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Chapter 17: A Diversity of Galaxies
Distance Scaling
Naturally, the farther away a light bulb (or a star) is the dimmer it appears.
Watch the "Distance Scale Animation (Light Bulb Metaphor)" movie. 1) How many times as far away must you move a 1000-watt light bulb to make it appear as bright as a 250-watt bulb? 2) How many times as far away must you move a light bulb to make it appear one-tenth as bright?
Visit the Distance Scaling web site
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The Hubble Constant
Knowing the value of the Hubble constant is very important to galactic astronomers.
1) What two values for a galaxy must be measured to calculate the Hubble constant? 2) For determining which of these values is the Hubble Space Telescope more valuable? Why?
Visit the Edwin Hubble: The Hubble Constant web site
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The Local Group of Galaxies
Our Galaxy is part of a cluster of galaxies known as "the Local Group."
1) Name the most massive members of the Local Group. 2) Name some galaxies (other than the Milky Way) that were known before the invention of the telescope. 3) What causes the shape of the Local Group to change?
Visit the The Local Group web site
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Jets Near Light Speed
Einstein's theory of relativity says that the speed of light is the highest possible speed. Jets of protons and electrons released from some celestial objects reach nearly this speed.
1) What is the source of the energy for material that moves at such great speed? 2) Where are the jets located relative to the disk of the black hole?
Visit the Gas Jets web site
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