Something remains to be done. Is there something about the Sun that is common to other types of
stars; stars that are perhaps larger and hotter than the Sun, or perhaps smaller and cooler, or a
different color, like blue or red, instead of yellow? The answer is yes. I actually found something
in ancient Vedic knowledge, in the Hindu traditions. Apparently, in Hindu yoga the number 108
is an important number. I read that yogis today noticed that the diameter of the Sun is about 108
times the diameter of the Earth and that the average distance from the Sun to the Earth is about
108 solar diameters, with 108 being a significant number in yoga. So I wrote the equivalent:
or for any star and habitable planet:
the radius of the star. the orbital radius of the habitable planet. We consider the HR
diagram that plots temperature versus luminosity of stars. We see the O, B, A stars are the more
luminous stars, which is because they are bigger and more massive and the the F, G stars are
medium luminosity, mass, and size (radius). Our Sun is a G star, particularly G2V, the two
because the spectral classes are divided up in to 10 sizes, V for five meaning main sequence, that
it is part of the S shaped curve and is in the phase where the star is burning hydrogen fuel, its
original fuel, not the by products. And the K and M stars are the coolest, least massive, least
luminous.
Let us consider the habitable zones of different kinds of stars. In order to get , the
distance of the habitable planet from the star, we use the inverse square law for luminosity of the
star. If the Earth is in the habitable zone, and if the star is one hundred times brighter than the
Sun, then by the inverse square law the distance to the habitable zone of the planet is 10 times
that of what the Earth is from the Sun. Thus we have in astronomical units the habitable zone of
a star is given by:
the luminosity of the star, the luminosity of the Sun. AU the average Earth-Sun separation,
which is 1. The surprising result I found was, after applying equation 4, hypothetically predicting
the size of a habitable planet, to the stars of all spectral types from F through K, with their
different radii and luminosities (the luminosities determine , the distances to the
habitable zones), that the radius of the planet always came out about the same, about the radius
of the Earth. This may suggest optimally habitable planets are not just a function of their distance
from the star, which is a big factor in determining their temperature, but are functions of their
size and mass meaning the size of the Earth could be good for life chemistry and atmospheric