Mon June 26, 2023 HEBER CURTIS
The American astronomer Heber Curtis was born on June 27th, 1872. He found strong evidence that the Milky Way was but one of many countless galaxies, what he called “island universes” in outer space. In 1920 he revealed that he had found novas, stars that periodically brighten and dim, nestled among many spiral nebulas. Because they were very dim, he calculated that these novas were millions of light years away – too distant to be within the borders of our own galaxy. He was right! Curtis studied and photographed many nebulas and galaxies, discovered a jet of matter shooting out from the giant elliptical galaxy M87, (we now know it is powered by an enormous black hole at the galaxy’s core), and carefully observed nearly a dozen solar eclipses in his career. A deeply spiritual man, he declared, “The more I know of Astronomy, the more I believe in God.”
Tue June 27, 2023 LOOK-BACK TIME
If you can manage to live a full century, go outside at night on your 101st birthday and look at the star at the end of the handle of the Big Dipper, in the northwest this evening. The light from that star, Alkaid, left there the day you were born – this distance measurement comes from the Hipparcos space satellite. Now go farther out: in the south is the star Antares, 500 light years away. If it went supernova today, we wouldn’t know about it for another 500 years. It takes light time to travel across the Universe. This phenomenon, Look Back Time, means that the farther something is from us, the older it is. So when we look at the Andromeda Galaxy, 2.5 million light years away, it’s what that galaxy looked like 2 and a half million years ago. What does it look like now? Not sure, but I’ll know, in about 2 and a half million years!
Wed June 28, 2023 PLANET SYMBOLS
Planet positions are often marked on star charts with a symbol. Each symbol is based on some aspect of that planet. Mercury, the messenger of the gods, has a walking stick symbol with two snakes wrapped around it (Yeah, that’d make me walk faster too.) A circle on a letter T makes a hand mirror - that’s for beautiful Venus. Mars, god of war, is symbolized by a shield and a spear. A stylized lightning bolt is the symbol for Jupiter, ruler of the sky. Saturn, a harvest god, has a scythe. For Uranus, it looks like somebody jammed a Mars symbol onto a sun symbol; it’s probably got something to do with sex, but this isn’t that kind of a program so let’s move on. The moon’s symbol looks like a crescent moon, while the sun is a dot inside a circle. Neptune is the king of the sea, so he bears a trident; and Pluto's is "P" and "L" combined. Can we talk about Pluto as a planet? Well, it’s got a symbol, so, yeah!
Thu June 29, 2023 ERATOSTHENES MEASURES THE EARTH
In late June, in the year 240 BC, the astronomer Eratosthenes calculated the size of the earth. He did it by using the changing angle of sunlight at different latitudes in Egypt. Eratosthenes made two assumptions: 1. the earth is round; 2. the sun is far away, so its rays fall parallel across the whole earth. At Alexandria, the sun is about 83 degrees, or 7.2 degrees off the zenith) at noon on the first day of summer. 500 miles to the south was a town called Syene, where on the same day, the sun’s image at noon could be seen reflecting off the water at the bottom of a deep well. There the sun was at 90 degrees altitude, directly overhead. The Alexandria - Syene distance must therefore be 7.2/360th, or a fiftieth of the earth’s circumference. Now Syene was 500 miles away, so he multiplied 500 by 50, and got 25,000 miles for an answer. He was off by a hundred miles – “pretty good work for 2,263 years ago!”*
*Carl Sagan quote from “Cosmos”
Fri June 30, 2023 TUNGUSKA
Several years ago, an early morning fireball lit up the sky over Chelyabinsk, Russia. Shock waves from the impact shattered windows, injuring over a thousand people. Now this was not the first time such a thing had happened. Back on June 30th, 1908, something really big blew up in the atmosphere above the Tunguska region in Siberia. Eyewitness reports sound a lot like the Chelyabinsk event. A brilliant blue light, like a second sun, flashed across the early morning sky. It was followed by a sonic shock wave that broke windows, killed wildlife, knocked people to the ground, and shook the earth. The Chelyabinsk impactor was a rock over fifty feet across, which broke apart about ten to 15 miles above the surface. The total energy of the blast was roughly equal to that of dozens of atomic bombs. The Tunguska blast was at least five hundred times more powerful.
