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Digger clams, Moon days, the Universe begins, solar sails revisited

Q: How do clams dig? — Laci, Centrailia, Washington

Digging for clams in the Pacific Northwest [US Fish and Wildlife Service]

A: Clams have a foot that they can push out and creep along or even make short jumps. Not all clams move, though. Many spend all or most of their lives anchored by tough threads they spin out of their bodies and fasten to rocks or ship hulls.

But some, like the razor clam, dig. A razor clam pushes her foot (the digger) into the sand below her shell. She spreads out the tip of her foot to form an anchor. She hauls her body to the anchored foot and pushes her foot down again.

Given warm temperatures and loose sand, she can blitz down, sometimes faster than a human can dig. A small young clam can rebury itself in 7 seconds. Some can dig several feet, at 9 inches per minute. Another was clocked at 1 inch per second but couldn’t dig long at that rate.

Moon days

Q: Does the Moon have day and night? — Carlos, New York City, New York

Moon and Earth: The view from 4 million miles away [NASA]

A: Yes, the Moon has daytime and nighttime. The Moon’s solar day lasts as long as its year — 27.32 days. The Moon orbits Earth in the same time as it spins once about its axis. Consequently, a lunar day lasts as long as a lunar year and it’s light there about half the time.

Further Surfing:

WonderQuest: Moon spin

USA Today weather resources: sun, moon, stars, time

US Naval Observatory: Sun and Moon rises

The Universe begins

Q: If dense, large concentrations of matter form black holes, how could the big bang ever have happened? Wouldn't it have stayed a black hole? — John, Albuquerque, New Mexico

Fast-flying black hole hurtling like a cannonball through our Milky Way galaxy. (artist’s conception) [ESA, NASA Felix Mirabel (French Atomic Energy Commission and Institute for Astronomy and Space Physics/ Conicet of Argentina)]

A: A horse is born to run, the Universe was born to expand. According to relativity theory, space doesn’t like to remain static. It either expands or contracts (except for a few special cases). We don’t know why it chose to expand but it did. Expanding overwhelmed contracting and the "big-bang" Universe didn’t stay a black hole. (A black hole is a region in space so dense that light and matter cannot escape gravitational forces.)

Why, then, didn’t the Universe collapse into a black hole? Matter was jammed together extraordinarily densely and such conditions are ripe for forming a black hole. So, why didn’t it?

Black holes can only form in space whose density varies. The early Universe was extraordinarily homogeneous — as smooth as butterscotch pudding. Thus, no black holes could form.

Further Surfing:

Scientific American: Why the early Universe didn’t collapse into a black hole

Solar sails revisited

Q: How do solar sails work? The idea of using sunlight to blow spacecraft across the Solar System will not work, suggests a new analysis by Thomas Gold. Is Gold right? [Answered Sep. 5, 2003]

Update on solar-sails question: "We have decided to delay the launch of Cosmos 1, our solar sail, from October 2003 until 2004... We will not rush or take any risky shortcuts."

So, we have to wait for the test a little longer.  Just keeping you posted...

Further Surfing:

WonderQuest: How do solar sails work and is Gold right?

(Answered Nov. 28, 2003)