Short answer: on September 15, 2026, NASA's Astronomy Picture of the Day featured the Moon sliding directly in front of Venus while the Sun was still up — an event bright enough, and precise enough, to photograph in a blue daytime sky. NASA's own headline calls it a "daytime eclipse," but the more accurate word for what the picture actually shows is an occultation. That's not pedantry; the distinction is exactly what makes the event make sense.
Eclipse or occultation — what's the real difference?
An eclipse, strictly speaking, describes one specific three-body lineup: the Sun, the Moon, and Earth, where the Moon's shadow falls on Earth (a solar eclipse) or Earth's shadow falls on the Moon (a lunar eclipse). An occultation is the broader family both belong to: any time a nearer object passes in front of a farther one and blocks it from view, from a given vantage point. When the Moon passes in front of the Sun, that's the special, famous case people call an eclipse. When the Moon passes in front of a planet, a star, or anything else, astronomers call it an occultation — and that's exactly what happened to Venus on September 15. NASA's headline borrows the more familiar word for a general audience, but "Moon occults Venus" is the precise description.
Why Venus, and why in daylight?
The Moon can occult plenty of stars and even other planets throughout the year, but almost none of those events are visible without a telescope, and essentially none are visible in daytime — the sky is simply too bright. Venus is the exception because it is, after the Sun and Moon, the brightest natural object in Earth's sky. Even with the Sun up and the sky lit blue, Venus can be bright enough to pick out with the naked eye if you know precisely where to look, and easily bright enough for a telescope or camera to capture crisply as the Moon's dark limb slides across it. That combination — a bright daytime sky plus an unusually bright target — is what turned an otherwise routine occultation into a photographable, shareable event.
Why this happens at all: the geometry behind it
Occultations of planets aren't random. They happen because the Moon's orbit around Earth is tilted only slightly — by about 5 degrees — from the plane in which Earth and the other planets orbit the Sun, the ecliptic. Venus, like every planet in the solar system, always appears somewhere close to that same ecliptic line as seen from Earth. Because the Moon crosses that band of sky as it makes its roughly monthly orbit, it periodically lines up with whatever planet happens to be sitting along that same path at that moment. On September 15, that planet was Venus. The event is a direct, visible consequence of the fact that the Moon, Venus, and Earth all share very close to the same orbital plane — the same geometry that also makes solar eclipses possible, just applied to a different pair of bodies.
What to actually watch for
Unlike a star, which is so far away it behaves like a single point of light and blinks out from the Moon's limb almost instantly, a planet like Venus has an actual visible disk. That means an occultation of Venus isn't instantaneous — the Moon's edge takes a few moments to fully cover the planet's disk, and a few moments again to uncover it on the other side, rather than a single clean vanish-and-reappear. That gradual disappearance is part of what makes these events worth watching closely when they're visible: you're not just seeing a light switch off, you're watching one real disk in space physically slide behind another.
See the geometry for yourself
This kind of alignment is much easier to understand by looking at the actual positions of the bodies involved than by reading a description of it. On the real-time 3D simulator at Solar System Live, you can look at where the Moon and Venus currently sit relative to Earth and to the ecliptic plane, and get a direct sense of why these lineups happen when they do — the same orbital mechanics that produced this daytime disappearing act on September 15, playing out continuously, whether or not a camera happens to be pointed at the sky to catch the next one.