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Exam 25: Celestial Timekeeping and Navigation

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Question 1

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The average length of a solar day is

A) 23 hours 56 minutes.
B) 24 hours.
C) 365.25 days.
D) 12 years.
E) 26,000 years.

F) All of the above
G) A) and D)

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Question 2

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Your Local Sky a.Where is the north (or south)celestial pole in your sky? b.Describe the meridian in your sky. c.Describe the celestial equator in your sky. d.What is the range of declinations that makes a star circumpolar in your sky? Explain. e.Describe the path of the Sun through your sky on the fall equinox. f.Describe the path of the Sun through your sky on the winter solstice.

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Answers will vary with latitude;the following is a sample answer for latitude 40°N. a.The north celestial pole appears in the sky at an altitude of 40°,in the direction due north. b.The meridian is a half-circle that stretches from the point due south on the horizon,through the zenith,to the point due north on the horizon. c.The celestial equator is a half-circle that stretches from the point due east on the horizon,through an altitude of 50° due south,to the point due west on the horizon. d.Because the north celestial pole appears due north at an altitude of 40°,a star is circumpolar if it is within 40° of the north celestial pole.The north celestial pole has a declination of +90°,so within 40° means declinations greater than +50°. e.On the fall equinox,the Sun rises due east,reaches an altitude of 50°S on the meridian,and sets due west. f.On the winter solstice,the Sun rises more than 23.5° south of due east,reaches an altitude of 50° - 23.5° = 26.5° on the meridian in the south,and sets more than 23.5° south of due west.

Question 3

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Choose the appropriate star from Table S1.2 for the following questions: Table S1.2 -Which star remains above the horizon for the longest time each day at latitude 40°N?

Choose the appropriate star from Table S1.1 for the following questions: Table S1.1 -Which star lies closest to the celestial equator on the celestial sphere?

The lunar month is longer than the sidereal month because

All the following statements are true.Which one explains why our calendar has leap years?

The Sun's declination on June 21st is

Suppose you have a time-keeping device that always reads precisely 12:00 when the Sun crosses your meridian.What kind of time is this clock keeping?

Each of the following lists a constellation and a bright star.In all cases but one,the star is part of the constellation.Which one is the mismatch?

For the following questions,refer to Figure S1.1,which shows a portion of the sky visible in the early evenings in the fall.Note that five bright stars are labeled with lowercase letters and five constellations are labeled with capitals.A few hints are also given. -Which constellation (capital letters)is Perseus?

The amount of time between successive passes of any given star across the meridian is

Suppose it is January and the Sun remains above your horizon all day long.Where must you be located?

For the following questions,refer to Figure S1.2 which shows a portion of the sky visible in the early evenings in winter.Note that five bright stars are labeled with lowercase letters and five constellations are labeled with capitals.A few hints are also given. -Which constellation (capital letters)is Canis Minor?

What kind of time can be read directly from a sundial?

Suppose you live at the North Pole.Describe the path of the Sun through your sky for each of the following days: a.the day of the spring equinox b.the day of the summer solstice c.the day of the winter solstice

The three bright stars that make up the Winter Triangle are

For the following questions,refer to Figure S1.2,which shows a portion of the sky visible in the early evenings in winter.Note that five bright stars are labeled with lowercase letters and five constellations are labeled with capitals.A few hints are also given. -Which constellation (capital letters)is Orion?

The three stars of the Summer Triangle are

Note to instructors: The following question assumes you gave a "lost at sea" question on your midterm.

Which of the following is the reason for the solar day being longer than a sidereal day?