Comet not as close, but should still put on spectacular display

Press, 5 December 1985, Page 42

Comet not as close, but should still put on spectacular display

Halley’s Comet

By

JOHN HARFORD

Halley’s Comet will not come as close to the Earth as it did in 1910. There is also much more ambient light now which could interfere with viewing, but the comet should still put on a spectacular display, especially for viewers in the southern hemisphere. Last time round, the comet passed between the Earth and the Sun. The resulting tail spread right across the night sky and the Earth actually passed through the tail. Although’* the comet’s display will not be as spectacular to Earth-bound viewers this time, Comet Halley will reveal more to mankind on this journey

past our planet than ever before.

Not only are telescopes and binoculars of a much higher quality than in 1910 but this is the first time the

comet has visited during the Space Age. A joint-venture spacecraft launched by European countries is hurtling through space to meet the comet in March. Two spacecraft from the Soviet Union and one from Japan have also been sent to rendezvous with Comet Halley. The unmanned craft areunlikely to return to Earth but they will send back information on the comet which could unlock many of its secrets.

An International Halley Watch organisation was set up a few years ago to coordinate observations. The Mount John Observatory near Lake Tekapo will play a big part in the worldwide observation network. It will help to accurately update the comet’s orbit so that the spacecraft can be

directed close to its nucleus, photograph its tail, and measure the comet’s production of gas and dust.

About 200 of the world’s most powerful telescopes will be trained on the comet at the same time. The Soviet Union has 10 of its best observatories ready for the comet and also intends to watch from several South American locations. All the main telescopes in the United States and Europe will also be tracking the comet.

In Christchurch, the Canterbury Astronomical Society is getting ready for an influx of northern hemisphere tourists heading south for a better view of the comet in March and April. Some tour parties have already booked sessions at the society’s observatory at West Melton. The society has also suggested to local bodies that street lights be turned off between midnight and 12.30 a.m. from March 30 to April 16 to allow a better view for people who are not able to leave the city. The small Central Otago settlement of Omarama will become a mecca for comet watchers throughout the world. The town is on a high plateau, well above sea level — leaving less atmosphere for observers to have to peer through. It is also well away from any brightly lit cities, and has a high percentage of clear skies at that time of the year.

Halley’s Comet will be almost right above Omarama on April 11 when it makes its closest approach to Earth, two days after a new moon.

The observatory there is expected to be so popular it is not expected to be available to anyone who has not booked in advance. Amateur astronomers from around the South Island will help man the observatory during the prime viewing period. , In early December Halley’s comet will be above the north-eastern horizon at sunset, rise towards the north and set in the northwest. It will have a short tail and should be visible through a binocular, away from well lit areas. Glare from the growing Moon will interfere with viewing in the last two weeks of the month.

In January the comet will be in the western sky at sunset. It is now moving well away from the Earth towards the other side of the Sun. The Moon, growing full during the last half of the month, will again further hamper any observation.

In early February the comet will be behind the Sun. It will reappear late in the month to a sky with a full moon. In March, as the comet swings away from the Sun’ and towards the Earth, its tail will appear to grow 1 longer. It will rise about 2.30 a.m. in the east early in

the month (after daylight time ends) and be lost in the sunrise about 5 a.m. Late in the month it will rise about 1 a.m. Its closing distance from the Earth will help offset the effects of a full moon in the last days of March.

Early to mid-April will provide the best time for viewing Comet Halley, especially if Christchurch’s street lights are turned off during part of the night. It will rise in the south-east by mid-evening and will climb high into the sky by midnight and early morning. Although then moving away from the Sun it will be moving towards it closest approach to Earth on April 11. The Moon will fade into a new moon on April 9 and the comet will be at its brightest for Earth-bound viewers.

By now Halley’s tail could stretch across a quarter of the sky. After April 11 the comet will rapidly lose its brightness, a combination of it moving away from the Sun and the Earth, as well as a waxing moon. A total eclipse of the Moon on April 24 will allow viewers in some parts of the world to witness the comet as it apparently “reappears” in a swan-song before returning to the outer solar system. Binoculars and telescopes will be needed to view the comet in the early part of May, after the full moon. It will be almost overhead by mid-evening.