Sunday, June 15, 2008

Excel almanac

As I was building the visual almanac patterned off the graph in the RASC Observer's Handbook, I couldn't help but think that there must be a faster, mathematical way of doing this...

So, I did some surfing to try to track down the R.A. and Declination of the Sun and the planets for the year. I was hoping to find this all in one spot, in one table. In the end, I settled on the U.S. Naval Observatory web site and the Astronomical Applications Department's Data Services. I found that I could calculate (or have generated) the "Geocentric Positions of Major Solar System Objects and Bright Stars." Perfect.

I copied, for each planet (yes, including little Pluto) and Sol, 24 periods of data for 2008 into Microsoft Excel. Parsed the text into separate columns. Converted the h-m-s R.A. data into decimal from. Then assembled all this data into a table. Then, I let Excel build a line graph based on this data. Finally, I spent some time "tuning" the graph to look similar to the one in the handbook (but in colour).

What do you think?

I also like how now this is ready to be reused in the future...

The last thing that I added, in a flash of inspiration, was a vertical line which corresponded to the current date. In my Excel spreadsheet, every time I open it, the green date line, tied to the TODAY function, will shuffle along.


I've got some bad news, I think... I believe in the course of assembling this data, I found an error in the 2008 RASC handbook, on page 95. Pluto is way off. The RASC reference shows Pluto between R.A. 19 and 21 through the year. The USNO says that it is very steady at 17.9 and 18.1. Who's right? I quickly checked in some astronomy software to confirm all the R.A. values for the Sun and planets. It showed Pluto in the location USNO states.

I just clued in! The labels in the handbook are inverted! The Jupiter and Pluto labels need to be flipped.

No comments: