If you’re in North America right now, as I am, and if skies are clear, then you need only look up to see one of the most interesting lunar eclipses in years in progress. Although not especially rare, total lunar eclipses are always a treat. This one was particularly anticipated because of the possible effects of two volcanic eruptions this year — Iceland’s Eyjafjallajökull last spring and, more recently, Mount Merapi in Indonesia.

A lunar eclipse is total when the Moon slides completely into the darkest part of Earth’s shadow, known as the umbra. At such times, the bright lunar disk goes dim and usually turns a coppery red colour. The colour is caused by sunlight passing through Earth’s atmosphere and scattering around the limb of our planet to fall on the Moon’s surface.

Sometimes, lunar eclipses can appear vividly red; at other times they are darker. Based on nothing but my own recollections of previous lunar eclipses this one seems to be on the darker side. The reason may well be because of the excess of dust in the upper atmosphere thanks to this year’s two major eruptions.

A notably dark lunar eclipse was observed in 1992, one year after the spectacular eruption of Mount Pinatubo. Quantitative measurements will eventually reveal how tonight’s event stacks up.

Well understood since ancient times lunar eclipses nevertheless have a remarkable allure and ability to spark human curiosity about all things cosmic. With my six-year-old daughter watching alongside me seeing the moon go dark for the first time, this was a particularly special lunar eclipse for me. I hope yours was equally satisfying. Tell us about it!

Image 1: Crude picture of tonight’s eclipse (achieved by holding a point-and-shoot digital camera up to a pair of binoculars).