Challenged by Asteroids!
Dr. Rita Bremer
“For heaven’s sake all those asteroids!” I groaned, releasing my reaction to the steadily growing discoveries of minor planets as those who entered into the ranks of the privileged numbered ones reached 3000 in February of 1984. My common sense told me to get up and wave good-bye. The invasion of the multitude of the asteroid population into the present system of conventional astrology left me bewildered for a while. Today I am looking at them as our solar system’s largest jigsaw puzzle.
The minor planets are too small to be seen without the aid of a telescope. As early as 1802 no other than William Herschel named these objects of our solar system “asteroids” because of their star-like appearance (Greek: Asteroeides).
The main bulk of these minor planets are orbiting around the Sun in a space between Mars and Jupiter which is called the asteroid belt or the main belt. This is a difficult transition zone, which lies between the rocky terrestrial planets and the gaseous giants, a zone perturbed by Jupiter’s complicated gravitational laws and zones of resonance.
As I read along, I found the emphasis on groups rather striking be it by orbits, composition or even names. Other outstanding features were the many exceptions and superlatives. 1 Ceres the largest has a diameter of 953 kilometers and represents 30% of the total mass of all asteroids combined, while 2340 Hathor, an Aten object, is the smallest among the numbered minor planets with a diameter of only 200 meters. 434 Hungaria and its family members are orbiting at the inner border, while the lonely outsider 279 Thule is orbiting at the outer border of the main belt. 4 Vesta and 44 Nysa are the brightest, while 2101 Adonis, a Venus-crosser, is one of the faintest. 1580 Betulia and 2 Pallas have the most inclined orbits and 349 Dembowska is looked upon as exceptional because of its composition. The latter asteroid was named after the Italian astronomer Baron Ercole Dembowska (1812-1881). 349 Dembowska and 16 Psyche share the peculiarity of an orbit that repeats itself almost exactly every five years in respect to their position to the Sun and Earth. For example, on February 10, 1974, 1979 and 1984, Dembowska was at 14:40 Virgo (+/- 0.03), while Psyche was at 15:40 Capricorn (+/- 0.03).
There are numerous asteroids outside the main belt with unusual orbits in unusual places. An interesting group of 59 is made up of Earth-crossers, of which 2212 Hephaistos is the largest with a diameter of 10 km, while the above mentioned 2340 Hathor is the smallest of this group. Hathor has the smallest orbit, which is smaller than the Earth’s, while Hephaistos belongs to a group whose members have large aphelion distances suggesting cometary origins. The closest approach to Earth by an asteroid was observed in 1937, when Hermes came as close as 800,000 km. But this asteroid has not been seen since and remains lost.
Astronomers talk about an apparition or flyby, when an asteroid or a comet approaches the Earth. As the word apparition indicates, these objects are out of sight in between times. So it is no small wonder that many of this type of objects went through the department of lost and found. There were timely apparitions of 433 Eros in November/December 1979 coinciding with the Iranian hostage crisis and the Afghan invasion and again in November/December of 1981 during the Polish crisis. 1862 Apollo zoomed by in November of 1980 and again in May of 1982 making a timely flyby during the Falkland crisis. Apollo will not make another close approach to Earth until the years 2005 and 2007. This asteroid was discovered in 1932, lost for 41 years and rediscovered in 1973. 2101 Adonis made a close approach to Earth in the early part of July 1984 and will not make another close approach to Earth until the year 2036. The interesting thing about Adonis is, that it is believed to be a source of meteoroids. Adonis was discovered in February of 1936, the year of the ascension to and abdication of the throne of England by King Edward VIII. Love was stronger than holding power, but also brought a great deal of grief.
The space exploration program is planning an asteroid mission and under consideration is an asteroid exploitation for mineral mining. Many more orbits of asteroids are being carefully determined. With the help of computers, many astronomical events are now predictable such as planetary appulses and occultations.
To correlate such data with mundane events is quite a challenge. After all, as above, so below. To begin with, I zeroed in on the three occultations of the brightest stars by asteroids for the year 1983. The data were selected in January 1983 from a list of predicted occultation events published in the Sky and Telescope January 1983 issue. Occultations of stars with a brightness of 8-10 magnitude or less are not infrequent, but occultations of the brightest stars be it by major or minor planets, are rare indeed.
What is an occultation? As seen from the Earth, a close approach of a planet to a star or to another planet is called a planetary appulse which may be seen at a certain locality as an occultation. When a planet passes in front of a star or a planet it blinks out its light and the planet casts its own shadow. If that shadow intersects with the Earth, we have an occultation that can be observed under favorable conditions. If such an event involves the Sun, it is called an eclipse. For all other objects it is called an occultation. Astronomers use occultations by asteroids as an Earth- bound technique to measure the asteroid’s diameter. It is said that such measurements carry a high degree of accuracy. No need to say that in order to arrive at correct measurements, numerous observation points are necessarily staged along the path of the shadow.
The three occultation events were:
1. May 29, 1983 Occultation of 1- Vulpecula by 2 Pallas. NATO-Missile Crisis and the Economic Summit Meeting.
2. September 11, 1983 Occultation of 14- Piscium by 51 Nemausa. Day of National Mourning for victims of Flight KAL 007. International outcry!
3. October 23, 1983 Occultation of Epsilon Sag. (Kaus Australis-The Southern Bow) by 804 Hispania. Grenada Crisis and the Beirut Bombing.
One can hardly deny the concurrence of the astronomical events with mundane highlights that made newspaper headlines.
Cunningham, Clifford, “William Herschel and the first two Asteroids”, The Minor Planet Bulletin, Vol. 11, Number 1, 1984, p.3.
Gehrels, Tom, Asteroids, The University of Arizona Press, 1979
Gunter, Dr. J.U. Tonight’s Asteroids Bulletin, No. 84, 1984, p. 1 Psyche; No. 80, 1984, p. 8 Dembowska
Helin, Eleanor F. “Earth-Crossing Asteroids, an Update”, The Minor Planet Bulletin, Vol. 11, No. 3, 1984, p. 19.
Sky and Telescope, February 1982, p. 173, Celestial Calendar; “The Winter’s Visit by Minor Planet Eros”; May 1982, p. 528, Observer’s Page: “Eros crosses NC 1647”; April 1982, p. 389, Celestial Calendar: “Flyby of Apollo”; January 1983, p.58, Celestial Calendar: “Planetary Occultations of Stars”.
Taylor, Gordon E., “Planetary Appulses and Occultations”, p. 121, Observers Handbook, 1984. The Royal Astronomical Society of Canada, Editor Roy L. Bishop.
Tholen, David J., “Asteroids News Notes: Number 3000 now exists!” Minor Planet Bulletin, Vol. 11, No. 2, 1984, p. 18.