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Skywatch for the week of October 19, 2020


Can you identify the thirty-third largest constellation in the sky? It is bordered on the north by Ophiuchus the Serpent Bearer, on the south by Lupus the Wolf, Norma the Level and Ara the Altar, on the west by Libra the Scales, and on the east by Sagittarius the Archer and the Southern Crown. Its tail dips into the Milky Way, and there are many nebulae and star clusters within its borders. This constellation’s brightest star is Antares, a red giant hundreds of times larger than the sun. In the South Pacific it’s called Maui’s fishhook, while ancient Greek mythology identified it as the animal that killed the hero Orion the Hunter, and it is kept in check by Sagittarius’ arrows. Just a few thousand years ago the Romans turned its claws into Libra the Scales. Tonight the crescent moon rests above its head. Can you name this star figure, the eighth constellation of the zodiac? The answer is Scorpius, currently visible in the southern sky after sunset.


There’s a meteor shower going on right now. The Orionid meteors seem to come out of the constellation Orion, which is why they’re called the Orionids. The dust and debris that cause this shower have a distinguished pedigree – they’re from the tail of Halley’s Comet. This year the shower will probably be at its best after midnight, with most of the meteors appearing from then until dawn. But if that’s too late to stay up, then go out as late in the evening as you can to see some of these “shooting stars”. Protect yourself against mosquitoes, dress warmly, take along a lounge chair so you don’t get a stiff neck looking up at the sky, and most importantly, get away from any bright lights that might keep you from seeing a clear, dark sky. You won’t need binoculars or a telescope, just face toward the east and watch for these shooting stars – perhaps a dozen visible each hour. But if it’s cloudy, you won’t be able to see them as they burn up above the atmosphere’s cloud layer.


In colonial America, Benjamin Franklin was hoping to observe a lunar eclipse on the evening of October 21, 1743. Anticipation soon turned to dismay however, as an hour before the eclipse was to begin, clouds and rain blew in from the northeast, and treated his hometown of Philadelphia to a most violent thunderstorm. He was all the more surprised therefore, when his brother in Boston told him that they had also had a storm, but it happened after the eclipse, which he got to see. But the storm had come from the direction of Boston. How did it hit Philadelphia first? Franklin reasoned that this must have been some special kind of storm. He gathered together weather reports and found that the storm had moved up the Atlantic seaboard, moving counter to the local surface winds. And so Ben Franklin was the first person to discover the cyclonic nature of a hurricane, and thus turned an astronomical defeat into a meteorological windfall!


Subrahmanyan Chandrasekhar, born on October 19th, 1910, was the astronomer who figured out just how massive a star had to be in order to turn into a black hole. If a star is one and a half to almost two and a half times more massive than our sun, when it dies, it explodes and becomes a supernova. But if a star has over 2.4 times the sun’s mass, the final gravitational collapse is so powerful that the star doesn’t blow up – it blows in to become a black hole! The imploding star shrinks down to a singularity, a point of ridiculously high density. We can’t see black holes directly, but we know that they are out there, because as their gravity pulls matter in, accretion discs form, just outside the event horizon (the boundary where in order to escape the black hole, you have to go faster than the speed of light – an impossibility.) X-rays and other radiation are made by the collision of this in-falling matter; the escaping radiation reveals the presence of these “jaws” of outer space.


Friday Oct 23 DEATH OF TYCHO
“Let me not seem to have lived in vain.” These were the last words of the Danish astronomer Tycho Brahe, who after eleven bed-ridden days of suffering, died on October 24, 1601. Working before telescopes were invented, Tycho accurately measured the positions of stars and planets, proved that comets were objects in outer space, and believed that while some planets orbited the sun, the sun orbited the earth. A popular legend says that Tycho died because he didn’t go to the bathroom on time. He was at a banquet, and did not wish to insult his host by leaving early. As a result, his bladder burst, which killed him. In 1993, Brahe’s body was exhumed, and analysis of his hair seemed to show a lot of mercury; as an alchemist, had he accidentally poisoned himself? But a more recent autopsy shows that his mercury levels were almost in the normal range, supporting the opinion of the doctor who attended the astronomer as he lay dying; Tycho may actually have died from a burst bladder.