Comets and meteors are slightly different. Comet or satellite cometae, i.e. “hairy stars”, as they were formerly called, are bodies which moving under the influence of the sun’s gravitation, appear in the heavens at irregular intervals. A comet, as it draws neat the sun on its approach, moves more and more rapidly. Its temperature rises.
The pressure of the sun’s radiation drives the small dust out from the head- the bright head of a comet is not solid body but it is a loose collection of rocks, stones and particles of dust, producing the luminous tails pointing away from the sun. The tail is gaseous.
The length of the tail of naked eye comet may be few million miles only, or in some cases may exceed the distance of the sun from the earth, with a volume some thousand of times that of the sun.
Most of the comets are members of the solar system. About one fourth of the recorded comets are known to revolve round the sun in elongated orbits and most of them are believed to do likewise. A few may possibly be transient visitors to the solar system. The great majority of comets are periodic, i.e. they return at regular intervals which may vary from 3 ½ years to hundred or thousand years.
The investigation of the orbits of the short period comets revealed their relationship to some planets, specially, Jupiter. Such comets are said to form a family group and the existence of such a group is based on “Capture” theory.
Halley’s Comet, which appeared in 1910, moves in elongated eclipse and returns in about 76 years. Halley, working on the laws of gravitation as enunciated by Newton, worked out the paths of many comets and calculated the orbit and periodic time of this comet which is now named after him.
Meteors or shooting stars
Closely connected with comets are meteors or shooting stars. Meteors are small bodies which exist in great numbers in the solar system and probably arise from the breaking up of comets by the attraction of the sun or some large planet.
Shooting stars may be seen on any clear moonless night, though on some nights they are much more frequent than on others. The brightness of the majority noted is approximately equal to that of the naked eye stars.
The brighter ones leave trains which may persist as long as two or three minutes. Occasionally very bright meteors are observed, which from their appearance, are called fire balls. The luminosity of a meteor is due to the heating produced by friction from its rapid motion through the earth’s atmosphere.
The energy of motion of the meteor is communicated to the molecules of air which it hits and a cap of heated air is formed in front of the meteor; this communicates heat to the surface layers of meteor itself which become vaporized.
Thus an envelope of heated air and vaporized material forms about the meteorite and trail behind it; the luminosity of the meteors arises mainly from this incandescent vapor and persist till the meteor has been completely vaporized.
It is observed that the mean height at which they are observed in 80 miles and that at which they disappear is 50 miles. Many of the meteors have velocities greater than 60 miles per second. The large meteors or fire-balls first become visible at great heights, up to hundred miles and penetrate more deeply in to the earth’s atmosphere, sometimes to the height of only 5-10 miles.
The velocity decreases rapidly during their flight on account of the resistance of the earth’s atmosphere to motion. The flight of fire-ball is accompanied by a succession of explosions by which fragment of torn off from the principal body. The number of shooting stars which may be observed is very large.
It has been computed that the total daily number of meteors which enter the earth’s atmosphere can not be fewer than several millions. Very few of these ever reach the earth’s surface, the large majority being burnt up by the heat generated by friction in the earth’s atmosphere before they reach the surface.
Aerolites or meteorites
Such meteors as reach the surface of the earth are generally called aerolites or meteorites (meteoric stars). They are probably, essentially, the same as the normal meteors or shooting stars, the distinction being one of size only.
The majority of aerolites (which are found or are observed to fall) consist of masses of stones, limestone, magnesia or siliceous stone, generally mixed with grains or globules of iron.
A small percentage consists of nearly pure iron, usually alloyed with a relatively small amount of nickel. Some contain iron and stone in nearly equal proportions. No chemical element has been found amongst them which are not known on earth.
The mass of aerolites may vary from a few ounces to several tons. The entering of the meteors into the earth’s atmosphere is continually adding to its mass but the rate of growth is, relatively. Exceedingly slow, because the additions as compared to the mass of the earth are negligible.
The remarkable shower of meteor was seen by European observers on October 9, 1993. It lasted for four hours, and the rate of fall was counted to be 5,700 in 30 minutes. They belong to the Leonid Meteors family.
The swarm of meteors moving in an orbit of about 33 years is seen to radiate from the points in the constellation of Leo about the middle of November. The swarm of 1933 belonged to the same family which was observed in 1833 and then in 1866 and subsequently in 1900 and 1901.
Impact of comets and meteors on weather
There may be a possibility that comets and meteors affect the world’s rainfall. The formation of raindrops in the lower atmosphere is, in part at least, a process of condensation on small nuclei such as minute dust particles.
Fine meteoric material, whether as debris from the usual range of meteor sizes, or as micrometeorites dust, will drift slowly down from meteoric heights to the weather region in about a about a month. Some statistical evidence has been presented to show a connection between rainfall and meteor showering monthly earlier. Although the research is intriguing, the data are extremely difficult to analyze.
Comets and meteors affect radio communications
Normally, no communication can be established between a low powered radio transmitter, using a frequency in the range 30/100 mc/sec, and a receiver several hundred miles distant, because the earth’s curvature cuts off the direct wave and the sky wave penetrates the ionosphere and is lost.
However, whenever a suitably orientated meteor trail appears in the upper atmosphere, roughly halfway between the stations, the radio wave may be reflected to the receiver as long as the trail endures, which may be for a fraction of a second or for several seconds.
In practical communication system there is a transmitter and a receiver at each end of the link, with one or both transmitters emitted unmodulated carrier waves. The message to be transmitted is stored on high speed tape, which can be started and stopped quickly.
When a meteor reflection occurs, and the carrier wave is received at either end, the tape is started and the intelligence is transmitted just as long as the trail lasts.
Despite the intermittent nature of the operation, this comets and meteors system has several unique features which have led to its adoption as a useful member of the family of point to point communication systems.
High power ionosphere scatter system also depends on meteor trails to a great extent. In this case, it is the myriad of small meteors that assist in maintaining a weak but continuous signal between the stations.
Meteors, comets and space travel
Collision with meteoric particles will be among the many hazards to face the space travelers. The kinetic energy released by a small high speed meteoroid of iron or stone, if it were to strike a large body like a space ship could be such a thousand times greater than the explosive energy of an equal weight of TNT.
A pinhead particle might blast a hole in the shell of the vehicle that would allow the air within to escape in a few seconds. A meteoric pellet the size of a grape would almost certainly destroy the ship.
Fortunately for the astronaut the possibility of serious damage is very small. He should be able to travel for days before having to patch minor leaks in the ships shell, while many years might elapse before a catastrophic collision took place.
His chances for survival will be enhanced by steering clear of cemetery orbits end the steroidal belt between Mars and Jupiter.