“This is bogus.” That’s what one of my co-workers said about International Observe the Moon Night item in yesterday’s blog. “I appreciate the moon every night. It’s a contrived event, but at least there’s no commercial angle to it.” OK, OK, he’s got a point. There’s no special happening on the moon that night, no spacecraft impact or alien check-passing ceremony. But why not go out and pay attention to that special orb? The “event” is more of a reminder to look up and appreciate what we sometimes take for granted. I always need reminders about things, like making sure to catch a good movie in town or having enough socks on hand to get me through the week.
This coming weekend and into next week is the best time of the year to catch the planet Mercury in the morning sky for northern hemisphere observers. With the sun rising later, it’s more likely your schedule will allow you to see the planet without losing much, if any, sleep.
Being the innermost planet, Mercury never strays far from the sun, so we always see it in twilight. When it’s orbit takes it east of the sun, it’s nicknamed the “evening star”. When west of the sun, as it will be in the days ahead, it’s the “morning star”. People in ancient Greece considered Mercury two separate planets for a time. It was Apollo in the morning sky and Hermes in the evening. Not until around 350 B.C. did the Greeks realize they were looking at the same planet. The Romans gave Mercury the name we use today, which means messenger of the gods. They most likely chose it because the planet moves so quickly from one side of the sun to the other – its year is only 88 Earth-days long. That adds up to four complete evening-morning appearances every year for sky watchers.
Messenger is also the name given to the space probe soon to become the first craft ever to orbit Mercury. Over the past couple years, it’s taken many pictures during two flybys of the planet. Once it settles into orbit next March, you can expect gigabytes more plus a thorough investigation of Mercury’s surface composition, magnetic field and tenuous atmosphere. Because the air is as close to nothing as an atmosphere can be, Mercury has extreme temperatures. On the sunny side, the mercury (excuse the pun) reaches 800 Fahrenheit, while during the mercurial night it plummets to 300 below.
This broiling hot/bitter cold world is a rocky body like the Earth but only 1 1/2 times the size of the moon. Its surface is covered in craters and lava-filled basins; signs of volcanism, including peculiar crater pits, abound. Mercury’s craters are named for famous deceased artists, musicians and authors. Mozart has a lovely hole of his own up there as do Debussy and Picasso.
While Mercury’s year is 88 days long, its day is double that. That means a day on the planet lasts two Mercury-years! If there was ever a challenge for calendar makers, I don’t know a better one. Now, imagine how brutal the heat must be under the sun for so long. It wouldn’t set for nearly three months. Not to mention that it’s three times larger and 11 times brighter than when seen from Earth. Definitely a place for the tough-at-heart.