Fraunhofer lines are dark absorption lines in the solar spectrum that can be seen when sunlight is passed through a prism to separate it into the colors of the rainbow. They occur because cooler gas, which is higher in the Sun's atmosphere, absorbs some colors of the light emitted by hotter gas lower in the Sun's atmosphere.
Sir Isaac Newton (1642-1727) discovered that if white light is passed through a prism, it separates into a rainbow, which is called a spectrum. While studying the spectrum that sunlight made, Joseph Fraunhofer (1787-1826) discovered some dark lines scattered among the colors. These dark lines were segments of colors missing from the complete spectrum. Fraunhofer counted 574 of these lines, which we now call Fraunhofer lines.
Spectroscopy is the original form of astro-imaging which Sir Norman Lockyer and Frank McClean used their telescope to study our sun and star within our galaxy. Both of them were interested in the composition and life of stars, and the spectra shows up the Fraunhofer lines which show us what elements a star is made of.
Within the observatory we have stored many of the original glass plates with the spectra on. Our aim during this centenary year is to reproduce some of these spectra using modern equipement.
Below is the star analyser which we use, attached to our cameras, in place of the prismatic cameras used by Lockyer and McClean. Click the picture for more information
RSpec is a program recently created to assist in calibrating spectrum images and allows you to create a graph and image of the spectrum.
Each year there are special projects which come out to look at stars which are under going change. While we will still participate in these I thought it would also be good if we had our own project which followed up on the work Sir Norman and the other astronomers who worked at the NLO carried out.
To that end I have been through the list of glass plates and chosen stars which they focused on and for which we have a range of spectra to compare ours to. To learn more and see our targets just the heading of this section.
Over the next few months data will be collected from many sources and the spectral plates will be calibrated so they can all be compared. As this happens the information and images will be uploaded here.