Figure: The Earth-Moon system and the Earth-Moon distance in units of Earth radii

Image 1 Caption: 2-body Earth-Moon system, approximately to-scale.

Further explication:

1. As illustrated in the Image 1, one can see that Earth and Moon are both pretty small compared to their separation distance.

2. Now the Earth equatorial radius R_eq_⊕ = 6378.1370 km and

     R_Moon = 60.2684 R_eq_⊕
            = 2.57*10**(-3) AU  
            = 384,399 km ≅ 400,000 km .  

   The number to remember is R_Moon ≅ 60 Earth radii.
   Note that distances between astronomical objects are usually center-to-center distances if there are well defined centers. If there are NOT well defined centers, then more specifications are needed about what distance means.

3. Note the Moon's elliptical orbit eccentricity = 0.0549006 which means the Moon's distance varies by about 11 % from perigee to apogee.

   

4. Image 2 Caption: The Sun-Earth-Moon system shown not-to-scale.

   For further explication of this image, see the Astronomical unit figure, Image 2 Caption

Images:

1. Credit/Permission: © David Jeffery, 2005 / Own work.
   Image link: Itself.
   
2. Credit/Permission: © David Jeffery, 2003 / Own work.
   Image link: Itself.