the optimum observing conditions on Mauna Kea (steady laminar airflow over the peak aided by the fact that the observatory is completely surrounded by the Pacific Ocean) produce sub-arcsecond resolution!
The NASA InfraRed scope has a 3 meter (120 inch) primary mirror with an f/ratio of f/2.5. The small hyperbolic secondary mirror provides a cassegrain focal ratio of f/35. The small secondary size and long focal ratio both minimize the thermal emissions that might degrade infrared observations. The small secondary is mounted on an oscillating mount that allows it to rapidly alternate between target and open sky at up to 4 times per second. This allows instrumentation to "subtract" sky radiation and obtain a "true" reading of the infrared data. Getting a chance to walk around this scope and take a number of photos was a nice added bonus to our trip to the summit.
By the time we finished at the NASA scope and then drove down and peeked inside the Keck domes, we were "bushed". The altitude had taken its toll! But, it was a very productive and unforgettable excursion. At about 2 in the afternoon we made our way back down the mountain. After a quick restroom stop at the Visitor Center, it was back to the Kohala Coast to recuperate! We slept well that night, and were glad that the next day would be spent lolling on the beach!
bottom of page