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Skywatch for the week of September 6, 2021

Skywatch 9-6-2021.mp3


If you imagine that the earth is surrounded by a vast, invisible celestial sphere, you can come up with a way to chart the positions of stars and planets on the sphere’s surface. When you stand at our planet’s north pole, and look up to the zenith, you’ll see the star Polaris, often called, the North Star, very close to that north celestial pole. At earth’s south pole, if you extend a line from it straight out, you’ll find the celestial south pole – but there don’t happen to be any bright stars near that point in space, so we have no South Star. Extend the earth’s equator out into space, and you get the celestial equator, which is at a 23½ degree angle to the earth’s ecliptic, the line that traces out our planet’s path around the sun. Finally, as the earth travels in its orbit of the sun, the sun is orbiting the center of our galaxy – and the solar system’s orientation with that path is about 60 degrees over from straight up and down.

Skywatch 9-7-2021.mp3


The terms, “mass,” and, “weight,” are often used interchangeably, with weight being expressed in English or Imperial units of ounces and pounds and tons, and mass using metric units of grams, kilograms, milligrams, and so on. But this only works on the planet Earth, because while mass measures the amount of matter, or stuff, that the object contains, weight very much depends on how much gravity is exerted on that mass. Go to another planet or moon or asteroid, and while your mass remains the same, your weight changes, again depending on how much gravity that other celestial object possesses. The moon has 1/6th the earth’s gravitational pull, so you weigh 1/6th what you’d weigh on earth. If you weigh 180 pounds, then on the moon you’d weigh a mere 30 pounds – just divide your earth weight by six, and that’s all there is to it. You’d weigh about 10% less on Venus, but 3 times more in the high cloud tops of Jupiter. And on tiny Deimos, a Martian moon, you could launch yourself into a low orbit just by running and jumping!

Skywatch 9-8-2021.mp3

Wed Sep 8, 2021 STAR TREK

Fifty-five years ago, the first Star Trek TV episode aired on September 8, 1966. I saw that first episode, which was about an alien that would suck the salt out of you when you weren’t looking. So of course, like many young space enthusiasts, I was immediately captivated. I liked the show’s vision of a promising future (not counting the part where you get the salt sucked out of you,) and the portrayal of humans as daring explorers of the galaxy, curious about what they would find out there. The science and astronomy in it showcased the beauty and vastness of outer space – grand nebulas, lush planets, exotic moons. The writers built on the best of classic science fiction, and the science was, for the most part, well-researched. There were no intergalactic aliens in Star Trek (well, once or twice, like with the Kelvins, but they were from the nearby Andromeda galaxy, so that was kind of like getting to know the neighbors next door.) The writers understood that our Milky Way alone, was big enough to contain us. For now, anyway.

Skywatch 9-9-2021.mp3

Thur Sep 9, 2021 SCUTUM

The fifth-smallest constellation in the sky is very difficult to see, but it has an interesting history. Scutum, the “shield of Sobieski,” has no bright, or even middling-bright stars within its borders, and as it’s wedged into the summertime Milky Way, between Aquila the Eagle, Sagittarius the Archer and the Serpent’s Tail, (Serpens Cauda,) finding it is more like a process of elimination than actual discovery. It was introduced to star charts by the astronomer Johannes Hevelius to commemorate the lifting of the siege of Vienna which had happened on September 12, 1683. King Jan Sobieski of Poland led his hussars and men gathered from England, France, Germany, Austria, and even a great many displaced Tatars who had settled in Poland, in an attack that routed the Turkish army, which had lain siege to Vienna. Scutum has a couple of open star clusters – M11 (the Wild Duck Cluster,) and M26; the globular star cluster NGC 6712, plus a planetary nebula, and even a pulsar.

Skywatch 9-10-2021.mp3


Of the eighty-eight official constellations, can you identify the twenty-ninth largest one? It is bordered on the north by Serpens Caput, the Serpent’s Head, and Virgo the Maiden; on the east by Scorpius and Ophiuchus the Serpent Bearer; on the south by Hydra the Swamp Monster and Lupus the Wolf; and on the west by Virgo the Maiden. This constellation was invented by the Romans about 21 hundred years ago when they formed it from the claws of Scorpius, and they often portrayed it as being held by Virgo, who represented Astraea, goddess of Justice. This constellation has no bright stars or notable deep sky objects like galaxies or nebulas, but tonight the waxing crescent moon and the brilliant planet Venus appear just to the west of it at sunset. Can you name this star figure, the seventh constellation of the zodiac, and the only zodiacal figure that is not a person or an animal? The answer is Libra the Scales, currently visible in the southwestern sky after sunset.