From: The London Times, 24 Nov. 1890, page 6, column b
Mr. Eddie, F.R.A.S., reports from Grahamstown that a comet was seen at 7:45 p.m. on the 27th ult. [October] and observed until 8:32 p.m. when the last trace faded in the south-eastern heavens. It travelled from nearly due west around the western and southern horizon at an altitude from about 20 to 25 degrees, and disappeared in the south-east, performing during that very brief interval a journey stretching over at least 100 degrees. It was at its longest fully 90 degrees in length, while in width it did not exceed half a degree, except where it became very faint and slightly spread out at its posterior extremity, and where there were also faint indications of lateral diversion. The preceding portion was a point in cometary form, but no nucleus could be discerned.
When first seen it was inclined at an angle of about 45 degrees towards the south, and was about 30 degrees in length, but as it moved southward it became almost parallel to the horizon, with an altitude of about 20 degrees, till it stretched along the southern horizon an enormously long, narrow, almost parallel, weird-looking riband of gray light moving visibly across the sky. It passed over several bright stars, notably Alph Centauri and Beta Aryo Navis, but did not appear to dim their lustre. The moon was at the full. --Reuter
* John Lewis mentions this observation on page 85 of Rain of Iron and Ice [QB721.L42 1996] and notes that at a typical geocentric velocity of 40 kilometers per second the comet had to have come as close as a fifth of the distance to the moon to traverse 100 degrees in 47 minutes.
On the same page Lewis also mentions another dangerously close brush with a comet that was seen by astronomers at the European Southern Observatory in March of 1992. This object moved through 20 degrees of arc in three minutes! Using the same velocity as above puts the comet within two Earth diameters or 26,000 km. The nucleus of this object had a brightness of first-magnitude which, depending upon its surface reflectivity, would suggest a diameter between 170 and 300 meters. As Lewis points out a 300 meter across mixture of ice and rock impacting at 40 km per second would release kinetic energy equal to about 15,000 MTs of TNT!
Relatively small objects like those mentioned above are not easy to spot from the surface of Earth--weather and places for eyes to watch from are major obstacles. We really need space-based observatories dedicated solely to the task of locating near-Earth-objects. If we keep dragging our feet on this we up the odds of being slammed by something with virtually no warning.
It would not take a terribly large impact event to produce a considerable amount of social chaos--it would depend on where and at what time of the year the disruption occurred. Recently we were buzzed by an object labeled 1996 JA1. This NEO came about as close to Earth as the Moon and its size was large enough to harbor at least the kinetic energy of 3,000 MTs of TNT. What this means is that on May 19, 1996, less than four hours of Earth travel (~30 km/sec) insulated us from an impact event which, had it occurred in the northern hemisphere, could have disrupted an entire growing season! Such an unfortunate mishap could lead to a chain of events which would make it virtually impossible to implement a defense system for the Biosphere any time soon. Given the evidence to date, it is irresponsible to approach this problem with a fiscally conservative mind-set--the potential consequences are too dire. It is quite literally stupid to allocate billions of dollars in resources to build B-1s and such when this very natural and, if not prevented, inevitable eventuality looms over us!
So the reader will not think that the idea of defending our planet is just too new to have been given adequate attention yet, the following piece of history is provided:
From the ATLANTA CONSTITUTION (July 26, 1966):
Asteroid Collision Called Earth Peril
SYDNEY, Australia (UPI)--An Australian scientist says if an asteroid now speeding toward the earth veered just slightly, it would crash into the planet with the impact of 1,000 hydrogen, bombs.
Prof. S. T. Butler, professor of theoretical physics at Sydney University, made the statement in an interview with the Sydney Telegraph.
He said the asteroid known as Icarus was speeding toward the earth at 70,000 miles per hour and was expected to pass four million miles away in 1968.
"If Icarus hit the earth, it would be like the explosive power of 1,000 hydrogen bombs,'' Butler said. He added that four million miles away from the earth was "only a stone's throw for outer space.
Butler said scientists in the United States, Britain and the Soviet Union were closely studying the elliptical orbit of the asteroid. He said it could possibly be destroyed with a high altitude rocket armed with a nuclear head if it neared the earth.
"It sounds fantastic," Butler said, "but we could land a rocket with pinpoint accuracy 50 million miles away and destroy it. This is where billions spent on space research pays off ."
He said the scientists were keeping close tabs on the asteroid.
Butler said scientists feared that if the asteroid altered its course a fraction of a foot, it would come within the earth's gravitational pull.
by David Farley 04/11/96
"Today's asteroid encounter was a near miss, but some scientists warn that an actual impact could have serious long-term effects on life on Earth as we now know it."