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Lab 6: Planets / Lab Supplements

Sections

  1. Student Preparation which includes Quiz Preparation.
  2. Special Instructions For Instructors See also Diane Smith's Instructor Notes.
  3. Startup Presentation
  4. Post Mortem

  1. Student Preparation

    2. Required Lab Preparation:

    1. Required Reading: Lab 6, Appendix D (telescope operation), Appendix F (planetary configurations). It is hard to understand equipment without first seeing and playing with it, but insofar as possible you should be ready to use the C8 telescopes.
    2. Read the Startup Presentation.
    3. Read IAL 2: The Sky section 8 only on planets, etc. and IAL 4: The History of Astronomy to Newton sections 9--11 only on the Copernican revolution, etc.
    4. Read the Post Mortem. Better before than after actually.
    5. Read a sufficient amount of the articles linked to the following keywords, terms etc. so that you can define and/or understand the terms etc. at the level of our class: C8 telescopes, conjunction (inferior conjunction and superior conjunction), ecliptic coordinate system (geocentric longitude and heliocentric longitude), elongation (greatest eastern elongation and greatest western elongation), Kepler's 3 laws of planetary motion, naked eye astronomy, opposition, planets (Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, Neptune, ex-planet Pluto, inner planets, outer planets, inferior planet, superior planet), planetary configuration, planetary system, quadrature, Solar System, syzygy.

    Supplementary Lab Preparation: The items are often alternatives to the required preparation.

    1. Bennett (2008 edition): p. 70--78 on Copernican revolution, p. 95 on planetary configurations, p. 208--226 on our planetary system, p. A-14--15 on planetary data.

    Quiz Preparation:

  2. Special Instructions For Instructors

    1. Check as needed:
      1. Usual Startup
      2. Usual Shutdown

    2. As usual for inside-outside labs, check the weather online at NWS 7-day forecast, Las Vegas, NV in advance and by personal visual inspection at/during the lab period.

      In case the weather is not good for observing, you need to have an alternate inside lab ready.

      Usually, that inside lab should be from the current semester lab schedule.

      Alternatively, since the observing part of Lab 6 is relatively small, you may just go ahead and omit the observing part altogether or leave it for the next week.

      If none of the above is feasible, yours truly suggests Lab 16: Hubble's law since that is pretty short and easy and takes little prep.

      Someone will make an executive decision.

    3. Since this is a planet observation lab, you should check what planets are in the current night sky. See one of:

      1. TheSky: You'll have to go to a computer with this software installed.

      2. Sky & Telescope: This Week's Sky at a Glance: Scroll down to "This Week's Planet Roundup", but it is not all that great.

      3. Sky map: Las Vegas, current time

        Your's truly---after trying everything else first---has used the Customise page to make Fourmilab: Your Sky give a Las Vegas sky map at the current time.

        Fourmilab: Your Sky is a bit tricky at first---not reading the instructions is a real hold-up---but you can use it to get a sky map above the horizon for any time and place.

        I didn't set all possible options on. That would make the sky map too cluttered. But I did click on ecliptic-celestial equator, planets-Moon and constellation names.

    4. You will need to set up the C8 telescopes on the roof before the lab period and review their usage well in advance if needed.

      The C8's usually should be sky aligned for this lab, so that the planets to be observed stay fixed in the field of view while the students sketch them.

        It's nice if they are sky aligned, but it's not absolutely essential.

        The students can sketch quickly and slew the C8's as needed.

      See Telescope Operating Procedure and List of Tricks for C8 Telescopes for procedures and tips.

      animation of double pendulum in chaos It is possible to cover all parts of the lab in one week, but be sure to decide among the instructors how to proceed in order to avoid CHAOS on the roof.

      As many C8's as needed should be set up and the instructors should decide ahead of time how to share them.

    5. You will need smaller focal-length eyepieces than the standard 40-mm eyepieces.

      The smaller ones are in boxes labeled by their focal length.

      The 40 mm eyepieces should be back on the C8's at the end of the night and all the smaller ones in their appropriate boxes.

      The smaller focal-length eyepieces are good for viewing and needed for the angular diameter measurements---yours truly recommends that you do NOT do the angular diameter measurements---just give the students the fiducial times given below.

    6. The CCD camera will have to be set up by someone if any images are to be taken. Maybe there won't be any images or maybe you will not need to do the set up.

      See CCD Camera Instructions if the CCD camera is to be set up.

