Yesterday I mentioned that after discovering the moons of Jupiter, Galileo went on to observe the phases of Venus, which further reinforced the idea that the Earth moved about the Sun. So just how do phases of a planet prove it revolves around the Sun?
Moons of Galileo
In the first few months of 1610, Galileo Galilei pointed a small twenty-power telescope at Jupiter. What he observed changed the way we understood the universe.
With his telescope, Galileo saw what appeared to be three faint stars in a straight line near Jupiter. The next evening he saw what appeared to be the same three stars, but it seemed Jupiter had moved in the opposite direction to its expected motion. Within a few days it became clear that Galileo wasn’t observing the motion of Jupiter relative to some faint stars, but rather these stars were moving along with Jupiter.
Wish Upon a Star
In the early 1900s there was much debate over how our solar system could have formed. One idea was the nebular hypothesis, made popular by Pierre-Simon Laplace in the late 1700s. In this model stars and planets formed together from a primordial cloud of gas and dust.
Father and Son
William Herschel was an astronomer of the 1700s and early 1800s. He is most famous for his discovery of the planet Uranus. But Herschel made several other important discoveries, including work on double stars, showing that some of them (what we now call binary stars) orbited each other under gravitational attraction. He also discovered infrared light, by passing sunlight through a prism, holding a thermometer just beyond the red light of the spectrum, and demonstrating that the thermometer was heated by in invisible light we now call infrared. He was the father of one son, John.
Tradition
Growing up, my father was a loving but strict parent. To this day I address my elders as Sir or Ma’am as easy as breathing. My father encouraged me to learn about crop rotation and animal husbandry, but those didn’t hold much interest for me. I worked the farm as required, but didn’t look forward to it with fondness. I’d much rather stand in the field outside our house at night and look at the stars.
Seeing Red
Ever since Henrietta Leavitt discovered the period-luminosity relation for Cepheid variable stars, and Edwin Hubble used her work to demonstrate the relation between the redshifts of galaxies and their distances, we’ve had a pretty good idea that the universe was expanding. Since then we’ve gathered much more evidence on the connection between redshift and cosmic expansion, including redshift observations of distant supernovae that show the universe is undergoing cosmic inflation due to dark energy. While cosmic expansion is now well established, there have been some interesting mysteries along the way. One of these involves some seemingly strange behavior of quasars.
Signs and Portents
In 1066 a comet appeared in the sky, larger than Venus, and unusually bright. Like many comets, its appearance was taken as an omen. This happened to be the same year as the Battle of Hastings, in which the Anglo-Saxon King Harold II clashed with Duke William II of Normandy in a battle which sealed the Norman conquest of England. After the battle it became clear that the comet was an omen of William the Conqueror’s victory, which is commemorated in the Bayeux Tapestry. The comet is included in the tapestry, as you can see.
Legacy
Marie Skłodowska-Curie was a pioneer in the study of radioactivity. She in fact coined the term. She developed a method for isolating radioisotopes, and discovered two elements (radium and polonium). She worked on radiation therapy of tumors, and developed established military radiological centers during World War I. She is the only person ever to have won a nobel prize in two scientific fields (Physics in 1903, and Chemistry in 1911). She also happened to be the mother of two daughters.
Star Light, Star Bright
The Sun is a star like many others. It is special to us because it provides Earth with light and heat, but on a cosmic scale our Sun is an average, rather smallish star. How we came to understand this fact is a story with origins in the ancient past.