February 28, 2013

Ancient astronomy

The above image is the first slide that I use to introduce the topic of ancient astronomy in my introductory astronomy course. It's something I put together a few years ago, and although I still sort of like it, I have a hard time remembering exactly what all the thumbnails are supposed to be representing.  As best as I can remember, the points I was trying to illustrate when I first put this slide together were:

1.) Many cultures around the world had at least rudimentary knowledge of the night sky, and in many cases had knowledge of astronomical alignments related to the calendar.

2.) We don't have time in class to talk about all of the interesting things that these cultures knew about. There is a LOT of interesting material that we could go into, but in the interest of getting to some modern astronomy topics, we have to pick and choose some ancient astronomy topics and leave the rest mostly untouched.  That's not to say that non-Western cultures did not know about or explore the cosmos.

From left to right in the above image, then:

The pyramid is El Castillo, also known as the Temple of Kukulkan located at Chichen Itza (not Chicken Pizza, as my tour guide told me when I went there a few years ago).  The temple is aligned such that on the equinoxes the sun casts a shadow over the steps of the pyramids which connects to the heads of serpents carved into the base of the steps. It's a pretty neat effect, and shows the Mesoamericans knew when the equinox would arrive and how to align the structure to accomplish the effect.  The Chichen Itza site also has what is thought to be an astronomical observatory on it. The tour I went on did not allow for a very close approach to the building, nor did the guide we have know much about that particular structure.

The middle image is (I THINK) a photo of the ruins of Babylon.  I do not believe that the particular image had any astronomical significance. Rather, I think I was trying to point out that many cultures in the middle east (Babylonians, Sumerians, Assyrians) at least attempted to understand the night sky. Clearly, I am not a historian, anthropologist, or archeology expert. I would like to know more about the ancient astronomical knowledge of the middle east.

On the right is a photo of a an armillary sphere at the Purple Mountain Observatory in China. This type of sphere was used by ancient astronomers to measure the position of stars in the night sky. What is not clear from the article that I linked to is whether or not the pictured instrument is an original or a replica.  I seem to recall that the armillary sphere at the Purple Mountain Observatory is actually a replica of the ancient instrument. I think that the replica is itself relatively old, but again, it's not clear from the page I linked to.

Maybe in the future I can dig up the original references I was using to piece together this slide.  For now, I'm happy with what I have.

February 27, 2013

Browser clutter - February 2013 edition

This is where I dump some links that I've had in my browser tabs for awhile.  I don't want to forget them, but I don't have a better place to put them.

Music inspired by astronomy - from the Astronomy Education Review.  I wish the pieces in the article had better links.

Inertia games - We have some REALLY OLD computers at school that we keep mostly to do this for algebra based physics courses.  If I could find a port of this to some new platform it might free up some space and time in the labs. (Alternative link)

Love2D - an open framework for making games.  Maybe could write an Inertia Games clone in this.

Over the winter break I was able to go to the national AAPT meeting and give a talk on the history of modal analysis.  I titled the talk something like "From Chladni to the present, a history of modal analysis".  In preparing for the talk, I was surprised to learn about a bunch of pseudoscience that has taken from the work done by legitimate scientists and applied to all sorts of nonsense.  At the risk of increasing traffic to their sites, I will point out some of the more laughable crap that I came across:

Harmonic Resonance Theory - weird.

Cymatics history - history of, uh, cymatics (whatever that is) "research".

"How the leopard gets its spots" - In 1988 Scientific American published this article, which may or may not be good science. All I know is that the inference that the modal analysis of a metal plate cut in the rough shape of a animal skin is related to how the patterns of spots appear in the animal's fur is just bizarre to me.  (Google search)


Making cloud chambers - I've tried this a number of times, and they never quite work for me.  :(

More links later!

February 26, 2013

What can you tell about this scene?

I'm going back into the archives for this comic strip. This is a "Rose is Rose" strip from January 22nd, 2007.  I like this strip not because there is anything wrong with the astronomy (as far as I can tell), but because I can use this comic strip to ask the following questions:

What time does the couple go out for a walk?

What direction are they walking?

More generally, depending on when I use this strip in class, I could ask: What can you tell about this scene?  Then, the class can discuss things like the time of day and/or the direction the characters are facing.

February 25, 2013

What, if anything, is wrong with this comic?

Image Credit: Creators Syndicate, originally published 5-30-2005
This is the first few panels from a Sunday "Wizard of Id" comic from several years ago.  I would like to use it as a "What, if anything, is wrong with this picture?" challenge for my astronomy students.

So: what, if anything, do you think is wrong with this comic?

February 23, 2013

A few blogs you're probably not reading, but should be

A few weeks ago, Brian Frank posted a link on twitter to a blog about PER that he thought many physics teachers might not know about. I wanted to point out some people that I really like reading that I suspect many people don't know about, either.

Patrick Len posts a lot of questions from his physics and astronomy classes and quizzes over on his blog. Some of the questions are peer-instruction style questions for use in class, but recently he's been posting questions related to current events in astronomy. He also posts a lot of useful materials for activities and demos that can be done in class.

Matthew Francis is a physicist now working as a science writer. I came across his blog, Galileo's Pendulum, when I was tracking down some information about a local science landmark. He writes about a wide swath of science topics, many of which aren't covered by other writers.

Dr. Drang is fairly well known in certain nerd circles. He remains anonymous online because his day job is engineering consulting for lawyers working on cases that may end up in court. He feels that keeping his online presence separate from his day job is the best choice for him. Nevertheless, he often posts really great stuff related to math, engineering and physics.

February 06, 2013

Python learning opportunity

I have an honors student this semester who is working on vpython simulations of general physics systems.  She knew no programming as of two weeks ago, but tonight was really close to having a projectile motion simulation done.

In trying to put velocity vector components on the projectile's position every 10 time steps, she was running into a problem: using the modulus operator only worked on the first two vectors, then did not.

Here was her code:

 while ball.y >= -2.75 and int_velo > 0:  
   t = t + dt   
   ball.pos= ball.pos + ball_velocity*dt  
   ball_velocity.y = ball_velocity.y - 9.81*dt  
   if (t*100)%10 == 0: #doesn't work!!!   
     vel_xvec = arrow(pos=(ball.pos.x,ball.pos.y,0), axis=(int_xvelo,0,0), shaftwidth=0.5)    
     vel_yvec = arrow(pos=(ball.pos.x,ball.pos.y,0), axis=(0,ball_velocity.y,0), shaftwidth=0.5)  

The comment tells the story. I guess I should know more about the modulus operator in python. It seems simple to use, but I couldn't really figure out what the problem was initially.

The short version of this story is that my student gets to learn about computer round-off errors and how to debug code by sticking a print command in the code so that she can figure out these problems without too much intervention on my part.

Here's my debug line I ended up using, followed by the fixed if statement:

   print t, t*100, (round(t*100)%10.0)  
   if (round(t*100)%10) == 0: #works now!!!   

I'm looking forward to a fun semester of python projects!