How hot is it? Not hot enough to fry an egg on the sidewalk.

It's an expression we've all probably hard: "It's so hot you could fry an egg on the sidewalk."

But, sadly, it's not usually possible — at least it hasn't been in one of the hottest places around: Death Valley National Park. The park usually has several days every summer that crack 125 degrees Fahrenheit. 

"Clearly the hotter the better for it, and it's not that easy to fry an egg here," park management assistant Abby Wines told KPCC. "I tried it once and failed."

It was about 125 degrees outside, Wines said. She took a more sanitary approach than cracking the egg straight onto the sidewalk.

"I took a frying pan from my kitchen, put it on my asphalt driveway, cracked an egg, put it in there, and then watched the egg turn into dehydrated rubber," Wines said. "It definitely got warm, but it didn't turn into something that I would want to eat."

A little closer to home, KPCC's own John Rabe tried cooking an egg on blacktop when it was 107 degrees outside in the San Fernando Valley. No luck.

The Library of Congress did its own research and found that while it's possible to fry an egg on the sidewalk, most just don't get hot enough, even in scorching temperatures. 

An egg needs to reach 158 degrees Fahrenheit to become firm, and sidewalks don't usually get that hot, even on broiling hot days days. Pavement isn't a good conductor and the egg itself cools the sidewalk. You may be able to get part of the way there, but your more likely to end up with a runny mess.

For success, use a covered skillet or metal surface

Wines has a coworker who succeeded in cooking an egg using raw sunshine. The secret: Putting a lid on the skillet to keep the moisture inside.

And while it can be a fun hands on science experiment to try cooking an egg outside, Wines has an appeal to anyone making the attempt: Do it in a frying pan, especially if you're out in nature. It makes a mess and can be dangerous to the animals it attracts.

"[On] their car hood would be fine too — but something other than the ground itself. Other than on the asphalt, or on the sidewalk, or on a road, or on a rock. Because then, once they've cooked the egg, whether or not they succeed, they're going to have a really hard time picking up all the scraps of food, and that leaves food on or near a road surface, which attracts coyotes, road runners, other animals that will come to where people are, possibly get hit by cars," Wines said.

Death Valley National Park had a huge problem with that back in 2013. The idea went viral and left park roads covered in gooey yolk, according to Wines. Visitors have since gotten the hint to keep it in a skillet.

Pro tip: Bake dashboard cookies instead

Wines recommends an alternate project that she says is a lot more doable than frying a sidewalk egg: baking cookies on your car's dashboard.

"We would go out and put a small cookie sheet on the dashboard, so inside the vehicle, on the dashboard, with the windows all rolled up so animals can't get inside, and just leave that in the sun," Wines said. "And when it's time to go home at the end of the day, we had almost fully cooked but not quite fully cooked warm, gooey chocolate chip cookies — and the vehicle smelled wonderful."

So go ahead and see if you can bake some cookies — it should at least make a nice replacement for your car's air freshener.