<p>I understand that the orbit of a planet will always be flat, so there is no point on making a sphere out of the HZ when we consider one star, but what about binary stars? For example, this binary system (taken from <a href="http://astro.twam.info/hz/" rel="nofollow noreferrer">here</a>):</p>
<p><a href="https://i.sstatic.net/YSGmd.png" rel="nofollow noreferrer"><img src="https://i.sstatic.net/YSGmd.png" alt="enter image description here" /></a></p>
<p>The habitable zone of this binary surrounds both stars, but what if the orbit of the planet isn't contained in the binary's orbit plane? For example, orbiting the star on the left with an inclination of, say, 20 degrees? Wouldn't it have to be two spheres and not two disks? Or is the HZ calculated assuming coplanar orbits?</p>

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2020-10-15T09:54:22.913Z
Personally I consider HZ as a sphere. At least if there is not a planetary system around the star. Of course the only planet will be orbiting on a plane.
Alchimista
<habitable-zone><astrobiology>
Why the habitable zone of a binary star is a disc and not a sphere?
Carlos Vázquez Monzón
# Why the habitable zone of a binary star is a disc and not a sphere?

(Asked by: username_0 on 2020-10-15)

I understand that the orbit of a planet will always be flat, so there is no point on making a sphere out of the HZ when we consider one star, but what about binary stars? For example, this binary system (taken from [here](http://astro.twam.info/hz/)):

[![enter image description here](https://i.sstatic.net/YSGmd.png)](https://i.sstatic.net/YSGmd.png)

The habitable zone of this binary surrounds both stars, but what if the orbit of the planet isn't contained in the binary's orbit plane? For example, orbiting the star on the left with an inclination of, say, 20 degrees? Wouldn't it have to be two spheres and not two disks? Or is the HZ calculated assuming coplanar orbits?

**Tags:** habitable-zone, astrobiology

> **Comments:**
> **username_1**: Personally I consider HZ as a sphere. At least if there is not a planetary system around the star. Of course the only planet will be orbiting on a plane.  

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## 0 answers

