* Astronomy

We prefer the identification of 40 Eridani as Vulcan's sun because of what we have learned about both stars at Mount Wilson. The HK Project takes its name from the violet H and K lines of calcium, both sensitive tracers of stellar magnetism. It turns out that the average level of magnetic activity inferred from the H and K absorptions relates to a star's age; young stars tend to be more active than old ones (Sky & Telescope: December 1990, page 589). The HK observations suggest that 40 Eridani is 4 billion years old, about the same age as the Sun. In contrast, Epsilon Eridani is barely 1 billion years old.
Based on the history of life on Earth, life on any planet around Epsilon Eridani would not have had time to evolve beyond the level of bacteria. On the other hand, an intelligent civilization could have evolved over the aeons on a planet circling 40 Eridani. So the latter is the more likely Vulcan sun.
In that case, Mr Spock's daytime star is a 4.4-magnitude multiple system about 16 light-years from Earth. Presumably Vulcan orbits the primary star, an orange main-sequence dwarf of spectral type K1. Data from the HK Project reveal that it has a starspot cycle of roughly 11 years, just like the Sun.
Read more