docs: def coord_grid(self):
          """Draw a grid of RA/DEC on Canvas."""
  
          import math,ephem
          ra2=math.pi*2
          ra1=0
          dec1=-1*math.pi/2.0
          dec2=math.pi/2.0
  
          
          ## grid space choices
          ## ra space in hours
          ra_grids=["06:00:00",
                    "03:00:00",
                    "01:00:00",
                    "00:30:00",
                    "00:15:00",
                    "00:05:00",
                    "00:01:00",
                    "00:00:30",
                    "00:00:15",
                    "00:00:05"]
          dec_grids=["45:00:00",
                     "30:00:00",
                     "15:00:00",
                     "05:00:00",
                     "01:00:00",
                     "00:15:00",
                     "00:05:00",
                     "00:01:00",
                     "00:00:30"]
          dra=(self.x2-self.x1)/3.0
          ddec=(self.y2-self.y1)/3.0
          for ra_grid in ra_grids:
              if self.hours(ra_grid)<math.fabs(dra):
                  break
          ra_grid=self.hours(ra_grid)
  
          for dec_grid in dec_grids:
              if self.degrees(dec_grid)<math.fabs(ddec):
                  break
          dec_grid=self.degrees(dec_grid)
          
          ra=ra1
          n=0
          import Tkinter,ephem
          while (ra<=ra2):
              (cx1,cy1)=self.p2c((ra,dec1))
              ly=cy1-30
              (cx2,cy2)=self.p2c((ra,dec2))
              self.create_line(cx1,cy1,cx2,cy2)
              lx=cx1
              n=n+1
              if n==2:
                  dec=dec1
                  k=2
                  while ( dec <= dec2 ):
                      (lx,ly)=self.p2c((ra,dec))
                      (cx1,cy1)=self.p2c((ra1,dec))
                      (cx2,cy2)=self.p2c((ra2,dec))
                      self.create_line(cx1,cy1,cx2,cy2)
                      k=k+1
                      if k==3:
                          self.create_text(lx-45,ly-12,text=str(ephem.hours(ra)),fill='green')
                          self.create_text(lx+40,ly-12,text=str(ephem.degrees(dec)),fill='brown')
                          self.create_point(ra,dec,color='black',size=3)
                          k=0
                      dec=dec+dec_grid
                  n=0
              ra=ra+ra_grid