ASTRONOMY. l6l 



The diurnal motion in his orbit 4 5' 22". 

 The periodic time 87 d .97 nearly. 



160. The points in which a planet has no la- 

 titude, are called, as in the case of the Moon^ 

 the Nodes qf the Planet. The Planet is then 

 in the ecliptic, and one-half of its orbit lies 

 on the north, the other on the south side of that 

 plane. 



a . The line of the nodes of every planet, or the com- 

 mon section of the plane of its orbit, with the 

 plane of the ecliptic, passes through the Sun. This 

 was discovered by KEPLER. See Dr SMALL'S Ac- 

 count of KEPLER'S Discoveries, p. 154. 



b. The node through which the planet passes into the 

 northern signs, is called its Ascending Node ; that 

 through which it passes into the southern, is call- 

 ed the Descending Node. 



c. The Heliocentric place of a planet, is its place as 

 it would be seen from the Sun : the Geocentric, as 

 it is seen from the Earth, 



161. When the Earth is in the line of a pla- 

 net's nodes, or, which is the same, when the Sun 

 is seen from the Earth in that line, if the pla- 

 net's elongation from the Sun, and its geocen- 

 tric latitude be observed, the inclination of the 

 orbit may be found ; for, the sine of the elon-* 



VOL. II. L gatiow 



