Download Mon Dec 19, 2011 INERTIA, MOTION AND ACCELERATION Inertia

Mon Dec 19, 2011
INERTIA, MOTION AND ACCELERATION
Inertia is the tendency of things at rest to remain at rest, and of things in motion to remain in motion, unless
acted on by an outside force. In the case of the moon orbiting the earth, the moon's inertia carries it in a straight
line, which is at a right angle to the pull of the earth's gravity. The continuing resolution of these two motions
results in a curved path around the earth. If something is moving (and everything is moving in some way in this
universe,) then it’s either moving at a constant velocity along a straight-line path, or it’s speeding up, or it’s
slowing down, or its path is changing. Any change in the speed or direction of an object’s motion is called
acceleration. If you go faster, you’re accelerating. If you slow down, you’re also accelerating, but negatively
(this is called decelerating.) And if your path turns left or right, up or down, that’s accelerating too. So next time
you make a hard turn around the corner, just remember, it’s acceleration at work!
Tue Dec 20, 2011
WINTER’S BEGINNING AT NEWGRANGE
Many years ago, I had the chance to visit an archaeological site in Ireland. It was called Newgrange, but there
isn’t anything new about it – in fact, it’s literally as old as the hills, being a hill itself. This is of course, an
artificial hill – five thousand years ago, a lot of people went to a lot of trouble to build this giant mound, over an
acre across, and walled in by great stones etched with intricate swirls and other megalithic designs. Ancient
tomb, ancient temple, Newgrange probably served both these functions. Like many other archaeological
wonders, such as the Great Pyramid of Khufu or the Giant’s Dance known as Stonehenge, Newgrange has an
astronomical alignment. For a few days before and after the winter solstice - the beginning of winter - sunlight
travels through a roof box or window over the main doorway. The shaft of sunlight travels all the way down a
long, narrow corridor, until it lights up a small chamber at the center of the mound.
Wed Dec 21, 2011
URSID METEOR SHOWER
The Ursid meteor shower is at peak activity during the next couple of nights. These “shooting stars” seem to
come out of the bowl of the star group known as the Little Dipper, more formally called Ursa Minor, the
constellation of the Little Bear. These particular meteors are made by bits of dust from the tail of the comet 8P
Tuttle. As the earth plows through this region of space, it picks up the comet debris, which shoots earthward at
speeds of about a hundred thousand miles an hour. The compressional heating caused by such rapid speed burns
up the dust and also makes the air through which it passes light up, causing that momentary streak of light in the
night sky – a meteor. This shower is best after midnight, but if that’s too late, then go out as late in the evening
as possible. Look from the north up to the top of a clear, dark sky, and you may see a few meteors each hour.
Dress warmly, take along a lounge chair, plus friends and family to share this shower.
Thu Dec 22, 2011
WINTER SOLSTICE, WINTER “EVENING STARS”
Winter began today, Thursday, December 22nd, at 12:30 AM, Eastern Standard Time – just a half hour past
midnight. It's at this point in time that the sun's rays fall most directly on the Tropic of Capricorn, 23 and a half
degrees below the equator. Often on these long winter nights, you can find a couple of bright evening stars in
the sky after sunset. There’s a brilliant evening star over near the western horizon – but it’s not really a star, it’s
the planet Venus! The next star that appears is also not a star, but Jupiter, the biggest planet in our solar system.
You’ll find it well up in the southeastern sky at dusk. Venus is almost as large as earth, and Jupiter has a
diameter that’s eleven times that of our planet, but Venus and Jupiter are millions of miles away, so they look
like bright stars. As the evening progresses, Venus sets a little after 7:30 tonight, while Jupiter drifts over into
the western sky, and sinks down below the western horizon a little after 2 AM.
Fri Dec 23, 2011
NATIVITY STAR
Who were the Wise Men, the Magi, and what did they know about the sky? Our best guess is that they were
Zoroastrian astrologer-priests of Babylonia, which lay to the east of Judea. Two thousand years ago, from
September 3 BC through May 2 BC, the Magi may have witnessed a triple conjunction, three separate passings
of the planet Jupiter and the star Regulus, a significant sky event for them. Jupiter appears as a bright star that
wanders against the background of constellations, caused by the combined motions of Jupiter and the earth as
they orbit the sun. Regulus, in the constellation Leo the Lion, was the signal star of the Babylonian king. Jupiter
was the king planet, and its appearance near Regulus may have set the Magi on their course eastward toward
Bethlehem to seek out the new king. You can see Jupiter and Regulus tonight; Jupiter appears in the south after
sunset, while Regulus is over half a sky away, rising out of the east before midnight.
Mon Dec 26, 2011
MOON AND VENUS
There’s a very pretty conjunction of the moon with the planet Venus tonight. Go outside about 6 o’clock this
evening, just after sunset, and look toward the west. You’ll find the moon over there, a thin new crescent above
the western horizon. To the left and slightly above the moon there is a brilliant evening star, but this star is
actually the planet Venus. The moon’s phase is crescent, but if you look at Venus through a telescope, you’ll
discover that its phase is gibbous – that is, it looks like a tiny, slightly out-of-round ball. You’d think that both
Venus and the moon would be crescents, but even though it looks like they’re right next to each other, Venus is
actually much further back, millions of miles away, and just coming around from the far side of the sun. By 8
o’clock tonight, Venus and the moon will have set, so look for them between 6 and 7:30 PM today.
