Sunsets... what's the deal?

I took advantage of the gorgeous weather (80 and sunny!) and drove (top-down, of course) to Carmel Beach for the sunset. It's a dog friendly beach, and there are always tons of dogs there, so it's not a bad place to go alone since there's plenty to see.

There were dozens of adorable dogs, but what I ended up doing was people watching. I noticed (or maybe re-realized) an odd phenomenon. What's the connection between sunsets and romance? There were at least 10 couples making out. Not all teenagers, either. Teenagers usually seem to be the least self-conscious group when it comes to PDA... but add in some sunset and POOF! Adults (even OLD ones) are making out like crazy. It's it physics? Gravitational pull?