Spectrometer Calibration

Notes on DADOS Calibration Lamp from Baader Planetarium Website

The following explains why the light kept switching on and off when Lee and I changed the plug at RAG mid-monthly meeting last Friday!

It also explains the black ring under the lamp – this appears to be so that it can fit over 2 inch end of a spectrograph – will it do same on my CCDSPEC?



Notes on DADOS Calibration lamp

The Neon calibration lamp only shines in the dark due to a twilight switch. So incidence of extraneous light while taking spectra of this Neon lamp is avoided. Please fix the Neon lamp with its adapter directly at the 2 inch entrance of the DADOS spectrograph to focus DADOS and to take reference spectra. The brightness of this Neon lamp is adequate in this configuration.

However, the lamp is too faint to be used in front of a telescope. The visually perceived color “Neon red” is a quite unique color between dark-orange and light-red due to the spectral distribution of the emission lines.

RELCO Starter Spectrum from CCDSPEC at LRO graphed against Three Hills Observatory ALPY data and with lines identified including those used by ISIS for calibration

On the RELCO starter spectrum below, my CCDSPEC spectrum is graphed against the ALPY spectrum from Three HIlls Observatory from Robin above, and I have marked the lines I identified together with those lines that ISIS use for calibration – this gives some more lines for me to use at LRO.

Comment from Robin at Three Hills Observatory (https://stargazerslounge.com/topic/226911-neon-lamp-to-set-spectroscope/), “Your spectrograph has roughly the same resolution as the ALPY (R~500) and these lines are known to be reliable and give a very accurate calibration to better than 1A with the ALPY.  I have attached a list of wavelengths of the 13 lines. They correspond to lines identified in the spectrum by Richard Walker using his DADOS with 200l/mm grating (R 900).  If you identify as many of the lines in your spectrum as possible and make a 3rd order fit,  any wrongly identified lines will immediately stand out as they will have larger errors.”

Lines used by ISIS to calibrate ALPY

  • 3946.1A
  • 4158.59A
  • 4510.73A
  • 4545.05A
  • 4657.9A
  • 4764.87A
  • 4965.08A
  • 5400.56A
  • 5852.49A
  • 6266.49A
  • 6506.53A
  • 7147.04A
  • 7383.98A


Identifying lines on my CCDSPEC RELCO Starter Spectrum using Atlas of Emission Lines

Here is my go at identifying emission lines on y RELCO Spectrum using the Atlas of Emission Lines 200 lines/mm spectrum.


My RELCO with my attempt at identifying lines:

I used the following spectrum from http://www.ursusmajor.ch/downloads/sques-relco-sc480-calibration-lines-5.0.pdf from which to identify above lines:

Attempting to calibrate RELCO Starter against 12V Compact Fluorescent Lamp in order to work out the wavelengths of the main lines on RELCO spectrum

Today, I have had a go at calibrating the homemade RELCO Starter bulb calibration lamp I made against 12V compact fluorescent lamp bulb in order to determine the wavelengths of the main lines on the CCDSPEC spectrum of the RELCO bulb.

Download calibration files from analysis by clicking on link below – calibration files RELCO vs CFL CCDSPEC no telescope 30/9/2018:

Spectrum RELCO Starter on CCDSPEC without telescope 300918

Also look at https://stargazerslounge.com/topic/226911-neon-lamp-to-set-spectroscope/?tab=comments#comment-3521335 to find out what happened when I tried to compare the lines I identified below with the atlas of lines from http://www.ursusmajor.ch/downloads/sques-relco-sc480-calibration-lines-5.0.pdf – sadly they don’t seem to match!


RELCO Starter Bulb spectrum taken with CCDSPEC Spectrometer (below):

Spectrum of compact fluorescent light bulb taken with CCDSPEC (below):

Graphing both above spectra together:

Calibrating spectra of both RELCO and CFL using above two lines in RSPEC gives following calibrated spectra:

The following is my final labelled image showing main lines on RELCO starter bulb spectrum (below):

Spectroscopy of Arcturus – re-analysis of spectrum from 4/8/2018 on 26/9/2018

Hi All

The following images are of my analysis of a spectrum of Arcturus I took using my CCDSPEC spectrometer. On this occasion, I used my Sky Watcher Equinox Pro 120mm OTA on EQ6 Pro (although I was hand guiding it rather than using the drives). The camera is a QHY6 and the acquisition software was EZCAP which comes with the camera. I took the spectrum in Lichfield, Staffordshire, UK on 4/8/2018 and analysed it 26/9/2018 using RSPEC software.

Attached are:

  1. Uncalibrated spectrum line graph (x-projection).
  2. Calibrated spectrum of Arcturus – I used an amateur spectrum on the internet to provide three data points for the RSPEC Calibration Wizard (linear approximation).
  3. A plot of my calibrated spectrum against the closest reference spectrum I could find in RSPEC. Arcturus is spectral type K1.5IIIFe-0.5 but closest match I could find on RSPEC was K1iv, so I have plotted against that. In spite of the slight differences, I have been able to identify almost exact matches for range of lines between the two spectra – it amazes me how amateurs can obtain incredibly precise data using spectroscopes on their very modest backyard setups!
  4. From this I have generated a calibration graph for my own future use which I have also posted here – if you have a better/alternative one you have created please do upload it in response to my post here.


Comparison of spectra of 12V Compact Fluorescent Light Bulbs

The 12V Compact Fluorescent Light Bulbs I have purchased come in two flavours – 2700K and 6400K (later is daylight). Tonight, I took spectra of both types using my CCDSPEC spectrometer to determine whether the peaks shown on the spectra were the same. It turns out that they are and hence can be readily used for calibration purposes on my spectrometers. The main difference between the two is the intensity of the peaks with the 2700K light bulb having much lower intensities than the 6400K light bulbs.

Information on different colour temperatures of compact fluorescent bulbs can be found at http://www.lamptech.co.uk/Documents/FL%20Colours.htm


2700K spectrum:

6400K spectrum:

The Compact Fluorescent Bulb Spectrum as a standard calibration spectrum for low resolution spectrometers in astronomy, and comparisons with alternative calibration light standards

I have annotated the following compact fluorescent light spectrum with the wavelengths of the main peaks, in order to make the diagram most useful for spectrometer calibration purposes. I am indebted to Wikipedia for the source information on which this graph is based.


The above is useful for calibrating my CCDSPEC and Science Surplus DIY Spectrometers and other similar spectrometers.

The process involves me taking a spectrum and then identifying the lines on it and calibrating the spectrometer using the process in the relevant software package. This is a spectrum from the Science Surplus DIY Spectrometer of a Compact Fluorescent Light:

The compact fluorescent spectrum can be used to help identify lines on other calibration lights, such as one made from a RELCO neon fluorescent bulb starter:

Further enhancement of calibration can be achieved using alternative calibration standards such as the solar spectrum – here I have annotated that spectrum with the Fraunhofer elemental lines:

Another alternative to calibration standard lights is to use an LED light – this one provides lines in red, green and blue, and is from on a variable colour strip light I purchased from ebay:

Compare the above to a commercially sold white LED calibration light: