METEOR® — WHIPPLE 243 



than these craters suggest. The Harvard geologist Daly (1947) 

 gives convincing evidence that the great Vredefort dome in South 

 Africa was once a meteorite crater some 50 miles in diameter. In 

 the hundreds of millions of years since it was formed the crater 

 has been filled by sediments, tilted over at a considerable angle, and 

 its edge greatly eroded. Many astronomers suspect that such fossil 

 craters on the earth are "blood relatives" to the great craters that 

 we see on the moon. Baldwin (1949) has strongly supported this 

 view in his book, and scientific evidence is accumulating to support 

 his theory. 



The great meteorite craters and the meteorites themselves present 

 a myriad fascinating problems. Since I cannot do even summary 

 justice to both meteorites and meteors I must regretfully abandon 

 the former and discuss meteors alone in the remainder of this ar- 

 ticle. Before leaving the subject of meteorites, however, I must 

 mention that the majority of meteoriticists favor the theory that 

 many or most of the meteorites originated in two or (many?) more 

 small or minor planets, which have mutually collided and broken 

 up to form both the asteroids and the meteorites. A cometary origin, 

 as we shall see, is indicated for most of the smaller bodies that pro- 

 duce the usual visual and subvisual meteors. Thus the sources of 

 meteors and meteorites still constitute a major area of research. 



For nearly a century, since Schiaparelli (1871) identified the 

 Perseid meteor shower as being associated with the comet of 1862-III, 

 astronomers have accepted a cometary origin for recurrent meteor 

 streams. At the same time, most investigators have agreed that 

 broken fragments of small planets must contribute to the sporadic 

 meteors, those that do not appear in showers. There have, however, 

 been great disagreement and much discussion as to whether some 

 of the meteorites and some of the meteors may not be visitors from 

 interstellar space rather than from our solar system. To distinguish 

 interstellar from solar-system meteors we need only measure their 

 speeds and trajectories through the atmosphere. After correcting 

 for the resistance of the atmosphere, the rotation and attraction of 

 the earth, and the earth's motion about the sun, we can calculate the 

 meteor's original speed and its orbit about the sun. If the speed 

 was less than 26.3 miles per second, the orbit was closed, i. e., ellipti- 

 cal, and the body belonged to the solar system. If the speed exceeded 

 26.3 miles per second, the orbit was open or hyperbolic, and the body 

 came from out among the stars. 



The visual methods, unfortunately, have not been adequate to settle 

 this long-standing controversy over the origin of meteors. Even 

 though extremely sensitive and quick in detecting faint fast-moving 

 meteors, the eye is not an accurate measuring device for determining 

 the precise geometry either of altitudes or of angular velocities across 



