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up and along the side of it we saw a star exactly in line with its 
face we should know that the star bore at that instant the same 
angle from our local East that the wall did. But this would not 
tell us what angle the star bore from the East point of the 
heavens. For in every 24 hours, as our Earth turns on its axis, 
our East point turns with it and performs a complete circuit, 
pointing each hour 15 degrees East of the point in the heavens to 
which it looked the hour before. 
Let us further understand that there is a point in the heavens 
which astronomers have fixed upon as the Celestial East point, 
with which for one moment in the year our Terrestrial East point 
agrees. That point is what the astronomers call the First Point 
of Aries. It is that position among the stars and in the Ecliptic 
which the Sun occupies when the plane of our Equator if produced 
would pass through the centre of the Sun, as it would at the 
Equinoxes. Let us first consider the position at the Vernal 
Equinox. At that moment the East point of the Earth coincides 
with the East point of the heavens. And, if looking along the 
wall at that instant of time we saw the star exactly in line with 
the face of the wall we should know that the star bore the same 
angle from the Celestial East point that both the star and the 
wall bore from the local Terrestrial East point. 
Now astronomers have observed and set down the positions of 
all the principal stars. And their method is analogous to that of 
the geographers with their Meridians of Longitude, and Parallels of 
Latitude. For they note the star’s azimuthal distance from a 
great vertical circle which passes through the First Point of Aries 
and they reckon it along a great horizontal circle called the Equator 
or Equinoctial circle which is divided into 24 hours. And the 
distance of the stars from the First Point of Aries is reckoned in 
hours and minutes and seconds along the Equinoctial circle ; and 
is called the Star’s Right Ascension. And the position of the star 
in altitude is reckoned from the Equinoctial circle in degrees, 
minutes and seconds, and is called North or South Declination 
according as the star is North or South of the Equator. 
