The Umbra of Earth
The dark, inner shadow of planet Earth
is called the umbra.
Shaped like a cone extending into space, it has a
circular cross section most easily seen during a
lunar
eclipse.
And on the night of September 7/8 the
Full Moon passed
near the center of Earth's umbral cone,
entertaining
eclipse watchers around much of our fair planet,
including parts of Antarctica, Australia, Asia, Europe, and Africa.
Recorded from Zhangjiakou City, China,
this timelapse composite image uses
successive pictures from
the total lunar eclipse,
progressing left to right, to reveal the curved cross-section of the
umbral shadow sliding across the Moon.
Sunlight scattered by the atmosphere into Earth's umbra
causes the lunar surface to appear reddened during totality.
But close to the umbra's edge, the limb of the eclipsed Moon shows a
distinct blue hue.
The blue eclipsed
moonlight originates as rays of sunlight
pass through layers high in the upper stratosphere,
colored by ozone that scatters red light and transmits blue.
In the total phase of this
leisurely lunar eclipse,
the Moon was completely within the Earth's umbra for about 83 minutes.