Skywatch for the week of May 10, 2021
Mon May 10, 2021 ANNIE CANNON’S OBAFGKM
99 years ago, on May 9th, 1922, astronomers formally adopted Annie Jump Cannon’s stellar classification system. Annie Cannon worked at the Harvard Observatory, where she sorted and catalogued stars by their spectra. When you look at the light of a star through a specialized prism, a spectroscope, you can see that within the rainbow spectrum of the star’s light there are thin gaps where the color is missing. These gaps result when the outer atmospheres of those stars absorb the light, and the spacing of the gaps can be matched up with similar lines made by gases on earth, which tells us what elements are present in those far-away stars – kind of a cosmic bar code. Cannon sorted the stars, and after some adjustments that had to be made because of things like high temperature ionization, resulted in a ranking of stars from hot to cool: O, B, A, F, G, K and M, which countless astronomy students have memorized by using this simple phrase – “Oh, Be A Fine Girl (or Guy,) Kiss Me!
Tue May 11, 2021 GENERAL RELATIVITY DAY
Today, May 11th, marks the 105th anniversary of the announcement of Albert Einstein's General Theory of Relativity. This 1916 posting supplemented his earlier work on "special relativity", which stated that electromagnetic energy, or light, travels at the same speed, whether you are moving toward the source of the light, or away from it. With general relativity, Einstein suggested that space and time are interwoven, and that space itself is curved, the amount of curvature depending on the gravity fields of massive objects like stars and galaxies. Planets don't follow orbits because the sun is pulling on them; rather, they revolve because the sun's mass makes a big dent in the fabric of space-time, and the planets travel like marbles rolling on the inside of a funnel. Our sun’s gravity field is so great that the starlight of distant stars are displaced if they venture too near it. It's all pretty deep.
Wed May 12, 2021 BERENICE'S HAIR
The Big Dipper is in our northern sky this evening. To the south of the dipper’s handle are some faint stars that form the constellation of Coma Berenices, or Berenice's Hair. This strange constellation is based on a true story. Berenice was the wife of one of the Ptolemies of Egypt. Just before a great battle, she promised to cut off her hair and offer it to the gods if Ptolemy should win. He did, and she did. Then somebody stole the hair from the temple - a classic case of hair today and gone tomorrow! Ptolemy was angry; he grabbed his men by the head and shoulders and told them to comb the palace until they found the hair; some of them tried to give him the brush-off, but one man made up a bald-faced lie when he pointed to this part of the sky and declared that Berenice’s hair had risen up to the heavens to commemorate the occasion. So as a result, Berenice's Hair is now a permanent constellation, all because of a great hair-raising battle from long ago.
Thu May 13, 2021 MOON AND MERCURY, VENUS
It’s very hard to see the planet Mercury; our innermost planet never strays far from the sun, so you can only get a glimpse of it either shortly before sunrise or shortly after sunset, and it’s always close to the horizon. But this evening, you’ll have a little help in locating this elusive world, because the new crescent moon will be nearby Mercury. Again, you will need a clear view toward the horizon, with no trees or buildings or clouds blocking your view. As twilight begins, look above the sunset and you should be able to find the moon, a very thin sliver of a crescent. As it gets darker, look just below and to the right of the moon, and you’ll find a star – but it’s not a star, it’s the planet Mercury! Now you have to be careful here, because the planet Venus is also nearby, a bit farther below the moon. It’s quite bright, and a beautiful evening star just by itself; but head back to the moon (and isn’t it high time we did?) and look for Mercury, our second evening star tonight.
Fri May 14, 2021 NAME THAT CONSTELLATION - MAY
Can you identify the thirtieth largest constellation? It is bordered on the north by Lynx the Bobcat and Auriga the Charioteer; on the east by Cancer the Crab; on the south by Canis Minor the Lesser Dog and Monoceros the Unicorn; and on the west by Orion the Hunter and Taurus the Bull. This constellation was created thousands of years ago, and its stars seem to trace out a long rectangle in the heavens. In the Middle East, these stars were seen as a stack of bricks, while in the American southwest, the Navajo regard it as the Place of Decision, where a hero paused to choose his peoples’ path into the sky country. In Italy, they represented Romulus and Remus, the founders of Rome. The Greeks named them Castor and Pollux, which are also the names of this constellation’s two brightest stars. Tonight the waxing crescent moon lies at the feet of these twin brothers, while the planet Mars is in the mid-section of the twins, to the west of Castor and Pollux. Can you name this star pattern, the third constellation of the zodiac? It is of course, the Gemini, visible in the southwestern sky after sunset.