Story: Astronomy – overview

Page 4. Mt John Observatory

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New Zealand was slow to embrace astrophysics – the branch of astronomy that seeks to understand the nature and properties of stars and associated objects in space. It was not until the Mt John Observatory was established that such research was undertaken in New Zealand.


Mt John Observatory is a high-tech research observatory, founded in 1965 as a joint project between the universities of Pennsylvania and Canterbury. It is at Lake Tekapo, in the centre of New Zealand’s South Island – where there is the greatest chance of dark, clear skies.


The first major instruments to be installed were three telescopes for sky photography. They were used in the late 1960s to produce a photographic map of the southern sky, known as the Canterbury sky atlas.

In 1970 and again in 1975, 60-centimetre Cassegrain telescopes were installed. One is used for photometry (the measurement of light intensity), mainly of variable stars (stars that vary in brightness). The other is dedicated to observations of gravitational microlensing.

The McLellan telescope

A large 1-metre Dall-Kirkham Cassegrain telescope was installed at Mt John in 1986. Known as the McLellan telescope, it is used mainly for high-resolution spectroscopy of stars with a Hercules vacuum echelle spectrograph (spectroscopy is the study of the way atoms absorb and emit electromagnetic radiation). The data can be used to measure star velocities, temperatures, pressures, chemical composition, rotation rates and other parameters.

The MOA project

MOA stands for microlensing observations in astrophysics. Microlensing is caused by the bending of light rays by the gravitational field of a massive object (the lens), with the result that the light from a distant star can be amplified in brightness, typically for 3–5 weeks.

The MOA project began at Mt John in 1995, mainly supported by Auckland, Canterbury and Victoria universities in New Zealand and Nagoya University in Japan, for detecting and observing microlensing events. Fifty or so events are discovered annually by astronomers at Mt John. In 2003 MOA researchers discovered a planet orbiting a distant star, 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

A fourth reflecting telescope, constructed in Japan, was installed at Mt John in late 2004. It has a 1.8-metre aperture and a large electronic camera mounted at the prime focus. This telescope, New Zealand’s largest, is used for photometry as part of the MOA project, and is the largest telescope in the world dedicated to microlensing.

Aoraki Mackenzie International Dark Sky Reserve

In June 2012, 4,367 square kilometres of the South Island – including Aoraki/Mt Cook National Park and the Mackenzie Basin – became an international dark sky reserve. Aoraki Mackenzie International Dark Sky Reserve is the largest such reserve in the world and the first in the southern hemisphere. Its aims are to promote star-gazing and protect astronomical research at the Mt John Observatory.

How to cite this page:

Maggy Wassilieff, 'Astronomy – overview - Mt John Observatory', Te Ara - the Encyclopedia of New Zealand, (accessed 19 April 2019)

Story by Maggy Wassilieff, published 12 Jun 2006