Ask Dr. Universe

Episode 5: Seasons, Black Holes, Ponds, Shadows

January 27, 2021 Washington State University
Ask Dr. Universe
Episode 5: Seasons, Black Holes, Ponds, Shadows
Show Notes Transcript

Welcome back, young scientists. On this episode, our questions take us to outer space the bottom of the pond and into the fascinating world of light and shadows.

A big thanks to our kid narrator from Regional Theatre of the Palouse. Thanks to our friends at Washington State University for helping with the science: Vivienne Baldassare, Sukanta Bose, Joan Wu and Anya Rasmussen.  And thanks to you for listening. If you enjoy the podcast, leave a review for Dr. Universe on your favorite podcast app.

As always, you can submit a question for a chance to be featured on a future podcast at

Dr. Universe  0:05 
Welcome back young scientists. I'm Dr. Universe and if you're anything like me, you've got lots of big questions about our world. On this episode, our questions take us to outer space, the bottom of the pond, and into the fascinating world of light and shadows. A big thanks to our kid narrator from Regional Theatre of the Palouse. RTOP is a proud sponsor of STEAM learning. Discover the art of science, technology, engineering and mathematics. STEM makes life possible and art makes it worth living.  Support your local arts and humanities programs. Together STEM is gaining steam. Let's get started.

Beatrice  0:41 
Hi, I'm Beatrice, an RTOP kid. Bella, age 9, in North Carolina asks, Dr. Universe, why do we have seasons?

Vivienne Baldassare  0:51 
So my name is Vivienne Baldassare. I am a professor of physics and astronomy at Washington State University.

Dr. Universe
Thank you for helping us investigate this question. What can you tell us about the earth seasons?

Vivienne Baldassare
The Earth goes around the sun, right, the Earth orbits around the sun and completes one orbit every roughly 365 days. So that's our year-- the time it takes us to go all the way around the Sun once. And the earth also spins. But the earth doesn't spin straight up and down. It's actually a little bit tilted.

Dr. Universe  1:28 
Okay, young scientists, remember that the Earth has an equator like an imaginary line around its middle. We call the part above the equator the Northern Hemisphere and the part below the equator the Southern Hemisphere.

Vivienne Baldassare
And what this means is that some times of the year, the Northern Hemisphere is pointed more at the sun and the Southern Hemisphere is pointed away. And other times of year at the Southern Hemisphere is pointed more towards the sun and the Northern Hemisphere is pointed away.

Dr. Universe
This also means that when it's winter in places like Washington state or North Carolina, people who live in places like Brazil or South Africa are having summer. Each season brings new changes for life on earth but do other planets have seasons?

Vivienne Baldassare  2:11 
Other planets definitely do have seasons, all you need in order to have the season is the tilted axis.

Dr. Universe 2:17 
Here is Beatrice with some cool facts about the seasons on other planets.

Beatrice  2:23 
 A year on Mars is about two Earth years. Mars also has four seasons nearly twice as long as those on Earth. Venus and Jupiter don't have much of a tilt compared to the earth. The seasons change slowly on these planets and each season is about three years.

Dr. Universe 2:41 
Thanks for those fun facts. One more thing listeners. It's not often I meet another cat while talking to scientists, but it just so happens that Vivienne's cat jumped up on her desk during our Zoom call.

Vivienne Baldassare  2:52 
She's named after Henrietta Leavitt, who is a prominent 20th century woman astronomer.

Beatrice  2:58 
While we're out in space. Here's our next question from Krishna at age nine in New Jersey, how many black holes are there in the galaxy, and universe?

Dr. Universe 3:10 
While we can't see black holes with our eyes, astronomers have figured out how to spot these objects in our universe. Our next guest is really curious about black holes. When we talked on zoom, he was in India working with Lego India and observatory that will help scientists learn more about the cosmos.

Sukanta Bose  3:27 
I'm Sukanta Bose. I'm a professor at Washington State University in Pullman, I work on understanding what black holes are and also what are some of the densest objects in the universe. It turns out that these objects are basically related to the fate of stars.

Dr. Universe  3:47 
One kind of black hole is a stellar mass black hole. These are the kinds of black holes that form when stars die. There are likely 10 million to a billion right here in the Milky Way galaxy. But there are other kinds of black holes called supermassive black holes. Scientists think these supermassive black holes may be found in the center of most large galaxies.

Sukanta Bose  4:09 
Because of the way galaxies are formed, we expect almost every galaxy to have a black hole at the center...

Dr. Universe  4:15 
A supermassive black hole, adds Dr. Bose.

Sukanta Bose  4:17 
Then one way to answer this question is to say okay, just count the number of galaxies simply because galaxies are easier to see, Black holes are not enough focus only on supermassive black holes, we can answer this question by saying that okay, just count the number of galaxies and then you will have roughly an equal number of supermassive black holes in the universe.

Dr. Universe 4:36 
Of course, counting objects in the universe isn't always so easy.

