Specifically, I’m taking an existing code base (the AIAA SGP4 code which is written in C/C++), wrapping it with python, and then eventually putting a web front end on it. The end goal is that astronomers will be able to use this code/website to check their observations to see if there was a satellite in their field of view when they took their measurements.

Since I’m using a known library in to create something new, this seemed like a really great opportunity to use some Test Driven Development (TDD) to ensure that as I build up the parts of the system, the numbers stay true and that the code stays honest.

This is working out really well. Combining python’s unit test module with nosetests allows me to quickly bang out a test to make sure that the positional numbers that the SGP4 code generates is what the documentation says it should be. By using TDD I can map out where the code needs to go a little better: As I find something that is missing I can write out a quick test that will fail. When I run nosetests, I have that failure glaring at me telling me where more code is needed.

For example, I have one set of test data that gives the observer’s location in standard latitude and longitude coordinates. My code isn’t quite expecting this, the MPC format is a little bit different. This is a problem that is easy to fix, but I have a plethora of problems at the moment and I need to make sure this one gets taken care of properly. So I opened up the python file that tests the Observatory class and added in a failing test that called testLatLongToXYZ(). When I run the tests I now see that this is a failing method which gives me the mental kick in the pants to go and implement that method, even if it is just a stub.

Why do I say just a stub? Because putting in the stub lets  me do two things: 1) I’ve now got something there, and 2) I can now update the test to call that stub. The secret is that the test should now call the stub and expect it to pass, but the stub should always return something (None, False, -1, etc.) to indicate that it failed.

This acts as a pointer to an area that needs improvement in the code. This is what TDD is all about. You keep repeating this process until you converge on a “correct” answer which is a method that does just what it needs to do. In theory, and so far my practice confirms this, the resulting code should be smaller and more accurate.

For me this is a great thing because it encourages code that is more honest. What is honest code? To me, it is code that does what it says and nothing else. The shorter the code is, the more focused it is. The python language is very expressive and allows you to do a lot without saying a lot. This power can lead you to try and do too much in one function. Once you have a function that not only converts Lat and Long, but also converts polar coordinates and writes satellite data to the database, can you really honestly call that function convertLatLongToXYZ()?

This is especially valuable in the scientific context of this astronomy related code. The code is open source, and in the event there is a problem with it, as people dig into the code they need to have confidence that the code is relatively well written. At a high level the tests give them the numerical sense of ease that it is working when the tests run and show the proper numbers being returned. At a low level, seeing that the code is broken up into small logical sections gives the confidence that once  problem is found it can be corrected, tested, and shown that there are minimal side effects in other parts of the program.

As the lone developer on this project, this type of check-and-balance gives me a lot of hope that I’ll be able to produce something that is accurate and useful to the community at large. Openness and honesty help build confidence and trust. If you are interested in the project, be sure to check it out:

ObsSatId: A python astronomy project to wrap the SGP4 code to check for satellites

To me this begs the question: Why risk humans (and the fragile shuttle) to repair the ailing satellite, when for probably the same amount ($900 million) they could just launch one or more new Hubble-class satellites? The big thing about Hubble is that it is serviceable, but what if it wasn’t? Wouldn’t that make it cheaper?

It just seems to me that it would be smarter, faster, and cheaper to take that money and launch a couple of new replacements.

But this is NASA we’re talking about. Logic doesn’t seem to have a place in their planning when it comes to topics like the shuttle, the ISS, or the Hubble. *sigh*

But after reading this article about the differences between planets and asteroids, I’ve changed my mind. I think Pluto should be demoted and the planet count set to 8.

In the article Alain Maury points out that if you graph the mass and orbital inclination of the planets and the asteroids (and KBO’s and TNO’s) that something really interesting happens: the two cluster seem to form, one for planets, and one for everything else. Pluto and 2003 UB313 (and several other new discoveries) don’t fall into the planet group, they land in the “asteroid” group.

After seeing these charts I’m inclined (har har) to say that unless an object can show by a combination of its mass and orbital inclination that it belongs in the “planet” group, that it is not a major planet.

Something tells me that once we are able to explore other solar systems we will probably use that type of a guideline when marking new planets. Of course at some point it won’t matter, the sheer number of objects found across the stars will make it impossible to name and keep track of everything.

This article talks about a telescope that has been setup to monitor the moon for the these types of collisions. On its first night in operation it captured the explosion of a 12cm meteor impacting the lunar surface at 27 km/s! The resulting explosion was equivalent to 70 kg of TNT and it is thought to have left a crater 3 meters in diameter!

An interesting tidbit from the article is that they are reviewing the data from the telescope by watching it, not by having a computer process it. That blew my mind, these explosions from impacts would probably be really short lived events. Plus imagine all of the cross checking the computer could do: As it finds a flash it could look to see if there were any satellites in the vicinity, then check the duration of the event to make sure it wasn’t a cosmic ray, it could cross check with another telescope to make sure it wasn’t a fluke camera malfunction… The possibilities are endless. I really need to get more involved in virtual astronomy, there is just so much coolness happening there.

Once they are able to get some telescope time they are going to try and determine the orbital period which will give a pretty good mass estimate for the planet. Yes, I said planet, it sure seems like it is one crazy orbit or not.

I found out that there was a Yahoo! group called the Minor Planet Mailing List which has a mailing list where a lot of astronomers talk about what they are finding, how they observe, etc. I joined this list and was expecting to read some really interesting (if not over my head) tidbits about the heavens.

Was I in for a surprise.

It turns out that the announcement of the new objects was stirring up quite a controversy. Allegations of hacking, blackmail, theft, and all kinds infractions were flying back and forth on the list. A good little explanation of what was (and still is) going on was put out in Scientific American today: Breaking News – Astronomer denies improper use of web data.

This incident has really riled up this community of star gazers. They are all really passionate about their craft (which is a great thing) and the controversy has made some really big waves. It still strikes me as funny that I joined the list to read some scholarly discussions about what lies out beyond the orbit of Neptune, and instead I walked into a flame war like you would see on Slashdot.

Despite the action on the list, I have learned a lot just by reading it. In fact, reading the list has inspired me to learn more about astronomy so that if nothing else I can understand more of what they are talking about.