I have been working recently with galaxy data available from HyperLeda. Things have really changed since I got my first set of professional deep-sky catalog data on CD about 17 years ago. Back then, I ordered a set of CDs from the ADC and had to get a friend to let me use his CD drive to extract data - I didn't have a CD drive yet! Now days, oodles of data is available online and is updated constantly. Using the data wisely, of course, is the key.
I have been intrigued with the huge variation in magnitude and size data reported in some of the astronomical software I use. It's just not clear sometimes what data is reported by a given product. In the case of PGC data, most objects have size and B magnitude info, and some have B-V info that can be used to compute a V magnitude. I have one product that shows V magnitude if possible and B otherwise. It takes detective work to discern which is used for
magnitude filtering. The situation with size information is even more adventuresome. We have sizes in arcseconds, arminutes to tenths, arcminutes to hundredths; it's all over the place. The metric used for size in the catalog is a logarithm based on where the object fades out to 25th (B) magnitude. I have to wonder how meaningful size reported to arcseconds is when the surface brightness of many of these objects is above 23 mags/square arcsecond, but at least it's a consistent metric.
Maybe the most entertaining find of the day is that NGC 7009 is listed in HyperLeda as a galaxy. I've observed this object many times, mostly with 8 and 20 inch aperture telescopes, and found the usual classification of planetary nebula to be pretty plausible. Blinking an OIII filter does what you might expect with a planetary. It will take more research to understand why HyperLeda lists the Saturn Nebula as a galaxy...
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