Our sun becoming a red giant If our sun was already in the process of becoming a red giant, would the gradual rise in luminosity be noticeable to our eyes at some point in human existence?
If our sun was already in the process of becoming a red giant, would the gradual rise in luminosity be noticeable to our eyes at some point in human existence?

I'd say no for a couple of reasons.

@PM2Ring's comment:

FWIW, in about 1.1 billion years it will be too hot for most lifeforms currently on Earth, long before the Sun starts moving off the main sequence and becoming a red giant. See Timeline of the far future.


Our eyes and vision processes accommodate (adjust for) changes in brightness, we walk indoors from a sunny day to a well lit room and the brightness of things has dropped by 99% or nearly a factor of 100 within a few seconds and yet though we are somewhat aware of the change of tens of percent per second we hardly notice it.

Our vision system is constantly adjusting its white point to accommodate changes in the color of available light.† A white sheet of paper looks white to us even as the color of ambient light changes because our vision is always &quot;color balancing&quot; (not exactly the right term but it's something like that).


†From @Luaan's comment

It's called &quot;white balancing&quot; - calibrating vision for ambient light to make white surfaces (hopefully) appear white. Sometimes it doesn't quite work properly, and you get fun things like The Dress (since different people's vision chooses different arbitrary ambient conditions, and end up disagreeing wildly about the colors involved)