#====================
# Figure 16.1.R.
# R script to draw coordinate system
# for the earth's orbit calculation,
# showing acceleration components due
# to gravitational attraction between
# the Sun and the Earth.
#====================
x=5
y=3
p=5/3
par(pin=c(4.6,3))
plot(x,y,xlim=c(-1,6),ylim=c(-1,3.5),axes=FALSE,ann=FALSE)
x0=c(5,5,5)
y0=c(3,3,3)
x1=c(5,5-p,5-p)
y1=c(2,2,3)
arrows(x0,y0,x1,y1,length=.1)
x0=0
y0=0
x1=5
y1=3
segments(x0,y0,x1,y1)
segments(5,0,5,-.2)
segments(0,3,-.2,3)
abline(h=0)
abline(v=0)
th=2*pi*(0:500)/500
r=.3
xx=r*cos(th)
yy=r*sin(th)
points(xx,yy,type="l")
text(1.4,.4,expression(theta),cex=1.5)
text(.5,-.5,"Sun",cex=1.5)
text(5.7,3.2,"Earth",cex=1.5)
text(2,1.5,expression(italic(r)),cex=1.5)
text(5.3,2.6,expression(italic(a[y])),cex=1.5)
text(4.2,3.3,expression(italic(a[x])),cex=1.5)
text(4,2.2,expression(italic(a)),cex=1.5)
text(5,-.4,expression(italic(x)),cex=1.5)
text(-.4,3,expression(italic(y)),cex=1.5)