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Volcanic ash closes Mexico regional airport

An airport serving Mexico's fourth-largest city has suspended operations due to volcanic ash from the Popocatepetl volcano.Full story

What Ancient Roman Concrete Could Teach Modern Builders

Contemporary concrete is designed to last for about 100 years. Yet at the bottom of the Mediterranean Sea lie the remains of Roman harbors, buildings and other structures that have remained surprisingly intact for almost 2000 years. What's the secret to their phenomenally durable concrete? Full story

If it's not blue, why is it a 'blue moon?'

The next blue moon will occur on the last night of August. Although it will appear no bluer than on any other night, it will nonetheless fit the modern definition of the term by being the second full moon in a calendar month. But this technical meaning of "blue moon" arose fairly recently. The phras Full story

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Mount Etna spews volcanic ash during an eruption on Sicily
Mount Etna spews volcanic ash during an eruption on Sicily

Mount Etna spews volcanic ash during an eruption on the southern Italian island of Sicily March 4, 2012. REUTERS/Antonio Parrinello/FILE PHOTO

A woman cleans a sidewalk covered with volcanic ash in Santa Lucia Cotzumalguapa
A woman cleans a sidewalk covered with volcanic ash in Santa Lucia Cotzumalguapa

A woman cleans a sidewalk covered with volcanic ash in Santa Lucia Cotzumalguapa, south of Guatemala City, Sept. 14.

A car is covered with volcanic ash in Santa Lucia Cotzumalguapa
A car is covered with volcanic ash in Santa Lucia Cotzumalguapa

A car sits covered with volcanic ash in Santa Lucia Cotzumalguapa, south of Guatemala City, Sept. 14.