What determines that an earthquake is really an aftershock?

Aftershocks are earthquakes, and seismologists use the term, along with foreshocks and mainshocks, to describe the relationship between the intensity of various earthquakes. The mainshock of an earthquake sequence is generally the event with the largest magnitude. Aftershocks do not have a precise definition but are less intense than a mainshock and occur in the same area. Any subsequent earthquake in the same area, but with less magnitude, is considered an aftershock, until activity in that area returns to normal. Aftershocks are generally caused by the "readjustment" of Earth's crust in response to a larger earthquake. Aftershocks occur even after very small earthquakes.

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Where does dust come from and what is it?

Dust is particles of less than one millimeter in diameter, regardless of its content. A significant portion of dust is dead skin fragments from human bodies, tobacco smoke, airborne particles of pollen and plants, industrial smoke, clay, and other mineral (soil) matter. Major volcanic eruptions also produce thousands of tons of dust, and dust from outer space can be yet another source.

Where does the word propaganda come from?

The Latin verb propagare means "to reproduce (a plant) by cuttings; spread for sprouting; propagate; enlarge." The modern use of the term, however, is grounded in the Roman Catholic Church. Pope Gregory XV, in 1622, created a congregation specifically for organizing all of the Roman Catholic Church's missionary activities under his control. He called it the Congregatio de Propaganda Fide or, roughly translated, "the congregation for propagating the faith." It began being referred to informally as "Propaganda." The common English usage of the word as we know it today was established by the 1790s.

Why doesn't evaporated milk have to be refrigerated?

Evaporated milk, which is thickened through the process of evaporation (hence the name) has a long shelf life because it is sterilized in the can through a steam-heating process that destroys potentially harmful micro-organisms. You may notice it can develop a darkish, off-color after about a year, but it is still safe to consume.

I've heard that if you cut your hair on a full Moon, your hair grows healthier and faster. Is this true?

According to folklore, if hair is cut during the Moon's waxing phase (between new and full), growth is encouraged. The opposite will occur if hair is cut during the waning phase (the day after the Moon is full to the day before it's new).

Why are rain clouds dark, when rain is light and see-through?

Clouds always contain water particles. When these particles are small, they reflect light and are perceived as white. When water particles in the clouds become large enough to form raindrops, they absorb more light and appear dark to us.

Doesn't it say somewhere in the Bible that the sun stood still in the sky? How could this happen without the solar system falling apart?

In the book of Joshua, the Bible tells of a battle between the Israelites and the Amorites. Joshua 10:12-13 says "The sun stood still...the sun stopped in the middle of the sky and delayed going down about a full day." Some Biblical scholars argue that Joshua's soldiers may have needed to avoid fighting under a blazing sun, so the expression "stood still" simply means "stopped shining."

What does it mean to add sour milk to a recipe?

This does not mean to add that stuff that has curdled at the back of your refrigerator. To "sour" milk, add 1 tablespoon vinegar or lemon juice to 1 cup milk, minus 1 tablespoon. Stir and let stand 5 minutes.

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