TO KNOW THE S TARRY HEAVENS 



309 



the first of the faint summer constella- 

 tions, Virgo, with its promise of the 

 time when warmer days shall come. All 

 of the winter groups are still with us 

 during this, the last of the winter 

 months, but by April, Taurus will have 

 begun to sink below the ground, Virgo 

 will have entirely emerged, and even 

 the Balances will be visible in the east 

 and the transformation of the winter in- 

 to the summer sky will be well under 

 way. 



The March Stars. 



One of the very interesting con- 

 stellations is Hydra, the Watersnake, 

 which now stretches entirely from the 

 horizon in the southeast to the meri- 

 dian. Only half of this interesting 

 figure is as yet visible ; the tip of the 

 tail will not reach the meridian until 

 the early evenings of June, and by this 

 time the head will have begun to set. 



On the back of this long, winding 

 constellation there are the figures of 

 the Crow and the Cup, while a group 

 of faint stars over the tail of the Water- 

 snake (not yet risen) was formed into 

 a little figure known as the "Solitarv 

 Thrush." 



Twenty centuries ago the Crow lay 

 half above and half below the Celes- 

 tial Equator; the slow precession of 

 the equinoxes has changed its position 

 in the sky until it is now no less than 

 twenty degrees below. When first let- 

 tered, the star at A was indicated as the 

 brightest star of this group, but it is 

 now less than one-sixth as bright as 

 the star at C and less than half as 

 bright as the other three most import- 

 ant stars of the figure. It is now of an 

 orange color; as early Arabians de- 

 scribed it as red, it has probably 

 changed both in color and brightness 

 in recent times. 



The star at D is of a pale yellow color 

 but it has a deep blue, eight and five- 

 tenths magnitude companion twenty- 

 four seconds away. There are 

 many variable stars in this constella- 

 tion ; the two at V sink from the 

 seventh to the thirteenth magnitude in 

 the course of eight to ten months. The 

 orange star at B is also probably a var- 

 iable and is a typical example of the 

 second great type of stars whose 



spectre resemble very closely that of 

 our sun. 



At a distance below the bright star 

 at F equal to four times the diameter 

 of our moon there is a remarkable 

 planetary nebula which resembles 

 Jupiter in the color and steadiness of 

 its ligfht. It is described by some ob- 

 servers, however, as of a steely, bluish 

 light and is rather difficult in small 

 telescopes. 



The observer will welcome the great 

 golden yellow Antares, at H, which is 

 so bright and yet so immensely far 

 away. And indeed the whole region of 

 Bootes as well as the sky between this 

 constellation and the Great Dipper will 

 well repay exploration. In the center 

 of the Constellation Leo, at the point 

 K, will be found one of the starless re- 

 gions of the sky, while at O, almost 

 in a line with the Stars L and N, there 

 is a celebrated variable of a fiery red 

 color which varies from the fifth to the 

 tenth magnitude in a period of about 

 ten months. 



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The Precession of the Equinoxes. 



This slow change of the equator of 

 the heavens, which has been referred 

 to in speaking of Corvus, produces as 

 the ages go on a great change in the 

 apparent positions of the constellations 

 in the sky, but it does not change the 

 form or appearance of these constella- 

 tions themselves. It is, in fact, merely 

 the equator which is slowing moving. 

 The intersection (V, Figure 1) of this 

 circle with the apparent path of the 

 sun among the stars SVT. is slowly 

 moving westward, completing the cir- 

 cuit of the heavens in twentv-five 

 thousand eight hundred years. Thus 

 in six thousand years it will have 

 reached Gemini : this constellation will 

 then lie on both sides of the equator 

 and will rise in the east and set in the 

 west, never rising higher in our sky 

 than Orion does at present. The latter 

 constellation will then be far below the 

 equator. To observers north of fiftv 

 deerees north latitude the Dog Star, 

 Sirius, will not be seen at all. Six 

 thousand years later the latter star will 

 be wholly invisible throughout the 

 United States and the former star 

 group, which is now so conspicuous 

 in our evening heavens, will just rise 



