SKY AND SPACE with Dr Colin Keay
Colin has published a vast array of
articles over the years with the Newcastle Herald. Here you will
find those articles with a new feature article presentation on
this page each month.
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November 8th 2011
"AN ASTEROID four
times the length of a football field will pass closer to Earth
than the moon when it hurtles through our solar system tomorrow
morning.
The asteroid is the first object of its size to come so close to
Earth, flying within 320,000 kilometres of our planet, in more
than 30 years.
But its trajectory had been well studied since it was discovered
in 2005 and there was no threat of an Earth collision for at
least the next 100 years, NASA said."
Read More:
Sydney Morning Herald
September 1986 - Colin Keay
With the recent news of asteroid
2005 YU55 I thought I put up an article Colin wrote back in
1986.
The final formative event of our Earth was a
long drawn out bombardment of primordial material of much the
same composition as the Earth's crust, for that is what it
became. The bombardment continues to this day, although its rate
is now almost insignificant. About once a century we are struck
by an interplanetary object large enough to flatten a city. The
Tunguska devastation in 1908 was caused by one such object.
Smaller objects rain upon us all the time.
Late in July a large firball dropped a meteorite the size of a
basketball just north of Lismore. The elasticity of the soil was
such that it bounced into the scrub and was lost, leaving only
the evidence of the initial impact. Later in the month a very
bright fireball was photographed from the Siding Spring
Observatory and from Tamworth, the two photographs revealing
that it probably dropped a meteorite into the Pilliga scrub
region. A very high proportion of these scientifically valuable
objects are never found.
Then there are the near misses. The Earth
presents a very tiny target when viewed against the vast
backdrop of space. About once every few years we detect
asteroidal objects passing within six million kilometers. One of
these could wipe out half a continent. Simple arithmetic shows
that the chance of the Earth being struck is one in a million or
thereabouts. In other words we stand to meet with one of these
agents of destruction every few million years.
Warning of such disasters is now possible,
even if mass evacuation on a sub-continental scale is not. On
the fourth of May this year a small asteroid called 1986 JK was
discovered approaching the Earth. Later in the month it became
the closest interplanetary object to be studied by radar as it
passed less than 4.4 million kilometers from us. As a result of
optical and radar observations the orbit of 1986 JK is now known
well enough to predict that it will again pass close to us in
1995.
Asteroids having orbits which cross that of
the Earth are collectively called Apollo asteroids. Of these,
Hermes appears to be the one which has strayed closest to us,
actually passing within the distance of the Moon's orbit. Icarus,
having a diameter of about one and half kilometers, is the
largest of the group and has the distinction of passing closer
to the Sun than any other asteroid. Its elongated orbit also
brings it on occasion within a million kilometers of the Earth.
Comets as well as asteroids may have very
close encounters with our planet from time to time. Comet Halley
passed barely six million kilometers from us on its most
spectacular visit in the year 837 AD. Many smaller comets pass
even closer. In fact there are a growing number of reports of
very faint rapidly moving comets being sighted through
telescopes. They appear as diffuse blobs moving as fast as ten
degrees (20 moon-diameters) per hour. Just this very kind of
cloudy object could have been responsible for the Tunguska event
in which no actual fragments were ever found.
