THE SUN AND SOLAR PHENOMENA. 



59 



drawn to the earth from the upper and lower limbs of the sun and moon define the conical 



shadow projected by the latter, or the umbra, 

 which, wherever it falls, occasions a total ob 

 scuration of the solar orb. Similar lines drawn 

 to the earth along opposite edges of the two 

 bodies define the limits of a fainter shadow, or 

 the penumbra, caused by the moon only hiding 



parts of the sun's disk; and, within the space it includes, the eclipse is more or less partial, 

 according to the situation of an observer. 



As a general rule, it may be stated that an eclipse will diminish in magnitude about 

 one digit for every two hundred and fifty miles from the centre where it is total a digit 

 being the twelfth part of the solar or lunar surface. The lunar shadow may, however, 

 terminate, when the earth is in a direct line with it, without reaching its surface. When 

 the sun is at the least distance from us, and the moon at the greatest, the shadow will 

 fall short of our globe by about twenty thousand miles, though when these elements are 

 reversed it is sufficiently long to extend nearly the same distance beyond us. In the 

 former case the sun has his greatest apparent diameter, and the moon her least. She is 

 unable, therefore, to cover his entire face, and appears projected upon his disk, with a 

 slender ring of dazzling light around her dark body. This is termed an annular eclipse, 

 from the Latin, annulus, a ring. 



Annular Eclipse, 



An annular eclipse is a rare occurrence. The last, on the morning of October the 9th, 

 1847, was very imperfectly observed owing to cloudy weather. 



There may be five solar eclipses iu a year, and the least number which can take place 

 is two. As the moon passes through that part of her orbit which lies between the sun and 

 the earth once a month, we should obviously have an eclipse every month, every new moon, 

 if she moved in the plane of the earth's orbit. This is, however, not the case the lunar 

 path is inclined to that of the earth. She is above it during one half of her course, 

 and below it during the other, crossing it twice a month at two opposite points, called her 

 nodes. It is only when the moon is between the sun and the earth, at or very near her 

 node, that is, when her path cuts the plane of the earth's orbit, that she intercepts to us 

 the solar light, and eclipses occur ; at other times, she passes either above or below the 



