Halley’s Comet visible soon in morning sky

Press, 25 February 1986, Page 27

Halley’s Comet visible soon in morning sky

Readers will hope to see Comet Halley soon, after it appears higher in the morning sky. The times quoted in this article are standard times as Daylight time ends on Sunday, March 2. It should also be noted that the times are approximate as those quoted will vary slightly from place to place.

The best views will be obtained under dark, clear skies well away from city lights, or even the glare on the sky from such lights. The comet, this time round, will not be nearly as spectacular as it was at the previous return in 1910. That is because of the less favourable relative positions of the Sun, Earth and comet and the greater distance of the comet from us.

The head of the comet, consisting of its nucleus and coma, will probably appear to the unaided eye as a hazy and rather faint oval patch of light of about fourth magnitude — roughly as bright as the faintest star visible from the normal suburban backyard screened from lights. The tail should be several degrees in length and that will increase as the month progresses. The dust tail will be pointing towards the west away from the Sun. Its visibility will depend to a great extent on the contrast effect with the starry background. The latest reports received at the time this article was written indicate that there was considerable activity in the tail as it swung around the. Sun as the comet commenced its outward journey back to the far confines of the solar system.

The best time to view the comet is when the Moon is absent from the sky so that times near full Moon should be avoided. The Moon will be at last quarter on March 4 and at first quarter on March 19. Full Moon is on March 26 followed by last quarter again on April 2. The best viewing will be between March 5 and 19. On March 5 the comet rises slightly south of east at 2.52 a.m. Gradually the rising point moves to the south-east and on March 19 the comet will rise there at 0.50 a.m. This will mean that before the first glimmer of dawn the comet will be at a reasonable altitude.

The comet, during the first three weeks of the month, moves through the constellation Capricornus towards Sagittarius, through which it will pass in April. Capricornus is not a rich starry area of the sky so there should be good contrast against a dark background.

The viewer will have to decide whether to get up early or to stay up late to view the comet. Probably the former will be the choice of most people. A

clear view towards the south-east will be needed and they will see the comet best if they avoid bright lights before going outside. Those restricted to a city site should endeavour to screen out all artificial lights while viewing the comet.

The best views will be with the unaided eye or with binoculars as these will enable the entire comet to be seen at the same time. Telescopes naturally magnify the object but provide a more restricted view. If a telescope is used it is best to use a low-power eyepiece. Many people may prefer to wait until April to view the comet as for most of that month it will be visible all night and hence high in the sky at midnight. The comet will be closest to the Earth on April 11 at a distance of 0.45 astronomical units, roughly half the mean distance between Earth and the Sun.

Giotto, the European spacecraft, is due to pass close to the head of Comet Halley in early March. This should provide, if all goes well, some excellent close-up photos of the comet. The two Russian spacecraft were due to fly by the comet at the time this article was written. They will be much further out from the head than Giotto. The two Japanese spacecraft are to investigate the comet’s envelope and will therefore fly by at a con : siderable distance from the head as the comet approaches its nearest point to the Earth. The recent flight past Uranus of the Voyager spacecraft has shown that there are many more smaller bodies in the. region of this planet than were expected. Some astronomers are already suggesting that possibly some of these may actually form the proto-comets. A great deal more evidence is required on that point which may come after the data has been fully analysed.

Mars will attract a great deal of attention this month as it moves from Ophiuchus to Sagittarius. That is because it has now become very bright and by the end of the month will rival Rigel in brightness. The distinctive reddish hue of this planet will enable watchers easily to pick it out from the surrounding stars' which it will exceed in brilliancy. Mars will continue to increase in brightness until it reaches opposition in July.

On the morning of March 14 Uranus will be found just to the south of Mars. A telescope will show Uranus as a small, greenish disc just above the limit of naked eye visibility. Actually before they rise the two planets will be less than half a degree apart but at that time they will not be

visible from our latitudes. Mars will rise about 11.30 p.m. on March 1 and at 10.50 p.m. on March 31. Mercury is too close to the Sun in the evening twilight to be seen before it reaches inferior conjunction on March 17, passing into the morning sky. There it can be seen very low in the east just before dawn at the end of the month.

Venus sets shortly after the Sun throughout the month. Its great brilliancy of magnitude -3.9 will enable it to be seen briefly in the bright evening twilight, provided there is a clear and low horizon to the west.

Jupiter is too close to

the Sun to be of much interest. It starts to rise before dawn at the end of the month. The other bright planet, Saturn, is in Ophiuchus and in a good viewing position. It rises about 11 p.m. on March 1 and at 9.10 on March 31. The Moon at 1.0 a.m. on March 31 will pass one degree north of Antares, the bright red star in Scorpius. Actually the star will be occulted but this event will not be visible from New Zealand. Two hours later the Moon will pass five degrees to the south of Saturn. The Moon will also be close to Saturn on the evening of March 3 and to Mars the next morning.