Ch. 2 Observing the Sky_Review Questions and Answers

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Astronomy

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Oct 30, 2023

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Ch. 2 Review Questions/Problem – Run as a Slide Show So that you can answer the question before confirming your response is the correct answer. Try writing the answer to the question instead of just thinking about it.

An asterism is a group of stars that is not formally recognized as a constellation by the International Astronomical Union (IAU). Many asterisms are part of larger constellations. There are 88 constellations officially recognized by the IAU. Examples of asterisms include the Big Dipper (part of Ursa Major), the Great Square (part of Pegasus), the Water Jug (part of Aquarius), the Summer Triangle (composed of three bright stars in the constellations of Lyra, Cygnus, and Aquilla), and Medusa's Head (part of Perseus). 1. What is the difference between an asterism and a constellation? Give some examples.

The Greek-letter designations generally indicate the brightness because the stars in a given constellation were given Greek-letter designations running in alphabetical order from brightest to faintest within that constellation. This system does not allow us to compare the relative brightness of stars in different constellations with certainty since the brightest star in each constellation is generally designated , but not all constellations contain a really bright star. 2. How does the Greek letter designation of a star give you a clue to its brightness?

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The word apparent in apparent visual magnitude means simply that it is the magnitude of the star as it appears to us when viewing the star from here on Earth. Apparent visual magnitude does not take into account any corrections for the star's distance, size, temperature, or the amount of dust between us and the star. It is simply the brightness as it appears to us in the night sky. 3. What does the word apparent mean in apparent visual magnitude?

To see the north and south celestial poles at the same time, one needs to be at Earth's equator. Due to the refraction of light by the atmosphere, an observer on the equator would observe the north celestial pole approximately 0.5° above the northern horizon and the south celestial pole about 0.5° above the southern horizon. An observer at latitudes between 0.5° S and 0.5° N could see both celestial poles above their horizon. 4. Where would you go on Earth if you wanted to be able to see both the North Celestial Pole and the South Celestial Pole at the same time?

A celestial pole will be on your zenith if you are at a latitude of 90° N, the north geographic pole, or at 90° S, the south geographic pole. 5. Where would you go on Earth to place a celestial pole at your zenith?

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Circumpolar constellations are those constellations close enough to the celestial pole so that they never pass below an observer's horizon, but instead pass directly between the observer's celestial pole and northern or southern horizon at their lowest points in the sky. At different latitudes the celestial pole will be at different distances above an observer's horizon. If the observer is at a latitude of 60° N, then all constellations within 60° of the north celestial pole will be circumpolar. However, if an observer is at a latitude of only 30° N, then only those constellations within 30° of the north celestial pole will be circumpolar. 6. Why does the number of circumpolar constellations depend on the latitude of the observer?

Star A is the brightest, Stars A and B are visible to the unaided eye, Star A is 16 times brighter than Star B. Problem: Star A has a magnitude of 2.5; Star B, 5.5; and Star C 9.5.Which is the brightest? Which are visible to the naked eye? Which pair of stars has a brightness or flux ratio of 16 - or which star is 16 x brighter than one of the others?