Venus displays a crescent phase when positioned almost directly between the Sun and Earth, as shown in this image captured by Thierry Legault. This alignment occurs once every year and a half. The backlit atmosphere of Venus refracts and scatters sunlight, creating a glowing crescent arc that extends beyond 180 degrees. The tips of this arc are called the "horns."
The crescent can be seen with a small telescope or binoculars during twilight. Those with exceptionally acute eyesight may see it with the unaided eye. Ancient Babylonian astronomers may have been the first to study Venus' brightness changes, which relate to its phases. Many other cultures have similar astronomical records, including the oldest surviving Maya book.