Skywatch for the week of September 11,2023
Mon Sep 11, 2023 SCUTUM
The small constellation of 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 few star clusters plus a planetary nebula, and even a pulsar.
Tue Sep 12, 2023 THE EARTH’S ORIENTATION IN SPACE
If you can imagine extending the Earth’s north and south poles out into space, you’ll find a celestial north pole and a celestial south pole. Extend the Earth’s equator outward, and you can establish a celestial equator in the heavens as well. Polaris, also called the North Star, lies very close to our north celestial pole; but there is no bright South Star to find at the earth’s south celestial pole. As our Earth orbits the sun, the path it follows is not the celestial equator, but another line called the ecliptic, which is inclined 23 and a half degrees to the equator. Now while our planet orbits the sun, the sun in turn orbits the center of our galaxy – but our solar system’s orientation with that path is about 60 degrees over from straight up and down – we’re moving sideways through the Milky Way!
Wed Sep 13, 2023 ELEVEN DAYS MISSING!
Here in America, there was no September 13th in the year 1752. There wasn’t a 3rd through the 12th either! The Julian calendar, established by Julius Caesar, was inaccurate; it was behind by ten days when Pope Gregory introduced the Gregorian calendar to Catholic countries in 1582. But England and its Protestant colonies kept using the old Julian calendar, until 1752, when, in order to fix the calendar, eleven days had to be chopped out. Riots broke out in London as landlords charged their renters a full month’s rent, even though the month was just 19 days long. “Give us back our eleven days!” they shouted. But in America, Ben Franklin counseled his readers not to “regret.. the loss of so much time,” but to give thanks that one might “lie down in Peace on the second of the month and not… awake till the morning of the 14th.”
Thu Sep 14, 2023 HOW TO SEE A BLACK HOLE
Three bright stars called the Summer Triangle can be found overhead this evening. Inside this triangle, in the neck of the constellation Cygnus the Swan, there is something that is invisible to the eye, but which nevertheless can be detected - that enigmatic phenomenon known as a black hole. It is called Cygnus X-1, and we can't see it because its gravity field is so intense that light can't escape it. But we have discovered an incredible amount of x-rays pouring out of this part of the sky, which tells us it’s there. Gas is being pulled from a nearby star and funneled into the black hole. When it collides with the hole’s accretion disc, a lot of energy pours out into space, and is then detected by our x-ray telescopes. Cygus X-1 is a black hole roughly 2500 parsecs, or 48 quadrillion miles away.
Fri Sep 15, 2023 DELPHINUS AND ARION
There are three bright stars spread out across the zenith this evening. These three stars – Vega, Altair and Deneb, form the Summer Triangle. The brightest star is Vega; it marks the constellation of Lyra the Harp. In Greek mythology, the harp was played by a musician named Arion, who was once rescued by a dolphin named Delphinus. Arion had been thrown overboard by some greedy pirates who wanted all the gold he’d won at a concert. They made him sing a song first, then they tossed him into the ocean. Now the dolphin also heard the song, and it saved him, carrying him to dry land. When the pirates arrived later, they were arrested and voted off the island. Arion’s harp is Vega and a few nearby stars, while Delphinus the dolphin is a small, faint cluster of stars on the opposite side of the Summer Triangle.