Download Observing the Solar Spectrum

WJP X, XXXX.XX (20XX)
Wabash Journal of Physics
1
Observing the Solar Spectrum
Daniel Brown and Micah Milliman
Department of Physics, Wabash College, Crawfordsville, IN 47933
(Dated: November 7, 2008)
The solar spectrum gives a lot of information about the elements that make up the Sun and that
are used in the fusion reaction. We looked at solar spectrum using a MEADE LX-200 8 inch and
a Red Tide spectrometer and found the spectral lines given by the elements. We found evidence of
hydrogen, helium, nitrogen, dioxide, and oxygen.
The Sun is the most prominent feature in our solar
system. It supports all the planets and life forms in our
solar system. The energy from the Sun that sustains us
is created deep within the core of the Sun. The temperature and pressure there is much greater than on Earth
and is the perfect conditions for nuclear reactions to take
place. In the core of the Sun gravitational forces accelerate hydrogen atoms and make them collide. The collision
causes hydrogen nuclei to fuse together to form a helium
nucleus. This means that the Sun generates its energy by
the nuclear fusion of hydrogen nuclei into helium. The
helium atom is much smaller than the hydrogen and the
difference in mass is expelled as energy in the form of a
photon and is carried to the surface of the Sun. Through
convection the light and heat is released into the atmosphere and felt on Earth as heat and light. This energy
can be harnessed through many different natural and synthetic processes. Photosynthesis and solar cells use solar
power to generate power and energy.
Spectroscopic analysis separates light emanating from
the Sun into a pattern of colors. This allows scientists
get an idea of the proportional breakdown of elements
that are present in burning solar masses. Each element
is related to a specific wavelength according to its energy.
The Sun’s spectrum ranges from 350 nanometers to 950
nanometers. Using this process we can confirm which
elements make up the Sun and which are involved in the
fusion reaction. The spectrum should mostly consist of
hydrogen and helium lines.
To observe the solar spectrum we used a MEADE LX200 8 inch, seen in FIG. 1. The telescope gave us a clear
imagine of the Sun but the light was far to intense to look
at directly. We added an 8 inch solar screen over the lens
of the telescope so that we could view the Sun without
damaging our eyes or flooding the measuring equipment.
The solar screen blocks out all of the Suns light except
for 1/10,000th. This allows us to safely view the Sun.
We then attached a fiber optic adapter to the eyepiece
of the telescope and a fiber optic cable that led to a Red
Tide spectrometer, shown in FIG. 2.
The spectrometer is an optical instrument used to measure properties of light over a specific portion of the electromagnetic spectrum. The spectrometer produces spectral lines and measures wavelength and intensity using a
CCD camera. The data collected is then sent to LoggerPro were we plotted the results. To align the telescope
with the Sun we first removed the solar screen and took
FIG. 1: The figure shows the telescope that we used for this
experiment. We used the MEADE LX-200 8 inch telescope.
We placed a solar screen that allowed 1/10,000th of the light
in over the 8 inch lens and looked at the Sun. We then connected the Red Tide spectrometer, shown in FIG. 2 to the
telescope using a fiber optic cable and we were able to measure the solar spectrum of the Sun.
off the eyepiece. We held a piece of paper up against
the eyepiece hole and moved the telescope lens vertically
and horizontally using the control knobs until the light
on the paper was brightest. We then placed the solar
screen over the lens and attached the fiber optics cable.
The LoggerPro program was set to fast collect and we
made small adjustments to the vertical and horizontal
positioning and the focus until the intensity was maximized. We then changed the the collection period. We
performed ten trials. The first five had collection periods
of 1000 ms and the next five had collection periods of 600
ms.
While examining our results we noticed that the data
did not fit the exact shape that we expected. The Sun
is a black body and the shape of the spectrum can be
described by Planck’s Law
I(λ, T ) =
2πc2 h
1
,
λ5 ehc/λkB T − 1
(1)
where λ is wavelength, T is temperature, c is the speed
of light, h is Planck’s constant, and kB is Boltzmann’s
constant.
WJP X, XXXX.XX (20XX)
Wabash Journal of Physics
2
in our data. Using the Basic Atomic Spectroscopic Data
supplied by NIST, we identified helium, hydrogen, fluoride, dioxide, nitrogen, and oxygen spectral lines. All
these elements are found in either the atmosphere of the
Earth or the Sun. This means that our solar spectrum
measurement is a good representation of the Sun. For
future trials of this experiment their some improvements
that can be made. More research should be done about
the sensitivity of the CCD camera in the Red Tide spectrometer. There may be an adjustment that can be made
or maybe a constant to multiply the data by. Also, it may
be better to calibrate the data using a black body with
a higher temperature than the incandescent light bulb.
We suggest trying an arc lamp or a halogen light bulb
We found that our raw solar spectrum data did not fit
this. We attributed this difference to the response function of the CCD camera in the Red Tide spectrometer.
To fix this difference we took data with an incandscent
light bulb, which is also a black body. We placed the
fiber optic cable in a dark box and collected spectrum
data. We randomly changed the voltage to create a different temperature for each trial. We preformed this ten
times using different voltages each time. We calculated
the expected value using Planck’s law and divided it by
the actual data to get the calibrated data. We then normalized this data by dividing by the maximum. We took
the solar spectrum data and averaged tthe ten trials and
normalized it by dividing by the maximum. We then
multiplied the normalized calibrated light bulb data by
the normalized calibrated solar spectrum data to get the
final calibrated data. shown in FIG. 3.
We checked the accuracy of our solar spectrum measurement and calibration by identifying the spectral lines
[1]
[2]
[3]
[4]
He
H O2 F
N
N
O
0.14
0.12
0.1
Intensity (I)
FIG. 2: This figure shows the schematic for the Red Tide
spectrometer that we used for the experiment. Light enters
the spectrometer from a fiber optic cable(1) and goes through
a small slit(2). The light then passes through a filter (3) and
reflects off a collimating mirror(4) that focuses the light. Next
the light enters a diffraction grating(5) and directs the light
towards a focusing mirror(6). Finally the diffracted light is
incident upon the CCD camera(7) and the data is sent to
LoggerPro.[4]
0.08
0.06
0.04
0.02
0
400
500
600
700
800
900
Wavelength (nm)
FIG. 3: The graph shown in this figure shows the results the
calibrated spectrum of the Sun. We calibrated this data to
eliminate the response effects of the CCD camera. We can
see the spectral lines that are emitted from the Sun and the
spectral lines from the light interfering with the atmosphere.
This lines were in agreement with NIST’s Basic Atomic Spectroscopic Data[1].
instead.
physics.nist.gov/PhysRefData/Handbook/periodictable.htm
and Operation Manual”, Ocean Optics, Inc., Dunedin, FL,
http://en.wikipedia.org/wiki/sun
pages 20-21.
http://www.solarviews.com/eng/sun.htm
[5] www.meade.com
Red Tide USB650 Fiber Optic Spectrometer, ”Installation