what is the fourth phase of the moon
Lunar phase In Western culture, the four principal lunar phases are new moon, first quarter, full moon, and third quarter (also known as last quarter). These are the instances when the Moon's apparent geocentric celestial longitude minus the Sun's apparent geocentric celestial longitude is 0째, 90째, 180째 and 270째, respectively.[a] Each of these phases occur at slightly different times when viewed from different points on the Earth. During the intervals between principal phases, the Moon appears either crescent-shaped or gibbous. These shapes, and the periods of time when the Moon shows them, are called the intermediate phases. They last, on average, one-quarter of a synodic month, roughly 7.38 days, but their durations vary slightly because the Moon's orbit is slightly elliptical, and thus its speed in orbit is not constant. The descriptor waxing is used for an intermediate phase when the Moon's apparent size is increasing, from new moon toward full moon, and waning when the size is decreasing.