Date: December 12, 2009

Title: Heat!

Podcaster: Slacker Astronomy

Description: It’s cold outside! So Michael, Doug and Mike from Slacker Astronomy discuss heat (or lack of heat) and how it relates to astronomy.

Bio: Slacker Astronomy is a light-hearted podcast that wanders the astronomical road-less-traveled. Visit us at http://www.slackerastronomy.org/.

Today’s sponsor: This episode of “365 Days of Astronomy” is sponsored by Claire Weston, and is dedicated to Angus Weston, my father, who took his sleepy daughters outside to view the night sky majestical meteor shower, and to Rosemary Dixon, my mother, for making me attend Jodrell Bank and the Natural Science Museum EVERY school holiday. These are magical memories. I love and thank-you both.

Transcript:

Michael Koppelman: Hello again and welcome to 365 Days of Astronomy hosted by Slacker Astronomy, the podcast about astronomy done by Slackers. It’s December 12th. I don’t know where you are but where I am it is cold and it’s snowy and it’s winter.

I’m in the north, it is winter, it’s cold, etc. That brings our minds to heat, right? Heat – we want heat, we long for heat.

Doug Welch: Basically we want to be in Australia or New Zealand. [Laughter]

Michael: But we’re not.

Mike Simonson: I would just like for the sun to shine for a couple of hours [Laughter]

Doug: It’s out there. The sun is out there.

Michael: So anyway, what is heat? I’m going to ask and not answer that question for a second but I want you to think about it. What is heat?

Here’s a little sort of anecdote or story to get you thinking about heat. You have a can of pop sitting outside.

Doug: Or soda or tonic, depending on where you are.

Michael: Thank you. I reveal my Midwestern roots with that pop word. So you have a can of soda sitting outside. It is 80 degrees outside. The word thermal equilibrium literally means that everything is the same temperature.

If your can of soda is sitting outside and it has been for a long time it will be at thermal equilibrium with the outside and will thus be 80 degrees say if the air is 80 degrees.

Doug: That’s 80 degrees Fahrenheit which is a system used [laughter] by the U.S. and the Malagasy Republic.

Michael: It’s 28 degrees C. [Laughter] No, I’m sticking with Fahrenheit, and I apologize. So anyway you take this can of soda, bring it in and you put it inside your house and inside your refrigerator because you want it cold.

What that can of soda is going to do inside the refrigerator is come to thermal equilibrium with the inside of the refrigerator. Let’s just say for round numbers that it’s 40 degrees F. This heat stuff, whatever it is.

Doug: Or 4 degrees Celsius for those of you living in the real world.

Michael: Thank you Doug.

Doug: No problem.

Mike: Captain Conversion. [Laughter]

Michael: So now this heat stuff that was in that can of pop, gets pulled out of the can of pop somehow. We’ll talk more about this but it does that by warming up the air inside the refrigerator.

The heat in the can of pop sort of gets dissipated into the air inside the refrigerator. The refrigerator goes “Uh-oh, I’m getting too warm”; the compressor kicks in and it sort of pumps that heat out the back of the refrigerator. Now it’s in your house.

If you live in a warm climate, perhaps you air condition your house. You now have this little extra bundle of heat from that can of pop floating around your house. At some point your air conditioner goes “Uh-oh it’s getting too hot in this house” and it turns on and it pumps that heat back outside.

Doug: And that’s why we have global warming. [Laughter]

Michael: The End – thank you for listening to the 365 [laughter]

Mike: I was thinking of the same exact thing. Boy, all that just to cool my six-pack of beer. I feel so guilty.

Michael: Well, anyway that was all just to get the wheels turning. So now, Doug, please PhD, rocket science astronomer, what is heat?

Doug: We have this thing called temperature which we all relate to. We hear it on the weather. We see it out our window. Then there is this thing which is heat or lack of heat which we experience. That is an amount of energy.

There is a very, very fundamental difference between temperature and heat. Temperature just says “if I go in there and take a census of how fast these molecules are moving, on average they’re moving this fast.” We say this gas has that temperature.

What that doesn’t take into account is how much gas is there. Heat is a total amount of the energy. You’ve probably experienced this if you’ve been outside in reasonable temperatures wearing regular clothes and then you go into a swimming pool which has the same temperature.

But the swimming pool has a far better ability to conduct the heat out of you to bring you to equilibrium. Your body being 38 degrees Celsius and the swimming pool being 20 Celsius your body doesn’t like that. Your body gets cold.

