Phases of the Moon: Angular Separation Question

[kepler]

Hi,

Just a stupid doubt...when the moon is in FIRST QUARTER or LAST QUARTER, their angular separation is of 90 degrees; question: is it the TRUE angular separation or is it the difference of ecliptic longitudes?

Kind regards,

Kepler

 

[mathman]

First and last quarter moons result from the earth-moon line being 90 deg. from the earth-sun line.

 

[kepler]

That was my initial guess :)

Thanks,

Kepler