Re: "Limb"?
"Limb, in astronomy, the curved edge of the apparent disk of a celestial body (star, planet, moon, etc.), as in lunar limb, limb darkening, atmospheric limb sounding, etc.; related to horizon"
"Limb, in astronomy, the curved edge of the apparent disk of a celestial body (star, planet, moon, etc.), as in lunar limb, limb darkening, atmospheric limb sounding, etc.; related to horizon"