      Actually, nowadays, students can take pretty good images just with their cell phones if they want images.

    7. Things to put out:

      1. You will need to get protractors out of the storeroom from wherever they are now. They may be in the lab room.

        You'll need one for each group---don't take more or the other lab instructors will become hostile.

        You'll have to give some students a lesson in using a protractor.

      2. Put out the summer and winter mercator sky maps. You only need one set per group.

        The students need to mark the positions of all the planets on them.

        Alternatively you can print out the Your Sky sky map below for today's date and approximate observing time: , .

        You will have update the time to your approximate observing time.

        Credit/Permission: John Walker: Fourmilab: Your Sky, 2003 / Public domain.

        Image linked to Fourmilab: Your Sky.

      3. List of Tricks for C8 Telescopes if you think it is needed---probably not. You only need one set per group.

    8. Some labs are well enough described in the manual that the instructor can pretty much wing it without having done the lab themselves at all.

      Lab 6 is NOT one of those.

      There are too many glitches in the manual.

      At the least, the instructor should run through Excel spreadsheet.

  3. Startup Presentation

    1. Hand back old reports and quizzes.

    2. At 7:30 pm sharp, start.

    3. Give tonight's agenda: quiz, Post Mortem on the last lab, Startup Presentation, lab. Be brief.

    4. Then give the quiz. It will be 10 minutes or so. Late arrivals have to write the quiz at the tables in the hall.

    5. Post Mortem. Be brief.

    6. Then tell them to form new groups, report to a computer, launch Firefox, click on Jeffery astlab on bookmarks, click on Lab Schedule, click on tonight's lab, and srcoll down past the foxes.

    7. Objectives: To get learn something about the structure of the Solar System, the location of the planets on the sky, and observing the planets with the telescope.

      The observing component of the lab is relatively small and can be omitted or left for the following week if the weather conditions are not good.

    8. The Planets on the Sky:

      The planets that are currently in the sky are illustrated in the sky map below.

    9. Nicolaus Copernicus (1473--1543):

      Nicolaus Copernicus (1473--1543) was the first person put into the permanent record of history the heliocentric solar system as a well supported hypothesis.











      He also put the planets in their correct place to 1st order as his own illustration below shows.

    10. The Astronomical Unit (AU):

      The natural unit for Solar-System distances is the astronomical unit (AU): 

                   1 AU = 1.49597870700*10**11 m  exactly by modern definition.
      The astronomical unit is the mean Earth-Sun distance to very high accuracy.

      No one can think of Solar-System distances in meters or miles, but in astronomical units it is straightforward to think of those distances.

      Copernicus himself first discovered the true relative Solar System distances in terms of the astronomical units.

      This was made possible by his adoption of a heliocentric solar system model.

      No one known to history before Copernicus knew what those relative distances were.

      Below is modern diagram of the inner Solar System plus Jupiter.

      The diagram is to scale and the caption gives the mean orbital radii in astronomical units.

      The animation below shows the inner Solar System motions to scale it seems.

    11. Planetary Configurations:

      The following diagram illustrates some of the jargon used in studying planetary configurations.

    12. Kepler's 3 Laws of Planetary Motion:

      The lab also touches on Kepler's 3 laws of planetary motion which are illustrated in the figure and animation below.

    13. Protractors:

      We will be using protractors.

      The figure below shows how to use a protractor.

      Let's do a quick example on the board:

      1. Draw three dots: Earth, planet, Sun.
      2. Take the Earth as your vertex.
      3. Put the protractor center on the vertex.
      4. Align the protractor axis with the Sun.
      5. Read off the angle to the planet.
      6. This angle is called the elongation of the planet. The elongation can be either east or west of the Sun.

    14. Features/Tips/Glitches:

      Now features/tips/glitches for the lab, TheSky, and Excel spreadsheet.

      1. Do NOT plot the horizon for Question A2 on the sky map, just the planets

        We have done the horizon once already and once is enough for that tricky job.

      2. For TheSky, it is VITAL that you have the right date () and time (9:00 pm):

        See List of Tricks for TheSky if needed.

      3. In Table 6.2 for heliocentric distance for the Sun, put the heliocentric distance for the Earth---this makes no sense---do it anyway.

      4. ROUNDOFF the entries in Table 6.2 to the nearest degree. NO arcminutes, no arcseconds. Above 30 arcminutes, round up, otherwise round down.

