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Skywatch for the week of May 3, 2021

Skywatch 5-3-2021-PG1-SWMO.mp3


Divide the year up into four parts or quarters. Each quarter is marked by the beginning of a new season. The quarter days of Summer and Winter are known as solstices, when the noontime sun reaches its highest or lowest altitude in the sky; while during the equinoxes of Spring and Autumn, nights and days are of fairly equal length. Now divide those seasons in half and you get cross-quarter days, the midpoints of each season. May 1st marks the cross-quarter day for Spring, called Beltane in the old Celtic calendar. In traditional maypole dances, everyone moved clockwise around the maypole, mimicking the sun’s motion across the sky through the day. At the beginning of spring, the stars of the constellation Virgo, the springtime maiden, appeared in the east after sunset. Now Virgo is well up in the southeastern sky, and at summer’s beginning it will be high in the south. But as autumn approaches, Virgo will sink into the west, and we’ll lose sight of it as we move toward winter.

Skywatch 5-4-2021-PG1-SWTU.mp3

Tues May 4, 2021 ASTRO QUIZ 1

Here’s a small astronomy quiz: What’s the closest planet to the sun? What do we call the seven brightest stars in the constellation Ursa Major, the Great Bear, which is overhead in our sky this evening? And what’s the other name for the Seven Sisters, who are low in the west? Which is bigger – a galaxy or a solar system? What did Clyde Tombaugh discover? Here are the answers. The planet Mercury is closest to our sun, at a mere 36 million miles. Seven stars form the back and the tail of the Great Bear, but we know them better as the Big Dipper, upside down in our northern sky tonight, while the Seven Sisters are called the Pleaides. Solar systems are billions of miles in diameter, but galaxies are hundreds of trillions of miles across – much bigger, and what’s more, galaxies contain hundreds of billions of solar systems. Lastly, Clyde Tombaugh discovered Planet X, back in 1930 when he was just 24 years old. It was later named, Pluto. Can I still call it a planet? Guess so.

Skywatch 5-5-2021.mp3


The Eta Aquarid meteor shower is at peak activity tonight. These particular meteors are bits of dust from Halley’s Comet, plunging into our atmosphere, where they are vaporized, heating up the air around them and causing that momentary streak of light you see in the night sky. Most meteor showers are best after midnight, and this one’s no exception, at least until the old crescent moon rises a couple of hours before dawn. If that’s too late for you, then go out as late in the evening as possible. If skies are free of interfering clouds or streetlights, face east and look up toward the top of the sky. Dress warmly, protect yourself against mosquitoes, get away from the bright lights, and use a lounge chair so you can recline and enjoy the shower. Meteor showers are not like fireworks displays – sometimes you can go for an hour and not see anything; but every so often, you’ll be rewarded by the appearance of a streak of light in the sky, a shooting star or meteor.

Skywatch 5-6-2021.mp3


Stars are formed out of great clouds in outer space called nebulae or nebulas. Stars shine by light produced through nuclear fusion in their cores, as hydrogen is converted into helium at a temperature of millions of degrees. In time the hydrogen is used up, and the star begins to die. The less massive the star, the longer it lives, the more massive, the shorter the lifespan. There are small, cool red dwarf stars shining today that burned when the Universe was young. Our own sun has been producing light for five billion years, and will shine for another five billion years. Blue giant stars will only last for a few hundred million years at most – the more massive the star, the more profligate the energy and matter loss. When stars like our sun die, they don’t explode; they just shrink, heat up and brighten becoming a red giant star, then collapse down to a white dwarf, and then slowly go out. But the biggest, most massive stars explode as supernovas, or implode to become black holes.

Skywatch 5-7-2021.mp3


Halfway up in the eastern sky this evening there is a star that doesn’t belong here – an interloper. It’s Arcturus, the fourth brightest star in our night sky, and it’s a visitor from beyond the galactic disc. Arcturus is an old red giant, and while most of the stars you see up there are moving along with our sun, traveling in nearly circular orbits about the hub of our Milky Way galaxy, Arcturus moves at a sharp angle to all the others. Our sun and planets are embedded within the Milky Way’s disc, and our orbit carries us along in the plane of the disc as we revolve. But Arcturus is plunging along an elliptical path through the disc from up above. Tonight, it’s a mere 37 light years away, that’s a bit more than 200 trillion miles, but in a half million years or so it will have shot down below us, and its ever-increasing distance will make it too dim to see without a telescope. So, enjoy viewing Arcturus while it’s still in the neighborhood!