Skywatch for the week of July 12,2021
Mon Jul 12, 2021 FAREWELL, SKYLAB
Forty-two years ago, Skylab burned up as it re-entered earth’s atmosphere. It was America’s first space station, built from hardware left over from the Apollo moon missions. The station was made from the Saturn 5 rocket’s third stage, and was launched in 1973. Over the next year, it was visited by three different Skylab crews, providing these astronauts with a base for observing the earth and the sun and the stars. And it provided lessons that would help people who flew on future missions, such as those aboard the current space station, during long-duration flights. There was even a race track reminiscent of the one seen in the movie 2001: A Space Odyssey, where astronauts could run laps around Skylab’s inner circumference! One of my duties when I interned at the Hayden Planetarium was to provide daily updates on the anticipated re-entry time of Skylab. It was indeed a sad day, July 11, 1979, when it broke up over the South Pacific Ocean and Australia.
Tue Jul 13, 2021 NAME THAT CONSTELLATION – 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. 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 planets Venus and Mercury are together, in conjunction just to the east of it, and the new crescent moon is below its head and near its heart, the bright star Regulus, also called “the King star”. Can you name this constellation, the fifth sign of the zodiac? The answer is Leo the Lion.
Wed Jul 14, 2021 THE MILKY WAY AND THE LOCAL GROUP
The Milky Way, part of it at least, can be seen tonight under clear dark skies. It spreads across the eastern sky, from Cassiopeia in the north to Sagittarius in the south. The Milky Way is our home galaxy; we live on a planet orbiting a star about two-thirds of the way out from its center. Other galaxies surround ours, all bound together by gravity. We have satellite galaxies, most notably the Large and Small Magellanic Clouds. And there’s a bigger spiral galaxy about 2 and a half million light years away: its catalog number is M31, but we know it best as the Andromeda Galaxy. Now besides the Milky Way and M31, there are about 30 other, smaller galaxies in the immediate neighborhood (and by “immediate neighborhood,” we mean anything that’s within a million parsecs of here.) This cluster of galaxies is known as the Local Group. Most of them are fairly small and contain only a billion or so stars. M31 and the Milky Way are the Group’s gravitational “anchors”.
Thu Jul 15, 2021 STARS OF THE SUMMER TRIANGLE
The Summer Triangle is made up of three bright stars that are well-placed in the eastern sky after sunset at this time of the year. The highest star, Vega, is the brightest of the three, but the star Altair, below and a little to the south of Vega, is almost as bright. The third star, the northernmost one, is called Deneb, and it’s no match for the brightnesses of the other two. But that’s because, as you may have guessed, Deneb is much farther away from us, so its light is correspondingly dimmer. Altair is a mere seventeen light years away – that’s a little over a hundred trillion miles. Vega is a little farther away, twenty-five light years, but it’s an intrinsically brighter star, and that extra luminosity makes it brighter. But Deneb, which is the dimmest star, is also about a hundred times more distant; if Deneb were as close to us as the other two, it would be bright enough to cast shadows!
Fri Jul 16, 2021 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.