Lunar eclipse facts

Think you have mastered the knowledge of the sky? Here are some lunar eclipse and winter solstice facts that might surprise you.

The Earth has a shadow and it isn't gray or black -- it's red.

The winter solstice can be calculated down to the second and only lasts a moment before the earth's axial tilt changes.

Recent lunar eclipses have also cast a turquoise shadow on the moon, which is new to observers. The turquoise comes from the effect the ozone layer has on the sun's light that creates the Earth's shadow.

A lunar eclipse can only occur on a full moon and a solar eclipse can only occur with a new moon.

The day will be short, the night long, and the moon a brilliant shade of red.

All of this will happen because the winter solstice and a total lunar eclipse will be a package deal this year, both occurring on Dec. 21.

In Boulder and the surrounding areas, viewers should begin to look to the skies around 11:15 p.m. on Dec. 20 to see the eclipse, said Douglas Duncan, Fiske Planetarium director.

At 11:33 p.m., the moon will begin to go into the darker central shadow from the Earth and from 12:41 a.m. to 1:53 a.m. on Dec. 21 it will be completely eclipsed.

"One of the nice things about lunar eclipses is that half the world, the half where it is night, gets to see a total lunar eclipse," Duncan said. "A total eclipse of the sun is so rare and you have to be standing in the just the right place on Earth to see it."

Two ingredients are necessary for a total lunar eclipse: a full moon and a path passing through Earth's shadow. If these two occurrences happen at the same time, the moon can glow any color from red to turquoise for one to three hours as it passes through.

According to Duncan, most people don't realize Earth has a shadow. The Earth casts a shadow just as buildings or people do, but Earth's shadow is more brilliant -- it's red.

Human shadows are somewhat mundane as they lack an atmosphere. The Earth, however, has a spectacular atmosphere that changes day to day. This makes every lunar eclipse different in terms of color.

"The reason the moon is orange (during an eclipse) is the same as the reason the sky is blue," said Duncan. "When sunlight goes through Earth's atmosphere, blue light bounces around more and stays with us, making our sky blue. Orange, yellows and reds, however, continue on and hit our moon."

Fiske Planetarium on the University of Colorado campus is hosting a free event for the eclipse, complete with telescopes and binoculars and a 45-minute presentation on what to expect with an eclipse. Doors will open at 10 p.m. on Dec. 20.

The upcoming total lunar eclipse will be the second, and last, lunar eclipse this year. A partial lunar eclipse occurred on June 26, but the view was not favorable from North America.

The next total lunar eclipse visible from North America won't happen until Dec. 10, 2011. For those who may be traveling next summer, however, June 15 will hold another total lunar eclipse that can be seen from most other parts of the world, including Europe and South America.

Lunar eclipses are one of the easiest space phenomena to observe with the unaided eye. When the sun sets and the moon rises, viewers need only to step outside their doors.

The winter solstice, however cannot be seen. It refers to the moment when Earth is tilted farthest from the sun. While it technically occurs only for an instant, the day it takes place is the shortest of the year and the night the longest. The winter solstice will take place at 4:38 p.m. Mountain Standard Time on Dec. 21.