Tue Dec 27, 2011
JOHANNES KEPLER
The astronomer Johannes Kepler was born on December 27th in the year 1571. Kepler was a Copernican. That
is, he subscribed to Nicholas Copernicus’ theory that the earth was not the center of the universe, but instead
orbited the sun along with the other planets. But while Copernicus had a beautiful idea, it didn’t work any better
than the geocentric theory; both ideas were riddled with errors, bad observations and mistaken assumptions.
Copernicus held on to the ancient idea that the orbits of planets were perfectly circular, but the data that Kepler
used, obtained from the painstaking observations of the Danish astronomer Tycho Brahe, didn’t support that
notion. Unlike past theorists, Kepler refused to toss out the data. Instead he got rid of the theory and introduced
a new one: the orbits of planets are elliptical. Once elliptical orbits were calculated, the motions of the planets
became understandable and predictable.
Wed Dec 28, 2011
TELESCOPE HELP
If on Christmas morning, you found a telescope under your tree, and now here it is a few days later and you still
haven't figured out how to get it to work, here’s some basic advice. You've either got a reflector, which has a
big round mirror at the bottom end of the telescope, or a refractor, usually a long white tube with a big glass
lens mounted at the top end. The refractor’s eyepiece, which does the magnifying, goes into the draw tube at the
small end of the scope. If you have more than one eyepiece, use the eyepiece with the biggest number - this will
give you the least magnification, which is what you want to start out. You probably also have something called
a Barlow lens which doubles or triples the magnification - this attachment probably gives you way too much
magnification and makes your instrument unwieldy, so put it aside for now. As a general rule, don’t magnify
more than 50 power for each inch of aperture, the width of your main lens or mirror.
Thu Dec 29, 2011
MORE TELESCOPE HELP
If you got a telescope for Christmas, but so far haven't been able to find anything with it, you probably need to
align your finder scope - that's that small tube mounted on the side of the main tube. When you look through the
finder you'll see the crosshairs - two lines which cross each other. The idea is to first look through the finder and
put the crosshairs over the object you're trying to zoom in on. But when you look through the main tube's
eyepiece, it’s not there! To align the finder with the main scope, start by putting any distinctive, far away
landmark into view through the eyepiece of the main tube. Clamp down the telescope, then go to the finder, and
by screwing and unscrewing the three little bolts which hold it in place, you can then center the crosshairs on
the landmark. Now you're aligned, and everything else will be easier to find.
Fri Dec 30, 2011
NEW YEAR’S AVATAR
2011 is drawing to a close. Often the outgoing year is portrayed as a very old man, or Father Time. Father Time
in turn is based on the Greek mythological god Kronos, whom the Romans associated with Saturn, an
agricultural god. The planet Saturn takes 29 years to orbit the sun, so to sky-watchers of long ago, it seemed as
if this slow-moving, unhurried planet must somehow be associated with time. In late December great festivals
like the Saturnalia were held in honor of Saturn. Gifts were exchanged, homes and streets were decorated, there
was music and dancing, and everybody was in a happy party mood. After this came the solstice and celebrations
of the sun, then another holiday for Janus, the Roman god of new beginnings, and for whom the month of
January is named. If you want to see Saturn tonight, go outside tonight after 2 AM and look to the east; that
bright yellow star-like object near the horizon is the ringed planet.
Mon Jan 2, 2012
MOON AND JUPITER
The new year begins with a pretty conjunction of the moon with the planet Jupiter. Both can be seen well up in
the southern sky after sunset tonight. The moon is just past first quarter, and it’s waxing toward full over the
next week. The planet Jupiter appears as a bright, star-like object right below the moon. Of course, this
conjunction, or close alignment of the moon and Jupiter is an optical illusion. When we take into account the
actual distances to these worlds, the great depths of space are revealed. The moon is roughly a quarter of a
million miles away. Back when astronauts traveled to the moon, in the 1960’s and ‘70’s, it took a little over
three days to get there using the Apollo spacecraft. Moving at those same speeds, it’d take years to get to
Jupiter, which is almost half a billion miles away! Both Jupiter and the moon are on the border between the
constellations Pisces and Aries, the stars of which are trillions of miles away, and to travel to those stars nobody has that kind of time!
Tue Jan 3, 2012
JANUARY AND THE NEW YEAR
January is named for Janus, the Roman god of new beginnings: He had two faces, one which looked back
toward the past, and another which looked forward to the future. This is also the year 2012, which according to
the calculations of a Roman monk, Dionysius Exiguus, marks the 2 thousand and twelfth year following the
birth of Christ – AD – Anno Domini – in the year of Our Lord - 2012. Dionysius was a good historian, but his
count is off by at least one year. Our calendar goes from 1 BC to AD 1 – there is no zero year, because the
numerical concept of zero was not used in Europe back then. “Zero” was later introduced by mathematicians
from India and the Middle East. Here’s another puzzle - why does the new year start now? There's nothing
particularly special about this time of year, astronomically speaking; and astronomers are the ones who invented
calendars in the first place. Before 1751, New Year's in America used to start on March 25 th, the beginning of
spring. Well, no matter how you reckon time, the earth just keeps on rolling along.