NZ's largest telescope to search for rare star alignments

Use this chart to locate four of the bright planets this month. It shows the sky looking north just before dawn.

Today marks a significant milestone in New Zealand astronomy - the official opening of the new 1.8m telescope at Mt John University Observatory overlooking Lake Tekapo.

The country's largest optical telescope has been the 1m McLellan Telescope, which has operated at Mt John since 1986.

The new instrument has been developed for a consortium of astronomers from the universities of Auckland, Canterbury, Massey and Victoria and from Nagoya University in Japan.

The name of the project is Moa, standing for Microlensing Observations in Astrophysics, so the telescope is called the Moa scope.

It has been designed to search for rare chance alignments of stars along our line of sight.

If an alignment is sufficiently precise, the gravity of the nearer star will act like a lens and magnify the light of the more distant one.

The Moa telescope will be the largest in the world dedicated to these searches.

From analysis of the brightness changes, astronomers can learn a great deal about the two stars involved - information that can be derived in no other way.

In particular, if the intervening star happens to have a planet, it can be detected and key details such as its mass and orbit measured.

This new branch of astronomy is called "gravitational microlensing" and provides the only practical method of detecting planets thousands of light years from Earth.

These precise stellar alignments are rare so the astronomers have to measure the brightness of millions of stars every clear night to detect enough events to study.

Once an event has been detected, other observatories take over the task of measuring the small changes in brightness that may signal the presence of a new planet.

The Auckland Stardome Observatory has been contributing follow-up observations of these gravitational microlensing events for about a year.

The bright planets

The planet Saturn rises at midnight and lies close to the Gemini Twins, Pollux and Castor. By dawn Saturn can be seen sitting about 30 degrees above the northern horizon.

Jupiter rises at 3.20am and by dawn is shining brightly in the east near Spica, the brightest star in Virgo. Lower down and to the right of Jupiter you will spot Venus close to Mars.

The only other bright planet is Mercury, which sets about an hour after the Sun and can be seen low in the western sky in the evening twilight.

The feature constellations to watch for this month are Orion, Taurus, Canis Major and Gemini rising above the eastern horizon in the early evening.