The Sun’s closest planets are appearing close to each other in the early evening sky. Venus is the brilliant “evening star.” Mercury is close to its lower left this evening, but will slide above Venus over the next few nights.

Mercury is the Sun’s closest planet. It’s also the smallest planet – a dense ball of rock and metal about half-again the diameter of the Moon.

At its equator, noontime temperatures climb to about 800 degrees Fahrenheit. But some deep craters near the poles never see daylight. So temperatures there hit a couple of hundred below zero.

That’s not the case on Venus – not even close. Even though Venus is tens of millions of miles farther from the Sun, it’s much hotter. That’s because Venus is more massive than Mercury, so its surface gravity is stronger. That’s allowed Venus to hold onto its atmosphere.

Heat from the Sun has baked gases out of its rocks, making the air especially thick – the surface pressure is about 90 times the pressure on Earth. And the atmosphere is made mainly of carbon dioxide, which traps heat, preventing the heat from escaping into space. So the average temperature across the planet is about 865 degrees. It’s blazing hot even at the poles. The only places that aren’t that hot are mountaintops – the cool spots on the solar system’s hottest planet.

Venus and Mercury are quite low in the west during evening twilight. They’ll stand side by side in a couple of days.

Script by Damond Benningfield