CHICAGO (WBBM) – On the longest night of the year, Monday night into Tuesday, there will be full lunar eclipse at 1:40 a.m.

LISTEN: Newsradio 780’s Dave Marsett Reports

Weather permitting–and the forecast isn’t favorable in the Chicago area, calling for clouds building Monday and snow overnight–the eclipse will be visible everywhere in the continental United States.

At its darkest, the moon will be halfway up from the horizon in the south-southwest sky.

Unlike a solar eclipse, when the moon stands between Earth and the sun, a lunar eclipse, when Earth stands between the sun and the moon, is safe to watch with the naked eye.

The Adler Planetarium invites all to a free Total Lunar Eclipse Party starting at 11 p.m. Monday and ending 4 a.m. Tuesday.

Adler educators and astronomers will be on hand to help visitors view the eclipse. Visitors can bring their own telescope or use ones provided by the Adler.

At 12:32 a.m. Tuesday, the moon will drift into Earth’s shadow. By 1:40 a.m. it will be covered in shadow, most deeply at 2:17 a.m. At 2:53 a.m. it will begin to slip out of the shadow and be totally clear of it at 4:01 a.m.

The last time a total lunar eclipse could be seen in the Chicago area was Feb. 20, 2008.

There won’t be another total lunar eclipse visible in the Chicago area until April 15, 2014 and not another that coincides with the night of the winter solstice for 84 years.

Astronomical winter–the winter solstice–officially begins at 5:38 p.m. CT Tuesday.

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