NATURAL PHENOMENA 



island as it was originally charted in size but about 305 feet high. 

 It was erupting once every 20 minutes. It commenced to erupt in 

 the middle, then ejected smoke and vapor, then was enshrouded by a 

 bank of smoke that billowed to over 4,000 feet in the sky. The 

 Premier of Tonga landed on the island in June 1928, and hoisted the 

 Tongan flag. In October of the same year the height of the island 

 was observed to be 405 feet with steam emitting from the crater. 

 In 1930, the height was again reported as 475 feet. 



In 1936, the H.M.S. Leith steamed around the island about 

 V4 mile off. The north side rose in a gradual slope to its 200-foot 

 summit, falling in a perpendicular cliff at its southern end. Little 

 volcanic activity was apparent, but eruptions were observed every 

 15 minutes from a submarine crater off the southeast end. The 

 island was about iy2 miles long, north to south, and about Vz mile 

 wide. 



In 1937, the H.M.S. Achilles passed 1 mile northeastward of the 

 island and reported no sign of volcanic activity. In June 1938, the 

 H.M.S. Leith estimated the height 'to be about 30 feet about Vz mile 

 from its southern end but with no activity. The MV Maui Pomare 

 observed the island in March, 1941, emitting jets of steam. 



Little is known of its activity during World War II. In February 

 1949, the H.M.N.Z.S. Hawea reported that the island had again dis- 

 appeared, and that the least depth found in the vicinity was 9 

 fathoms. 



In 1959, it was again reported that no above water features were 

 visible in the vicinity of the island. 



LOCUST RADAR TARGET 



In July of 1959 at the Strait of Bab El Mandeb, at the south- 

 eastern entrance of the Red Sea, a ship observed a radar target at 

 a distance of about 10 miles. Visually the target appeared as a 

 sandstorm approaching from northwestward and to be about 8 miles 

 long northeast to southwest, about 6 miles wide, and oval in shape. 

 The target advanced until the ship was in the midst of a hugh swarm 

 of locusts. The target moved southeastward until it disappeared at 

 a distance of about 10 miles. 



In the Middle East swarms of locusts are known to migrate from 

 Africa into Asia Minor plaguing crops and other vegetation since 

 Biblical days. 



METEORS 



Interplanetary space is by no means empty. As the earth revolves 

 around the sun, it swims through an ocean of rarefied gas, thinly 

 strewn with solid objects that range in size from dust specks to 

 minor planets. Both the zodiacal light and the outermost part of 

 the sun's corona are interplanetary solid particles illuminated by 

 sunlight. But the most familiar indications that space between the 

 planets is not empty are the meteors seen as the earth collides with 

 small bodies. 



Meteor Swarm 



THE EARTH IS REPRESENTED MOVING IN ITS OHBTT AMONG THE PARTICLES IN SPACE. AN OBSER- 

 VER IS LOCATED ON THE FORWARD— MOVING SIDE OF THE GLOBE AFTER MIDNIGHT, AND 

 THEREFORE ENCOUNTERS A GREATER NUMBER OF SPORADIC METEORS. 



Astronomers have recently realized that the solid grains in our 

 solar system are of two very different kinds. One variety consists 

 of bits of stone and iron, which travel around the sun in nearly 

 circular, low-inclination orbits, in the same direction as the earth. 

 These are regarded as debris from collisions of asteroids, or perhaps 

 material from a planet between Mars and Jupiter that long ago 

 broke up (or failed to form). Any meteor observed brighter than 

 Venus is probably the result 6f one of these asteroidal fragments 



passing at high speed through the earth's atmosphere. 



The second kind of particles moving in orbits like those of 

 comets. These include almost all the fainter meteors that we see. 

 Several of the prominent annual meteor shows are caused by objects 

 moving in the same orbits as known comets; thus it is definitely 

 established that the Perseid meteors seen about August 12th each 

 year are debris of Comet 1862 III. The fact that the Perseids appear 

 every year means that fragments have spread out along the entire 

 orbit, forming a ringlike stream that the earth cuts through each 

 August. 



At the height of the Perseid shower, a naked-eye observer may 

 count a meteor per minute that is a member of the shower. All 

 Perseid paths, if extended backward across the sky, originate in the 

 same radiant (actually a small area rather than a point). This is a 

 perspective effect; the Perseids are actually moving along widely 

 separated parallel paths in space as they come into the earth's 

 atmosphere. 



The number of distinct showers is large but indefinite. Every 

 gradation exists between conspicuous rich showers and others so 

 sparse that they contribute less than one meteor an hour. 



If we imagine the sporadic meteors to result from a random scat- 

 tering of particles, moving at random in a swarm through which the 

 earth is moving at an orbital speed of 62,000 miles per hour, then we 

 can deduce that during the night the number of meteors visible per 

 hour should increase steadily from dusk to dawn. At sunset we are 

 on the trailing edge of the earth, and can see only those meteors 

 moving fast enough to overtake our planet. But as night progresses, 

 the earth's rotation carries us around until near sunrise, we are on 

 the leading edge of the planet. Then the hourly rate of meteors 

 becomes much greater because head on collisions occur, and slow 

 moving meteors are overtaken by the earth. 



This picture is valid even though the motions of sporadic meteors 

 are not quite random. Those going around the sun in the same 

 direction as the earth tend to have shorter periods and low inclina- 

 tions; those traveling the other way have longer periods and high or 

 low inclinations. 



For many years astronomers debated whether these were visitors 

 to our solar system from interstellar space. The practical criterion 

 for recognizing such an intruder is high velocity. An object at the 

 earth's distance from the sun is traveling in a hyperbolic (open) orbit 

 only if its velocity exceeds 42 kilometers a second. Since we observe 

 from the earth, which moves at 30 kilometers a second, a meteor 

 found to move significantly faster than 72 kilometers a second must 

 be an interloper in the solar system. 



Photo of meteor trail 



Accurate velocities for thousands of individual meteors have 

 been obtained from modem photographic and radar observations, but 

 so far not a single certainly hyperbolic case has been established. 

 Interstellar meteors are extremely rare and are not within present 



49 



