This week’s question was asked by friends.
QUESTION: What are the most common questions that kids ask?
ANSWER: A recent survey in both the United States and England found that the five most often asked science questions from kids were: Why is the moon out during the daytime? Why is the sky blue? Will we discover aliens? How much does the Earth weigh? How do airplanes stay up?
It was found that about two-thirds of the parents said they struggled with the answers. Twenty percent admitted that if they didn’t know the answer, they made up an explanation or said that no one knows. I will own up to using both techniques when our kids were growing up.
Let’s tackle several of these questions.
Why is the moon out during the daytime? The moon is visible as many hours during the day as it is visible at night. In order to be visible, the moon must be above the horizon. On average, the moon is above the horizon for 12 hours a day. The moon can be seen during the day nearly every day, except for when it’s close to a New Moon or a Full Moon.
The best times of the month to see the moon during daytime hours are at first and third quarter. That’s when the moon is 90 degrees away from the sun in the sky. Most any calendar will show the phases of the moon.
Why is the sky blue? Light, traveling as a wave, comes from the sun and is made of many colors. Each wavelength is associated with a different color.
The colors can be remembered as ROYGBIV (red, orange, yellow, green, blue, indigo and violet). Red, orange and yellow have long wavelengths and the blue, indigo and violets have a shorter wavelength. Green is in the middle.
When light from the sun passes through our atmosphere, it runs into molecules of moisture, water droplets, dust, smoke, and other particulate matter. The size of these particles is closest to the size of the shorter wavelengths, which are the BIV, or blue, indigo, and violet colors. So those waves are scattered the most.
That means the blue is reflecting and ricocheting all over the place, including the ground and our eyes. A logical question: Indigo and violet are shorter than blue, so why don’t we see indigo and violet? Answer: Our eyes are more sensitive to blue, and not very sensitive to indigo and violet.
Will we find aliens? There’s no telling if Earth people will ever discover any alien life in the universe. SETI (Institute for Extra Terrestrial Intelligence) scientists are fairly confident that we will find something in the next 20 years. They base their guestimate on improved technology in radio telescopes that scan the heavens, plus the rapid pace in discovering planets suitable for life. I do believe the 20-year figure is way too optimistic.
How much does the Earth weigh? Kind of a tricky question, and it can be answered in two different ways.
First, the Earth doesn’t weigh anything because it is in free-fall around the sun.
It’s the same reason the astronauts are “floating around up there.” They are technically in free fall all the way around the Earth. If they step on a scale in space, the scale would read zero because the scale is also in free fall. If you or I jumped from a building while standing on a scale on the way down, the scale would read zero.
The only difference between jumping from a building and the astronauts in space, is that the astronauts are moving forward at a speed of five miles per second at the same time they are in free fall.
Secondly, if we look at the mass of the Earth, that is a different story. Mass is not dependent of its position in space. It is basically “how much stuff there is.”
The mass of the Earth is about 1.3 times 10 to the 25th power, pounds. Make that 1.3 and add 25 zeros on the end. Or one hundred million billion Titanics.
I believe the second answer is what most people want to know. If you could pick up the Earth and put it on a scale, what would the scale read?
Send questions and comments to: firstname.lastname@example.org.
Larry Scheckel is a retired Tomah High School physics teacher.