Why does the Moon completely disappear once a month?
- Ric Kearbey
- 4 days ago
- 3 min read
About once every month, the Moon seems to completely disappear from the sky. Astronomers call this the new moon, and your weather or astronomy app may even describe it as 0% illuminated.
But here’s the weird part: half of the Moon is still brightly illuminated by the Sun.
So how can something roughly 2,159 miles across seemingly vanish?
Why does the Moon completely disappear if half of it is still illuminated?
Because during a new moon, the Moon is positioned roughly between Earth and the Sun. The half illuminated by the Sun faces mostly away from us, while the nighttime half faces Earth.
When an app says the Moon is 0% illuminated, it doesn’t mean sunlight has stopped reaching the Moon. It means essentially none of the lunar disk we see from Earth is directly illuminated.
But darkness is only half of the disappearing act.
Where is the Moon when you can’t see it?
Here’s something that initially feels backward: the new Moon is usually in the daytime sky.
It rises around sunrise, travels across the sky roughly alongside the Sun, and sets around sunset. With its dark hemisphere facing us and the brilliant Sun nearby, it becomes extraordinarily difficult to see.
That’s also why you won’t find the new Moon overhead at midnight.
But give it another day or two and something beautiful happens.
Why does a tiny crescent suddenly appear after sunset?
The Moon keeps moving around Earth, gradually increasing its angular distance from the Sun in our sky. Soon, just enough of its illuminated hemisphere becomes visible to create a razor-thin waxing crescent.
Look low toward the west shortly after sunset and you may spot it hanging in the twilight. That’s not a coincidence. The Moon has only recently moved away from its position near the setting Sun, so the young crescent follows the Sun below the western horizon not long afterward.
And if you look carefully at that crescent, you may discover something even cooler.
Why can you sometimes see the “dark” part of the Moon?
Sometimes the bright crescent surrounds a ghostly gray outline of the entire Moon.
That’s called earthshine, and the light has taken one hell of a trip.
Sunlight shines on Earth. Some of that light reflects from our planet toward the Moon, softly illuminating the Moon’s nighttime landscape. A tiny portion then reflects all the way back to Earth and into your eyes.
In other words:
Sun → Earth → Moon → you.
That beautiful gray glow is partly our own planet lighting up the lunar night.
Does the Moon actually have a dark side?
Not permanently.
The famous “dark side of the Moon” is really the far side, the hemisphere that always faces away from Earth because the Moon’s rotation is synchronized with its orbit. Both hemispheres experience sunlight and darkness as the Moon travels around Earth.
And that brings us back to the supposedly invisible Moon.
What makes a 0% illuminated Moon so special?
A new moon gives the nighttime sky something astronomers love: no competing moonlight. Fainter stars, galaxies and meteor showers become easier to see under truly dark skies.
It’s also the only lunar phase capable of producing a solar eclipse. Usually the Moon passes slightly above or below the Sun from our perspective because its orbit is tilted. But when everything lines up just right, that supposedly invisible Moon passes directly across the Sun.
Suddenly, 0% illuminated becomes very visible indeed.
The next evening you spot a delicate crescent hanging over the western horizon, look closely at the dim gray Moon nestled inside it.
That faint glow traveled from the Sun to Earth, from Earth to the Moon, and from the Moon back to you.
Sometimes the best way to notice the Moon is right after it disappears.
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