# What's the eccentricity of our sun's orbit around the center of the galaxy? [duplicate]

Just thinking about "galactic habitability zones." Is this even a valid question?

• I doubt that it's Keplerian. Keplerian elliptical orbits only apply to a central gravitational field, but the galaxy's field is not a $1/r^2$ field. – user4552 Nov 21 '18 at 1:43
• It is indeed a valid question! You certainly do not want to be bobbing around the huge black hole on a 16-year orbit at the speed of 5 Mm/s. These things are not going to last. But elsewhere... it's probably survivable. I've seen worse. But I do not really know enough on galactic habitability to write an answer, sorry. – kkm Nov 21 '18 at 1:49

EDIT: I am getting down-voted, and as per the comment below me this seems to be because I failed to answer the question. I thought the question was about Galactic habitability zones as the description mentions but it seems I was wrong. If your question is about the eccentricity of the Sun's orbit around the center of the galaxy, then that question has already been answered here: How can one get the eccentricity of the orbit of the Sun around center of the Milky Way?. I'll leave the rest of my answer in case you were interested in the "habitability" of our galaxy. Cheers.

So "habitable" in the context of our solar system is really talking about radiation flux, where if too much of the sun's radiation is hitting the surface of our Earth, the Earth's atmosphere will heat up too much and the environment would be unsustainable for the development of life. So the Earth is close enough to the sun that the sun has a very strong effect on the dynamics of Earth's environment (obviously, since all of life feeds in some indirect way on the sun!)

However, in terms of the Earth in the context of the Galaxy, I want to clarify that the distance between stars in any galaxy is actually massive compared to the distance between the Earth and the sun. Really, the chance that our solar system will interact with any other star or solar system in the next few billions of years is virtually zero.

With this in mind, I'd say the only consideration about a "Habitable Zone" would be, as someone else has said, our distance from the super-massive black hole at the center of the Milky Way. But since this only makes up a tiny portion of our galaxy, the entire galaxy is really "habitable" for our solar system.

Hope that helps!

• This doesn't answer the question, and the second paragraph seems totally unrelated to the topic. – user4552 Nov 21 '18 at 2:28
• Ok, I answered what I thought they were asking, I've edited my answer. – CuriousHegemon Nov 21 '18 at 3:22
• IMHO, the body of the question is just as relevant, if not more so, than its title. So I think your answer is reasonable. Still, it might not be healthly living <1000 lightyears from the centre, due to the higher rate of energetic events like supernova, and other stuff that can cause gamma ray bursts. – PM 2Ring Nov 21 '18 at 4:26
• I disagree with your assertion that a single criterion establishes the galactic habitability zone. But, this isn't my argument, look up "Rare Earth Hypothesis" and galactic habitability zones. Rather fascinating. – Jimmy G. Nov 21 '18 at 22:13
• Can you send me a specific link? I don't think I have time to read the entire wiki article. Is your argument that there is indeed a galactic habitability zone and that the Earth is the only planet with life partly because of this reason? – CuriousHegemon Nov 23 '18 at 0:25