/// <summary>
/// this is the helper method used in the GController to add the current star into the star group
/// </summary>
/// <param name="tar"></param>
public void addStar(star tar)
{
this.starGroup[tar.getID()] = tar;
}
/// <summary>
/// if we redraw the world, we need to remove the current star from the star groups
/// </summary>
/// <param name="star"></param>
public void removeStar(star star)
{
this.starGroup.Remove(star.getID());
}