Download Mon Apr 8, 2013 ARCTURUS AND BOOTES If you look off to the

Mon Apr 8, 2013
ARCTURUS AND BOOTES
If you look off to the east tonight, or any night this month or next, you’ll find a star low in the sky after sunset. That
eastern star is named Arcturus, which means, “bear chaser.” It’s called the bear chaser because Earth’s rotation causes
this star to follow or “chase” the constellation of Ursa Major, the Great Bear in the Sky. The bear is to the north of
Arcturus (you’ll recognize its back and tail as the Big Dipper, well up in the northeast.) Arcturus is in the constellation
Bootes, the Herdsman. This is an agricultural constellation that farmers and shepherds used long ago to keep track of
when to plant and harvest and tend to the sheep. In the springtime, Bootes is a celestial reminder for those who watch
over their flocks at the time when lambs are born. And in the fall, Bootes is low in the western sky after sunset, a cosmic
post-it note to farmers - bring in the crops.
Tue Apr 9, 2013
PERSEPHONE AND SPRINGTIME
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.
The scientific reason for why the air is warming up is not quite so romantic, but it is beautiful. Each day, the sun rises
slightly farther north than it did the day before, and is a little higher in the sky at noon. Sunlight is more direct, which
heats up the air and we get spring and summer. The sun’s path across our sky changes because of the earth’s tilt as it
orbits the sun.
Wed Apr 10, 2013
STAR COMPARISONS
In our Milky Way galaxy alone there are an estimated 200 billion stars. They vary in mass and size. Some, like the red
supergiant star Betelgeuse, which can be found in the constellation Orion over in the western sky this evening, are as
large as the span of the inner solar system. Others, like the blue giant Rigel, also in Orion, are many times hotter and
more massive than the sun. Then there are white dwarf stars like the companion star to Sirius in the southwest - only
the size of the earth. Smaller still are neutron stars, just a few miles in diameter. And what about black holes, mere
pinpoints of superdense matter. From red and blue giants to yellow suns, white dwarfs, neutron stars and black holes,
from solitary suns to multiple star systems, and great globular clusters, each star is unique, possessing within it the
secret of its own creation and demise.
Thu Apr 11, 2013
SUN, SOLAR YEAR AND ECLIPTIC
Watch the sun and you’ll discover it gets around. But of course you can’t watch the sun, because it’s too bright to look at
without hurting your eyes. If you could somehow dim down the sun enough, you could also see the stars in the sky at
the same time. (Actually, there are times when this happens – during total solar eclipses.)Assuming you could see the
sun and stars at the same time, you’d notice the sun drifts eastward like the moon, although not as fast as the moon.
The moon moves 13o a day; the sun only moves about 1o a day. After 365 days, the sun would return to conjunction with
the star it had been beside exactly a year ago. A solar year, then is the amount of time it takes the sun to go once around
the heavens, and the invisible line that traces out that path is called the ecliptic. The constellations through which the
sun passes each year is called the zodiac, and the ecliptic is its central line.
Fri Apr 12, 2013
THE OLD MOON IN THE NEW MOON’S ARMS
You may have seen the moon yesterday, a very thin crescent, low near the western horizon at sunset. If you missed it,
that’s all right, because you can see it again tonight. Go outside at sunset, and look off to the west – that’s where the
sun went down. Watch for this new crescent moon to appear as nighttime approaches. While you're looking at the
moon, see if you can find something called, "the old moon in the new moon's arms". That's when you can see the entire
disc of the moon, even though only a slim crescent is lit up, because the sunlight that shines on the earth is reflected out
into space and lights up the moon, very faintly, allowing us to see it. This effect give the moon a real three-dimensional
appearance: we see it as a round object, not just a flat circle in the sky. Over the next week, you can watch the moon
wax fuller in our sky, and also it will drift eastward from night to night. On Sunday night it will appear near the planet
Jupiter.