LK.^n.YS IN 





the refractive power of the Earth's atmosphere. A the ray* of 

 the Son are putting along in the direction* A c and a c, aone 

 i >f thorn are refracted or bent inwarda ao a* to reach the Moon. 

 Some of them are likewise absorbed, and other* are refracted 

 more than the rest, BO that it in chiefly the red rays that reach 

 the Moon, and hence ahe present* a rnddy hue. 



In some states of the atmosphere this is seen much more 

 distinctly than in others. In the eclipse of the 6th of February, 

 1860, it wa especially noticed, the light of the Moon being so 

 strong and so red that many were unaware of the fact of its 

 being oaosed by an eclipse, and 

 were puzzled to account for the 

 appearance. In other instances 

 the Moon has been totally invisi- 

 ble during the eclipse. 



The duration of a total eclipse 

 of the Moon may be as great as 

 1 hour 50 minutes. This is when 

 the Moon passes directly through 



the middle of the umbra. At other times it passes near the 

 edge, and then is only obscured for a short period. When it 

 passes through the centre of the shadow, the total duration 

 from the first contact with the penumbra to the last may be five 

 hours and a half. 



Fig. 38 shows at one view the phenomena of both lunar and 

 solar eclipses. The solar eclipse represented here is an annular 

 one, as the shadow of the Moon terminates at w before it reaches 

 the Earth. A moment's careful inspection of this diagram will 

 show that an eclipse of the Sun can only take place at the 

 period of the new moon, as the enlightened hemisphere is turned 

 away from the Earth. An eclipse of the Moon, on the other 

 hand, can only occur at full moon. 



At first sight, we should suppose from this that these eclipses 

 ought to occur at every new and full moon, and the question 

 naturally occurs why it does 

 not happen so. The Moon 

 is between the Earth and 

 Sun every new moon. Why, 

 then, do eclipses only occur 

 at comparatively rare inter- 

 vals, instead of once every 

 lunar month ? 



The simple answer to 

 these questions is found in 

 the fact that the orbit of 

 the Moon is not in the same 

 plane as that of the Earth, 

 but is incliaed to it at an 

 angle of about 5 9', so 

 that during one-half of its 

 journey the Moon is below 

 the plane of the ecliptic, 

 and during the other half 

 it is above it. Now the 

 shadow of the Earth is in 

 the same plane as its orbit, 

 and hence at the period of 

 full moon the shadow may 

 be above or below the Moon, 

 and in either case no eclipse 

 will occur. 



The points in which these 

 planes intersect are known 

 as the nodes, and hence we 

 may say that there will be 

 an eclipse of the Moon 

 whenever a full moon hap- 

 pens to occur with the Moon 



at or near one of the nodes. In a similar way a solar eclipse will 

 occur when the Moon is near one of the nodes at the time of 

 now moon. 



The position of the nodes of the Moon's orbit is continually 

 changing at the rate of 19 20J' in a year, so that they per- 

 form a complete revolution in a trifle less than 18 years and 

 219 days. After an interval of 346'62 days, however, they come 

 again into the same position with regard to the Sun, and this 

 period is called a si/nodical revolution of the node. Now, it 

 happens that nineteen of these periods are almost exactly equal 



to 888 synodioal revolutions of the Moon, so that after this 

 interval the Bon, Earth, and Moon are again almost in the same 

 relative positions, and the same series of eclipses is therefore 

 reported. This period of 6,585 days, or 18 years and 10 days, 

 is called a eyeU of the Moon, It was known to the ancients, 

 and called the Ham, and by means of it eclipse* wet* roughly 

 calculated before any great progress had been made in the 

 science of astronomy. 



It might be supposed from this srsssnssjt that if we had a 

 complete list of eclipses for this period, nothing more would be 

 wanted, but that by repeating thk 

 ssriss over and over again, we 

 should have a perpetual list. This 

 is not, however, strictly accurate, 

 for, as the periods do not exactly 

 agree, there is a slight change 



of the eclipse, and sometimes one, 

 after a time, passes off the list 



altogether. Generally speaking, however, the eclipses are thna 

 repeated, the number usually occurring in this period being forty* 

 one solar and twenty-nine lunar, or a total of seventy. 



Another question that arises is, How many eclipses can 

 possibly occur in one year ? and we find that there mtut be at 

 least two of the Sun, while there may be as many as five. The 

 number of lunar eclipses may be as great as three, but in some 

 years there are none at all. Beckoning both together, there 

 cannot be more than seven eclipses, nor loss than two, in one 

 year, and in the hitter ca* both are solar. 



As the Moon and planet* are constantly changing their placet 

 with respect to one another and to the rest of the heavenly 

 bodies, it not nnfrequently happens that one of the heavenly 

 bodies is concealed by their coming between them and the Earth, 

 This occurrence is known as an occupation. A solar eclipse is, 



in fact, merely an ooculta- 

 tion of the Sun by the Moon, 

 though, on account of its 

 importance, it is called by 

 a special name to distin- 

 guish it. 



It is only at very rare in- 

 tervals that one of the 

 planets occults another 

 planet or a star. The most 

 common occultations are 

 those in which the Moon 

 passes in front of a star or 

 planet. As the Moon's disc 

 is very large, many star* 

 are thus hidden by it. Ita 

 light is, however, usually so 

 bright that it is only the 

 occnltation of very bright 

 stars that can be seen, the 

 smaller ones being lost in 

 the brilliancy of its rays. 

 A table showing those of 

 the larger stars which are 

 thus hidden by the Moon is 

 inserted in the " Nautical 

 Almanack " for each year. 



When the Moon is only 

 partly illuminated the star 

 either disappears or re- 



appears at the dark edge of 



**. WJ her disc. From new mooD 



to the full this dark edge 

 travels foremost, and hence 



the star suddenly disappears, without any apparent cause, some 

 little distance before it reaches the illuminated crescent. In a 

 similar way, after the full moon, the star suddenly re-appears 

 in the clear sky, the luminous side of the Moon's disc now being 

 the foremost. 



Many observers, in watching these occultations, have been 

 much struck by one remarkable circumstance often noticed in 

 connection with them. The star does not disappear gradually 

 by the Moon's disc creeping over it, but actually appears to 

 travel some little distance on to the Moon's disc, and then 



