Astronomical Spectroscopy
Investigating the Spectra of Astronomical Phenomena
Equipment
- Camera
- Diffraction Grating
- RSpec Software or other spectrometry software
- Computer
Recent developments in grating technology and CCD cameras have placed the ability to perform interesting and scientifically useful astronomical spectroscopy within the reach of amateurs. The idea is exceedingly simple: a diffraction grating is mounted in place of the lens on a CCD camera such as a DSLR, FITS or astronomical camera, which is then used to take a photograph of a star or planet. This can be achieved by inserting the camera into the eyepiece of a telescope or by using an adapter with a DSLR camera so that the user does not even need access to a telescope: the grating fits over the lens so the user can go out and shoot away at the stars.
The diffraction grating and mount is called a Star Analyser and it is available directly from the manufacturers; Paton Hawksely, from First Light Optics, or ordered from the RSpec website (see links).
The star's light is split by the diffraction grating which produces an image showing the point of light from the star on the left and the spectrum of the starlight spreading across the image to the right. Sometimes the spectrum is not horizontally aligned as shown below, but this is not a problem as it can be rotated using the spectrum analysis software
The image is saved as a file and uploaded to spectrum analysis software that produces a histogram showing light intensity across the range of light frequencies. It does this by counting the illuminated pixels along the length of the spectrum. Where there are Fraunhofer lines (the black absorption lines discussed in Theory) the number of illuminated pixels will be zero or at least much lower than the values either side, so the histogram wuill show a sudden dip.
The Fraunhofer lines correspond to different elements, so by taking a picture of a star using a diffraction grating mounted on a camera, and using spectrum analysis software to process that image, you can actually determine the elements that make up the star even though it may be tens or hundreds of light years away!
In my opinion, a very good place to get started is to visit the RSpec website, where you will find details of the RSpec software written by Tom Field, and video tutorials. RSpec is astronomical spectrum analysis software. It is affordable and easy to use with hellpful tutorials and an online user group.
