Maybe I shouldn't have started this blog now, not with everything that's been going on.

David and I finished the last of the laboratory practical exams yesterday, with only two people who were absent last Wednesday making up for their exam then, and without any need for a formal excuse letter at that.

At the start there were only around 12 out of the expected 16 that signed up, and again most of them avoiding the earlier time slots. After the first examinees though, we skipped the blank times instead of waiting and called the next names on the list. The list filled up during the exams themselves.

We still finished after almost two hours though. And I couldn’t leave the lab after that. There were still three students who wanted to make up for their absences in two sessions: two in Experimental Errors, and one in Composition of Concurrent Forces.

Two of those three students had already been working on two other activities in the Robotics Lab next door during the practical exam: Graphs and Equations, and Significant Figures, since the first one did not use any equipment unless they wanted to use a computer, and the second one used calipers which are not needed in the practical. We’re still expecting around half a dozen make up sessions in the last two days of classes next week.

It’s also that time of the week again to talk about the astronomy program undergraduate thesis of the students from the College of Computer Science. Here’s what I think of the behavior of the graphs for the path of the Moon during one month as seen from one point of observation.

From what I saw, for March 2004, the path of the Moon during the first night started out in the northeast, curved towards the zenith, then tilted to the northwest again. The next night was similar, except that the curve is now a little to the south. This pattern continues and the curve becomes a little more linear until, in the middle of the month, it is a straight line found just south of the ecliptic. Then it makes its way north again, ending the month in more or less the same position as when the month started.

Of course this is from the perspective of a three-dimensional hemispherical surface as viewed in a flat two-dimensional circle-bordered standpoint. Drawn on a bowl, the curve will probably look more straight and the line more curved.

The cause that I think accounts for this behavior is the fact that our point of observation is north of the equator, although still near enough to the equator to see 85% of the celestial sphere in the course of one year.

After all, the North Celestial Pole is visible from the Philippines, and from it emanates concentric circles that describe the paths of the stars and other celestial bodies in the course of one night. This means that towards the north, smaller more curved circles are described, with the most linear being along the equator.

Since from the Philippines the pole of the southern celestial hemisphere is not visible, thus paths of the stars there appear as linear as the celestial equator, if not even more so.

Part of what affects this is also the tilt of the ecliptic to the celestial equator of 23.5 degrees, and the fact that from the Philippines, the celestial equator is actually 14.5 degrees to the South a line across the sky from East to West that passes through the zenith, and parallel to it.

Now I’m just waiting for the students’ plotting of the other months to verify that.