Period Gallery

Phases of the Moon

Phases of the Moon. Composite image showing the Moon at each stage of its 28 day cycle (a lunar month). Along the top row, the Moon is a waxing (growing in apparent size) crescent, reaching a half Moon after 7 days. For the next seven days it is a waxing gibbous (between half and full), reaching a full Moon (far right of second row) after 14 days. The Moon is then a waning (decreasing in apparent size) gibbous, reaching another half moon 21 days into the cycle. On the bottom row it is a waning crescent, reaching the new Moon stage at bottom right. The phases of the Moon are due to it revealing differing amounts of its sunlit face as it orbits the Earth. Photographed from Santorini on 3rd - 30th June 2000

© ECKHARD SLAWIK/SCIENCE PHOTO LIBRARY

Waning crescent Moon

Waning crescent Moon. Image 27 of 27. Optical image of a waning (decreasing in apparent size) crescent Moon 27 days into its 28-day cycle. The lunar phases arise as the Moon's orbit of the Earth shows the Earth-facing side moving into and out of the light of the Sun. This Earth-facing side of the Moon is locked in place by the gravitational influence of the Earth. This results in a lunar day that equals the length of the lunar Earth orbit. On a waning Moon the day-night line (terminator) marks the lunar sunset. The Moon is crescent when it is less than half full. Taken in October 2001. A sequence of the monthly cycle of Moon phases is shown on images R340/644-670

© ECKHARD SLAWIK/SCIENCE PHOTO LIBRARY

Uterus lining during menstruation, SEM

Uterus during menstruation. Coloured scanning electron micrograph (SEM) of the lining of the uterus being shed during menstruation. The upper layers (red) are being shed and the breakdown of the underlying blood vessels releases red blood cells (red dots). Menstruation occurs for a few days during a woman's menstrual cycle. Prior to menstruation, the uterine lining (endometrium) thickens to prepare it for the reception of a fertilised egg. If a fertilised egg enters the uterus, it implants in the wall and develops into an embryo. If the released egg is not fertilised, the thickened wall is shed

© STEVE GSCHMEISSNER/SCIENCE PHOTO LIBRARY