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Skywatch for the week of October 5, 2020

On October 4, 1957, the world’s first artificial satellite, Sputnik, was sent into earth orbit from a launch site in the Soviet Union. A few months later, the United States successfully launched Explorer 1, and another satellite now revolved about the earth. Today, there are thousands of satellites in orbit; and every so often, you can see one passing overhead. It looks like a moving star, or like a light from a high-flying jet, but the satellite moves along at a pretty good clip, crossing the sky in only a matter of minutes, and yet you can't hear any sound coming from it. These satellites reflect sunlight down to the darkened earth, and so are visible for a couple of hours after sunset or a couple of hours before sunrise, a time when we are in earth's shadow, but the satellite is just outside it. Satellites typically travel from west to east, except for those in polar orbits which move along a north-south path.


Tue October 6, 2020 ROBERT GODDARD
Dr. Robert Goddard, the father of rocketry, was born on October 5th, 1882. When he suggested that rockets could take us to the moon, the New York Times announced that he was wrong, because everyone knew that rockets couldn’t work in outer space because there was no air for them to push against. But Goddard understood that a rocket’s exhaust did not push against the air; the action of the combustion in the rocket created the reaction of the exhaust pushing against the rocket itself (Newton’s Third Law.) In fact, rockets work even better in the vacuum of space than in atmosphere, as there’s no air to have to push out of the way. In 1926 he launched the first liquid-fueled rocket (before this, all rockets relied on solid, gunpowder-style-fueled propulsion.) The problem with solid-fuel rockets is that once you light them, they go until they run out of fuel. The advantage of liquid fuel is that you can throttle back the engines and obtain a great deal more control over the flight of the rocket.


Wed Oct 7, 2020 LAGRANGE POINTS Between the earth and the moon, or between the earth and the sun, or between any two masses, there are five Lagrange points.
Named for the mathematician Joseph Lagrange, these are positions in between objects, behind objects, and beside objects where the gravity is balanced, creating a “sweet spot,” meaning that anything in that position doesn’t have to work hard to stay there. For the earth and the sun, L1 is a million miles sunward, where SOHO, the solar observatory is currently parked; L2 is a million miles the other way – great for deep space observing, which is where the James Webb telescope will go. L3 is in the earth’s orbit, but 180 degrees away from our position. Since an L3 object would share our orbital speed, we wouldn’t be able to see it, the sun would always be in the way. But don’t worry - we’ve checked it out with spacecraft, there’s nothing there. L4 and L5 are also in our orbit, 60 degrees ahead of us and 60 degrees behind us. These are the two most stable Lagrange points.


The astronomer Harlow Shapley once suggested two possible ways that the world could end. In one scenario, the earth loses its forward momentum, and the sun’s gravity pulls our planet inward to a fiery destruction. Another theory supposed the opposite might happen, that the earth might drift outward and suffer a frozen death like Mars. Of course, both “fire and ice,” may be our ultimate fate. Five billion years from now, when the sun runs out of fuel, gravity will take over and collapse it. This will heat it up, and the sun will expand to become a red giant star, engulfing the inner solar system, including earth. Then, when the last bit of helium fuel is exhausted, the sun will collapse again, heating up, turning into a high energy white dwarf! But then, after a great long time, it will cool off to become a black dwarf. What’s left of the earth will continue to circle the dying sun in a dark, cold orbit. So, let’s make it a point, five billion years from now, to get off the planet!


Fri Oct 9, 2019 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!