import math


def Sun_radius_vector(e, tar):
  """
  Distance between the Sun and the Earth

  There are a set of higher accuracy terms not included here.

  @param e : eccentricity of the orbit
  @type  e : float

  @param tar : Sun's true anomaly (radians)
  @type  tar : float

  @return: AU
  """
  return 1.0000002*(1. - e**2)/(1. + e*math.cos(tar))