28 May 2005
What bright object in the night sky this evening has highlands and seas? If you guessed the Moon, you are on the money - sorta.
Tonight the Full Moon shines bright as it rises in the southeastern skies. Its incredible glare lights up the sky so much that it’s hardly worth mentioning other objects up there, seeing as they can’t be seen.
But a look at the Full Moon will reveal some interesting characteristics about our nearest planet-like neighbor.
See there the vast dark areas surrounded by bright whiteness. Some see in the overall view the traditional “man on the moon.” I see a dark rabbit as if it’s being lifted up - head and ears to the “left,” body arching over to the long back legs on the Moon’s “right” side. Don’t see it? It’s OK.
Neither do most of the students in my class. Alas!
We might agree, though, that the full Moon is pretty bright. But surprisingly it’s only as bright as the asphalt on your street. It’s albedo, a fancy word that tells us how much light is reflected off of something, is only 0.06. Translation: it reflects only 6% of the light it receives. Earth, that bright beauty with all its reflective cloud cover and polar caps has an albedo of 0.39, more than 6 times that of the Moon.
But why are there the dark parts of the Moon (the bunny) and the light parts? It was a mystery for a long, long time.
Galileo was first to see the detail on the Moon with his fancy new telescope. He could see that the bright areas were covered in crater-shaped “mountain” ranges. The dark parts, which he called seas, or “maria,” were to him craterless.
It wasn’t until this last century that we finally figured out what it all was.
The light parts, heavily pockmarked with craters, were not the result of volcanic activity or mountain-building processes as was widely held. Those were impact craters and their debris, from lots and lots of giant impacts.
This idea didn’t fly well at first since huge impact craters smacked of catastrophe, something that didn’t happen according to the prevailing philosophy of the day, a worldview that said that things happened slowly over long periods of time.
Then what on earth were the Moon’s dark areas made of? Why didn’t the impactors impact all over? They did, in fact. But these dark spots turned out to be lowlands, which filled in with moon lava and covered old craters billions of years ago when the Moon was still geologically active.
These smooth and relatively safe areas, the “seas,” were where the first Apollo missions landed. Hence the famous “Sea of Tranquility,” the landing site for Apollo 11.
It wasn’t until we sent spacecraft to the Moon that we could see the far side of our satellite. Here we discovered just about nothing but crater-filled highlands. The maria turn out to be pretty much a show exclusively for Earthlings.
And all these moon craters, great and small, got scientists to ask the obvious questions. If the Moon, smaller and with less gravity got hit that often, what happened to us? Why aren’t we chock full o’ craters?
It turns out we’ve been hit a lot more than the Moon. But we have this excellent recycling program set up on our planet that resurfaces many of the impacts and buries others with plate tectonics. Our atmosphere also helps to break up many before they hit us, and our vast oceans hide many scars.
But there are still dozens and dozens of impacts above ground like Barringer Crater in Arizona - reminders that overall we’ve got it pretty good here on this beautiful planet of ours.
Go out tonight after sunset and see again, but with new eyes, our amazing satellite.
07 May 2005
For someone trained in the sciences there is always the problem of turning a perfectly beautiful experience into a mere compilation of data. Studying nature too deeply for some puts calluses on their senses of beauty and design. They suffer from the proverbial missing-the-forest-for-the-trees syndrome.
Maybe the best way to observe an object in nature lies somewhere between the arts and the sciences. Let me give you an astronomical example of what I mean.
There is an amazingly beautiful picture of our home planet at a NASA website called Blue Marble (http://earthobservatory.nasa.gov/Newsroom/BlueMarble/). It is a stunning composite made of countless images of our planet, all sewn together into one marvelously detailed blue, green, brown, and white image.
Many see this and are simply awed by the grandeur of it. I have to be told to close my mouth and quit staring.
But allow me to try and enhance this magnificent image at the risk of seeming like a cold, clinical scientist.
Looking at this planet I can, with my mind’s eye, see down through the surface, deep into the center, where lies the inner core, an intensely hot and glowing ball of solid iron and nickel.
Thanks to a miraculous collision by a Mars-sized planet over 4 billion years ago, a collision that spilled the guts of the impactor into a newborn Earth, we inherited a larger, hotter core than we had when Earth was conceived. The radioactive heat from that terrible transfusion keeps our planet in a somewhat molten state, critical for life.
Enveloping the inner core is a thick outer core of hot liquid metal that swirls around in gigantic eddies. The churning creates a protective magnetic field encompassing the earth, saving us from dangerous, electrically charged particles spewed from the sun and providing us with the beautiful aurorae at the poles.
Surrounding both these cores you can imagine a thicker, cooler, hardened layer reaching nearly to the outer surface of the globe. On this “mantle” is painted a thin layer of crust, the layer we call home. This paper-thin coating is just thick enough to allow some pretty amazing phenomena.
As hot material rises from the lower layers it forces our crust to move about on colossal slabs called tectonic plates. This movement is important because it provides us with volcanoes and mountains, hills and valleys, coasts and islands.
Where plates collide we have island chains and gigantic mountain ranges, like the Aleutians, the Andes, Japan, and the Philippines. Where they split apart we have oceans and immense rift valleys, like the entire Atlantic Ocean and the Horn of Africa. Where the huge landforms scrape by each other, they crushingly reshape the land as they have in California.
If that visible, colorful crust were thicker, there’d be no movement. If it were thinner, we’d have considerably more deadly tectonic activity. The thickness of the crust at this moment in our history scores a perfect 10. It couldn’t be better.
The image of our planet shows us the fragile, thin atmosphere we have been given. It is composed of about 80% nitrogen and 20% oxygen - perfect for complex life like us. Not much more than a trace of carbon dioxide remains from the early days of infant Earth. But there’s just enough to warm us and keep those plants alive.
Also invisible in our thin cloak of atmosphere is a layer of ozone, protecting life below from deadly ultraviolet rays.
The clouds are more obvious, sweeping magnificently across the globe. Those are wisps of life there. They are water carriers delivering their precious cargo to all parts of the planet. A planetary scientist sees this as perfection. There is not too much cloud cover, not too little – it’s just right.
And the elegant, sweeping shapes of the clouds remind us that the planet is spinning at just the right speed; not too fast, not too slowly.
Seeing a picture like this strikes in us a profound sense of beauty, like staring at Michelangelo’s David or Raphael’s Sistine Madonna. There is just something inherently exquisite and aesthetic here. It is a beautiful ball in the heavens, probably the only one of its kind, and a work of cosmic art.
And the more we find out about her - the more we know of her inner design, her deliberate activity on the surface, the sensitive, frail atmosphere covering her - the more lovely she appears.
Maybe the best way to look at this Blue Marble, our great gift of a home, is with the heart of an artist and the mind of a scientist.