Raven lays out eight paper circles on the Sky Deck step, each shaded differently. "Eight phases. Put them in order."
Rocket rushes. "Dark, sliver, half, big, full, big, half, sliver." He slides them into a line. "Done."
"What do you notice about the two slivers?" Raven asks.
Rocket looks closer. "One is lit on the right. One is lit on the left."
Nova hovers over the line, her light tracing it. "Growing is called waxing. Shrinking is called waning," she says.
"So the right-lit sliver is waxing," Rocket says. "It comes right after new." Nova hums. "Now name them all."
NASA lists eight lunar phases in order. They are new Moon, waxing crescent, first quarter, waxing gibbous, full Moon, waning gibbous, third quarter and waning crescent.
Waxing means the lit part is getting bigger. Waning means it is getting smaller.
In the Northern Hemisphere, a waxing crescent is a thin crescent of light on the right. A waning crescent is lit on the left.
Gibbous comes from a Latin word meaning hump. A gibbous Moon is between half and full.
| Phase | How much of the Moon's face we see lit | Growing or shrinking |
|---|---|---|
| New Moon | None; the Moon is invisible | start of the cycle |
| Waxing crescent | A thin sliver, lit on the right | growing |
| First quarter | Half; a half Moon | growing |
| Waxing gibbous | More than half | growing |
| Full Moon | The whole face | peak |
| Waning gibbous | More than half | shrinking |
| Third quarter | Half; the opposite half from first quarter | shrinking |
| Waning crescent | A thin sliver, lit on the left | shrinking |
At first quarter, the Moon is one quarter of the way around its orbit. We see half of its lit side, so it looks like a half Moon.
At third quarter, it is three quarters of the way around. Half of the visible side is again dark, the opposite half.
The Moon moves eastward about 12 degrees in the sky each day. That is about 24 times its own width.
Because of this eastward motion, the Moon rises later each day. OpenStax says the delay averages about 50 minutes.
| Statement | True or false? |
|---|---|
| Full Moon comes right after waxing gibbous. | ? |
| A waning crescent is lit on the right in the Northern Hemisphere. | ? |
| The Moon rises about 50 minutes later each day on average. | ? |
| Third quarter comes before full Moon. | ? |
Strong work. Tomorrow is Sky Deck Lab: your head is Earth, and a ball on a pencil is the Moon.