Sky and Telescope - September 2018 - 71

Average box at the bottom of the Proﬁle
screen. That will steady the graph down.
I let my video play until I came to a section that showed the dips, the spectral
lines, distinctly. I then paused the video
and began the calibration process.
Open RSpec's Calibrate window using
Tools > Calibrate. Looking at the Proﬁle,
you'll notice a thin spike on the left
separate from the rest of the graph. That
is the star itself, which you use as the
ﬁrst calibration point. Move the mouse

cursor to the spike's peak and click. The
star's pixel value will be automatically
entered in the Calibrate Point 1 ﬁeld.
Below that is a ﬁeld for wavelength. Tick
the Zero box to its left.
Calibration Point 2 is on the actual
spectrum to the right of the spike. The
goal is to click on a dip caused by a
known absorption line. That's why it's
important to use a prominent A-type
star for calibration. A-types show the
hydrogen Balmer lines strongly, and the

RSpec also allows you to
label the elemental lines
in your spectrum.

The spectrum of the Ktype star Arcturus looks
very different from that of
an A-type star like Vega.

Another interesting feature of RSpec is its ability
to overlay and compare
the spectra of different targets. This graph
compares the spectrum
of Vega to that of another
A-type star.

H-beta line is particularly easy to locate;
it's the ﬁrst dip to the left of the Proﬁle's
peak. Click on that "valley" and enter
"4861" in the wavelength ﬁeld. And
that's it - calibration is complete and
should be saved for use with other stars.
The program can overlay lines of
various elements on the calibrated
Proﬁle so you can verify your calibration is accurate. Clicking the Elements
icon (three vertical lines) in the Proﬁle
section's toolbar yields a window with
a list of various element lines. Tick the
Balmer Series box and the Balmer lines
will be drawn on the Proﬁle. If the
hydrogen beta line runs through the dip
you selected, you are good.
Note that due to poor seeing and
other factors, spectral lines may not
always coincide exactly with the Proﬁle's valleys. Also, some of the dips may
not be strong depending on the sensitivity of the camera and the spectral
dispersion the telescope delivered. I was
thrilled to see my graph showed the
Balmer lines right where they should be.
RSpec offers plenty of features. You
can use the Elements utility to identify
other elements and features in the spectrum. Once calibrated, the proﬁle graph
can even be converted into a rainbow
using the Synthesize function. While
not really as useful as the graph, it's
prettier and impresses my students.
The next step is imaging different
star types. Analyzing the spectra of various star classiﬁcations combined with a
little reading can teach a lot about stars
and stellar evolution. Once you are
proﬁcient at analyzing the absorption
lines of stars, you might try examining
the emission lines of nebulae.
Beyond that? Amateurs equipped
with RSpec and modest telescopes like
my 8-inch SCT are doing some amazing
science, which range from analyzing
the atmospheres of the solar system's
gas giants, to determining the red shifts
of distant objects including quasars.
Thanks to RSpec, the limit is not your
equipment but your imagination.
■ Contributing Editor ROD MOLLISE
enjoys getting some real science out of
his time at the telescope.
sk yandtelescope.com * S E P TE M B E R 2 018

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Sky and Telescope - September 2018

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