Herald-Bobroff chart references for the SAC database of deep-sky objects
The Saguaro Astronomy Club (SAC) Database is the result of more than 20 years of devotion to create and maintain a list of more than 10,000 worthwile deep-sky objects within reach of many amateur astronomers. The database is managed by Steve Coe and has a historic data format. It contains lots of information about these objects, such as the object type, celestial coordinates (RA and Dec), brightness, position angle etc. but also links to charts in the first release of Uranometria 2000.0 and in the Tirion Sky Atlas 2000.0.
A number of new star atlases have been produced since, but so far the SAC database does not provide references to charts in those new atlases.
For this reason I started a small project while travelling in a TGV in the summer of 2008 to add references to Herald-Bobroff charts. The approach I took was:
- First, collect the chart boundaries (RA and Dec ranges)
- Then, for each object and each chart, compute whether the object can be on the chart:
- If the object is on the chart, compute its relative position with respect to the center of the chart; I defined this point as the midpoint in the RA and Dec interval. This does not make much sense in the few polar plots, but let's move on.
- For all charts of a given type, define the fittest chart as that chart where the object is plotted closest to the center. This is computed as the minimum of the Euclidian distance between the relative position computed in the previous step, and the center of the chart (0, 0).
- Merge the results in one column per Herald-Bobroff chart series (B to F).
The way I did this was by means of an Excel sheet and a couple formulas. I added one column for each chart, and a summary column for each series of charts. I also wanted to keep track of other charts on which the object is visible. For this purpose I surrounded the 'non-best' charts with parentheses. For example, the result for NGC 51 looks like: (B-01), (B-02), B-03, which should be interpreted as "NGC 51 is best seen on chart B3, but is also visible on charts B-01 and B-02".
What I could also do (but did not yet implement), is to provide location information for quicker lookup of the object on the chart. This is all possible thanks to the approach in which I compute the relative location of the object with respect to the center of the chart. Using NGC 205 (M 110) I could produce more verbose output like:
- (C-03) far bottom, far left
- (C-20) far bottom, right
- (C-21) top, far left
- C-38 top, far right
On this page you can download the current Herald-Bobroff index for version 8.0 of the SAC database. This index only adds a couple columns after the original SAC database columns:
- Columns A-S: original SAC DB v8.0
- Column T: blank
- Column U: RA in decimal format (e.g., +12.3456)
- Column V: Dec in decimal format (e.g., -5.3210)
- Column W: blank
- Columns X-AB: index to B, C, D, E, F charts of the H-B astro atlas
Hope you enjoy!