Class Project: A
Solar Spectroscope for the Visitor Information Station
The students of the University of Hawaii at Hilo, Astronomy
450 course (Advanced Instrumentation) have built a small solar spectroscope as
a class project.
The goal of this project was, primarily, to introduce the
students to all major steps in
the design and construction of optical instruments. However,
it was intended to produce
a useful instrument for the Onizuka Center Visitor
Information Station. The VIS
already operates a solar telescope for daytime visitors, and
a spectroscope, showing
the absorption lines in the solar spectrum, was a nice
addition to this telescope.
The project proceeded along these steps:
the scientific goal of the project. In our case the goal was to provide a
visual spectroscope to the solar instrumentation package of the Visitor
Information Station that has sufficient resolution to show a large number
of absorption lines in the solar spectrum.
technical requirements. In the case of our project, the requirements
included a sufficiently large visual image of the spectrum, a clearly
defined exit pupil of the instrument with sufficient eye relieve for
people wearing eyeglasses, the ability to focus the instrument. Further,
we estimated the limits of sufficient brightness of the spectrum, comfort
limits to the brightness, and safety limits, and discussed safety
consequences of failure modes of the instrument. Finally, a design
requirement for ruggedness of the instrument and elimination of most modes
of mishandling was identified.
basic instrument layout was established based on a paraxial model of the
required optical components.
available components were identified from the Edmund Scientific catalog. A
detailed Zemax model using the optical data of the selected components was
mechanical dimensions established with the Zemax model were transferred to
an AutoCad layout of the instrument.
components, the slit holder and the grating mount, that could not be purchased
commercially, were design in detail for in-house fabrication.
slit holder was fabricated on a manual lathe, with each student doing at
least one fabrication step. The grating mount was prepared on a manual
mill and finished using a CNC with the help of the IfA machinist.
components were inspected, cleaned, painted, and test assembled.
collimator was focused using an alignment telescope, the slit position was
aligned using fluorescent light bulb as a source of line radiation.
all adjustable features were fixed in position with epoxy, the the
threaded components were secured with epoxy.
achieved “first light” observations of the solar spectrum in the last week
of the semester. By comparison with the atlas of the solar spectrum,
people with average eyesight can see a resolution of about 0.1 nm.
Optical Layout of the Solar Spectroscope
Mechanical layout of the solar spectroscope, drafted in
AutoCad. All optical components
and most mechanical elements were purchased from Edmund
Fabrication of the slitholder on the lathe.
The spectroscope is completed. “First Light” in the IfA
The solar spectroscope in use at the Onizuka Center Visitor
Information Station at Hale Pohaku. The other instruments are a 11”
Schmidt-Cassegrain used for white light observations of the solar disk, and a
small Hα telescope for the observation of flares and solar prominences.
An image of the solar spectrum, taken with a handheld
digital camera through the eyepiece of the solar spectroscope.
Most people can see more detail than is recorded in this
image. The sodium doublet in the yellow (orange here) part of
the spectrum can usually be seen as clearly resolved, for