Email: nexusmail at this Web site address
There are a number of other important stellar properties given in the Encyclopedia.
For historical reasons, astronomers defined the scale so the brightest stars visible to the naked eye are roughly magnitude 0, and the dimmest roughly magnitude 6. Here are the magnitudes of some representative celestial objects:
Most of the stars in the Encyclopedia are fairly faint. With the exception of Alpha Centauri, none is brighter than magnitude +3, and the majority are fainter than +4.5. None of the stars require a large telescope to see. However, from a city, where the city lights interfere with the night sky, those fainter than about +4.5 will often require binoculars (ordinary birding binocs are fine) to see clearly. From a very dark sky you will be able to see most of the Encyclopedia stars without binoculars, though the fainter ones (magnitude +6 and fainter) will be much clearer in binoculars or a small telescope.
The absolute magnitude is really just another way of describing the star's luminosity. The Sun's absolute magnitude is +4.85; stars similar to the Sun generally have absolute magnitudes in the range +3.5 to +7.
Astronomers usually measure metallicity by comparing the ratio of iron (Fe) to hydrogen (H) in a star. Although other elements can be (and are) measured, iron is the most commonly measured, and is widely used as a proxy for total metal content. Astronomers then divide the iron/hydrogen ratio by that of the Sun, whose chemical composition is well known, so a metallicity of 50% indicates an iron abundance (relative to hydrogen) that is only one-half that of the Sun.
The "luminosity class" code is a Roman numeral from I ("supergiants": extremely luminous) to VII (white dwarfs: extremely dim). Nearly all of the stars in the Encyclopedia, as well as the Sun, have luminosity class V: ordinary main-sequence stars. Only two (so far) have a different class: IV-V, representing a star that is just beginning to evolve away from the main sequence and become a subgiant (an intermediate stage between main sequence and red giant).
The Ca II H and K emissions of a typical star vary somewhat over the short term. The Sun, for example, produces measurably more of these emissions during solar maximum (high sunspot number and flare activity) than at minimum. Because of this, the age of a star has fairly high uncertainty (up to about a factor of 2). In the Encyclopedia, I give the ages to the nearest tenth of a billion years; in reality the uncertainty will generally be considerably larger than this, possibly a billion years or more. Nevertheless, the age figures are accurate enough to group stars into broad age groups, particularly into groups that are much younger than the Sun (less than ~2 billion years), similar to the Sun (~2 - ~6 billion years), and much older than the Sun (more than ~6 billion years). SETI enthusiasts and "hard" science fiction fans ought to be quite interested in older stars...
If a companion object moves quickly enough, astronomers can measure its position over time and determine its orbital elements -- the physical parameters that describe the orbit. The most important orbital elements are (a) the period, which is the time it takes the companion to orbit once; (b) the eccentricity, or how elongated the orbit is (larger numbers mean narrower ellipses), and (c) the semi-major axis, which is one-half the length of the long axis of the ellipse. The semi-major axis is usually expressed in arcseconds (i.e., apparent angle as seen from Earth), but if the distance to the star is known, astronomers can express the semi-major axis in units like kilometers or astronomical units. Since the distances to all the stars in the Encyclopedia are very well known, I have calculated the semi-major axes of all known orbits in astronomical units.
In the case of extrasolar planets, I give another figure: the estimated mass of the planet. Because of limitations of the techniques used to find these planets, their precise mass M cannot be determined; what astronomers actually measure is the quantity M sin i, which is the mass times the sine of the orbital inclination, as seen from Earth. Since the orbital inclination is unknown, sin i can be anywhere from 0 to 1, so M sin i is a lower limit on the planet's mass. The planet's mass could be many times the value of M sin i, but statistically speaking, most of the time it will be less than twice that value.
Stars orbiting very slowly or very far away do not have well characterized orbits. For these stars, I note that the period of the orbit is unknown, and give the apparent separation, which is simply the distance between the two stars in angular units (i.e., arcseconds). I also give the separation in astronomical units, assuming the line between the stars is perpendicular to our line of sight to them. Since the stars could really be in any orientation, without further information, this separation is a lower limit.