Venus catching up to Earth

By DR GRANT CHRISTIE


Over the last month Venus has been prominent low in the western sky just after sunset.

It has been catching up with the Earth in its orbit and on June 8 it will pass between the Earth and the Sun. This rare event is called a Transit of Venus, during which Venus will appear as a small, black disc silhouetted against the Sun.

Unfortunately, the transit on June 8 cannot be seen from New Zealand because it begins here just after the sun has set. It will be best seen from Asia and the Middle East, where the sun is high above the horizon over the 6.4-hour period it will take Venus to traverse the solar disc.

The previous transit was on December 7, 1882, when these rare events were still of great scientific interest. By combining observations of the position of Venus made from widely separated places on the Earth, it was possible to calculate the distance from the Earth to the Sun. This fundamental quantity (called the Astronomical Unit) fixes the dimensions of the solar system, determines the distance to the nearest stars and the size of the Universe.

For the 1882 transit, an American team came to New Zealand from the US Naval Observatory in Washington, DC, setting up their instruments on the hill, Pukekawa, where the Auckland Museum now stands.

Auckland amateur astronomer, John Torrens Stevenson, was accorded the honour of being able to site his telescope within the fenced-off American compound. Even though the transit was halfway through as the sun rose on that clear morning, the observations recorded by these astronomers were of great scientific value.

To mark the 2004 Transit of Venus, the Stardome Observatory has created a public programme on Tuesday, June 8, starting from 5pm. It will feature live webcam feeds, planetarium shows, talks and displays on the history and significance of the event.

Night viewing In the evening sky, Comet LINEAR (designated as C/2002 T7) is still faintly visible but it is fading as its orbit takes it away from the Sun and Earth - and out of the solar system altogether.

Three planets can be seen at sunset. Mars and Saturn are close together low in the northwest and Jupiter is the brilliant object due north. Mercury is bright in the northeastern sky just before dawn.

The landmark winter constellations of Scorpius and Sagittarius are rising in the east early in the evening and are high overhead at midnight. In the south, Crux (the Southern Cross) reaches its highest point at about 9pm.

* The Stardome is open for public viewing from Wednesday to Saturday. Phone (09) 624-1246.

* Dr Grant Christie is an astronomical researcher and chairman of the Auckland Observatory and Planetarium Trust Board.