Skywatch for the week of September 14, 2020
Mon Sep 14, 2020 ELEVEN DAYS MISSING!
Did you know that here in America, there was no September 13th in the year 1752? There wasn’t a 12th either, or a 10th or 11th, nor a 3rd through the 9th! It happened when the Gregorian calendar replaced the Julian calendar. The Julian calendar, established by Julius Caesar seventeen hundred years earlier, 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 ignored the papal edict, and 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.”
Tue Sep 15, 2020 ARCTURUS AND BOÖTES
If you look off to the northwest after sunset tonight, you’ll find a star low in the sky. That northwestern star is named Arcturus, which means, “bear guard” or “bear chaser.” That’s because Earth’s rotation causes this star to follow or chase the constellation of Ursa Major, the Great Bear in the Sky, to the north of Arcturus (you’ll recognize part of the Great Bear as the Big Dipper.) Arcturus is the fourth brightest star in the night sky; it’s about 36 light years away – that’s roughly two hundred and sixteen trillion miles from earth - in the constellation Boötes, the Shepherd. This is an agricultural constellation that ancient farmers used to keep track of when to plant and harvest the crops. In the springtime, Boötes can be found in the eastern sky after sunset; now, half a year later, the shepherd has gone over to the other side of the sky, a celestial reminder of harvest time.
Wed Sep 16, 20120 HOW TO SEE A BLACK HOLE
In the late summer evening sky, there are three bright stars high overhead which are known as the Summer Triangle. Inside this triangle, in the neck of the constellation Cygnus the Swan, there is a great mystery - something which is invisible to the eye, but which nevertheless can be detected by the astronomer - that enigmatic phenomenon known as a black hole. It is called Cygnus X-1, and we can't see it directly because its gravity field is so intense that light can't escape it. But we know that it is there, because we've discovered an incredible amount of x-rays pouring out of this part of the sky. Cygnus X-1 is part of a binary star system. Gas from its companion, a massive blue giant, is being pulled from it to feed the accretion disc surrounding the hole; it’s here that the x-rays are being made, just outside the black hole's event horizon - its point of no return, about 2500 parsecs, or a little less than 48 quadrillion miles from Earth.
Thu Sep 17, 2020 DELPHINUS AND ARION
Near the top of the sky this evening are three bright stars spread out across the zenith. 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 belonged to many people, including the musician Arion, who was rescued by the dolphin Delphinus. Arion had been thrown overboard by some greedy pirates who wanted all the gold he had earned at a concert. Before they tossed him into the ocean, they let him sing one last song, which was overheard by the dolphin. When Arion fell into the sea, Delphinus saved him, and carried him to shore; in fact he got back before the pirates. When they got off the boat, the pirates were arrested and voted off the island. To find the harp and the dolphin, you’ll need a very dark, clear sky. Lyra is a scattering of stars near Vega, and Delphinus is a small, faint cluster of stars on the opposite side of the Summer Triangle.
Fri Sep 18, 2020 HYPERION
On September 19, 1848, father and son astronomers William and George Bond discovered Saturn’s oddly-shaped moon, Hyperion. To the Bonds, it was just a little point of light that changed position as it orbited the ringed planet. But thanks to the Cassini spacecraft, we see it as another world.
Named for the mythical Greek god of observation, Hyperion was the son of Oronos and Gaia, and the father of the sun god Helios. This rugged moon is over 200 miles in diameter, and ordinarily such a large object should be round, but Hyperion is a rather beat-up looking object, covered with craters, and very irregular in shape, looking like an old meatball, or perhaps a lufa sponge. Its composition is mostly water ice, with some rock and dust added for texture. Hyperion tumbles erratically as it orbits Saturn, probably owing to its irregular shape and the gravitational influence of Saturn’s biggest moon Titan.