or ages, which rely on stellar luminosity to be calculated). Resolution B2 defines an absolute bolometric magnitude scale where corresponds to luminosity , with the zero point luminosity set such that the Sun (with nominal luminosity ) corresponds to absolute bolometric magnitude . Placing a radiation source (e.g. star) at the standard distance of 10 parsecs, it follows that the zero point of the apparent bolometric magnitude scale corresponds to irradiance . Using the IAU 2015 scale, the nominal total solar irradiance ("solar constant") measured at 1 astronomical unit () corresponds to an apparent bolometric magnitude of the Sun of . Following Resolution B2, the relation between a star's absolute bolometric magnitude and its luminosity is no longer directly tied to the Sun's (variable) luminosity: where is the star's luminosity (bolometric luminosity) in watts is the zero point luminosity is the bolometric magnitude of the star The new IAU absolute magnitude scale permanently disconnects the scale from the variable Sun. However, on this SI power scale, the nominal solar luminosity corresponds closely to , a value that was commonly adopted by astronomers before the 2015 IAU resolution. The luminosity of the star in watts can be calculated as a function of its absolute bolometric magnitude as: using the variables as defined previously. Solar System bodies () For planets and asteroids, a definition of absolute magnitude that is more meaningful for non-stellar objects is used. The absolute magnitude, commonly called , is defined as the apparent magnitude that the object would have if it were one astronomical unit (AU) from both the Sun and the observer, and in conditions of ideal solar opposition (an arrangement that is impossible in practice). Because Solar System bodies are illuminated by the Sun, their brightness varies as a function of illumination conditions, described by the phase angle. This relationship is referred to as the phase curve. The absolute magnitude is the brightness at phase angle zero, an arrangement known as opposition, from a distance of one AU. Apparent magnitude The absolute magnitude can be used to calculate the apparent magnitude of a body. For an object reflecting sunlight, and are connected by the relation where is the phase angle, the angle between the body-Sun and body–observer lines. is the phase integral (the integration of reflected light; a number in the 0 to 1 range). By the law of cosines, we have: Distances: is the distance