Skywatch for the week of June 8 , 2020
Tue June 9 RAINBOWS AT SUNSET Rainbows form when tiny water droplets in our atmosphere catch sunlight and, acting like prisms, break up the light into its separate colors. We sometimes see rainbows in the early morning, or more often, in the late afternoon, especially around sunset. Why at these hours instead of at midday, around noon? Rainbows always show up on the opposite side of the sky from where the sun is. At sunset, when the sun is near the western horizon, the rainbow appears well up in the eastern sky, its arc long and high. The lower the sun is, the higher the corresponding bow. That’s why you’ll never see a rainbow at noon, since it would place the sun below the horizon, unable to light up all those tiny water droplets. Sometimes you can see a secondary rainbow above the main one, but the colors are reversed: instead of the red being on the top of the arch and the violet at the bottom, the secondary bow has violet at the top and red at the bottom.
Wed June 10 STAR TRAILS: AS THE WORLD TURNS An elegant demonstration of the earth’s rotation is the motion of the stars across the heavens as the night progresses. Amateur astronomers have taken countless photographs of the sky at night, leaving their cameras open to record the stars as they rise and set. All it takes is a tripod, a camera that has a feature that allows you to leave the shutter open for minutes or hours, and a bit of patience. The result will be a photograph that shows star trails. Aim your camera east or west and you can get star trail lines that appear as diagonal streaks across the picture. Aim your camera south and you’ll get star trails that bend in broad, curving arcs that run along the southern horizon. But aim your camera north, with the star Polaris in the center of the viewfinder, and you’ll get star trails that move in nested circles around the North Celestial Pole. Even Polaris, the North Star, will show a very slight movement, as it is displaced from the earth’s pole by just under a single degree of angle.
Thu June 11 ORION ON THE RUN Orion the Hunter, which has dominated our evening skies since winter, is about to disappear. Tonight he rests on the western horizon at dusk. But this week, as the earth moves to a point in its orbit where the stars of Orion will drift behind the sun, we will lose it until it reappears in July, rising out of the east before dawn. In Greek myth, this disappearance was blamed on the arrival of the constellation Scorpius, Orion’s mortal enemy, which is on the opposite side of the sky from the hunter. Twenty-three hundred years ago, the poet Aratus wrote, "tis said that when the Scorpion comes, Orion flees to the utmost ends of the earth." You see, Orion once boasted that no animal on earth could hurt him. That kind of talk invariably leads to disaster, and sure enough, a scorpion rose up from the ground and stung Orion. The dying hero was given new life as a constellation, but he still fears the scorpion, for whenever Scorpius rises out of the east, Orion ducks down below the west horizon.
Fri June 12 FLAG DAY Sunday is Flag Day. On this day in 1777, our national flag was adopted by the Continental Congress, which also on this day established the U.S. Army. The flag held thirteen stars, one for each of the original colonies; and of course, the current U.S. flag has 50 stars, one for each state in the Union. The arrangement of stars on flags does not as a rule correspond to any actual constellation in the sky, and the U.S. flag has gone from a circle pattern to a series of rows and columns, and of course there was even an arrangement where the stars were made into a great star image, such as the one that flew over the fort in Fort Pierce when it was built back in 1838. Sometimes the stars on flags do reflect actual star patterns, such as the use of the Big Dipper and the North Star in the state flag of Alaska, or the use of the Southern Cross in the flags of Australia and New Zealand; and Brazil’s flag features the Southern Cross, Canis Major and Scorpius.