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I don't yet have any Frequently Asked Questions. Instead, I have Freely Anticipated Questions -- the sort that I expect to encounter regularly.
Except for Xi Ursae Majoris, all the stars in the Encyclopedia are in the Hipparcos catalogue. The typical error on Hipparcos parallaxes is 1 milliarcsecond, whereas the most distant stars in the Encyclopedia have parallaxes of 65 milliarcseconds. Thus, the relative uncertainty for the furthest stars is 1 / 65 = 1.5 percent. Most of the stars in the Encyclopedia are considerably closer, and have errors well under 1 percent.
Xi Ursae Majoris is only in the Gliese catalog, which gives an error of 13 milliarcseconds in its parallax, corresponding to a relative uncertainty of 13.5% in its distance.
Metallicity is somewhat difficult to measure. There are several ways of measuring it, the best (and most direct) being a detailed analysis of the spectral lines of iron and hydrogen. Estimates of the uncertainty vary, but uncertainties of 25% appear to be typical.
Stellar ages are the most uncertain data in the Encyclopedia. The main method for estimating ages, based on Ca H and K emission line strengths, can have an uncertainty of 100% (contrast this with the ~1% for distance and ~25% for composition described above). This is still normally sufficient to discriminate between very young, medium, and old stars. Nevertheless, data for ages are not very precise. I quote stellar ages to two significant digits, but in practice this is too much precision.
There are other ways of estimating stellar ages. The most reliable -- probably more reliable for many stars than the Ca emission measurements -- involves stellar evolution theory and models. Astronomers have calculated how the luminosity and spectrum of a star vary as a function of various parameters, notably stellar mass, composition, and age. In principle, if the luminosity, spectrum, mass, and composition of a star are well characterized, the age can be determined from these models of stellar evolution. I have not yet found a comprehensive source of stellar ages based on stellar evolution models, but may incorporate this information into the Encyclopedia if I can.
In general, I have omitted text descriptions for stars fainter than apparent magnitude +6.0, since these generally:
The key information for these stars -- luminosity, location, metallicity (when known), age (when known), etc. -- is always given in the information box next to the star chart. For most of these fainter stars, a text description would just repeat details that are already given, and not add much useful information.
I have always included a text description if the star has some unusual interest, such as a companion star, or unusual physical properties. I have also always given a text description, if only a brief one, when the star is well known by something other than a catalog number. For example, any star that has a Greek letter ID (e.g., Sigma Draconis or Alpha Mensae), or one of the Flamsteed numbers (e.g. 54 Piscium) has a description, often of the constellation it is in.
In the previous section, I describe metallicity as a ratio of a star's iron content to the Sun's iron content. In catalogs and research papers, though, astronomers usually go one step further. They calculate the common (base 10) logarithm of the ratio. Thus a star with the same metallicity as the Sun -- a ratio of 100%, or 1.00 -- would be given as 0.00, and a star with half the metallicity (50%, or 0.5) would be given as -0.30. Although this is the usual convention in research papers, I chose to give just the ratios in the Encyclopedia because the numbers are more meaningful to non-astronomers.