september: sun, moon, shuttle and shadow

In this photo, taken during the launch of the Space Shuttle Atlantis, a strange phenomenon can be seen: a shadowy line extends from glowing section of the shuttle's plume and appears to lead directly to the Moon. It is the elegant result of the photographer being in place at a very specific time - just after sunset on the night of the full moon.

Although at ground level the Sun has set, further up it is still daylight. Air travellers may have noticed this when taking off or landing around dawn or dusk, and anyone in a mountainous area will have seen how the peaks remain illuminated long after the valleys have become dark. Following down the plume, the whiteness of daylight is followed by the progressive colours of sunset and eventually the darkness where night has just fallen. The dark line is the shadow of the plume cast by the bright daylight above.

When the Moon is full it is always directly on the opposite side of the Earth to the Sun, and consequently rises just as the Sun sets and vice versa. This is why, in this picture, the Moon has just risen above the horizon, and the Sun's shadow appears to point directly towards it.

Image: NASA.