Spectrometer Shows More Blue light on cloudy Day....why?

[Newtons Apple]

This is sort of a sister thread to my other thread. But I've bought a spectrometer and have been playing around with it. I pointed it at the sun on a clear day and got as expected a nice full spectrum of color with a large spike of blue:

1. My first question is.. is the spike in blue range because of the scattered light from the sky? So all of that blue being scattered by the atmosphere is interfereing with the spectrometer and it's picking up more blue? OR is it because the sun emits such a large amount of ultraviolet, and this spectrometer doesn't really show deep violets?



Now, when I repeated the experiment on a cloudy day with no blue sky visible, I got this reading:

Far far lower direct sunlight so I much decreased LUX. However there is STILL a big spike in blue. So does this answer my previous question that the spike in blue was due to the atmosphere scattered the blue light? Why though am I still seeing this sharp blue spike when all of the other colors are depressed from the cloud coverage?

 

[DaveE]

There shouldn't be a blue spike if you measure the sun, as you can see here. Maybe try and also test it on an incandescent light bulb, that should also look like a blackbody radiator with a similar temperature.