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Skywatch for the week of October 12, 2020



Asteroid belts in our solar system range from inside the orbit of Venus all the way out to Neptune; but most of the asteroids can be found between Mars and Jupiter. They are leftover remnants from the solar system’s formation, and have been heavily battered by countless collisions over the years. The gravity field of Jupiter does have a disrupting influence on this part of space, which most likely has kept the asteroids from getting together. It was long feared that the asteroid belt would pose a hazard to spacecraft. But In October of 1972, the unmanned spacecraft Pioneer 10 found itself deep within the belt. When it emerged in February 1973, it demonstrated that navigating the belt was possible. Since then, many more spacecraft have safely made the journey: Pioneer 11; Voyagers 1 and 2; Galileo; Cassini, Juno and New Horizons. There’s a great volume of space between most of the rocks, and the chances of being
hit are slim.


Tue Oct 13, 2020 ALL TO SCALE
See if you can put these things in the correct order, according to size, going from the smallest to the largest: solar system; Jupiter; earth; Milky Way Galaxy; the sun; the Andromeda Galaxy; Pluto. Well, Pluto is the smallest, smaller than our moon, so small that some astronomers don’t even like to call it a planet, but Pluto doesn’t mind – it’s got five moons of its own! After Pluto comes our earth, over five times larger in diameter than Pluto. Then there’s Jupiter, which at 88,000 miles, makes it about 11 times wider than earth. Then there is the sun; a thousand Jupiters could fit inside the sun, or a million earths! The solar system comprises the sun, many planets (8 or 9, depending on what you call Pluto), comets, asteroids, electromagnetic fields and a lot of dust. The solar system is only one of billions however, that makes up the Milky Way Galaxy, which is over 600,000 trillion miles across! But 2 ½ million light years away there’s an even bigger galaxy beyond called Andromeda – it’s about a quadrillion miles in diameter!


Wed Oct 14, 2020 HOW MANY STARS?
How many stars are there in the Universe? Well, on a clear dark night you can see a couple thousand up there above you. The best estimates of the number of stars in the Milky Way suggest there are over 200 billion stars in our home galaxy. Beyond the Milky Way there are other galaxies, hundreds of billions of them, each containing billions or trillions of stars. So, how many stars? Here’s a good way to get an idea. Next time you’re at the beach, count the number of grains of sand you can hold in your hand. You’ll be at it a while; there’s roughly 10,000 sand grains in each handful. Now count all the grains of sand on the entire beach. Follow that up by counting all the grains of sand on all the beaches of Florida, and then for extra credit, count all the grains of sand on all the beaches of the world. There are more stars than that in our Universe. Of course, if those stars have planets that have sandy beaches, that’s really a lot of sand!


Most department store telescopes are refractors. A refractor has a large glass lens at the front end, usually two or three inches across. You can also find reflecting telescopes or reflectors in department stores. A reflector has a large mirror, usually between 3 and 10 inches, mounted in the bottom of the tube. Reflectors typically cost less than refractors, because mirrors are cheaper to make than lenses. So the reflector is a better buy; you can get a larger, or wider telescope for the same money. And the wider the mirror, the more light it can gather, which means more magnification. A good rule of thumb is fifty power for every inch of aperture. If a scope has only a three-inch lens or mirror, then you really should only expect it to magnify up to about a hundred and fifty power – after that, the image looks dim and fuzzy. Buy a reflector that has a mirror at least four inches to six inches across. That will give you the ability to magnify images up to 200 power or more.


Very few of the constellations look like what they're supposed to. Folks long ago who made up these constellations had a lot of imagination, but they didn't necessarily see the pictures either. They'd just name a bright star or group of stars after a hero or an animal, or a monster, and use those stars to tell their children stories about their adventures - in that way, the stories were remembered as myths centuries after they were first told. There are 88 official constellations today, decided upon by astronomers in 1930. Now in the ancient world of the Mediterranean and Middle East, there were less than sixty constellations, owing to a lack of knowledge of stars to the south that were never seen from those latitudes, and also to the creation of many more star figures in the 17th century, some of which were preserved, like Grus the Crane and Monoceros the Unicorn, and some of which were later discarded, such as Bufo the toad, Felis the Cat and Noctua the night owl.