Explanation: Our Moon's appearance changes nightly. This time-lapse sequence shows what our Moon looks like during a lunation, a complete lunar cycle. As the Moon orbits the Earth, the half illuminated by the Sun first becomes increasingly visible, then decreasingly visible. The Moon always keeps the same face toward the Earth. The Moon's apparent size changes slightly, though, and a slight wobble called a libration is discernible as it progresses along its elliptical orbit. During the cycle, sunlight reflects from the Moon at different angles, and so illuminates different features differently. A full lunation takes about 29.5 days, just under a month (moon-th).

Credit & Copyright: António Cidadão

 Courtesy of Astronomy Picture of the Day Index - Main Page & Astronomy Picture of the Day

• Astronomy Picture of the Day
• Earth Image of the day
• Earth Science Image of the day
• NASA Image of the Day
• NOAA Image of the day
• Woods Hole Oceanographic Institution Image of the day
• National Geographic Image of the day
• Space Weather
•  Past 7 Days of Astronomy Pic of the Day
•  Goddard Spaceflight Center News and Features
•  NASA's Photojournal: Images from the Universe Gallery
•  Yahoo! News: Space/Astronomy