Final answer:
If the sun's altitude had been 10 degrees instead of 55 degrees, the sunset would have appeared even more red and vibrant.
Step-by-step explanation:
If the sun's altitude had been 10 degrees instead of 55 degrees, the author's observation would have been different. When the sun is closer to the horizon, its light must travel through a greater distance of the atmosphere, increasing the chance that sunlight will be scattered.
This scattering of blue light makes the sun appear more red at sunset. Therefore, if the sun's altitude had been 10 degrees, the author's observation of the sunset would have been even more red and vibrant.