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Mon Apr 9, 2012
THE MOON’S TIDAL LOCK
Today the old gibbous moon rises out of the east near midnight.
Half the moon is always in sunlight; half is always in shadow, just
like on earth. And just as we experience daylit and dark periods on
earth, so the moon has both day and night. But the moon’s rotation
is slow; a lunar day lasts two weeks, followed by two weeks of
night. As the moon orbits the earth, its rotation speed as it spins
on its axis matches its revolution about the earth, so it rotates
once for every orbit. This is called a synchronous or tidal lock,
an effect of the earth’s tidal pull on the moon, which has slowed
down its rotation to be in synch with its revolution. Because of
this we can see only one side of the moon, called lunar nearside;
the farside of the moon (sometimes mistakenly called “the dark
side,”) can never be seen from earth. Or as Pink Floyd tells us,
there is no dark side of the moon; matter of fact, it’s all dark!
Tue Apr 10, 2012
PLANETARIUM SHOW: THE DIPPERS AND THE DIAMOND
The Big Dipper is about halfway up in the northeastern sky after
sunset tonight. This is a pretty easy group of stars to find: it’s
made up of seven fairly bright stars which trace out the pattern of
a saucepan. In the early evening the dipper’s bowl is about to tip
over and spill its contents out onto the northern horizon. A line
drawn through the two stars in the front of its bowl will point the
way to the North Star, Polaris, which is at the end of the handle
of the Little Dipper. If you’d like to see a show about the
Dippers, as well as a star group known as Virgo’s Diamond, then
join us at the IRSC Hallstrom Planetarium this weekend for, “The
Dippers and the Diamond.” These star talks are given on Friday
night or on Saturday afternoon. Call the IRSC Box office at 4624750 to get tickets and more show information, or from Martin,
Indian River and Okeechobee counties call toll free: 1-800-2209915.
Wed Apr 11, 2012
HOW TO LOSE WEIGHT
If you want to lose weight, you might consider moving to the
equator. Here’s why: The Earth is rotating, creating centrifugal
force - not really a force, just inertia at work – like when your
car turns a corner, you’re pushed against the side of the car –
actually it’s just you travelling in a straight line as the car
turns. The Earth’s spin hurls us out into space, but gravity holds
us back. Earth’s rotational speed is zero at the poles, but almost
a thousand miles an hour at the equator. And the Earth is a little
fatter around the equator than from pole to pole. So at the equator
we’re 12 miles farther away from Earth’s center, and there’s
slightly less gravity. This reduces our weight by a half of a
percent overall, or about two-tenths of one percent from our
position here in Florida. So if you weigh 150 and move to Ecuador,
you’ll weigh about a third of a pound less.
Thu Apr 12, 2012
LEVIATHAN MIRROR
On April 13, 1842, the mirror for the great Irish Leviathan was
completed. It was six feet across, and was designed and built by
William Parsons, the Earl of Rosse, at Birr Castle in Ireland.
Making a glass mirror that large was impossible back then; instead
it was made of metal, an alloy of copper and tin. Upon completion
and installation in the fifty-six foot-long telescope tube, the
instrument was named the Irish Leviathan, and for the next seventy
years, it was the biggest telescope on earth. Parsons observed
stars, the moon, and the planet Jupiter. Then the potato famine hit
Ireland, and the
Leviathan was shut down, But in April of 1845,
the telescope was running again and the Earl observed M51, a large
nebula in the constellation Canes Venatici. He called it the
Whirlpool, describing it as a "spiral nebula". Parsons even saw
individual stars in the Whirlpool, and suggested it was a distant
galaxy, similar to our own Milky Way. He was right.
Fri Apr 13, 2012
PLANETARIUM SHOW: THE DIPPERS AND THE DIAMOND 2
In mythology, Persephone was the daughter of the earth goddess
Demeter. Persephone was kidnapped by Hades, god of the underworld –
we call him Pluto today. Because her daughter was stolen, Demeter
neglected the earth and the crops died, the air grew cold, and
winter came to the land. When Persephone was found and returned to
her mother, Demeter caused the earth to bloom, and spring returned.
But because Persephone had eaten six pomegranate seeds while she
was with Hades, she had to return to the underworld for six months
of the year; then autumn and winter start again. This story is
featured in the planetarium show, “The Dippers and the Diamond,”
where we find the diamond of the constellation Virgo, who
represents Demeter. Shows are tonight and tomorrow – call the IRSC
box office at 462-4750. If skies are clear tonight, the Treasure
Coast Astronomical Society will also set up their telescopes for
viewing of the planets.
Mon Apr 16, 2012
THE NATURE OF ASTRONOMY
The universe holds great mysteries - well-kept secrets that might
someday be revealed... and secrets that might forever elude us. The
remarkable thing about astronomy is that we have been able to learn
as much as we have, given that the astronomer can never touch the
objects he studies. In the other sciences, hands-on experiments
can show us how things work. Biologists can study life directly,
either in the field or the laboratory. Geologists can break apart
the rocks and analyze the minerals. Chemists can pour chemicals
together, and if the result doesn’t destroy the lab, observe the
chemical reactions. But in astronomy, no one can weigh a planet by
putting it on a scale; we cannot determine how the sun will behave
by making it run through a maze; we cannot touch the stars. All
that we know about astronomy, save for a scattering of moon rocks
and meteorites, and the earth itself, has been discovered by
carefully observing those distant lights in the sky.