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Skywatch for the week of July 8, 2024

Skywatch Monday 7-8-2024.mp3


An observatory was built in 1769 in Philadelphia, a couple of hundred feet south of Independence Hall. It was built so that astronomers could observe a transit of the planet Venus that year. Transits occur when either Mercury or Venus passes directly between the earth and the sun; using strong filters, we can safely see those planets as small, dark round dots against the sun’s face. Transits of Venus are rare; they occur in pairs every hundred and twenty years. Seven years after colonial astronomers saw this transit the observatory’s balcony made an excellent platform for the first public reading of the Declaration of Independence, on July 8th,1776. During the Revolutionary War, the Philadelphia observatory housed British troops who occupied the city. And not too many years after the end of the war, the observatory fell into disuse, and sadly, is no longer there.

Skywatch Tuesday 7-9-2024.mp3


Can you identify the twelfth largest constellation? It is bordered on the north by Ursa Major and Leo Minor; on the south by Hydra, Sextans, Crater the Cup and Virgo; on the west by Cancer the Crab; and on the east by Virgo again and Coma Berenices. We’ve discovered planets orbiting many of its stars. This part of space is also the source of a meteor shower which peaks in mid-November. Many beautiful galaxies are found within its borders, one of which is a favorite of mine – the hamburger galaxy. In myth, the Babylonian hero Gilgamesh fought it, and so did Hercules, who defeated it after a month-long battle. And it’s also associated with the prophet Daniel. This evening the waxing crescent moon appear nearby its brightest star Regulus. Can you name this constellation, the fifth sign of the zodiac? The answer is Leo the Lion.


Skywatch Wednesday 7-10-2024.mp3


On July 6, 1868, the American astronomer Henrietta Leavitt was born. She worked at Harvard Observatory, and while cataloging a class of stars known as Cepheid variables - named for the fourth-brightest star in the constellation Cepheus the King - Leavitt analyzed the light curves of various Cepheids. Variable stars change their brightnesses over time; this is caused by the star’s expanding and contracting as it reaches the end stages of its life. When the star expands, it becomes brighter, when it contracts, it dims a bit. Henrietta Leavitt discovered that there was a relationship: Cepheid variable stars that were intrinsically brighter, or larger, than others, took longer to go from bright to dim to bright again. This made it possible to figure out how far away distant galaxies were, and gave us a much larger measuring stick to determine how far away things are in the Universe.

Skywatch Thursday 7-11-2024.mp3

Thu Jul 11, 2024 FAREWELL SKYLAB

On July 11th, 1979 America’s first space station – Skylab - disintegrated when it re-entered earth’s atmosphere, its debris scattered across the south Pacific and Australia. Built from Apollo moon mission hardware, such as the Saturn 5 rocket’s third stage, it was launched in 1973. Over the next year, three different Skylab crews lived in it and made observations of the earth and the sun and the stars. And it provided lessons that would help us stay alive on future long duration missions, such as those aboard the current space station. There was even a racetrack reminiscent of the one seen in the movie “2001: A Space Odyssey”, where astronauts could run laps around Skylab’s inner circumference! One of my duties when I interned at the Hayden Planetarium was to provide daily updates on the anticipated re-entry time of Skylab. It was indeed a sad day when Skylab met its end.


Skywatch Friday 7-12-2024.mp3


We are now three weeks into summer. With the change of seasons also comes a change in the sky and its constellations. The sun has moved from Taurus the Bull into Gemini the Twins, rendering that part of the sky difficult to see. The great constellations of winter, such as Orion the Hunter and Taurus the Bull, can now only be glimpsed just before sunrise, near the eastern horizon. Springtime star patterns such as Leo the Lion or the Big Dipper, which were once at the top of our northern evening sky, have now slipped over into the west, supplanted by Boötes the Shepherd, Hercules the Hero and Virgo the Maiden. And new star groups appear in the east – Libra and Scorpius, and the three bright stars of the Summer Triangle. The sky wheels about us, and the summertime constellations take their places in the heavens above.