Lab 9: Double Stars

Credit/Permission: For text, © David Jeffery. For figures etc., as specified with the figure etc. / Only for reading and use by the instructors and students of the UNLV astronomy laboratory course.

Group Number/Name:

Name:

Partner Names:

Favorite Report: Y / N

Task Master:

Task 1: Angular Separation of Castor and Pollux.
Task 2: Sky Map.
Task 3: Observations (IPI only).
Task 4: Angular Resolution.
Task 5: Geometrical Optics and Diffraction. Optional at the discretion of the instructor.
Task 6: Using the Rayleigh Criterion. Optional at the discretion of the instructor.
Task 7: Binaries.
Task 8: Naked-Eye Observations (RMI only).

End of Task

Task 1: Angular Separation of Castor and Pollux:
What is the angular separation of Castor and Pollux in fists? Explain how you got your answer.
Answer:

End of Task
Task 2: Sky Map:
Sub Tasks:
1. Print out the sky map shown in the figure below (local link / general link: sky_map_current_time_las_vegas.html) following the instructions given in the figure caption.
  RMI qualification: If you do NOT have access to a printer, you will have to hand-draw the sky map.
2. You should update the time on the Your Sky control panel to your approximate observing time (e.g., 8:00 pm, 9:00 pm, etc.) if needed.
  You will have to do a conversion from local time to Universal Time (UT) to update the time. How to do the conversion is explicated in the figure below (local link / general link: sky_map_current_time_las_vegas.html).
3. Find and highlight on the sky map all the double stars for your season shown below in the Observing Working Table for Double Stars (local link / general link: star_double_star_table.html).
  NOT all the double stars in the Observing Working Table for Double Stars are labeled on the printed-out sky map. You will have to click on the names of the unlabeled ones (on the printed-out sky map) in Observing Working Table for Double Stars to get a sky map with them located. Label the unlabeled double stars on your printed-out sky map.
4. Only one sky map is needed per group and it should be appended to the favorite report form---unless your instructor asks for each group member to make a sky map.
  RMI qualification: Whether you report your sky map in any way depends on the instructions for your particular semester of the Remote Instruction Course.
End of Task
Task 3: Observations (IPI only):
Sub Tasks:
1. When your instructor directs, go up to the roof and start observations.
2. You observe the double stars in the Observing Working Table for Double Stars below (local link / general link: star_double_star_table.html) for your season.
  Generally, you go down the list in order since the generally the double stars get harder to resolve going down the list, and so you gain experience as you go.
  However, if a double star is getting close to the horizon or being threatened to be clouded-out, you may have to observe it early. Double stars that may need to be observed early are marked with OE for "observe early".
3. Remember the steps in locating an astronomical object:
  1. Use the LCD keypad location tool to get to the vicinity of the double star. There is a menu for double stars.
    Of course, if you can locate the double star by eye using your sky map, you can just slew the C8 to the vicinity of the double star without using the LCD keypad location tool.
  2. Center the red laser dot of the star pointer on the double star.
  3. Then center of the finderscope on the double star.
  4. The double star should then be in the C8's field of view (FOV).
  5. If you are looking at some dim star that can't be seen with the naked eye, you are looking at the WRONG star.
    All the double stars in the Observing Working Table for Double Stars are bright enough to be seen with the naked eye even in Las Vegas though some barely.
    You could ask your instructor if you are doubtful.
4. Record in the Observing Working Table for Double Stars if a double star is observed and if it is resolved.
  Add a comment if needed: e.g., clouded-out, too close the horizon, the secondary star in the double star too faint to be seen compared to the primay star, awesome.
End of Task
Task 4: Angular Resolution:
Sub Tasks:
1. Read the above section Angular Resolution preamble and the above subsections Seeing, The Rayleigh Criterion, Human Eye Angular Resolution, The Dominant Angular Resolution Limit. Have you read them? Y / N
2. For the C8 telescope, what is the Rayleigh criterion limit θ_RV and the fiducial telescopic human-eye angular resolution limit θ_HT in two cases: 1) for the standard 40-mm eyepiece magnification; 2) the largest possible magnification? Give the first value to 3-digit precision and the others to 2-digit precision.
  Answer:
3. Which of θ_RV or the BEST θ_HT is the dominant limit? Why?
  Answer:
4. Given the last answer, how good does the seeing limit have to be before (θ_RV / the best θ_HT) becomes dominant? Are we ever likely to be limited by (θ_RV / the best θ_HT) in Las Vegas, Nevada? Why or why NOT?
  Answer:
5. Complete Table: Parameters to Equal/Surpass the Seeing Limit below.
6. What does the table show how to do?
  Answer:
  
