Mon Jan 20, 2025 THE PLEIADES
Near the top of the sky this early evening, you’ll find a small, distinctive group of stars known as the Seven Sisters. Even with street lights shining, you can find them, although the serious light pollution problems we experience here reduces the Seven Sisters down to just two or three, or possibly they may look like a little smudge overhead. But if you can get away from the bright lights, you’ll see between six to eight stars here, arranged in a very tiny dipper shape. In Greek mythology, the Seven Sisters were the Pleiades, the daughters of Atlas, on whose shoulders the world rested. Binoculars aimed at the Pleiades will reveal over a dozen stars, and astronomers have counted hundreds of stars in this open cluster.
Tue Jan 21, 2025 ROBERT FROST AND CANIS MAJOR
The American poet Robert Frost was a keen observer of the world and nature, capturing the simple majesty of the Universe. In his poem, The Star Splitter, he begins, “You know Orion always comes up sideways,” as indeed he does, first the forward shoulder and leg, then the hunter’s belt, and lastly the trailing shoulder and knee. Orion can be found in the southeast sky after sunset. If you trace the stars of his belt downward, you will find the star Sirius in the constellation of the Big Dog, Canis Major, and Frost wrote a poem about this too, placing Sirius in the dog’s eye: “The great Overdog That heavenly beast With a star in one eye Gives a leap in the east. He dances upright All the way to the west And never once drops On his forefeet to rest.” Because of the earth’s rotation, Canis Major does move across the sky just the way Frost describes it.
Wed Jan 22, 2025 WHERE’S THE MOON?
Did anyone happen to see the moon yesterday evening? I don’t think so, because the moon, now in the third quarter of its orbit about our planet, didn’t rise until the midnight hour. That moon gets around, constantly changing its location in the sky. It takes the moon about a month to go once around the earth, in an almost circular orbit. Now since a circle contains 360 degrees, then the moon must drift eastward through about 13 degrees of angle every 24 hours. The full moon, which is opposite the sun, rises at sunset. The third quarter moon then rises at midnight, and sets at noon. So if you want to see the moon this week, either go out after midnight – or look for it in the daytime sky during the morning hours, as it wanes toward its old crescent phase.
Thu Jan 23, 2025 ARISTOTLE AND THE EARTH’S MOTIONS
The Greek philosopher Aristotle argued that the earth did not rotate, because if it did, there would be great winds sweeping across the planet. Had Aristotle ever gone on an ocean voyage, he could have discovered these trade winds, which flow east and west due to the earth’s spin. Aristotle also said the earth didn’t go around the sun, because if it did, we’d see the stars exhibit parallax – that’s when you see something not too far away shift against a distant background when you look at it from two different places. The closer a star is to you, the greater the parallax. So nearby stars ought to shift position when we look at them from either end of the earth's orbit. Since they don't seem to do this, then the earth doesn't move. Either that, or those stars must be really, really far away. And as it turns out, they are!
Fri Jan 24, 2025 THE GREAT ORION NEBULA
A medium-power telescope can show you four tiny-looking stars buried within the Great Orion Nebula. These stars arranged in the geometric form of a trapezoid, are called the Trapezium. The brightest of these stars lights up the cloud, and ultraviolet radiation ionizes the nebula gas, illuminating it like a giant neon sign. The gas is mainly hydrogen and helium, but it contains a whole chemistry set of elements and compounds in smaller amounts too. The Orion Nebula is about 1300 light years, or 7,800 trillion miles away. So it’s not exactly next door. The cloud is trillions of miles across, and inside it, stars are being made as gravitational contraction heats the hydrogen and helium in the cloud. With the Hubble and the Webb space telescopes, we can even see places where solar systems are forming.
