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Skywatch for the week of July 20, 2020


Fifty-one years ago today, astronauts Neil Armstrong, Buzz Aldrin and Mike Collins were orbiting the moon. They were not its first visitors: six men had preceded them, in Apollo’s 8 and 10; but those astronauts never landed. When the lunar lander Eagle separated from the Apollo command ship Columbia, Aldrin and Armstrong piloted it down to the moon’s surface, and on July 20th, 1969, at 4:18 pm they landed on the southern edge of Mare Tranquilitatis, the Sea of Tranquility – a huge lava flow of dark basaltic rock. At 10:56 pm, Neil Armstrong stepped onto the lunar surface, followed by Buzz Aldrin about ten minutes later. They were outside for two-and-a-half hours, setting up several lunar science experiments and collecting about fifty pounds of moon rocks. Shortly before 2 pm Eastern Daylight Time, their lunar lander Eagle blasted off from the moon and rejoined Command module pilot Mike Collins who was on board the Columbia in orbit. All three returned to earth on July 24th, 1969.


Tue Jul 21, 2020    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 hundreds 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 about two-thirds of the way 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 constellation Cassiopeia in the north.


Wed Jul 22, 2020    LOOK-BACK TIME          

If you can manage to live for a full century, go outside at night on your 101st birthday and look at the star at the end of the handle of the Big Dipper, in the northwest this evening. The light from that star, Alkaid, left there the day you were born (This calculation comes from data collected by the Hipparcos satellite; some of my colleagues insist that Alkaid is really 104 light years away, so you may want to hang on a few more years just in case.) Now go farther out: in the south is the star Antares, 500 light years away. If it went supernova today, we wouldn’t know about it for another 500 years. It takes light time to travel across the Universe. This phenomenon, Look Back Time, means that the farther something is from us, the older it is. So when we look at the Andromeda Galaxy, 2.5 million light years away, it’s what that galaxy looked like 2 and a half million years ago. What does it look like now? Not sure, but I’ll know, in about 2 and a half million years! 



Toward the end of July in the year 1609, the Englishman Thomas Harriot made the first really good drawings of the moon as seen through a telescope. Galileo would make his drawings several months later, less detailed and accurate than Harriot’s, but while Galileo’s fame has continued through to the present day, hardly anyone has ever heard of Harriot. Galileo published his discoveries in his book, the Starry Messenger. Harriot on the other hand, put the bulk of his work in manuscript form, but never published an actual book for public consumption. Harriot led an interesting life, accompanying Sir Walter Raleigh to the Roanoke colony in America, serving as mathematician, navigator and interpreter. He was briefly imprisoned in 1605 on account of suspicions that he had been part of the assassination attempt on King James 1. He was innocent and released, but this may have made him less eager to publish, not wishing to draw attention to himself.



Of the 88 official constellations, can you identify the second largest one? It is bordered on the north by Boötes the Shepherd and Coma Berenices; on the south by Hydra the swamp monster and Corvus the Crow; on the west by Leo the Lion and Crater the Cup; and on the east by Libra the Scales and Serpens Caput. Planets have been discovered orbiting many of its stars, and a huge cluster of galaxies lies within its borders. In mythology this star figure is associated with the planting and harvesting seasons, and often portrayed as Persephone, daughter of the earth goddess Demeter, who holds its brightest star, Spica, which represents a spike of wheat, in her hand. Sometimes this constellation symbolizes Astraea, Winged Justice, who carries the scales of law, the constellation Libra. Tonight the fat crescent moon shines along its western border. Can you name this constellation, the sixth sign of the zodiac? The answer is Virgo the Maiden.