Saturn covered and uncovered by the moon earlier today by Dave Herald, Murrumbateman, Australia
Enjoy the video. Dave Herald did a great job recording this morning’s Saturn occultation. The images are very sharp. I always find it remarkable how atmosphere-less the moon is. There’s not a hint of softness in the planet as it’s devoured by the lunar limb. If there were substantial air, the planet would gradually soften and fade.
For a moon or planet to be completely without air is next to impossible. The solar wind knocks atoms from minerals on the lunar surface and sends them reeling into the virtual vacuum above the surface. Studies have found potassium, sodium, helium and argon in the moon’s exosphere, the name given to the lunar atmosphere. Bombardment of the moon’s surface rocks by micrometeorites and the solar wind release potassium and sodium; helium and argon probably bubble up from radioactive decay of those same rocks. Helium may also arrive via the sun’s wind.
At sea level on Earth, we breathe in an atmosphere where each cubic centimeter contains 10,000,000,000,000,000,000 (10 quintillion) molecules; by comparison, the lunar atmosphere has less than a million molecules in the same volume.
Comets and meteoroids striking the surface temporarily enhance the amounts of other atoms and molecules. But the sum total of all the sputtering and interacting is an atmosphere equal to the amount of air you’ll find 250 miles high where the space station plies it orbit. Not much.
At my house, we saw no occultation of Saturn, but the two did stand together in the southeastern sky at dusk. On the opposite end of the heavens, Mercury made a fine naked eye appearance in the northwestern sky.
I first caught it around 9:15 p.m. some 40 minutes after sunset and watched it for at least a half hour. Capella and Jupiter – both higher up in a darker sky – made for great sight lines to the planet.See yesterday’s map for details.
Jupiter in Gemini remains the most brilliant object in the western sky at dusk during early evening hours. I watched it from a nearby creek that rushed with water from snow melt and recent rains.
Mars stood between Jupiter and Saturn. This week the ‘boring’ hemisphere – the one with fewest dark markings – is turned toward western hemisphere observers.
But there’s still much to see – enough to easily stay up past your bedtime. The north polar cap on Mars remains visible despite the seasonal summer ‘heat’, and white clouds topping the planet’s major volcanoes are visible along the planet’s western edge. Check it out.