Mon Jul 4, 2022 EARTH AT APHELION
On this 4th of July, our planet just reached a place in its orbit called aphelion – it happened about an hour before midnight last night. Because the earth’s orbit is slightly elliptical, we are sometimes a little closer to the sun than at other times. The near point is called perihelion, and the far point is known as aphelion - that’s where we are right now. So how come we're having summer? Well, it’s summer now where we are, but winter has just begun for folks south of the equator. Temperature changes occur because our planet is tilted over a little, about 23 and a half degrees, from straight up and down. Right now, our hemisphere is leaning inward, which puts the sun higher in our sky, and causes summer; in the winter the top half of earth leans away from the sun, putting it lower in our sky, which cools things down. During tonight’s fireworks, you might also see the waxing moon up there, in the constellation Leo the Lion.
Tue Jul 5, 2022 NAME THAT CONSTELLATION – JULY
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. Its brightest star, Regulus, the king star, marks its heart. We’ve discovered planets orbiting many of its stars as well. This part of space is also the source of a meteor shower which peaks in mid-November. Many beautiful galaxies are found in this part of the sky, 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 moon can be found along its eastern border. Can you name this constellation, the fifth sign of the zodiac? The answer is Leo the Lion.
Wed Jul 6, 2022 HENRIETTA LEAVITT
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.
Thu Jul 7, 2022 TANABATA DAY: VEGA AND ALTAIR
Today is Tanabata Day in Japan, marking the reunion of the weaver princess and the cowherd. In this ancient story, the Sky Emperor’s daughter, Orihime, loved a herdsman, Hikoboshi. The emperor separated them by the great celestial river Amanogawa, so that they would not neglect their work. Orihime became the star Vega, and Hikoboshi is the star Altair - both these stars are well-placed in the eastern sky after sunset tonight. The river Amanogawa is the Milky Way, which when the skies are dark, you can see runs between these two stars. But on the seventh day of the seventh month, if skies are clear, magpies gather and with their wings form a living bridge across the Milky Way, so Orihime and Hikoboshi can be together once more. Part of a traditional poem recited at this time goes, “the stars twinkle on the gold and silver grains of sand... The stars twinkle, and there they will watch us.”
Fri Jul 8, 2022 DECLARATION OF INDEPENDENCE
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 this day, July 8th, in the year 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.