By Lee Johnson, Updated Mar 24, 2022

Understanding the moon’s phases allows you to track its progression toward or away from a full moon. With a 27.3‑day orbital period, the moon’s illuminated portion changes as it orbits Earth, creating eight distinct phases: new, waxing crescent, first quarter, waxing gibbous, full, waning gibbous, third quarter, and waning crescent.

DOC Mnemonic (or COD in the Southern Hemisphere)

The most widely used mnemonic is DOC—or COD for observers in the Southern Hemisphere—to remember the sequence and lighting direction of the lunar cycle.

• D (beginning) – an arch on the right followed by a straight line on the left indicates a waxing phase, with light on the right side.
• O – the full moon, where the entire face is illuminated.
• C (end) – a waning phase, with light on the left side, culminating in the waning crescent.

In the Southern Hemisphere, the mnemonic reverses to COD to account for the mirrored appearance of the moon.

Crescent and Gibbous Shapes

The moon takes on a crescent shape twice each cycle: just before the new moon and just after. The side of the crescent indicates whether the new moon is approaching (left) or has passed (right). A gibbous moon is almost fully illuminated, with a crescent of darkness on one side; it occurs immediately before and after the full moon, and the mnemonic tells you which side is dark.

Waxing vs. Waning

“Waxing” refers to the period from new to full moon, where the illuminated portion grows. The D in DOC signifies waxing with light on the right. “Waning” is the reverse—from full to new—represented by the C and light on the left.

Full and New Moon

The full moon is the peak of illumination, separating the waxing and waning phases. The new moon, conversely, is entirely dark. The O in the mnemonic represents this full illumination.

Mastering these simple mnemonics and visual cues will enable you to identify each lunar phase with confidence and clarity.