Atoms are made of electrons, protons and neutrons. Protons and neutrons are in turn made up of quarks. These are just some of the elementary particles that make up the foundation of modern particle physics. But how do we know about these particles when we can’t see atoms directly, much less their constituents? One of the early methods was through a device …
Island Universe
The visible universe is vast. It is 93 billion light years across, and contains more than 100 billion galaxies. The average galaxy contains about 100 billion stars, and untold numbers of planets. Yet a century ago there was serious doubt among many astronomers that the universe was much more than 100,000 light years across. Arguments about whether the universe was small or large became known as the Great Debate.
A Shapley Galaxy
In the 1700s, William Herschel mapped the distribution of visible stars to determine the shape our galaxy. The result was a rather irregular distribution, and while Herschel had no way to determine the center of the Milky Way, he assumed the Sun was near the center. It was Shapley who, in 1918, demonstrated the Sun was not at the center of the Milky Way.
Bok Globules
Bok globules are small, dense clouds of gas and dust, typically only about a light year across. They are thought to be dust clouds undergoing the early stages of gravitational collapse, on their way to becoming a stellar nursery. Since they are in the early stages of gravitational collapse, they haven’t formed any protostars to start generating heat. So they tend to be very cold as well as dense, meaning they don’t emit much light on their own.
If It Ain’t Got That Swing
A pendulum is a remarkably simple device that can be used in a range of scientific experiments. It can be used to measure the Earth’s rotation, for example. It can also be used as a timing mechanism. The period at which a pendulum swings depends upon the distribution of mass throughout the pendulum (known as the moment of inertia) and the distance of the swing point from its balance point (center of mass). The period also depends upon the acceleration of gravity, known as g. Because of that you can also use a pendulum to measure Earth’s gravity.
High Stakes Lab
In my introductory physics courses, I occasionally implement what I call “high stakes labs.” Take a set of measurements for a devices such as a ball launcher, use those results and your knowledge of physics to predict an outcome (such as where the ball will land) and then test your prediction. The catch is that the grade for the lab depends upon the accuracy of your prediction. It is stressful and challenging, but it demonstrates a common aspect of science and engineering. You can’t simply look up the answer in the book. You have to test your ideas in the real world.
Just a Phase
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.
Step by Step
In the 1860s James Clerk Maxwell published a set of elegant and beautifully subtle equations now known as Maxwell’s equations. Maxwell’s equations describe charges and magnets not by the forces between them, but by their fields of electricity and magnetism. Thus, a charge is surrounded by a field of electricity, a field that other charges can detect. Charges possess electric fields, and charges interact with the electric fields of other charges. Likewise, magnets possess magnetic fields, and interact with magnetic fields.