Skywatch week of July 1, 2019
Tue Jul 2, 2019 TANABATA DAY: VEGA AND ALTAIR/JULY FULL MOON We are coming up on Tanabata Day this weekend; it’s a summer star festival that marks the reunion of the weaver princess and the cowherd. This far-eastern story is over a thousand years old. The Jade Emperor’s daughter, Tanabata or Chih-Nu, loved a herdsman, Niu Lang. The father disapproved, and so he placed them up into the sky; Chih-Nu became the star Vega, and Niu Lang is the star Altair - both stars are well-placed in the eastern sky after sunset tonight. The Emperor then set Tien-Ho, the great Celestial River to separate them. Tien-Ho is the Milky Way, which when the skies are dark, you can see runs between these two stars. But on the seventh day of the seventh month, if skies are clear, magpies gather and with their wings form a living bridge across the Milky Way, so Chi-Nu and Niu Lang can be together once more. Part of a traditional poem recited at this time goes, “the stars twinkle on the gold and silver grains of sand... The stars twinkle, and there they will watch us.”
Wed Jul 3, 2019 APHELION Tomorrow the earth reaches aphelion – that’s 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 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 over a little, about 23 and a half degrees, from straight up and down. During summer in the northern hemisphere, the top half of earth leans inward, which puts the sun higher in our sky, and causes summer; in the winter the top half of earth leans away from the sun, putting it lower in our sky, which cools things down.
Thu Jul 4, 2019 4TH OF JULY COSMIC FIREWORKS On the 4th 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 the forward horn tip of Taurus, and you’ll find the Crab nebula, the exploded remains of a supernova - cosmic fireworks from nearly a thousand years ago.
Fri Jul 5, 2019 PLACES IN THE SKY FOR JULY Can you identify the twelfth largest constellation? It is bordered on the north by Ursa Major and Leo Minor; on the south by Hydra, Sextans, Crater the Cup and Virgo; on the west by Cancer the Crab; and on the east by Virgo again and Coma Berenices. Roughly a dozen of its stars are known to have planets orbiting them. This part of space is also the source of the Leonid meteor shower which peaks in mid-November, and every 33 years, the shower becomes a meteor storm, displaying dozens of “shooting stars” each hour. Many beautiful galaxies are found within its borders, one of which is a favorite of mine – the hamburger galaxy. In mythology, this creature was the first labor of Hercules, which was defeated after a month-long battle. Tonight the waxing crescent moon can be found nearby its brightest star, Regulus, sometimes called “the King star.” Can you name this constellation, the fifth sign of the zodiac? The answer is Leo the Lion.