THE GREAT LUNAR CRATER TYCHO.* 



By A. C. Ranyard. 



The late Prebendary Webb used to speak of Tycho as the metropol- 

 itan crater of tlie moon. Tliongh by no means the largest of the hmar 

 craters, it is one of the most striking features of the Innar landscape, 

 especially when the moon is near to the fnll, and the shadows of the 

 mountains liave all disappeared. The crater of Tycho is then seen as 

 a conspicuously wliite spot, from which radiate in all directions a great 

 number of whitish rays that extend over more than a third of the visi- 

 ble hemisi)liere of the moon, indicating that the crater has been the 

 center of a colossal disturbance which seems to have shattered the 

 lunar crust in all directions. We have, as far as 1 am aware, no evi- 

 dence in the terrestrial geologic record that a corresponding cataclysm 

 has ever similarly shattered the earth's crust; but onr terrestrial vol- 

 canoes are puny things compared with the giant craters of our smaller 

 companion planet. 



As might be expected, the strange phenomena presented in so nn^jar- 

 alleled a degree by Tycho have been a fruitful stimulus to speculation 

 as to the origin of the lunar craters and the radiating systems of rays 

 with which many of the moon's craters are evidently intimately con- 

 nected. Many able men have doubted whether there is any true 

 analogy between terrestrial volcanoes and the gigantic lunar ring 

 mountains and circular depressions which we ordinarily speak of as 

 craters. The ring of Tycho is 54 miles in diameter, and the great cra- 

 ter Clavius, which lies to the south of it, is more than 140 miles in 

 diameter; but Clavius is by no means the largest of the lunar craters. 

 If the lunar Ajjcnnines and the other mountains forming a broken 

 ring round the Mare Imbrium are the remnants of a crater, it must 

 have had a diameter of over 600 miles, while the largest terrestrial cra- 

 ters are not more than 15 or 16 miles in diameter.t Vesuvius and the 



*From Euowleilffe, August, 1893; vol. xvi, pp. 149-153. 



t According to Mr. G. K. Gilbert, in a paper published in the Bulletin of the Philo- 

 Boplricul Societii of Wanhiwjton, vol. Xii, p. 247, (1) the old crater coutaiuing Lake 

 Bomboii, Isle of Luzon, is mapped (Reclus) as 16 by 14 miles in extent; (2) the cra- 

 ter of Aso.siu, Isle of Kiushiu, .lapaii, is lo miles across (Milne): (3) Scrope men- 

 tions a circular crateriform lake, iibout 1.5 miles in diameter, in Northern Kam- 



89 



