Skywatch for the week of December 13, 2020
Mon Dec 14, 2020 HOW TO IDENTIFY A METEORITE
Here’s a short list for identifying a meteorite: Is it unusually heavy for its size? Do magnets stick to it? (even rocky meteorites will have some magnetism.)Does it have a fusion crust? This is a very thin blackish coating caused by the heat of entry? If it’s metallic, does it have a spatulate texture (feels like thumbprints in semi-hardened butter)? Does it have lots of vesicles (holes on the surface, typically from escaping gas)? Does it have visible crystals or fossils? If you said yes to numbers 1 – 4, then there is a possibility it is a meteorite. If you said yes to numbers 5 or 6, then it isn’t a meteorite but a meteorwrong, usually man-made iron slag. Iron meteorites are typically made of iron and nickel. They’re easier to identify than stony meteorites, as they really do have an out-of-this-world appearance. Stony meteorites tend to look a lot like rocks you’d find in your driveway. But they do attract a magnet!
Tue Dec 15, 2020 INERTIA, MOTION AND ACCELERATION
Inertia is the tendency of things at rest to remain at rest, and of things in motion to remain in motion, unless acted on by an outside force. In the case of the moon orbiting the earth, the moon's inertia carries it in a straight line, which is at a right angle to the pull of the earth's gravity. The continuing resolution of these two motions results in a curved path around the earth. If something is moving (and everything is moving in some way in this universe,) then it’s either moving at a constant velocity along a straight-line path, or it’s speeding up, or it’s slowing down, or its path is changing. Any change in the speed or direction of an object’s motion is called acceleration. If you go faster, you’re accelerating. If you slow down, you’re also accelerating, but negatively (this is called decelerating.) And if your path turns left or right, up or down, that’s accelerating too. So next time you make a hard turn around the corner, just remember, it’s acceleration at work!
Wed Dec 16, 2020 NAME THAT CONSTELLATION/JUPITER AND SATURN
Can you identify the 40th largest constellation? It is bordered on the north by Aquarius and Aquila the Eagle; on the south by Microscopium and the Southern Fish; on the west by Sagittarius; and on the east by Aquarius again. It contains the globular star cluster M30. This constellation lacks brilliant stars, but a scattering of 2nd magnitude stars trace out a kerchief or wedge shape. In Greek mythology it represented Pan, one of the nature gods, who taught people how to play musical wind instruments, including the flute, and the conch, a favorite of Floridians. Tonight the new crescent moon will be among its stars, plus the planets Jupiter and Saturn, which will be very close together, but not as close as next week! Can you name this star figure, the tenth constellation of the zodiac? The answer is Capricornus, the Sea Goat.
Thu Dec 17, 2020 SUMMER TRIANGLE IN WINTER/THE NORTHERN CROSS
Three bright stars – Vega, Altair, and Deneb - form a large triangle in the heavens; and as they’re found high overhead in summertime, are called the Summer Triangle. Each star marks its own constellation: Vega is in Lyra the Harp; Altair is in the wing of Aquila the Eagle; and Deneb represents the tail feathers of Cygnus the Swan. It’s often difficult to recognize these old fanciful star pictures, so sky watchers have come up with easier shapes to find. In the constellation of Cygnus the Swan, there is a simpler pattern called the Northern Cross. The tail of Cygnus, the star Deneb, marks the top of the cross; while the bird’s beak, the star Albirio, is at the foot of the cross; and the wings of Cygnus form the crosspiece. During early evenings in December, the Summer Triangle has moved toward the west, and the Northern Cross now stands upright on the west horizon after sunset. Now two planets can be found south of the triangle – Jupiter and Saturn.
Fri Dec 18, 2020 WINTER’S BEGINNING AT NEWGRANGE
There’s an archaeological site in Ireland called Newgrange, but there isn’t anything new about it – in fact, it’s literally as old as the hills, being a hill itself. Five thousand years ago, a great many people went to a lot of trouble to build this giant earth mound, over an acre across, and surrounding it they set up great stones, etched with intricate swirls and other megalithic designs. Ancient tomb, ancient temple, Newgrange probably served both these functions. And like the Great Pyramid of Khufu or the Giant’s Dance known as Stonehenge in England, Newgrange is astronomically aligned. For a few days before and after the winter solstice - the beginning of winter - sunlight travels through a roof box or window over the main doorway. The shaft of sunlight travels all the way down a long, narrow corridor, until it lights up a small chamber at the center of the mound. It happened long ago, and it happens now.