Curiosity Corner: Moon "phased" by changing positions

Moon “phased” by changing positions


by Dr. Jerry D. Wilson,
Emeritus Professor of Physics, Lander University
A couple of questions, one technical and the other better-rounded.
Question: The moon goes through phases – new, first-quarter, full and third- (or last) quarter. Yet, when we see a first- or third-quarter moon, the face of the moon we see is one-half illuminated. Is there something wrong? Shouldn’t we have half moons? (Submitted by a lunar-observant column reader.)

Reply: Well, the thing to keep in mind is that about half of the moon’s surface is always illuminated – the half of the spherical surface that is toward the sun. On Earth, we see phases, or different portions, of the moon illuminated because of the relative positions of the sun, Earth and moon.
 For example, we see first and third quarters when the sun is 90° east and 90° west of the moon, respectively. On Earth then, we see half of the moon’s face illuminated. (Think of someone shining a flashlight on a basketball and you are 90° from the person. Depending on whether they are shining the light from left or right, you’ll see only half of the ball [left or right] illuminated.)
 Got it? OK, the phase count starts with the new moon, when the sun and the moon are overhead at 12 noon. Astronomers refer to phase in reference to how far around the moon is in its orbit. One-quarter around, the moon is in first-quarter phase (6 pm), but we see it half illuminated as described above. Halfway around it is full moon (12 midnight – moon and sun on opposite sides of the Earth). Third-quarter moon (6 am), the moon is three-quarters around in its orbit, but again, only half of the moon is illuminated for us poor Earthlings.
Question: I bought a hat the other day, and I wear a size 7-3/8. Does the hat size number mean anything?
Reply: Checked into it, and oddly enough the size seems to be based on the roundness of your head (or hat). Most American manufacturers take the length, or circumference, of the band inside the hat and divide by pi (p = 3.14). This gives the diameter of the hat if you were round-headed.
 For example, if the hatband had a length of 23 inches, then 23/p = 7-3/8 (to the nearest 1/8). Of course, most of our heads aren’t really round, but the hat size number gives us an indication of fit. If you have a fitting problem, you can always try a baseball cap with the adjustable plastic strap in the back.

C.P.S. (Curious Postscript):  When somebody tells you nothing is impossible, ask him to dribble a football. ~Anon

See HERE for last week’s Curiosity Corner.

Curious about something? Send your questions to Dr. Jerry D. Wilson, Science Division, Lander University, Greenwood, SC, 29649, or for e-mail, Selected questions will appear in the Curiosity Corner. © JDW

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About robertstevenson

Dr. Robert Stevenson is an Associate Professor of Journalism and Director of Student Publications for the Department of Mass Communications and Theater at Lander University in Greenwood, SC. He received the Distinguished Faculty of the Year award for 2007-'08, and the Lander University Young Faculty Scholar Award in 2005-06. Stevenson also serves as chair of the Lander University American Democracy Project. First and Formost I am a dad of two wonderful boys.
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