Download Mon Jul 4, 2011 4TH OF JULY COSMIC FIREWORKS On the 4th of

Mon Jul 4, 2011
4TH OF JULY COSMIC FIREWORKS
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On the 4 of July in the year AD 1054, a bright star suddenly appeared in the eastern predawn sky. It was off in the
direction of the constellation Taurus, just behind the forward horn tip of the bull. For the next several weeks this new star,
this “nova,” was so bright that it could even be seen after sunrise, in the daytime! And then as summer drew to a close, the
star faded out of sight and was seen no more. In the western world there is apparently no written record of this star’s
appearance: either no one was looking up then, or more likely, the skies were overcast throughout the star’s appearance.
But in the east, Chinese astronomers made note of this “guest star,” as they called it, and that’s how we know about it
today. If you’re out before sunrise this month, aim your telescope at that part of space behind Taurus’ horn tip, and you’ll
find the Crab nebula, the exploded remains of a supernova - cosmic fireworks from nearly a thousand years ago.
Tue, July 5, 2011
APHELION
The earth is at aphelion today, July 5th. Aphelion is the point in our planet’s slightly elliptical orbit where it’s farthest
from the sun. On average, we're about 93 million miles from the sun, but right now we are roughly 94 and a half million
miles out. So if we’re now a million and a half miles farther from the sun than average, how come we're having summer?
Well, not everyone on earth is experiencing summer; winter has just begun for folks south of the equator. Our seasons
aren't caused by any variation in the earth-sun distance; after all, that extra million and a half miles only makes for a tiny
2% difference. Temperature changes occur because our planet is tilted about 23 and a half degrees, from straight up and
down. During our summer, the earth’s north pole leans inward, which puts the sun higher in our sky, and causes summer;
in the winter the north pole leans outward, which places the sun lower in our sky, and that cools things down.
Wed July 6, 2011
SUMMERTIME MILKY WAY
In the summertime, when the skies are clear and dark, it's possible to see a galaxy on display. This galaxy is called the
Milky Way, and it is our home, a giant star city, one of billions in the vast emptiness of the universe. The Milky Way is
shaped like a spiral disc or pinwheel, some hundred thousand light years or so across. One light year equals six trillion
miles, which means our galaxy is over six hundred thousand trillion miles in diameter - big! There are perhaps two
hundred billion stars in the Milky Way, and our sun is but one solitary star roughly halfway out from galactic center. Go
out tonight and look for the arm of the Milky Way - a faint hazy band of light arching across the sky. In the late evening,
around 10 PM, it stretches from due south – the constellations Scorpius and Sagittarius - toward the zenith – the three
stars of the summer triangle, and then down to the north.
Thu July 7, 2011
MOON AND SATURN TOGETHER IN VIRGO
There’s been a pretty crescent moon in our evening skies this week; lots of folks noticed it during the 4 th of July fireworks
a few days ago. The moon is waxing, and it’s now at first quarter, which looks like a half moon in the southern sky after
sunset. Half moons and first quarter moons are the same thing: it’s called a half moon because it looks like a half moon;
but it’s also called a quarter moon because the moon has traveled through the first quarter of its orbit since it was new.
Where else but in astronomy does one quarter equal one half? When you watch the moon tonight, you’ll find two bright
stars nearby. The one to the left of the moon is Spica, the brightest star of the constellation Virgo the Maiden. The star
above the moon is not a star at all, but the planet Saturn. With a telescope you can see the moon’s craters or the rings of
Saturn, but when you aim your scope at Spica, it’s so far away that it will still look just like a point of light – a star.
Fri, July 8, 2011
VEGA AND ALTAIR, TANABATA DAY
Yesterday was Tanabata Day in Japan, which marks the reunion of the weaver princess and the cowherd. The story is over
a thousand years old. The herdsman is Niu Lang, and the weaving girl is Chih-Nu. Chih-Nu’s father, the Jade Emperor,
grew angry because Chih-Nu no longer weaved for him, so he placed the two up into the sky; Chih-Nu became the star
Vega, and Niu Lang is the star Altair. Both these stars are well-placed in the eastern sky after sunset tonight. In order that
the two continue their work without distraction, the Emperor set Tien-Ho, the great Celestial River to separate the two.
Tien-Ho is the Milky Way, which when the skies are dark, you can see lies between these two stars. But so great was the
love of Chih-Nu and Niu Lang that on the seventh day of the seventh month, the magpies gather and with their wings
form a living bridge across the Milky Way, so that the weaving girl and the herdsman can be together once more.