Earth & Sky Ltd., P.O. Box 112, Lake Tekapo 7945, New Zealand.   E-mail: info@earthandsky.co.nz
Phone: +64 (0)3 6806960   Fax: +64 (0)3 6806950
The Mountain  :  The Observatory  :  The Telescopes

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Mount John

Mount John is a roche moutonnee, an asymmetrical rock shaped by the movement of ancient glaciers. The large mass of bedrock attains an altitude of 1031 metres above sea level, rising approximately 300 metres above Lake Tekapo below. One of Mount John's claims to fame is that the highest recorded New Zealand wind gust occurred here on 18th April 1970 — 250 km/h or 135 Knots. Fortunately for us, it's rarely that windy!

On the summit of Mount John is the University of Canterbury's astronomical observatory. During the day its domes can be seen from the Tekapo township. The mountain was chosen as the best observatory site in New Zealand because of its high number of clear nights throughout the year, the stability and transparency of the atmosphere and the uniquely dark skies in the Mackenzie Basin, devoid of city light pollution. It is internationally recognised as one of the best-situated observatories for viewing the southern night skies. For example, the Magellanic Clouds (satellite galaxies to our own Milky Way) can be seen continuously throughout the year.

In addition, it is arguably one of the most beautifully placed observatories in the world, with the magnificent surroundings of glacial lakes and moraine, and the Southern Alps — Return to Top of Page.

The University of Canterbury Observatory
After extensive testing of several possible locations, the Mount John observatory was officially opened on 10th July 1965 as a joint venture between the University of Canterbury and the University of Pennsylvania. In 1969 the US Air Force built a satellite tracking station adjacent to the observatory to monitor US and Soviet satellites. Because of developing technologies, the USAF facility was returned to the Crown in 1983 and soon thereafter the University of Canterbury incorporated it into the observatory. From that time the Department of Physics and Astronomy at the University of Canterbury have been the sole operators of the Mount John Observatory (though see the MOA project below) — Return to Top of Page.

The Telescopes
There are four primary telescopes on the mountain which are actively used by researching astronomers and physicists from New Zealand and all over the world.

The historic Cook Astrograph, built by J. W. Fecker in 1936, was the first instrument to be permanently installed at Mount John (the image right shows it in its heyday). It was commissioned to complete an all-sky photographic survey undertaken by the University of Pennsylvania, the images recorded for the southern hemisphere star survey becoming the Canterbury Sky Atlas, a copy of which is in the Observatory Library. Originally there were three f/7 cameras mounted one above the other. The objectives — 12.5cm, 25cm and 10cm — were designed by Frank E. Ross, using four lens elements in each camera to gather and focus ultra-violet and blue light. The 10cm camera has been replaced by one that is sensitive to a broader part of the spectrum, but there are plans to remount the former camera and restore the Astrograph to its original configuration. The Cook Astrograph is still fully functional, but now stands in well-earned retirement. You can inspect the craftsmanship of this classic instrument on one of our day tours.

In 1970, the 60cm (24-inch) Optical Craftsmen — 'OC' — reflecting telescope (shown left) was installed at Mount John. Its Cassegrain focus operates at f/16. Mounted on an equatorial fork, the OC telescope is normally reserved for photometry (the measurement of light intensity). In late 1991 the OC telescope was completely upgraded with new stepper motor drives and computer control, including automated dome setting.

In 1975 a second 60cm reflector was installed, known as the Boller & Chivens — 'B&C' — telescope. Its Cassegrain focus operates at f/13.5, but an alternative secondary mirror commissioned by MOA (see description below) means that the instrument can also work at f/6.25.

The 1-metre McLellan Dall-Kirkham reflecting telescope (image right) was built in the University of Canterbury’s workshops and was installed at Mount John in February 1986, 'first light' occurring one month later. It is used for a wide variety of astronomical research, most of it in stellar astrophysics: the study of stars and their evolution. In April 2001 HERCULES was commissioned. This is a vacuum fibre-fed échelle spectrograph made at Canterbury, greatly enhancing the McLellan telescope's capabilities.

Secondary optics are available on the McLellan for Cassegrain foci at f/7.7 and f/13.5. Much of the work is now performed at the f/7.7 focus, which has wide-angle optics that provide a 1° diameter field of view. The f/13.5 focus is only used for single stars on axis. The dome automatically tracks the telescope.

In 1996 the B&C (shown left) was first equipped to study gravitational microlensing events, where the bending of light rays by the gravitational field of a massive object (the lens) causes the light from a distant star to be amplified in brightness, typically for 3—5 weeks. The MOA (Microlensing Observations in Astrophysics) project is a combined effort between New Zealand universities (Canterbury, Auckland, Massey & Victoria) and Nagoya University in Japan. The aims of the project are to find objects such as extra-solar planets, black holes and other celestial bodies that constitute dark matter.

In 2003, the MOA team discovered a Jupiter-sized planet orbiting a star several thousand light-years away, the first such occurrence to have been detected with microlensing techniques. The subsequent discovery of a large planet in 2005 by a collaborative group of astronomers, including MOA researchers and two Auckland amateur astronomers, confirmed the value of microlensing for planet hunters.

New Zealand's largest telescope is the locally designed but Japanese-built (with a Russian-made mirror) 1.8-metre f/3 reflector that was commissioned in December 2004 (image right). The instrument sports a cooled 80 megapixel electronic camera (ten 2k x 4k chips) mounted at the prime focus used for photometry as part of the MOA project, and it is the largest telescope in the world dedicated to microlensing observations.

The prime-focus camera is 7.3 metres above the floor when the telescope is vertical. The 1.8-metre primary mirror of the telescope is perforated so that the instrument can be used in a Cassegrain configuration at a later date. The primary mirror is f/3 but the light ray cone, after the corrector lens assembly in front of the camera, is f/2.91. The CCD area is 12 x 15cm, yielding a field of view of 1.3° x 1.6°.

Completely computer controlled, the instrument is capable of observing many millions of stars each night. It is central to the MOA project and is used exclusively by project researchers and scientists.

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