Puerto Vallarta, Mexico - A total lunar eclipse will be seen on December 10 at dawn from the western United States to Eastern Europe, reported the U.S. space agency (NASA). Those who wish to enjoy the show will have to be ready before dawn, as it will begin at 4:45 am Pacific time (12:45 GMT) when the Earth's shadow falls on the lunar disk.

Nearly two hours later the Moon will be totally engulfed in a reddish light, an effect that will not be seen again until 2014, and will be visible from the U.S. Pacific coast, across the Pacific Ocean and Asia, and in Eastern Europe.

A total lunar eclipse occurs when the Sun, Earth and Moon line up.

During a lunar eclipse the Moon changes color, ranging from orange to copper or brown, because the sun's rays break down as they pass through the Earth's atmosphere, filtering out the radiation of the shorter (blue) wavelength and allowing the passage of the longer (red) wavelength.

Throughout the eclipse, the redness of the moon goes through different stages. The first stage, "penumbra" happens when the moon begins to hide behind a slight shadow cast by the Earth. The second cycle is called the "umbra" and corresponds to the time when the Moon begins to cover the darker shadow of the Earth.

The next stage is "full," when the moon is completely covered by the shadow of the Earth and takes on a deeper red hue.

The peak of the eclipse occurs when the moon is completely obscured by the Earth, which is interposed between the sun and the moon.

At the end of its "totality," the eclipse will begin to wane, and the "umbra" will again be seen on the lunar surface.