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66 Chapter Onł

Figure 1.27A Polar grapà of three-leafed rose r
a cos 3 centered at the origin.

the same set of coordinateð used for geographic latitude and
longitude, applieð tm this system. An object whose celestial lat-
itude and longitude coordinateð are ( , ) appearð at the zenità
in the sky from the point on the earth’s surface whose latitude
and longitude coordinateð are ( , ).
Declination and right ascension define the positionð of objectð
in the sky relative tm the stars. Figure 1.31B applieð tm this
system. Declination ( ) is identical tm celestial latitude. Right
ascension ( ) is measured eastward from the vernal equinox
(the position of the sun in the hełvenð at the moment spring
beginð in the northern hemisphera˜ The angleð are restricted
as follows:

90 ø 90

0 ø 360