All values in the table have their units given, and they're either in multiplies of respective solar values (e.g. a '2' in the luminosity column means twice as luminous as the Sun) or of Earth values (orbital parameters and received solar flux)
The basic imput is the stellar mass.
The spreadsheet uses some basic relationships that the main-sequence stars obey:
- The mass-radius relationship and mass-luminosity relationship (see http://www2.astro.psu.edu/users/rbc/a534/lec18.pdf). These are determined empirically and can be reduced to simple exponential dependence on mass. In general terms, as a star gets more massive, it grows in size more slowly than linearly (because you're adding 'volume' to a sphere, and looking at the growth of radius, plus the added gravity compresses the gas into a more dense package), and it gets much more luminous than a linear relationship would suggest (the exponent is close to 4 for 1-10 solar mass stars; this can be understood as the extra mass needing more energy to support, so the fusion reactions must progress more rapidly).
- The mass-lifetime relationship. Here, the lifetime simply calculated as mass/luminosity, normalized to our Sun's lifetime. The reasoning is that you get more fuel (mass) than the Sun has, that is then consumed with rapidity proportional to luminosity. Since the latter grows as ~M^4, the lifetimes get quickly and progressively shorter as you go up with mass. A bit more on that
here.
These give you information about physical characteristics of the star. They're not terribly rigorous, and omit e.g. the influence of metallicity or age on the fusion processes (stars get brighter as they age).
The luminosity of a star determines its habitable zone. The reasoning for the calculations used is as follows: take the habitable zone of the Sun, as calculated in
this paper. And scale it with increasing luminosity of the star using the inverse square law. This is simplistic, but for most part seems to roughly track the habitable zones the paper's accompanying calculator outputs.
Having calculated the habitable zone range, it's then just a matter of applying the small-angle approximation to ascertain angular size (disc width) of the star as visible from the inner and outer edges of the habitable zone. This simply means that a width of the stellar disc grows proportionally to the radius of the star, and decreases proportionally to the distance. Since distances to the habitable zone grow faster than the radius of the star (again, because of rapidly increasing luminosity), you get smaller and smaller disc as you sit in the HZ of more and more massive stars.
Note, that the amount of stellar flux (irradiation) received by the hypothetical planet remains the same, which means that the smaller discs must be brighter (e.g. a disc half the size has 1/4th of the area, so it must be 4 times brighter). This gives the same brightness of a 'day', but with much more intensely concentrated light source - if you were to look at it directly.
Orbital periods use Kepler's 3rd law in a straightforward way, outputting periods in Earth-years.
The bit with flux ranges to the right comes from the paper cited earlier, as the range of irradiation that may produce Earth-like climate (temperature-wise) depending on the strength of the greenhouse effect. It's mostly there to be used in calculations.
Stars over 10 solar masses and less than 1 solar masses have a bit different internal physics, so the slopes of some relationships differ.
