Has the sun become way brighter the last years?
Up to last year, I never got blinded by the sun in everyday situations (e.g. running towards it), at no time of the year I was. But since last christmas, it occured to me more often that I cannot watch in the direction where the sun is because it is so bright that it really hurts me.
My mother and my roommate have observed the same phenomenon independently of me.
This, of course, is only anectodal evidence, which is practically worthless. We all get older and we may have the same kind of "photophobia", or we just forgot about being blinded the last few years and just now consciously felt an remembered it.
Therefore I want to ask this question: is there any objectively observable increase of brightness over the last few months and if so, why?
Atmospheric effects can also change perception. I couldn't find any easy graphs that go to 2015. But here you can download a dataset for analysis of solar irradiance. http://www.nrel.gov/midc/ornl_rsr/
The Sun's luminosity is stable to 0.1% - it varies slightly in response to, or associated with, levels of solar magnetic activity (Solanki & Unruh 2012).
This variation would not be perceptible and is completely outweighed by the $\pm 3.4$% variation caused by the non-circular orbit of the Earth (the Sun is closest in January).
Obviously, if you live in the northern hemisphere, then the Sun is generally higher in the sky now (in May) than it was in December. Its direct light is less absorbed/scattered by the atmosphere. This is a much more perceptible effect. It could change the visual brightness by tens of per cent, and by even more in the short wavelength blue part of the spectrum. That is the only physics-based explanation I can offer.
Purely out of interest, do you have a reference for the "stable to 0.1%" claim? It'd be interesting to learn how such a measurement is made and how all the sources of noise and artifacts are taken into account.
is there any objectively observable increase of brightness over the
last few months?
No. It's entirely your subjective perception that has changed.
The Sun is pretty close to a black-body radiator. That means the amount of energy we receive from it depends on two factors: its temperature, and its apparent size (the angular size of the solar disk as seen from Earth).
The apparent size of the Sun has obviously not changed. Way too many things would go completely haywire if that happened - I'll leave that as an exercise to the reader.
Its temperature has not changed either. This could be measured in various ways - but there's another way which is simpler: this being a black-body radiator, its temperature and its apparent color are correlated. The color of the Sun has not changed, obviously.
TLDR: The Sun is still working as it always had.
"The color of the Sun has not changed, obviously." While that perhaps *should* be obvious, I've heard several people claim to have noticed a change in the sun's color in recent years, so it may be worthwhile to include measurements of the sun's spectrum to show that it is hasn't changed (within acceptable margins).
@called2voyage I'm pretty sure all actual scientists working in the field of solar science would have noticed any changes way before any random folks claiming to see changes in the shade of color of the daylight.