RANDY L. PHELPS

This is the Celestial Sphere Module

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Procedure

1.  For this module, please look through the "lecture" notes for "The Celestial Sphere" and "Celestial Navigation".  These notes contain the material, in condensed form, that I will expect you to become familiar with.  I am sure you will have questions about the material, especially since it is presented in the form of lecture notes.  To help you fill in the blanks, I have added web links that you can follow, in order to gain further insight into the material. 

2.  Additionally, you should complete the following Web exercises to help you understand the material, and reinforce the concepts:

     Web-Exercise 1: Exploring Motions in the Sky

     Web-Exercise 2: Determining Your Latitude

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Upon completion of this web assignment, you should be comfortable with the following material:

• Definitions and Concepts: Celestial Sphere, Altititude, Azimuth, Zenith, Meridian, Celestial Poles, Celestial Equator, Circumpolar Stars, Ecliptic.
• The brightness scale for stars
• How objects in the sky move, on a daily basis, as seen from the Earth's poles.
• What the unique aspects of the seasons are at the Earth's poles.
• How objects in the sky move, on a daily basis, as seen from the Earth's equator.
• How objects in the sky move, on a daily basis, as seen from intermediate latitudes on the Earth.
• The motion of the Sun in the sky
• Why it is that the Earth rotates on its axis in 23hr 56min, but a mean solar day is 24hr.  What a mean solar day is.
• Why seasons occur.

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Upon completion of this module, you should be able to answer these, and similar questions:

Basic Concepts

• What objects in the sky are bright enough to cast shadows?
• The Sun subtends what angle on the sky?
• The full Moon subtends what angle on the sky?
• What is the name of the star located near the North Celestial Pole?
• Is there a bright star located near the South Celestial Pole?  If so, what is it?
• The projection of the Earth’s poles into space gives rise to an equivalent concept in the sky, referred to as what?
• When do stars attain a maximum altitude above the horizon?
• The meridian divides the sky into which two halves, northern and southern, or eastern and western?
• Stars that never set below the horizon, and are always visible, are called what?
• Positions of objects on the celestial sphere can be specified by what parameters?
• The Sun moves along an imaginary circle in the sky, which is called what?
• What important information does the altitude of the celestial pole above the horizon tells us?
• As seen at the Earth’s North Pole, which stars, if any, are circumpolar?
• As seen at the Earth’s North Pole, where is the north celestial pole in the sky?
• As seen at the Earth's North Pole, where is Polaris in the sky?
• As seen at the Earth's North Pole, where is the celestial equator in the sky?
• As seen from the Earth's equator, which stars, if any, are circumpolar?
• As seen from the Earth's equator, where is the north celestial pole in the sky?
• As seen from the Earth's equator, where is the south celestial pole in the sky?
• As seen from the Earth's equator, where is the celestial equator in the sky?
• As seen from intermediate northern latitudes on the Earth, where is the north celestial pole in the sky?
• As seen from intermediate northern latitudes on the Earth, where is the south celestial pole in the sky?
• As seen from intermediate northern latitudes on the Earth, where is the celestial equator in the sky?
• The Sun stays above the horizon for 6 months at what location(s) on the Earth?
• The Sun stays below the horizon for 6 months at what location(s) on Earth?

• Native skywatchers in the Americas knew of a very bright, white "Morning Star" and "Evening Star" that were only visible just before sunrise or just after sunrise. What celestial object is this likely to have been?
• A navigator tells the captain of a ship that the south celestial pole is 25 degrees above the southern horizon. What is the latitude of the ship?
• A navigator tells a captain of a ship that Polaris is 48 degrees above the northern horizon. According to his almanac, the star Sirius was on the meridian in Greenwich, England 5 hours ago. He observed Sirius to be on the meridian 2 hours ago. What is the latitude and longitude of the ship?
• A navigator tells a captain of a ship that Polaris is 42 degrees above the northern horizon. According to his almanac, the Sun set in Greenwich, England 5 hours ago, although it is only now setting from his location. What is the latitude and longitude of the ship?

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In other words, for me to provide you with help, you must show me that you have undertaken a good-faith-effort to find the answers yourself, in a timely manner.

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