I am using the following R script to plot the moon phase and the moon's illuminated fraction:
library(oce) X11() t_start <- as.POSIXct("2017-02-23", tz='UTC') t_end <- t_start + 75 * 24 * 3600 # 35 days tm <- seq(from = t_start, to = t_end, by = 10000 ) moon <- moonAngle(t=tm, longitude=-8, latitude=47) fraction <- moon$illuminatedFraction phase <- moon$phase - floor(moon$phase) plot (tm, fraction, type="l", col='blue') lines(tm, phase , type="l", col='red' ) grid() # wait for mouse click or enter pressed locator(1)
The red lines indicate the phase (0 = new moon, 1/4 = first quarter, 1/2 = full moon etc.), the blue curve indicates the how much of the moon is illuminated.
I have expected the illuminated fraction to be zero exactly then when also the phase is zero. However, this is not the case.
So, is there something I am missing, am I doing something wrong in my script or is the implementation of