READY TO STUN ANOTHER WORLD

impacting on Jupiter.

THIS month an extraordinary phenomenon will occur when fragments of

Comet Shoemaker-Levy 9 impact on the night side of Jupiter out of sight

from any telescope on Earth. We will look at the brief history of the

comet and the four possible outcomes of the event. But first a look at

the other attractions for this month.

More stunning news concerning the constellation Virgo and the

increased possibility of a massive Black Hole within the group. M87, the

Giant Elliptical, is believed to have such a destructive force at the

centre of the galaxy. With the help of a newly-repaired Hubble Space

Telescope, scientists in America have been able to measure a disc of gas

rotating around the Black Hole at 1.2 million miles an hour. This

particular Black Hole will be a cannibal devouring stars in its path. It

was once a massive star itself; now it has collapsed and the

gravitational pull is so strong even light cannot escape.

Back in Britain we can expect the new moon on Friday, July 8 and the

full moon on Friday, July 22.

CONSTELLATION OF JULY

MANY bright stars shine well at this time of the year despite the

short periods of darkness. The south-eastern sky provides a backdrop for

Altair of the constellation Aquila and Vega of the group Lyra. Arcturus,

Spica, and Antares will be in the south-western sky; however Antares and

Spica are now quite low.

Lyra represents the Harp. In mythology it was fashioned by Hermes from

the shell of a Tortoise and given to Apollo, who later passed it on to

Orpheus. The legend states that Orpheus could charm any living animal on

Earth with his musical talent. He used this in an attempt to rescue his

dead wife from the underworld. Although he pleased Hades with his music,

he was instructed not to look at his wife until they reached the living

world. As they approached the light, Orpheus glanced back at her only to

lose her for the rest of eternity. A sad tale, but his harp was later

placed in the sky for his musical excellence.

The leading star in the group is Vega, a magnificent sight and clearly

blue in colour. Binoculars will show that it was a fifth magnitude

double star. Both stars themselves are doubles, which is why they are

known as the Double Double. In 1983 it was discovered that Vega has cold

dark dust surrounding it in a disc. This could indicate the birth of a

new solar system with planets in an early stage of development. However,

this is not certain and the development into a system resembling ours

would take billions of years.

Lyra is also the home of M57, the Ring Nebula, which can be difficult

to define. It is known as a Planetary Nebula because it is viewed as a

rounded object from a telescope. It has nothing really to do with

planets in themselves. South-west of the group is the Globular Cluster

M56.

PLANETS THIS MONTH

JUPITER can be located in Virgo near to Libra as an evening object. It

has a magnitude of -2.1. Venus is shining in the sky at magnitude -4.1.

It travels through Leo this month and will appear close to Regulus on or

around Sunday, July 10. Saturn is in Aquarius at Magnitude +0.8 and is a

morning planet. Very low in the southern sky is the constellation

Sagittarius and this is where to find Uranus and Neptune. Neptune cannot

be located without optical aid and comes to opposition on Thursday, July

14. Uranus reaches opposition on Sunday, July 17.

WHEN COMETS COLLIDE

THE sight of a comet in ancient times often ignited mass hysteria as

they were associated with dark and supernatural happenings. Despite

their rather awesome appearance, they are no more than dirt and ice with

an unsubstantial composition. Everyone is familiar with Halley's Comet,

which returned in 1986. A group of probes were sent to investigate and

shed more light on these nomadic objects. Giotto was really the only

success and it sent back information before it entered Halley's

hazardous tail. The big misconception about comets is that the tail

always points in the opposite direction to which it travels as with a

rocket or jet aircraft. In fact it is the heat from the sun which

propels dust and gas to produce the characteristic tail. I have

attempted to show this in the illustration with each individual comet

fragment sprouting a tail opposite the direction of the sun.

It was in March of last year that the discovery by Eugene and Carolyn

Shoemaker was made along with David Levy. At the Schmidt telescope at

Palomar Observatory tolerance of bad weather gave way to satisfaction as

a break in the cloud appeared. Using some damaged photographic film, the

trio began scanning the area around Jupiter. After careful analysis of

the film, a white streak was noticed. Was it an asteroid or a comet?

They were not sure and needed confirmation. With Jupiter reaching

opposition many eyes would be on the same area. The race was on for

ownership. If it were a comet then they would want to give their names

to it.

With a similar result from Jim Scotti of the University of Arizona's

Lunar and Planetary Laboratory, it was clear that a new comet had been

discovered. Information on the comet trajectory were next calculated.

After much debate and counting it was agreed that the comet would break

up and then finally impact on the far side of Jupiter in July of the

following year. It is the gravitational influence of Jupiter itself

which has ripped the comet into 21 pieces.

There is no chance of any part of Comet Shoemaker-Levy 9 reaching

Earth. The result of the impact has been highly disputed but there is no

need to wrap yourself in silver or wear dark shades, unless of course

you're heading out to an all-night rave.

The more realistic possibilities are:

* THE fragments will break up in Jupiter's upper atmosphere, resulting

in a spectacular meteor shower.

* IF THE fragments hold up in the atmosphere then we can expect a

shock wave to disrupt the cloudtops. The speed of the fragments is

estimated at 65km per second and hopefully the impact will cause a flash

visible only to the space probe Galileo.

* A FRAGMENT of the comet may be able to penetrate deep into the

atmosphere, where high pressure would compress it. A rise in temperature

may trigger a nuclear-type explosion, blowing a hole through the

cloudtops.

* AN EVEN deeper disturbance could produce another spot on Jupiter.

Another possibility will be the effect the impact has on the moons which

orbit the planet, but sophisticated optical and radio equipment will be

necessary. The cloud patterns should hold the key to any tell-tale signs

of disturbance.

GALILEO: THE ONLY LONELY OBSERVER

ON OCTOBER 12, 1989, the Space Shuttle Atlantis blasted off with a

very special payload. This cargo is to reach Jupiter by late 1995 in the

form of the Galileo space probe. With the successes of the Pioneer and

Voyager missions, many feel that their appetite for knowledge has been

moistened. However, this mission has been plagued with technical hitches

even before destination. Hopefully when the probe reaches our largest

planet a smaller device will be detached and sent down to the surface of

the clouds as planned. This will take measurements which should answer

questions on the make-up of Jupiter's chemistry. It is believed that

this giant ball of gas is made up of hydrogen and helium.

We can only wait until next year. Meanwhile Galileo has the viewing

position that many astronomers can only dream of. There are cameras,

sensors, and thrusters aboard which should make this lonely wanderer

adequate to relay information back home when the moment of impact

occurs. However, don't expect results right away, as the data-collecting

systems have also suffered delays. It could be months before any

pictures are released.

The results of this event are impossible to predict accurately. The

whole show could be a real disappointment with no signs of turbulence at

all. Astronomers know this and that is why there has been a no-nonsense

approach to the expectations. There are individuals who have made wild

prophecies but these should be taken with a pinch of salt. If there is

anything to be taken from this then it should be an understanding of our

celestial neighbours and the nature of the solar system which our

children's children may have to colonise one day.