Unafraid of the Dark
Study Guide for Episode 13
Episode 13: Unafraid of the Dark
People
• Martin Behaim made the oldest surviving globe, giving us a summary of what what known about Earth's geography just before Columbus's voyage to what we know now as the Americas.
• Viktor Hess discovered cosmic rays, developed new technology for detecting them, and showed that they originate from outer space.
• Vera Rubin's careful astronomical studies on the galaxy rotation problem confirmed the existence of dark matter, as postulated earlier by Fritz Zwicky. Rubin's evidence for dark matter was by far the strongest evidence up to that time.
• Fritz Zwicky's contributions make him, in Tyson's words, "the most brilliant man you've never heard of." His original ideas include supernovae, neutron stars, gravitational lensing, and dark matter.
Ideas
• Dark matter and dark energy. Only 4.9% of the mass and energy of the universe is visible to us (so-called ordinary matter). The remainder includes 1) matter that we see only by its gravitational effects (dark matter, 26.8%), and 2) energy that we see only by its effects on the rate of expansion of the universe (dark energy, 68.3%). In both cases, the term "dark" simply means mysterious.
• Where do cosmic rays come from?
• A universal standard unit of time. How would you express time intervals to an alien? In the Voyager messages, all references to intervals of time (such as the frequency of pulsars and the playback speed of the Voyager Golden Record) are based on frequency of a specific energy that a free hydrogen atom can absorb or emit. That frequency is (in case you were wondering) 1,420,405,751.7667±0.0009 Hz (Hz = cycles per second), and is called the hydrogen line, or the hydrogen hyperfine splitting constant. Waves of this frequency are about 21 cm in length, and lie in the microwave region of the EM spectrum. This spectral line is a fundamental property of hydrogen, the universe's simplest atom, and is also a frequency of electromagnetic radiation that pervades the universe and is not blocked by clouds of interstellar dust. It is hard to imagine that this fundamental constant would not be recognized by any intelligence that recognizes the basic physical laws of the universe.
• Standard Candles (recycled from Episode 8): Cepheid variables and Type Ia supernovae are called standard candles. Their inherent brightness is known (because of the physics that produces their light), and so their apparent brightness can tell us their distance (their light dims with the square of their distance). They help scientists measure absolute distances to stars and galaxies.
• How far away is that star? Different methods of measurement are used for stars that are near (closer than 500 light years), at intermediate distance (out to tens of millions of light years), or very far away (in other galaxies). The methods rely upon, respectively, on parallax, Cepheid variable stars, or Type-Ia supernovae (an example shown during this episode). Click HERE to learn more. To learn even more, look up each method in Wikipedia: parallax ---- Cepheid variable stars ---- type Ia supernovae. Look HERE for a pretty clear description of the current limitations of determining distances by the parallax method. There are numerous other methods for measuring or estimating distances in the cosmos. They make up what is known as the cosmic distance ladder.
Updates
• Recent detection of gravitational waves have further confirmed Einstein's view of the nature of spacetime as described in his general theory of relativity. (By the way, the term gravity waves refers to the much more mundane waves in water or air -- waves that result from the combined effects of wind and gravity.)
•
Readings
• The Voyager Golden Record at Wikipedia describes and explains the visible markings on the record cover, and the contents of the recording.
• The scientific community prizes efforts to bring science to the public, of which “Cosmos” is a fine example. For more on this subject, read the essay "Bringing Science to the Public," HERE at One Culture.
• Martin Behaim made the oldest surviving globe, giving us a summary of what what known about Earth's geography just before Columbus's voyage to what we know now as the Americas.
• Viktor Hess discovered cosmic rays, developed new technology for detecting them, and showed that they originate from outer space.
• Vera Rubin's careful astronomical studies on the galaxy rotation problem confirmed the existence of dark matter, as postulated earlier by Fritz Zwicky. Rubin's evidence for dark matter was by far the strongest evidence up to that time.
• Fritz Zwicky's contributions make him, in Tyson's words, "the most brilliant man you've never heard of." His original ideas include supernovae, neutron stars, gravitational lensing, and dark matter.
Ideas
• Dark matter and dark energy. Only 4.9% of the mass and energy of the universe is visible to us (so-called ordinary matter). The remainder includes 1) matter that we see only by its gravitational effects (dark matter, 26.8%), and 2) energy that we see only by its effects on the rate of expansion of the universe (dark energy, 68.3%). In both cases, the term "dark" simply means mysterious.
• Where do cosmic rays come from?
• A universal standard unit of time. How would you express time intervals to an alien? In the Voyager messages, all references to intervals of time (such as the frequency of pulsars and the playback speed of the Voyager Golden Record) are based on frequency of a specific energy that a free hydrogen atom can absorb or emit. That frequency is (in case you were wondering) 1,420,405,751.7667±0.0009 Hz (Hz = cycles per second), and is called the hydrogen line, or the hydrogen hyperfine splitting constant. Waves of this frequency are about 21 cm in length, and lie in the microwave region of the EM spectrum. This spectral line is a fundamental property of hydrogen, the universe's simplest atom, and is also a frequency of electromagnetic radiation that pervades the universe and is not blocked by clouds of interstellar dust. It is hard to imagine that this fundamental constant would not be recognized by any intelligence that recognizes the basic physical laws of the universe.
• Standard Candles (recycled from Episode 8): Cepheid variables and Type Ia supernovae are called standard candles. Their inherent brightness is known (because of the physics that produces their light), and so their apparent brightness can tell us their distance (their light dims with the square of their distance). They help scientists measure absolute distances to stars and galaxies.
• How far away is that star? Different methods of measurement are used for stars that are near (closer than 500 light years), at intermediate distance (out to tens of millions of light years), or very far away (in other galaxies). The methods rely upon, respectively, on parallax, Cepheid variable stars, or Type-Ia supernovae (an example shown during this episode). Click HERE to learn more. To learn even more, look up each method in Wikipedia: parallax ---- Cepheid variable stars ---- type Ia supernovae. Look HERE for a pretty clear description of the current limitations of determining distances by the parallax method. There are numerous other methods for measuring or estimating distances in the cosmos. They make up what is known as the cosmic distance ladder.
Updates
• Recent detection of gravitational waves have further confirmed Einstein's view of the nature of spacetime as described in his general theory of relativity. (By the way, the term gravity waves refers to the much more mundane waves in water or air -- waves that result from the combined effects of wind and gravity.)
•
Readings
• The Voyager Golden Record at Wikipedia describes and explains the visible markings on the record cover, and the contents of the recording.
• The scientific community prizes efforts to bring science to the public, of which “Cosmos” is a fine example. For more on this subject, read the essay "Bringing Science to the Public," HERE at One Culture.
