Determining the Diameters of Pluto and Charon
The purpose of this lab is to teach you how astronomers measure
the size of distant objects when fortunate events called occultations occur.
An occultation is an event when one celestial body passes in front of another.
If we know the distance to an object and that object's velocity in space, and
that object covers up a more distant object (an occultation), then by measuring
the amount of time for the more distant object to reappear will give us a measure
of the closer objects diameter. In this case, the alignment of Pluto and its
moon Charon was edge on relative to our line of sight. Pluto and Charon repeatedly
occulted each other and we were able to measure the diameters of both.
your left is the typical arrangement of Pluto and Charon as viewed from Earth.
You can clearly see the objects spinning around each other. This image was taken
on June 5, 2002 from the Gemini Telescope in Chile. In July 3, 2002 I was standing
atop Mauna Kea inside the Gemini Telescope twin. These are identical telescopes
with 8.1 meter mirrors. It was extremely impressive to stand inside a dome that
housed a telescope 7 stories high and weighed over 620 tons. However, the instrumentation
is so finely balanced that when it is doing an observing run, you could push
the entire scope with one hand.
Okay ... on to the lab. In this webpage are a series of scanned
pages from my "Activities in Astronomy" lab book. Since I have blatantly
copied these pages for this exercise, I want to take time to give credit to
Darrel B. Hoff, the chief author and editor. Kendall/Hunt Publishing Company
in Dubuque, Iowa, 1996. Since I am using these pages entirely for the purposes
of education and not for resale or profit in my part or that of Hopkins On-line
Academy, I believe that the "Fair
Use" rules of the Internet apply, and that I am fully within those
guidelines. If I were in a classroom setting, I would make copies of these pages
for those students as well.
Please read the following three pages of instructions and look
closely at the data from the Pluto-Charon occultations. Then print out the graph
paper to construct your light curve from the values you see on page three. Then,
answer the questions on the final page of this lab. I will not be asking you
to respond to discussion question #4, but everything else. Once you have finished
this work, then move to the mirror Pluto-Diameter
webpage where you can put your numbers and responses into those little boxes
that will come to me over the internet ... provided you press the submit button.
When you have completed the data sheet on your own, please move to a mirror
site where your answers can readily be placed in a file that I can receive via
Pluto, the Introduction
to Icy Worlds, the Introduction
to Planets, or to Syllabus. If
you want to wait on this lab until a later time and move forward to Comets,
well, who am I to stop you, but I prefer that you finish this first:)
| Home | Course
Introduction | Assignments | Teacher
Bio | Course Units |
Syllabus | Links |