Skywatch for the week of November 22, 2021
Mon Nov 22, 2021 DARKNESS WASTING TIME
By now I hope everyone has recovered from our semi-annual lurch in time. After more than half a year of Daylight Savings Time, we’ve finally returned to the more sensible Standard Time. Daylight Savings Time was implemented in the United States in 1918 by the Woodrow Wilson administration, and it has been with us pretty much ever since. Most astronomers I know really hate Daylight Savings Time. It's true that by setting our clocks ahead one hour, we can stretch out the afternoon and evening daylight periods, but for a stargazer, this can be a real nuisance. In the astronomy business, Daylight Savings Time is known as Darkness Wasting Time, because it makes us wait an extra hour for the skies to darken and let us see the stars. Now as nights get longer and daylit periods shorter, and a return to Standard time, at least for now we can get some serious observing done long before the midnight hour.
Tue Nov 23, 2021 EDWIN HUBBLE AND HARLOW SHAPLEY
Two 20th Century American astronomers were born this month: Harlow Shapley on November 2nd, 1885; and Edwin Hubble on November 20th, in 1889. Both these men made remarkable discoveries about our Universe. Shapley discovered that our sun and solar system were not at the center of the Milky Way Galaxy, but instead a little over halfway out, and that the Milky Way was much larger than anyone had previously thought, almost 600,000 trillion miles in diameter: big. But Shapley thought that the Milky Way was all there was to the Universe. It was Hubble who was able to measure the distance to the Andromeda Nebula, that is galaxy, some 15 million trillion miles away, which placed it far outside our own galaxy. Hubble also found evidence that the Universe was expanding, suggesting that everything began billions of years ago in what is now called, the Big Bang.
Wed Nov 24, 2021 THE MOON AND TIDAL LOCKS
Just as we experience daylit and dark periods on earth, so the moon has both day and night. But the moon spins slowly; a lunar day lasts two weeks, followed by two weeks of lunar night. As the moon orbits the earth, even though half of the moon is lit up at any time, we can’t always see the entire illuminated part. The moon’s rotation period matches its revolution, so it rotates once for every one orbit. This is called a tidal or synchronous lock, an effect of the earth’s tidal pull on the moon, which has slowed its rotational speed to match its revolution. Because of this we can only see half the moon (lunar nearside;) the farside of the moon (sometimes wrongly called “the dark side,”) can never be seen from earth. Or as Pink Floyd tells us, ”There is no dark side of the moon; matter of fact, it’s all dark!” But the sun lights up the dark side, sorry, farside, just as much as lunar nearside.
Thu Nov 25, 2021 WHY BUY A TELESCOPE?
You can spend lots of money buying a telescope and then be unhappy with the results. Before you buy one, ask yourself: what do you expect the telescope to do? If you want to see planets, nebulas and galaxies looking like they do in books and magazines, then you need the Hubble Space Telescope. We already have one of those, so you don’t have to buy another, just get the pictures, it’s a lot cheaper. Most small telescope views fall far short of the incredible images that we get from great observatories or space telescopes. So why buy a telescope? Well one of the principle joys of the telescope is the excitement of finding these objects in the sky, and knowing that they really are out there. A good starter telescope is a Newtonian reflector with a 6 inch mirror on a Dobsonian mount, which uses big one and a quarter inch eyepieces. Such a scope should cost between 200 – 400 dollars. Call me at 772 462 4515 for more free advice!
Fri Nov 26, 2021 BLACK HOLES PROPOSED
On November 26th in the year 1783, British scientist John Michell first proposed the existence of black holes, suggesting that there might be super-dense stars with powerful gravitational fields that could keep light from leaving them, rendering themselves invisible. This idea was far ahead of its time, coming as it did shortly after the American Revolution. But he was right, and only in the past several decades have we found evidence for these cosmic dead ends in space. There is a black hole above us tonight. Vega, Altair and Deneb, three bright stars that form the Summer Triangle are in the west sky this evening. We believe there's a black hole in the middle of the triangle – it’s called Cygnus X-1. We can't see it directly; these things are literally out-of-sight, but there is something there, because there’s an incredible amount of x-rays pouring out of this region, made, we think, by the black hole's gravity.