Mike: So heat is actually the process of transferring energy.

Doug: No heat is the total amount of energy. You know there can be a heat transfer that’s greater in the swimming pool than it is in the air because the water can conduct the heat away from your body far more rapidly than the air can.

But both can have exactly the same temperatures. If you looked at how rapidly the average energy of the water molecules in the swimming pool it’s such and such and that’s the average energy in the air as well.

Michael: It sounds like we really brought up three concepts there. One concept is that temperature is how fast things are going. To me that’s hugely important. The temperature is a measure of the jitter sort of, of molecules in one sense.

Doug: That’s right.

Michael: Then heat is how many molecules you have at that temperature. If I have one molecule at 20 C or 2 molecules at 20 C I’ve got twice as much heat if I have two molecules.

Doug: That’s right you often hear about the outer parts of the Earth’s atmosphere. If you look in these science books that show how the temperature of the atmosphere changes as you go higher and higher, you get to something called the exosphere.

This is where there is very little in the way of actually atmosphere anymore. You have a few atoms kicking around; way more than out in space but on average those things are moving around pretty quickly. They’ve actually been energized by things like cosmic rays or the solar wind.

They’re kicking around at high speed but there just aren’t many of them there. If you went out there and ripped off your clothes [laughter] you’d freeze to death even though the temperature might be over a thousand degrees according to the temperature of the gas.

Michael: Thank you because that explains something I’ve wondered about since taking astronomy. Galaxies I’m told tend to have this very high temperature sort of cloud around them like billions of degrees. Yet if you drove the starship Enterprise through it you wouldn’t get scorched at all because there’s not much heat there.

Doug: That’s right.

Michael: Now the third concept – we have temperature, we have heat- then the third thing you sort of mentioned is heat transfer.

That is, if everything is at thermal equilibrium, some things might feel colder than others. That’s because of how they transfer heat, not what temperature they are.

Doug: Right so on the surface of the Earth with humans, a lot of what we do is we’re interacting with the air or with actually touching things.

Heat gets transferred by what is called conductivity or convection. In most of the universe, the way this happens is with radiation.

Michael: This is an astronomy podcast so maybe before we go we could just sort of tie this in to some more how astronomers end up looking at heat in terms of stars, galaxies and planets.

Doug: You know the surface or the apparent surface of a star will be thousands of degrees. But once you’re out of there, it’s no longer the case that just because you see something at a thousand degrees that your temperature because you’ve received that energy is that high.

The fact is you’re both receiving energy and losing it. It’s that balance of losing it and receiving it that determines how hot you actually are.

Michael: What you see on the stove when you boil a pot of water, you’re putting the heat in faster than it can get out and eventually the temperature gets so high it boils. You sort of see all of these things every day in terms of how heat is moving around.

I remember Doug too about stellar astronomy that for awhile we couldn’t get stars hot enough in the middle to do nuclear reactions. We really didn’t know what powered stars so we were very interested in what was going on with the heat and temperatures inside stars.

Doug: That’s right that was awhile ago when we didn’t know about nuclear reactions which is oh like over sixty years ago now. One of the thoughts was, oh the star could be gradually collapsing on itself and giving up that energy.

Or it could be that things were falling down on the surface of the star like meteors and that can also provide energy.

When you went through the math, it just didn’t work out. Those time scales were too short to be useful.

It was only when it was appreciated that we had these nuclear processes going on at the centers of stars – extremely inefficient [laughter] I might add, which is why we have stars that last a long time. [Laughter]

That trade of having nuclear reactions going gradually losing that energy at the surface is what causes stars to shine.

Michael: Yeah when I was talking about a can of soda, the exact same processes are at work in a star as we were talking about with a can of soda going in your fridge. It is really cool.

Doug: And hot. [Laughter]

Michael: And what a great way to end this episode of Slacker Astronomy and thank you for a great 365 Days of Astronomy. It sounds like there is going to be a 365 Days of Astronomy in 2010 too.

I’m sure you’ll be hearing some Slacker Astronomy on that as well. This episode continues over at Slacker Astronomy. Visit us at www.slackerastronomy.org e-mail us at info@slackerastronomy.org – this is Michael saying so long.

This transcript is not an exact match to the audio file. It has been edited for clarity. Transcription and editing by Cindy Leonard.

End of podcast:

365 Days of Astronomy
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