      5. Re-zero the elongations in Excel spreadsheet to the range [-180 degrees,180 degrees] just as it says on p. 48.

      6. Get help if needed on how to use the Excel spreadsheet.

        Features, etc.:

        1. If the Excel spreadsheet is behaving funny, someone may have messed up equations and a fresh start may be needed.

        2. Double click somewhere on the line between B and C columns to get the date---don't ask me why.

        3. Question B7b tells you to get help for P(deg) column from the instructor.

            The easy answer is to measure the angle P (see Fig. 6.1) off your Solar System plot, e.g., 20, and then just type, e.g., "=20".

            This is cheating a bit, but it helps when the instructor is clueless.

        4. Note if Mercury is too close to a conjunction you will NOT get a very good value for the astronomical unit. The Excel spreadsheet arithmetic is sort of semi-demi precision.

        5. You have to learn to move lines around on the Excel spreadsheet graphs.

        6. When you print the Excel spreadsheet pages, go file/print preview and make sure things look good. Fitting to one page is usually best for a single Excel spreadsheet tab

        7. Frequently despite trying to follow the instructions for the Excel spreadsheet carefully, everything messes up.

          Don't worry about it. With the Excel spreadsheet, yours truly marks for effort.

      7. For the TheSky in Solar-System mode, see List of Tricks for TheSky:View/3D Solar System Mode and, in particular, note how to get the ecliptic axis straight out of the screen the easy way.

      8. On page 50, the two law of sines formulae are wrong. The first should have sin(C)/sin(P) and the second sin(P)/sin(C).

      9. For the time period you are supposed to use for Jupiter/Saturn just use the following fiducial times: t=40''/(15''/s)=2.7 s for Jupiter and t=18''/(15''/s)=1.2 s for Saturn.

        We will NOT be doing the time period measurements.

        They are too difficult without some significant practice time.

    15. Observations:

      When we go outside.

      You will just sketch the currently observable planets and enter the date for the sketch.

      But one additional datum is required by yours truly.

      Estimate angular diameter of the each planet in arcseconds---just by eye.

      This just an exercise in crude measurement.

      The following table will help you by giving the field of view size for comparison. 

          ________________________________________________________________

    Table:  C8 telescope specifications for available eyepieces
    ________________________________________________________________

    focal length  magnification     approximate
        (mm)          (X)          fields of view
                                  (arcminutes = ')
    ________________________________________________________________
         40            50               40
         25            80               30
         18           111               20
         12.5         160               14
          9           222               10
    ________________________________________________________________

      Observing Procedure:

      1. You should take the List of Tricks for C8 Telescopes outside. After the lab, just leave them on the benches.

      2. You will have to select the object from the pad menu and C8's will slew to it. You will have to do the fine centering yourself.

      3. When centered switch to smaller focal length eyepiece given to you by the instructor.

      4. Sketch the currently observable planets.

      5. Estimate the angular diameters by eye using the above table of the fields of view.

        The timing measurement specified in the lab is just too tough given the time we have available. So omit that part.

      6. Shutdown the C8's IF AND ONLY IF you are told you are the last users of the night.

        Level the C8's, turn off the star pointer laser and the crosshairs illumination, and turn off the C8 power.

    16. Planet Angular Diameter:

      You have estimated the angular diameters by eye based on the known field of view for whatever eyepiece you used.

      But for the Excel spreadsheet you need timings.

      Use fiducial times: t=40''/(15''/s)=2.7 s for Jupiter and t=18''/15''/s)=1.2 s for Saturn.

      You only do Jupiter or Saturn, not both.

      Do the one that was observed if either of them was.

      The range of angular diameters for the planets are:

      1. Mercury 4.5--13''.
      2. Venus 9.7--66.0''.
      3. Mars 3.5--25.1''.
      4. Jupiter 29.8--50.1''.
      5. Saturn 14.5--20.1'', excluding rings.
      6. Uranus 3.3--4.4''. Seeing Uranus as disky takes a bit of confidence/imagination since it's of order 1/200th of the field of view with the 9-mm eyepiece.
      7. Neptune 2.2--2.4''.
      8. ex-planet Pluto 0.065--0.115''.

    Boris Karloff, The Mummy

  4. Post Mortem

    5. Below are some generic comments for     Lab 6: Planets that may often apply.

    Any that are semester-section-specific will have to added as needed.

    1. Try harder.
    2. Be better prepared.
    3. Demand that the instructor be better prepared.