Astronomy Lecture Day 03: The Celestial Sphere, Local and Celestial Coordinates, and The Diurnal Apparent Motion of the Stars.

Key Terms:

The Celestial Sphere

The Celestial Equator

The North and South Celestial Poles (NCP & SCP)

Altitude and Azimuth

Zenith and Meridian

Celestial Coordinates Declination (dec) and Right Ascension (RA)

Sidereal Day

Slant Angle

Circumpolar Region

Southernmost Visible Star

Web Site:

University of Nebraska, Lincoln, The Rotating Sky at http://astro.unl.edu/naap/motion2/motion2.html

  1. Introduction
  2. Return HW
  3. Collect HW
  4. Questions
  5. Attendance
  6. Sample Test Question: How far away would Polaris, the North Star, be away from the Earth if all lengths and distances were scaled down so that the diameter of the Earth was only 1 centimeter? The actual distance to Polaris is believed to be about 434 ly. Express you answer in the most intuitively clear metric or astronomical length unit.
  7. Celestial Trails over Greece video http://apod.nasa.gov/apod/ap110504.html
  8. Goal: To identify the direction you are looking from the motion of the stars and to describe quantitatively the apparent motion of the stars as seen from any location in the northern hemisphere.
  9. Extra Credit HW due on Thursday
  10. The Celestial Sphere and its “Geography”
  11. The Concept: a model of the sky
  12. The Picture: Draw the 3-D and 2-D representations of the celestial sphere. Figure 5.5
  13. The Celestial Equator: How is it related to the terrestrial equator?
  14. The North Celestial Pole (NCP) and the South Celestial Pole (SCP): How are the celestial poles related to the north and south terrestrial poles?
  15. University of Nebraska, Lincoln, The Rotating Sky at http://astro.unl.edu/naap/motion2/motion2.html Two Systems - Celestial, Horizon Module
  16. Local and Celestial Coordinates
  17. Local Coordinates
  18. University of Nebraska, Lincoln, The Rotating Sky at http://astro.unl.edu/naap/motion2/motion2.html The Observer Module
  19. Altitude
  20. Azimuth
  21. Meridian
  22. Zenith
  23. Celestial Coordinates (Unit 5.5 and Figure 5.8)
  24. Declination (dec)
  25. Stars appear to move along their line of declination
  26. Right Ascension (RA)
  27. The Diurnal Apparent Motion of the Stars as seen by any observer in the Northern Hemisphere. Draw the pictures and annotate them.
  28. Important Website: University of Nebraska, Lincoln, The Rotating Sky at http://astro.unl.edu/naap/motion2/motion2.html
  29. Paths of the Stars Module: Set up four stars: southern, on celestial equator, northern and on the NCP
  30. Discuss the apparent movement and time scales
  31. Rotating Sky Explorer Module: Set up four stars: southern, on celestial equator, northern and on the NCP
  32. Rank the stars in order of decreasing time above the horizon.
  33. Add a circumpolar star and define the circumpolar boundary in declination.
  34. Add a star that never rises and define the declination of the southern most visible star.
  35. Where does the celestial equator intersect the horizon? Does the point where the celestial equator intersects the horizon depend on the latitude of the observer?
  36. How does the altitude of Polaris (The NCP really) depend on the latitude?
  37. Looking North
  38. Stars appear to circle counterclockwise around Polaris (NCP really) once every 23h 56m 4.09 s (The Sidereal day)
  39. The altitude of Polaris equals the observer’s latitude (Do the derivation)
  40. The boundary of the circumpolar region is equal to (90° - Obs. Lat.)
  41. Northern stars are above the horizon for greater that 12 hours
  42. Looking East
  43. The Celestial Equator intersects the horizon exactly due East for all observers.
  44. Stars rise along paths slanted to the South
  45. The slant angle of rising stars relative to the vertical equals the observer’s latitude.
  46. Stars near the celestial equator are above the horizon for about 12 hours
  47. Looking South
  48. Stars appear to follow downward curving arcs about a point (SCP) below the southern horizon.
  49. The southernmost visible star has a declination equal to (Obs. Lat. - 90°)
  50. Southern stars are above the horizon for less than 12 hours.
  51. Looking West
  52. The Celestial Equator intersects the horizon exactly due West for all observers.
  53. Stars set along paths slanted from the South
  54. The slant angle of rising stars relative to the vertical equals the observer’s latitude.
  55. Stars near the celestial equator are above the horizon for about 12 hours
  1. Sample test question: See next page
  1. Extra-credit assignment due on Thursday (10 points)
  2. Sketch or describe the apparent motion of the stars looking N, E and S (similar to our drawings in class) for the following locations: The equator, the North Pole, any capital city of any country in the world (you choice). Fully annotate your sketches as we did in class.


The pictures and questions below pertain the apparent motion of the stars as seen by an observer in Acapulco, Mexico. A map of Mexico below indicates the location of this city.

1.  Which of the labeled stars represents

Polaris?

2.  Which of the labeled stars is NOT a circumpolar star?

3.  In which direction would star A be apparently moving at the instant

pictured.

A.  It would not be moving at all.

B.  It would be moving straight up.

C.  It would be moving straight down.

D.  It would be moving to the left.

E.  It would be moving to the right.

4.  The stars as seen toward the East

would be following paths parallel to

which of the indicated rays. The

indicated angles are measured up from

the horizon.

A.  75° ray

B.  60° ray

C.  43° ray

D.  30° ray

E.  15° ray

5.  Stars seen looking East are above the horizon for approximately how long?

A.  24 hours

B.  Greater 12 hours but not 24 hours

C.  About 12 hours

D.  Less than 12 hours

6.  Looking south the stars would most closely follow which of the paths indicated below?

35)  An observer in Acapulco could see stars in the southern sky down to approximately which of the declinations listed below?

A)  -90°

B)  -75°

C)  -47°

D)  0°

E)  15°