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Category Archives: Phenomena
Why is the sky blue?
All the attention of today’s eclipse has raised interest in the sky’s color.
To understand why the sky is blue, we need to understand a little about light. Light is a form of electromagnetic energy. This form of energy does not need matter to propagate. Continue reading
Why does the shadow of an eclipse travel west to east?
The sun appears to rise in the east and set in the west. This happens because of how the Earth spins as it orbits the sun. If you are in space and look down on the North Pole, the Earth … Continue reading
What causes a double rainbow?
The classic rainbow is a single, bright, colored arc. Red is the outermost color of this arc, and violet is always the innermost color.
On occasion, you may have seen two rainbows at once. The lower rainbow is the primary rainbow and the higher, fainter, colored arc is the secondary rainbow. The color sequence of the secondary rainbow is opposite to the primary; red is on the inside of the arc and violet on the outside. Continue reading
What is a derecho?
A derecho (pronounced deh-RAY-cho, a Spanish word meaning “straight ahead”) is an hours-long windstorm associated with a line of severe thunderstorms.
It is a result of straight-line winds, not the rotary winds of a tornado — hence its name. Derechos in the United States are most common in the late spring and summer (May through August). Continue reading
Why is the grass wet in the morning, when it didn’t rain?
Recent spring mornings have produced wet lawns. To explain this, we start with the fact that air contains water in the gas phase, called water vapor. Dew is made of liquid water that has condensed from some of the water vapor in the air.
Dew occurs when objects cool. A common example of dew formation is when drops of liquid form on the glass of an ice-cold drink. Dew forms when the object, such as the glass, cools down to the dew point temperature. Continue reading
Category: Meteorology, Phenomena
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