Skywatch for the week of October 11, 2021
Mon Oct 11, 2021 OLBERS AND HIS PARADOX
Heinrich Wilhelm Olbers was born on October 11, 1758. An amateur astronomer, he discovered the asteroids Pallas and Vesta in the early 1800’s, and suggested that the asteroid belt was the remnants of a destroyed planet (today we think it’s material that was never able to build itself into a planet, thanks to the gravitational effects of Jupiter.) But he is best known for Olber’s Paradox. He asked a simple question: "why is the sky dark at night?" Now that seems a bit silly - after all, the sky is dark at night because the earth rotates into its own shadow, what we call night. ”I know that,” he said. But if the universe is infinite in size, then that means there's an infinite number of stars out there. So no matter where you look, you'll eventually find a star - the sky should be ablaze with light! But it's not. This suggests that the Universe is perhaps not infinite, and that there was a definitive point in time in which everything began, and also that our Universe is expanding!
Tue Oct 12, 2021 MAGELLAN’S END, SEEING VENUS
On October 12th, 1994, the Magellan spacecraft sent its final radio signal. The next day, the probe was destroyed. It had accomplished its mission, radar-mapping 98% of Venus’ surface. But after four years in orbit, its fuel spent, NASA-JPL ordered Magellan to de-orbit and plunge into the Venusian atmosphere. Through the cloud-piercing radar instruments of the Magellan spacecraft, we discovered a varied surface of highland continents and lowland rolling plains. There are folded mountain chains, pancake-like volcanoes and great circular features called coronae, which were created by rising magma currents that periodically warp and destroy the crust. If you want to see the place where the Magellan spacecraft orbited and eventually was destroyed, look off to the southwestern sky this evening, around the time of sunset. There you will find a brilliant star-like object, appearing even before darkness sets in. That very bright “evening star,” is the planet Venus.
Wed Oct 13, 2021 INDIAN SUMMER, THE SEVEN SISTERS
The tiny dipper-shaped cluster of stars known as the Pleiades can be found in the eastern evening sky this month. In Greek mythology they are the daughters of Atlas and the sea nymph Pleione. To the Iroquois Indians, the Pleiades represented seven dancing maidens. At this time of year, the weather often turns pleasant, a respite from the approaching cold weather. The Iroquois said that long ago, there was a village where the people forgot to get ready for the cold times; Harvest Moon came and went, and still they danced and played. When the first frosts appeared, they realized their folly, and called out to the Great Spirit to aid them. Mannito granted them their wish: for ten days summer returned; the people gave many thanks, and prepared food for the winter. But by the shores of the lake, there danced seven sisters, who paid no heed. Faster and faster they danced, until the West Wind took them in his arms and carried them up into the sky, where they became stars.
Thu Oct 14, 2021 MOON, JUPITER AND SATURN
At sunset tonight, you’ll find the moon well-placed in the southern sky. Actually, you can see the moon long before sunset, a waxing gibbous moon, appearing as a pale egg-shaped object in the blue afternoon sky. Folks don’t expect to see the moon in the daytime sky, but there it is. Anyway, as darkness sets in, you should see a couple of bright stars nearby it. There’s a very bright one, just above and to the east of the moon. It’s actually the planet Jupiter. Jupiter is very bright, but there’s another, even brighter evening star, well off to the west, above the sunset, and as you’ve guessed, it’s another planet, brilliant Venus. But there’s still one more planet in the evening sky tonight, and it can be found just to the west, or to the right of the moon. It’s dimmer than Jupiter, but it has a slight yellow tint. Find it, and you’ll have found Saturn, among the stars of the constellation Capricornus, along with the moon and Jupiter.
Fri Oct 15, 2021 HOW MANY STARS?
How many stars are there in the Universe? Well, on a clear dark night you can see a couple of 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!