If you’re north of the 37th parallel no appreciable UV will make it though the atmosphere 6 months out of the year.
Discussion
A good way to think of this is that if your shadow is longer than you are tall, you aren’t getting any vitamin D.
If you’re north of the 37th parallel no appreciable UV will make it though the atmosphere 6 months out of the year.
A good way to think of this is that if your shadow is longer than you are tall, you aren’t getting any vitamin D.