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The Spectrohelioscope

Rhian Chapman

An image taken by the solar telescope, showing an unusual ring pattern of sunspots and a separate sunspot group.

This image was taken by Rhian and Matt with the solar telescope. Note the unusual ring pattern of sunspots and the separate sunspot group.

This project is currently being undertaken by Rhian Chapman and Matt Lambert. The project is being supervised by Dr P. Mauskopf, based on an original idea by Dr J. Davies, with the ever-present help of Mr H. Lang.

The purpose of the project is to build a scanning spectroscope to attach to the solar telescope, to take spectra of different parts of the sun's surface. This will allow us to compare bright parts of the solar surface with sunspot regions.

Most recently, the exciting observations shown in the image on this page have been made of the white light image of the sun, as two very impressive sunspot groups have been observed and photographed, at least one of which has been associated with a coronal hole. The surface of the sun has been very interesting over the last two weeks, and it is hoped that this clear weather will hold out, allowing for more photographs to be taken, to allow tracking of the motion of these active areas.


The first step of this project was to obtain white light images of the sun using the department's solar telescope. Luckily the weather has been good enough recently that the sun has been available for observations for much of the day, aiding the set-up of the apparatus and some quick advances in this early stage of the project.

The image of the sun is projected onto a horizontal surface, and is just over 30cm in diameter, allowing easy study of the sun's photosphere: several sunspots have already been observed, and the granulation present on the sun's surface has also been seen.

In order to observe the sun's chromosphere a spectroscope must be used. This spectroscope was built by a previous student as a project, using the Hale spectrograph design, in which two mirrors and a reflecting diffraction grating are positioned between the entrance and exit slits of the spectrograph.

The sun's spectrum is projected across the spectroscope exit slit, and although the final image is not yet correctly aligned in the viewing plane, many absorption lines in the spectrum have already been observed and identified. The positions of the mirrors within the spectroscope require some fine-tuning, which will be most easily done once the heliostat is able to accurately track the sun across the sky.

Solving this inaccuracy in the heliostat tracking is the current task of this project: the image of the sun is not steady within the image plane, it must continually be manually re-centred. In an effort to correct this, the heliostat was carefully aligned with the North star, although this has not produced the expected results. Work is now concentrating on the computer program which drives the heliostat motion.