Showing posts with label zipp. Show all posts
Showing posts with label zipp. Show all posts

Saturday, January 31, 2009

Why are the sun and moon the same size in the sky?

It is one of the most glorious pieces of natural theatre. Assuming you spend your life on the same part of the Earth's surface, you might witness it once - if you are particularly lucky or very long-lived, perhaps twice. But a total solar eclipse is worth the wait. At the height of totality, the fit of sun and moon is so perfect that beads of sunlight can only penetrate to us through the rugged valleys on the lunar surface, creating the stunning "diamond ring" effect.

It is all thanks to a striking coincidence. The sun is about 400 times as wide as the moon, but it is also 400 times further away. The two therefore look the same size in the sky - a unique situation among our solar system's eight planets and 166 known moons. Earth is also the only planet to harbour life. Pure coincidence?

Almost undoubtedly, say most astronomers. But perhaps it is not so much of one as the bare numbers suggest. Our moon is different. The many moons of the large outer planets - Jupiter, Saturn, Uranus and Neptune - are thought to have originated through one of two processes: from the accretion of a disc of material in the planet's gravity field, in a miniature version of the formation of the solar system's planets, or through the later gravitational capture of passing small bodies. The second possibility is also thought to account for Mars's two small satellites, Deimos and Phobos, the only other moons in the inner solar system.

But our moon is simply too big relative to Earth's own size to have formed easily by either of these processes. Planetary scientists believe there can be only one explanation: in the first 100 million years of the solar system, when unattached debris was still zinging around the inner solar system, a Mars-sized object smashed into Earth. That impact radically remodelled our planet, expelling a huge amount of debris that eventually congealed into our oversized moon.

And here's the best bit. Such a big moon is a big boon for life on Earth. As Earth spins on its own axis, it has a natural tendency to wobble, owing to the varying pull on it from other bodies such as the sun. The unseen hand of the moon's gravity gently damps that wobble, preventing rotational instabilities which would otherwise have caused dramatic changes in Earth's climatic zones over time. Such instabilities would have made it much more tricky for life to get started on our planet.

Earth's position in the "habitable zone" around the sun where liquid water is abundant is undoubtedly the single most important factor in its fecundity. But the presence of a large moon - one large enough to cause total eclipses - might also have been crucial. If so, that has important consequences for the search for life on other planets.

Since the impact that created it, the moon has been moving steadily away from us, currently about 3.8 centimetres per year. The dinosaurs did not see eclipses like we do: the moon was too close 200 million years ago, more than big enough in the sky to block out the entire sun. Equally, any occupants of Earth in a couple of hundred million years' time will not see total eclipses at all, as the moon will appear too small.

Our luck seems the result of two coincident timescales: that of the recession of an impact-formed moon, and that for the evolution of intelligent life. If you should be fortunate enough to experience a total eclipse in your lifetime, consider this intriguing possibility: that large moon might be the reason you are there.

Wednesday, October 15, 2008


(NaturalNews) Xerox subsidiary Palo Alto Research Center (PARC) has developed a type of paper that, combined with a special printer, can print documents that erase themselves after a day so that the paper can be reused.

Xerox says that 25 percent of all documents get recycled the same day they are printed, and that 44.5 percent are intended only for a single viewing. Using the new printer and paper for one-shot documents like daily menus, work summaries and office memos could vastly reduce paper and energy use, the company said.

"Think of the Google map you printed to get here," PARC Area Manager Eric Shrader said at a product demonstration. "Thirty years ago, we said the future was paperless."

"Despite our reliance on computers to share and process information, there is still a strong dependence on the printed page for reading and absorbing content," said Paul Smith, manager of Xerox's new materials design and synthesis lab.

The new paper is coated with a chemical that turns dark upon exposure to ultraviolet (UV) radiation. In order to create a document, the printer simply bombards the paper with UV radiation in the appropriate places.

While the "ink" will eventually fade on its own, after 16 to 24 hours, the printer can also be used to erase a page and print something new. Tests by Xerox found that if it was not torn or crumpled, a single piece of paper could be put through the print-and-erase cycle hundreds of times.

According to Shrader, it takes 204,000 joules of energy to create a new piece of paper and 114,000 to recycle one. Printing onto a normal sheet of paper uses about 2,000 joules.

It takes only 100 joules to print one page of the special erasable paper. If the printer also has to erase the prior image, printing uses about 1,000 joules of energy.

The erasable paper and ink are available in a variety of colors. Xerox expects to take the new product commercial within the next few years.

Wednesday, May 21, 2008

In a Landfill, How Long Does Trash Really Last?

By: Brie Cadman (View Profile)

We’ve all been there—at the beach, empty beer bottle in hand, a trash can, but no recycling bin in sight. So we dump the bottle in the normal trash, perhaps feeling guilty we weren’t able to recycle it, perhaps not. Most likely, we rapidly forget about it—out of sight, out of mind, and onto the next beer.

The bottle, like the rest of our trash, may slip easily from our hands and minds, but it doesn’t leave our collective refuse piles so quickly. Landfills, which are lined with clay and plastic, layered with soil, and capped, are not extremely hospitable when it comes to microbial degradation. The three necessary components for decomposition—sunlight, moisture, oxygen—are hard to come by in a landfill; items are more likely to mummify than to break down.

But how long do things last? These rough estimates, compiled from U.S. National Park Service, United States Composting Council, New Hampshire Department of Environmental Sciences, and the New York City government, give an idea of how long our consumables remain after we’ve kissed them goodbye.

Glass Bottle—One Million Years
Okay, we don’t really know whether a glass bottle takes a million years, two million years, or a million years and one day to degrade since no one has been monitoring them for that long. But suffice it to say, when a glass bottle isn’t recycled, it sticks around for a really, really long time. Glass is primarily of composed of silica—the same material as sand—and doesn’t break down even under the harshest environments. Given the relatively inert conditions of a landfill, it’s likely the bottle of beer our forefathers sipped is still at large.

Plastic Bags—Unknown, Possibly 500+ Years
Plastic bags also have a hard time decomposing; estimates range from ten to twenty years when exposed to air to 500–1,000 years in a landfill. Since microbes don’t recognize polyethylene—the major component of plastic bags—as food, breakdown rates by this means in landfills is virtually nil. Though plastic bags can photodegrade, sunlight in landfills is scarce. Made with petroleum and rarely recycled, many cities have banned them in order to curb consumption and prevent their long-lasting presence in litter (e.g., the Great Pacific Garbage Patch—an island you don’t want to visit).

Plastic Beverage Bottles—Unknown, Possible 500+ years
Bottles face the same problem as plastic bags. Most soda and water bottles are composed of polyethylene terephthalate (PET), a petroleum-based product that tends to last a long time in a landfill. Even newer bottles that claim to be biodegradable or photodegradable may take much longer than advertised. According to the Air and Waste Association, biodegradable plastics made with the addition of starch may just simply disintegrate into smaller non-degradable pieces: they don’t break down; they break up.

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