Watch These Videos
First, here is an introduction to the basic problem of measuring cosmic distances: the distances to things you cannot reach with a measuring tape, from relatively nearby objects like our moon and the other planets, to very distant objects, such as other galaxies. The simplest method, which is called parallax, is the main subject of this video, but it contains hints about other methods that build on what we learn from parallax. These methods together are called the cosmic-distance ladder. Together, the methods allow scientists to measure how far away are the most distant objects we can detect, telling us, among many other things, the size of the visible universe. (For a list of the methods, see the last image on this page.)
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The Cosmic-Distance Ladder
The next video, the first of a series of short films (4 to 12 minutes), introduces half a dozen methods of finding cosmic distances. Succeeding films in the series take up each method in detail.
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Watch as many of the videos in this series as interest you, using this full list of the cosmic-distance videos. These videos move slowly, especially compared to Crash Course, but the explanations are very clear and accurate. Watch enough to get the flavor of the difficulties and uncertainties of some of the methods. You will also learn or review many very basic ideas in astronomy, all in a unifying context that makes for an effective learning experience. The unifying context or theme is this single very important problem: the problem of how to measure distances on all scales.
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This final video in the series reviews all methods, and emphasizes the uncertainties in each, as well as in our overall knowledge of cosmic distances.
If you like these short lectures and this teaching style -- low-tech but very clear and organized explanations, you might enjoy more videos by PhysicistMichael at his YouTube channel.
The beleaguered lecture is not dead.
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The Language of Science is the Language of Uncertainty
Science is a process of building reliable knowledge of the natural world (see What is Science?). A fundamental element of science is complete honesty about what we know and how accurately we know it. In all of these videos, notice the language of uncertainty about our knowledge of the cosmos. No one is trying to sell you anything, or to exaggerate how much we know, or to lie to you in order to get re-elected. Scientists are good at suspending judgment about what lies beneath uncertainty, until they find ways to reduce uncertainty and draw firmer conclusions. Politicians have often said that they can't get a straight answer from scientists. That's because truly scientific answers to questions contain honest assessments about uncertainties, and uncertainties are always present. When someone speaks in certainties, you would be well advised to doubt either their knowledge or their honesty.
