Published: 2018-01-03 10:48:00
Updated: 2018-01-03 10:48:33
Posted January 3, 2018 10:48 a.m. EST
By Tony Rice
The December solstice arrived on Dec. 21, the beginning of astronomical winter. On Jan. 3, though, the sun is about 3 million miles closer to Earth than it will be on aphelion in July.
This might seem paradoxical with temperatures outside in the mid-teens, but keep in mind that our seasons are controlled far more by the 23.4 degree tilt of Earth’s axis. The (northern hemisphere) winter sun falls less directly than the summer sun.
Though about 6 percent more solar radiation falls on us during the winter months, the northern hemisphere’s tilt away from the Sun spreads that energy out over a greater area. You can see this yourself by shining a flashlight directly over a surface and then again at an angle. Same flashlight, same amount of light, but a much different intensity between the two angles.
This isn't happening in a vacuum of course: Our atmosphere affects how much sunlight reaches us. Not only are there fewer hours of sunlight during winter months, but the sun spends that time lower on the horizon where there is more atmosphere between us and the sun. A lot more—38 times more.
This is why the sun appears brighter when it is at its highest in the sky near solar noon (around 12:19 p.m. this week) than at sunset.