  seeing limits.
```
_________________________________________________________________________________

Table:  Parameters to Equal/Surpass the Seeing Limit
_________________________________________________________________________________


Seeing   θ_S   D_in = 5''/θ_RV   D_in = 5''/θ_RV   M = 60''/θ_HT   M = 60''/θ_HT
                  (θ_RV=θ_S)       (θ_RV=θ_S/3)      (θ_HT=θ_S)     (θ_HT=θ_S/3)
         ('')       (in)               (in)             (X)             (X)
_________________________________________________________________________________

Poor      10
LV Strip   4
Good       1
Excellent  0.4
_________________________________________________________________________________ 
```
7. Read the below subsection An Example of Seeing. Have you read it? Y / N
End of Task
Task 5: Geometrical Optics and Diffraction:
Sub Tasks:
1. Read the figure below (local link / general link: optics_airy_disk.html). Have you read it? Y / N
2. Given that λ is wavelength and L is a characteristic size for aperatures and obstacles, λ/L → 0 implies you:
  1. are in the EXACT limit of geometrical optics.
  2. are in the INEXACT limit of geometrical optics.
  3. HAVE to consider the wave nature of light.
  4. do NOT have to consider the wave nature of light.
3. The diffraction pattern for plane waves perpendiculary incident on a circular aperture is the:
  1. Airy diffraction pattern which is a diffraction pattern with square symmetry.
  2. Airy diffraction pattern which is a diffraction pattern with circular symmetry.
  3. powder diffraction pattern which is a diffraction pattern with square symmetry.
  4. powder diffraction pattern which is a diffraction pattern with circular symmetry.
End of Task
Task 6: Using the Rayleigh Criterion:
Sub Tasks:
1. Read the figure below (local link / general link: optics_rayleigh_criterion.html). Have you read it? Y / N
2. Evaluate the Rayleigh criterion coefficient (4.952'')*(λ/0.5 μm) for wavelengths 0.4 μm, 0.5 μm, 0.6 μm, and 0.7 μm.
  Answer:
3. Now evaluate the Rayleigh criterion itself for these wavelengths and D_in = 8.
  Answer:
End of Task
Task 7: Binaries:
Sub Tasks:
1. Read the all of section Binaries above (local link / general link: Binaries). Have you read it? Y / N
2. Binary stars orbit their mutual ______________________ (AKA barycenter) in ______________________ in general with the barycenter at a focus. The other focus of each orbit is just an empty point in space.
  1. center of mass; circular orbits
  2. center of mass; ellitptical orbits
  3. enter of mass; hyperbolic orbits
  4. center of radiation; circular orbits
  5. center of radiation; ellitptical orbits
3. Which of the following is NOT a kind of binary:
End of Task
Task 8: Naked-Eye Observations (RMI only):
Modifications to the sub tasks in General Task: Naked-Eye Observations below:
1. Since you already have sky map printed/drawn in Task 2: Sky Map, you do NOT print/draw another one.
2. You should try to find all the double stars for your season shown above in the Observing Working Table for Double Stars (local link / general link: star_double_star_table.html) and located on your sky map. You CANNOT, of course, resolve the double stars into 2 stars with the naked eye.
  However, you should be able to find in the winter and spring not-too-late night sky Castor (α GEM) and Pollux (β GEM) which are "twin" stars even though NOT collectively a double star in the usual meaning. Their angular separation is 4°30'19.53'' at some epoch, maybe the J2000 epoch (see Distance between Pollux and Castor?). This angular separation is about half a fist at arm's length.
EOF
End of Task