Date: October 8, 2009
Title: Learning About Seasons in a Planetarium
Podcaster: Chuck Dibbs and Virginia Beach City Public Schools
Organization: Virginia Beach City Public Schools
www.planetarium.vbschools.com
Description: Having taught Astronomy in the planetarium for a decade now, I’ve discovered that one topic continues to give students and adults of all ages trouble. That is, what is the cause of Earth’s seasonal changes? A lesson that I teach to elementary school children inside the planetarium seems to be effective in dispelling any myths and misconceptions about why the Earth has seasons. This show is a portion of that lesson.
Bio: For the last decade I have taught Astronomy inside the Virginia Beach City Public Schools planetarium in Virginia Beach, Virginia. I teach preschoolers through college students and the planetarium delivers a weekly presentation free of charge every Tuesday night for the public. Before coming to this job I taught mathematics at the middle school level also here in Virginia Beach. I’ve been actively involved and deeply interested in astronomy and all things space-related since being exposed to the Apollo Moon landings as a small child, and am also a NASA/JPL Solar System Ambassador. I’m happily married to my wife of 6 years, Cara, and we have two small children: Nolan who is 4, and his sister Finley who is 2. They have already learned to identify the moon, some stars, and even some constellations in the sky. Hard to imagine a life much better than this one.
Today’s sponsor: This episode of “365 Days of Astronomy” is sponsored by Science Fiction Fandom, a web based TV show featuring activities at various science fictions conventions in the Boston,Massachusetts, USA area. Science, Science Fiction and Fantasy topics are covered. Visit www.bostonfandom.org.
Transcript:
Hi out there. My name is Chuck Dibbs and I’m the planetarium coordinator for Virginia Beach City Public Schools in Virginia Beach, Virginia. Our planetarium is a small, educational planetarium that serves our almost 90 public schools in our division as well as local school communities, colleges, private schools, organizations, and the general public at large. Admission is always free and we welcome all smiling faces and anyone eager for astronomical enrichment.
You know, we all know for most of us it is generally hot in the summer and cold in the winter with spring and fall falling somewhere in the middle. However, when asked, most people might not know why. Does the Sun heat up a little in the summer warming us up, or perhaps the Earth moves away from the Sun in the winter cooling us down. Not really sure.
Fortunately a planetarium is especially well equipped to deliver a lesson on why the Earth has seasons. For example, with a planetarium one can clearly see the altitude changes the Sun appears to have throughout the course of a year. And, you can see these changes against a backdrop of stars. That’s something you cannot see outside on a bright, sunny day. The Sun is simply too bright and obscures the other stars.
Personally, I believe that comparing the Sun to the other stars in the sky helps one understand the proximity that our own Sun is as well as the more extreme distances other stars are. And by the way, I’m sure if you’re listening you are well aware of the dangers of looking at the Sun directly. It can permanently damage your eyes.
Since we are an educationally driven planetarium, I thought for this show I’d contribute portions of a lesson I taught to fifth graders this past spring. Our third graders learn about the seasons and the fifth graders come back to the planetarium, some of them do, for a comprehensive review of some of their science standards. It works out pretty well.
So sit back and relax and let’s go back to the planetarium chamber. Maybe you remember visiting a planetarium as a child… maybe you’ve been to one recently. Hopefully, however, we’ll all go back again someday.
Now take a look at these two pictures of the Sun. Look carefully at those two pictures. Are they the same size?
No.
No, they’re not. Which one is bigger?
The one on the right is bigger, absolutely. It’s just a little bit bigger, right. Just a little bit, fractionally.
Now the Sun does not shrink and grow, it doesn’t do that. Not enough that we’re going to notice it to this extent. But what does happen is that at certain points of the year the Earth gets closer to the Sun, and it looks a little bigger to us.
That’s called perihelion… close to the Sun. When we’re closer to something it looks bigger. Same thing out in space, when we’re closer to the Sun it looks a little bigger. You won’t notice it with your eyes, so please don’t go outside and stare at the Sun, that’s terrible for your eyes.
Aphelion means away from the Sun and when we’re away from the Sun it looks just a little bit smaller in our sky, just a little bit.
Close to the Sun it looks larger, farther from the Sun it looks smaller.
Who, which one of those astronomers we talked about figured out that the Earth gets closer to the Sun and then farther away? Do you remember his name?
Started with a “K”… Kepler, yeah, he figured out that the planets orbit in elliptical shapes, not perfect circles.
Now I’ve got a question for you. Should be an easy question, right, which season – there’s winter, fall, spring, summer – which season is the Earth closer to the Sun?
Summer
Summertime, doesn’t that make sense? We already talked about how hot that star is, 11,000 degrees roughly on the surface. Naturally when we’re closer to it the temperature is going to go up on the Earth and we’re going to experience the season we call summer.
Except, there’s a problem. Take a look at this date right here. This date says January 2, 2005. January, January, what season is January in?
Winter.
January is smack dab in the middle of wintertime. And that’s when the Earth was closer to the sun, in the wintertime.
You’ll notice it says we’re about 147 million kilometers from the Sun at perihelion back in 2005. And then, if you look at the Aphelion picture, the one when we were farthest from the Sun, you’ll notice the dates says July 5, 2005 – what season is July?
Summer.
Summertime right. We are farthest from the Sun in the summertime.
So if I’m getting this right and I’m scratching my head, as we get farther from the Sun the temperature for us goes up. And as we get closer to the Sun the temperature goes down in the wintertime. Does that make sense?
No.
No it doesn’t make sense. Something is odd here. But, let’s not argue with what we see. This picture was taken January 2, 2005, in the middle of wintertime.
There must be something else causing the different seasons that we experience here on Earth.
If you remember nothing else today, I want you to rid yourself of the fact that you believe the Earth is closer to the sun in the summertime and that’s what causes the temperature to go up.
That’s not the case.
Here’s the visual evidence again. In the elliptical orbit that Kepler showed us, you can see that the Earth is approaching the sun in January. A lot closer, 147 million kilometers, six months later in July, in summer, 152 million kilometers.
That’s five million kilometers farther away. Wow, that’s a lot farther away.
And yet, the temperature increases.
So, let’s figure out right now why we have seasons… it’s not this. It’s not the proximity or closeness of the Earth-Sun system. Here is the reason, and we talked about it briefly earlier.
What’s going on with the Earth here? It’s tilted. Just like you see all the globes in your classroom or library, the Earth is tilted.
That’s significant. It has profound effects on our temperature and climate here on Earth. Even more so than this distance does. The Earth is tipped over about 23.5 degrees or so, and you can see in this diagram here, what’s that middle line called?
Equator.
The equator, that’s right. The equator divides the Earth into two halves. The bottom half we call the southern hemisphere. The northern half the northern hemisphere, thank you.
In this graphic you can plainly see the northern hemisphere is leaning towards the Sun.
Here’s now when you can believe what you see. If the northern hemisphere is leaning towards the Sun, the Sun’s rays and the Sun’s energy can impact the northern hemisphere more directly. It heats up the ground because it’s concentrating the energy at a much more direct angle.
What season do you think the northern hemisphere is experiencing here?
Summer.
Summertime, very good. That is correct. We lean into the Sun like that when we’re over here. It doesn’t matter that we’re 5 million kilometers farther from the Sun – that doesn’t matter. What matters is we’re now tipped towards the Sun. We being the northern hemisphere, which is where the United States is. And this is when we experience our summer.
Notice also, the southern hemisphere is opposite the northern hemisphere. You see how they’re tipped away? What season do you think they’re having down under?
Winter.
Winter, that’s correct. If we’re having summer, they’re having winter.
Well, as you can imagine, there’s much more to this lesson than we have time for here. Later in this lesson students are able to visualize how the Sun appears in front of different stars at different times of the year. All along while apparently changing its altitude while it moves amongst the constellations. And, the students are often surprised to learn the Sun isn’t the object moving in this demonstration.
There is much you can learn inside of a planetarium chamber. I hope you’ll join me here the next time you are in our part of the world.
Until next time this is Chuck wishing you many star filled nights.
End of podcast:
365 Days of Astronomy
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