Date:  January 5, 2009

Title:  The Seasons and Solar System Geometry

Podcasters:  Doug Welch and Michael Koppleman from Slacker Astronomy

Description:  Doug and Michael from Slacker Astronomy discuss the cause of the seasons here on earth and other aspects of the night sky as explained by simple geometry.

Organization:  Slacker Astronomy    

Bio:   Slacker Astronomy is a light-hearted podcast about the astronomical road-less-traveled hosted by Michael Koppelman and Doug Welch, with frequent contributions by Aaron Price and Travis Searle.

Today’s Sponsor:  This episode of 365 Days of Astronomy is sponsored by Shoe String Astronomy.

Transcript:

Michael:  Hey everybody, this is Michael.

Doug Welch:  And this is Doug Welch.

Michael: We’re from Slacker Astronomy.  We’re sort of a light-hearted podcast about Astronomy.  I think it’s about monthly Doug, bi-weekly, what do you say Doug?

Doug:    Easily.

Michael: But stop on by www.slackerastronomy.org we are really psyched to be doing a 365 Days of Astronomy Podcast – Podcast.  Our topic today is based on the fact that it’s January 5, 2009.

Christmas is over and Hanukah and the New Year and all that stuff is sort of behind us and it’s back to work.  Here in the Northern Hemisphere it is also like the beginning of the worst part of winter.

Doug:    And yet, strangely it is just about now that we are closest to the Sun.

Michael: That is strange.  That extra Photon density doesn’t help us huh? [Laughter]

Doug:   Well it doesn’t help us here in the Northern Hemisphere, but in the Southern Hemisphere it’s a different story.

Michael: Yeah in the Southern Hemisphere it’s like high, high summer right now so they basically have nothing to bitch about.

Doug: That’s right.

Michael: But I always take heart at this time of year because we’re past the Solstice so the days are actually getting longer again and the Earth is creeping back in its orbit for us Northerners back to the more favorable climates.  This is because of why Doug?

Doug:    Well the whole business of the seasons is something that seems to astound and alarm many people. [Laughter] It’s one of these things where if you’re ever doing a comedy show and you want to show up intellectuals you’ll ask them to explain the seasons.  It’s always a disaster.

The whole business of the seasons is really the result of the fact that the Earth is orbiting the Sun but it’s tilted and while it is spinning around once a day it is tilted in a way that means that at certain times of the year parts of the globe receive light more directly on their soil than at other times of the year.

Michael: Sometimes my kid will ask me about the seasons or other people will ask.  I just sort of go “Geometry”.  Why is there seasons, Geometry – that’s why.

Doug:    It is kind of nasty because not only do you have to explain this in two or three dimensions but there is also the time aspect and there are a lot of people that have a tough time visualizing this.

So it is the case that you have to think of yourself as a ping pong ball.  Not only the regular kind of ping pong ball but an inclined one – one that’s tilted a little bit say 23.5 degrees.  [Laughter]

If you do that and if you keep your tilt the same direction all the time and orbit your Sun, then you get an idea of why we have seasons.

Michael: Yeah, so the Earth is tilted with respect to its orbit around the Sun – it’s Orbital Plane and thus different parts of the Planet are sort of facing more directly to the Sun at any given time.

Doug:    That’s right so if you happen to be tilted in the hemisphere which is tilted toward the Sun so the Sun is falling more directly, more perpendicularly on your surface, then you’re having summertime.

And of course if you’re in the Northern Hemisphere at this time of year it is bad news because the Sun is very low in the Sky.  The sunlight is coming in a very grazing angle and so your average U.S. standard square area on the surface is not receiving much energy.

Michael: And it’s easy to visualize this if you have something nearby like a business card or a piece of paper or anything small and you look at it as you tilt it you can see less of it.

There’s less surface area visible to your eyes as you tilt it toward or away from you.  That is sort of the whole sum total of why there are seasons because the Sun is essentially delivering that much less energy to you.

Doug:    It’s a double whammy, not only is the Sun lower in the Sky but it stays up less time during the day.  You just lose all around.  This time of year, it’s the Northern Hemisphere, we’re the losers and the Southern Hemisphere – they’re the winners. [Laughter]

Michael: I don’t know that I know the answer to this. The Earth is tilted in respect of its Orbital Plane and how is the Orbital Plane of the Earth in respect to the Ecliptic Plane i.e. of all the Planets?  Is that all the same?

Doug:    Well the Ecliptic is basically the projection of the Earth’s Orbital Plane.  Since we’re on the Earth and we think we’re the center of the Universe for this purpose the Sun will appear to follow the path in the Sky which is just basically the opposite of what the Earth is following as seen from the Sun.

Michael: Right, got it.

Doug:    We have the other Planets in the Solar System except for the former Planet known as Pluto [Laughter] they all are fairly close to the same plane as the Earth.

Michael: How is that Plane, (and I always have trouble with this word) Ecliptic is sort of the plane the Planetary Orbits around the Sun and how is that orientated…

Doug:    Well it’s really the path of the Sun in the Sky very directly it’s the path of the Sun in the Sky.  It turns out that it’s very close to being the path of the other Planets in the Sky.

Michael: But I just think it’s cool on a summer night or I guess a winter night too, you can see the Milky Way like on a dark night you’re seeing sort of the Plane of the Galaxy in a sense. I just thought what we could learn about the Galaxy in terms of just by looking at those arms…I was just thinking it is interesting with our angle into all these things what we could figure out.

Doug:    It is true that if you go out on one of these dark nights with no Moon in the Sky and the Milky Way up and you understand that we’re in the plane of the Galaxy, it’s almost like you can have a three-dimensional moment.

You realize that the Stars all over the Sky away from the Galaxy must be nearby. You’re sort of embedded in this layer and then if you’re looking out of the Plane, all of those things must be pretty close to you.  That’s pretty much true.

Then you can also grasp that these more distant things in the Plane where it goes into this unresolved set of Stars and you see the dust silhouetting the background of even more distant objects, you can grasp that you’re in this three-dimensional object that’s flattened.

Michael: That’s kind of what I was trying to get at is like especially in the summer up north here, you can sort of see the center of the Galaxy in Sagittarius. You can see these big arms coming out from either side sort of and it’s all rotating around.

You can actually visualize our place in the Galaxy and because of everything else that we have learned about the Galaxy we can sort of do that better than previous generations. We are sort of really understanding our geometric place in our Galaxy.

Doug:   That’s right but to be honest, if all this happened in the Southern Hemisphere, we would have figured this out far sooner.  [Laughter] The Southern Hemisphere rocks when it comes to the Sky.  The Southern Hemisphere is the bomb as they say.

If you’re out under the Sky in August in the Southern Hemisphere you have the center of the Milky Way almost overhead.  It’s much, much brighter than all the other areas of the Milky Way.  You can clearly see it is different.

Here in the Northern Hemisphere it just hugs the Horizon and that extra air, that extra absorption just really takes the spirit out of it. I think we probably would have had another 100 years on Astronomy if we’d all started in the Southern Hemisphere.

So, let’s just say that from Slacker Astronomy to folks in the Southern Hemisphere, we worship you and envy you.

Michael: And for you Northern Hemisphere people like us, we want you to steel your resolve in the coming months because Geometry is now on your side. [Laughter]

Doug:    That’s right, enough for now.  Enjoy your International Year of Astronomy because it’s coming at you thick and fast.

Michael: So I hope you enjoyed January 5, 2009.  I’m looking forward to January 6, 2009.  Good-bye.

Doug:  Good-bye for now.

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

365 Days of Astronomy
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The 365 Days of Astronomy Podcast is produced by the New Media Working Group of the International Year of Astronomy 2009. Audio post-production by Preston Gibson. Bandwidth donated by libsyn.com and wizzard media. Web design by Clockwork Active Media Systems. You may reproduce and distribute this audio for non-commercial purposes. Please consider supporting the podcast with a few dollars (or Euros!). Visit us on the web at 365DaysOfAstronomy.org or email us at info@365DaysOfAstronomy.org. Until tomorrow…goodbye.

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