Short answers, pulled from the story.
A photon born in the core of the Sun takes between 10,000 and 170,000 years to reach the surface. It changes direction every time it encounters a charged particle during this long trek before escaping into space as electromagnetic radiation.
The spectrum of sunlight resembles a black body with an effective temperature of about 5,800 Kelvin. Different depths in the photosphere have varying temperatures which create deviations from a perfect black-body spectrum.
Modern calculations place perihelion around January 3 each year. The amount of total energy received at ground level in January is about 3.3% higher than average due to the closer distance to the Sun.
Researchers use sunshine recorders, pyranometers, or pyrheliometers to measure intensity. Direct normal illuminance accounts for atmospheric extinction and relative optical airmass while extraterrestrial solar illuminance corrects for Earth's elliptic orbit using the day number of the year.
Epidemiological data shows people with more sunlight exposure have less high blood pressure. Cardiovascular-related mortality decreases among those with higher exposure levels compared to those who avoid sun exposure.