Since the focus of this blog is on human-habitable and human-inhabitable environments, I thought I'd crunch the numbers and share some data on fundamental orbits and habitable zones of solar analog stars.
So, first, a table which lists—by spectral type—the fundamental orbits:
- Innermost Stable Orbit
- Inner Optimistic Habitable Zone Orbit
- Inner Conservative Habitable Zone Orbit
- Nucleal Habitable Zone Orbit
- Outer Conservative Habitable Zone Orbit
- Outer Optimistic Habitable Zone Orbit
- Frost Line Orbit
If you're not familiar with these orbits and how to calculate them, refer to my blog
Star Systems, Part 1: Fundamental Orbits.
Ideal Solar Analogs: Orbits With A Period of One Solar Year
In spectral classes F7 through F4, the optimistic innermost habitable zone orbit falls more than 1.0 AU from the star, so an orbit with a period of one Earth year would be closer than the innermost habitable zone limit. In spectral classes K3 through K0, the optimistic outermost habitable zone orbit falls less than 1.0 AU from the star, and thus an orbit with a period of one Earth year would be beyond the outermost habitable zone limit.
Remember that Apparent Brightness is calculated by the stellar luminosity over the distance squared:
Therefore, for the ideal solar analogs, the apparent brightness at 1.0 AU is equal to the luminosity in solar units, because D is always 1.0 AU.
The ideal solar analog types are highlighted.
Luminosity at the Nucleal Habitable Zone
Thus, solving for AB:
Orbital Period At The Nucleal Habitable Zone Orbit
As a reminder, below is a graph showing the apparent brightness range across the habitable zone orbital distances: