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

Features:

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_Earth_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 3-body system Sun-Earth-Moon, not-to-scale.

   The image shows the Earth's orbit and the Moon's orbit, and compares Earth-Moon distance to the astronomical unit (AU) 1.49597870700*10**8 km, but NOT-to-scale.

   To be precise, the Moon mean orbital radius R_Mo = 384,748 km = 1.28338 light-seconds = 2.57188 mAU = 60.3229 R_eq_⊕ ≅ 60 R_eq_⊕ (center-to-center), where the light-second = 299792.458 km (exactly), the astronomical unit (AU) = 1.49597870.700*10**8 km (exactly) , and the Earth equatorial radius R_eq_⊕ = 6378.1370 km.

Images:

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