The Sound of Science - "New Moons"

Apr 5, 2019

J: This is Jeremy Benson.

K: And Kate Powers from NIU STEM Outreach.

J: And this is the Sound of Science on WNIJ.

K: Today’s question comes from my friend Danielle, who asks, “Why can we sometimes see the full moon during the day?”

J: Great question, Danielle!  We’ve had good moon questions lately - I guess you could say we’re going through a phase!

NIU STEM Outreach

K: Oh brother…  I think what Jeremy means is that to answer Danielle’s question, we’re going to have to look at the different phases of the moon.

J: That's right! The moon’s phases are caused by its position relative to the earth and sun.  When the Earth is between the sun and moon, we can see all of the moon’s surface that is being lit by sunlight, so we see a full moon.

K: And when the moon is between the earth and sun the lit side faces away from us, and so we have a new moon.   

J: Which brings us back to Danielle’s question. During a new moon, the moon is out during the day because it’s in the middle.  That means we have to be on the daylight side of the earth to see it.  

K: But that would mean all the sunlight is hitting the back side of the moon, so how can we still see it?

J: Well Kate, some of the sunlight that hits the earth gets reflected, and some of that reflected light hits the side of the moon that faces us. That reflected “earthglow” is what allows us to see the new moon during the day.

K: Wait... if the Moon is between the earth and sun, doesn’t that cause an eclipse?

J: It can, but not always. If things line up just perfectly then the moon’s shadow will pass over the surface of the earth causing a solar eclipse. But usually the shadow ends up going above or below the earth.  

K: So it would be the same with a full moon. If things line up exactly with the moon on the other side, the Earth blocks light from reaching the moon and we get a lunar eclipse.  But usually the Earth’s shadow misses the moon so we don’t see eclipses every month. For an eclipse to happen, everything has to line up just right.

J: Exactly! Thanks for that illuminating question, Danielle. Be sure to send your questions to us at stemoutreach@niu.edu.

K: This has been the Sound of Science on WNIJ, where you learn something new every day.