Sukanta Bose  4:40 
So then how many galaxies do we find? Of course, we cannot see every galaxy. We see many galaxies that are closer because they're easy to see that much brighter. The farther you go, you have to use telescopes, very powerful telescopes and surveying the sky with telescopes is not an easy job because the deeper you're seeing the more there is to see, and surveying skies is a big effort that astronomers undertake time to time.

Dr . Universe  5:07 
That also means we have to make an educated guess based on evidence and current knowledge about the way things work. We call this inference. Using telescopes, math and inference skills, astronomers estimate there are 100 billion galaxies, and a similar number of supermassive black holes. And that's just in the observable universe.

Beatrice  5:31 
We are bringing it back to Earth with our next question, Rocky age 11, in California asks, Dr. Universe, Why does water in ponds not get soaked up by the dirt at the bottom?

Dr. Universe  5:44 
That's a great question. If we investigated the bottom of a pond, we might find a few different things. Besides a few fishes and frogs swimming around, we might observe mud, algae, rocks and soil at the bottom. I took your question to one of our hydrologists at Washington State University.

Joan Wu  6:00 
It's a good question. My name is Joan Wu. I am a professor in biological systems engineering department. My specialty is hydrology. From the beginning, let's just think about the surface of a body like a pond. It's like a bowl, it's like a basin, you think 'if I have a glass of juice or a bowl of cereal, that liquid doesn't seep out', it's the material of the container that wouldn't allow that liquid to leak out.

Dr. Universe  6:34 
Let's imagine we fill the jar with one of these Earth materials: rocks. Inside the jar, we would see some gaps between the rocks. If we poured water into the jar, what will happen? The water will move into those empty spaces. But now let's say we pour it in sand instead of water. This time the grains of sand would fill in the spaces between the rocks. Next, we could add particles of Earth called silt so small they could fill in any spaces between the grains of sand. Finally, we add an even smaller particles of clay in the jar or the bottom of a pond. These materials are packed together, the material isn't very permeable, which means it can keep the liquid from passing through it.

Joan Wu  7:16 
So the little particles fill in the large cavities pause and eventually, you have a pond bottom that's less permeable.

Dr. Universe 7:27 
Sometimes a little water does escape from the bottom of the pond. And meanwhile, a little water also escapes into the air from the pond.

Joan Wu  7:35 
Eventually you lose water on top and from the bottom.

Dr. Universe  7:41 
We lose some water because of something called evaporation. You may know about evaporation if you've ever seen a puddle on the sidewalk that was there one day and gone the next. When the sun heats the surface of the water the water can turn from a liquid into teeny tiny drops called vapor. The vapor rises into the atmosphere where it can eventually become clouds. Then those clouds help produce rain and snow that fall back into the lakes, rivers and ponds. Water also flows into ponds and lakes and rivers from other sources. Can you think about where else the water might be coming from? When we keep our eyes out we can find a lot of connections between our atmosphere water and the earth.

Beatrice  8:19 
Here's our final question for this episode. Aven, age 7, in Palouse, Washington asks, Can a shadow make a shadow?

Dr. Universe  8:30 
One way to find the answer to this question is with a little experiment. My friend Professor Rasmussen told me all about it.

Anya Rasmussen  8:42 
I teach a number of physics classes for ourPhysics Department at WSU including teaching a bunch of students who want to become elementary and high school science teachers. So I teach future teachers about science.

Dr. Universe  8:54 
That sounds like a fun job to me. Now for our experiment. First, you'll want to cast your shadow on a wall. Do you know how a shadow forms? Think about it for a moment. A shadow forms when an object such as your body blocks light and keeps the rays from reaching a surface like a wall. To see how this works. Ask a grownup or friend to shine a flashlight or lamp behind you and onto the wall.

Anya Rasmussen 9:25 
If you want to see can your shadow cast a shadow, shine a light on your shadow to see if it blocks the light.

Dr. Universe  9:29 
Alright young scientists It's almost time to reveal the answer. So if you want to try this experiment, push pause and come back later. But if you want to know the answer, get ready for a spoiler alert.

Anya Rasmussen  9:40 
So a shadow can't create a shadow.

Dr. Universe  9:42 
Unlike you and me a shadow cannot reflect or absorb light, it can't block rays of light and keep that light from reaching the surface. Light and shadows are not only an important part of understanding physics, but they're also a big part of creating art. When we look at paintings from impressionist artists like Claude Monet and Edouard Manet, we can see how they paid a lot of attention to these two important elements.

Anya Rasmussen  10:06 
But that's kind of the general idea of impressionist art is paying attention to the light and dark, the shadows and the bright spots.

Dr. Universe 10:17 
When we get questions like this one from listeners, it's always a bright spot in our day. That's all for this episode. Thanks to all the kids who submitted a question to all our friends at Washington State University who helped with the answers and to Beatrice at Regional Theatre of the Palouse for helping read the question on this episode.

As always, you can submit a question of your own app asked Dr. That's Who knows where your questions will take us next.