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Skywatch

Skywatch for the week of August 17, 2020

Mon Aug 17, 2020        HOW TO SEE A BLACK HOLE

In the summer evening sky, there are three bright stars high up in the east 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.

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Tue Aug 18, 2020         HELIUM DISCOVERED; SOLAR SAFETY 

On August 18, 1868, a new element was discovered – and it was found in the sun! During a total solar eclipse, astronomer Pierre Janssen used a spectroscope to break up visible light into its component colors, kind of like a prism, but with much more detail. In the sun’s spectrum he saw a series of dark absorption lines that had never been seen before. Janssen had found a new, unknown element. It was named after Helios, the Greek sun god. That’s right, helium was discovered in the sun before it was ever found on earth! A word of caution: don’t stare at the sun as it can blind you. Only with  proper solar filters, or during the brief moments of totality of a solar eclipse is it safe to view the sun; and if you never leave the United States, you won’t see a total solar eclipse until the year 2024.

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Wed Aug 19, 2020        AGE AND EDGE OF THE UNIVERSE

There have been many attempts to determine the age of the Universe by the means of refining the Hubble constant, the rate at which galaxies recede from the initial theorized Big Bang. According to many cosmologists – these are scientists who look at the really big questions in astronomy - the Universe is about 13.8 billion years old. Not everyone agrees with this estimate, but we are still talking about the likelihood of a very old, although not infinitely old, Universe. While cosmologists continue to search for the time when the Cosmos began, virtually no one is looking for the center or the edge of it. That’s because most astronomers agree that even if the Universe is finite in age and size, it is still unbounded. The Universe perhaps is like a great unending forest of stars and galaxies that curves back upon itself – with no defining edge, and therefore no center, for it is the edge that determines the center.

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Thu Aug 20, 2020         RAY BRADBURY

The science fiction and fantasy writer Ray Bradbury was born on August 22nd, 1920. He began his career by writing short stories for pulp magazines such as Planet Stories and Galaxy Science Fiction. His book, “The Martian Chronicles,” came out in 1950; it was a series of related short stories about the colonization of the planet Mars, something which is very much in the news these days. This evening the planet Mars shines low in the southeast, a very bright, slightly orange, “star”. We’ll be passing Mars in October at a distance of 38 million miles, so it will be getting brighter over the next couple of months. Bradbury envisioned terraforming Mars, also being discussed lately. While building pressure domes and living underground on Mars is achievable, trying to restore a viable Martian atmosphere is still well beyond our current technology. Well, like Bradbury, we can dream, and we can also gaze on Mars in Earth’s night sky.

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Fri Aug 21, 2020           PLACES IN THE SKY: AUGUST

Can you identify the second largest constellation? It is bordered on the north by Bootes the Shepherd and Coma Berenices; on the south by Hydra the swamp monster and Corvus the Crow; on the west by Leo the Lion and Crater the Cup; and on the east by Libra the Scales and Serpens Caput.  Planets have been discovered orbiting many of its stars, and a huge cluster of galaxies lies within its borders. In mythology this star figure is associated with the planting and harvesting seasons, and often portrayed as Persephone, daughter of the earth goddess Demeter. Sometimes this constellation represents Astraea, Winged Justice, who holds the scales of law, the constellation Libra. Tonight the waxing crescent moon can be found to the west of its brightest star, Spica, among a group of stars called, “the retreat of the howling dog”. Can you name this constellation, the sixth sign of the zodiac? The answer is Virgo the Maiden.