The Opposition Effect of Saturn

I’ve just assembled this new montage of images of Saturn from the 2007–8 apparition for publication in a book authored by my friend Dominic Ford. It shows the Opposition Effect, whereby Saturn’s rings become abnormally bright at low phase angle.

From the top, they are 2008 February 25 00:31 (taken within eight hours of zero phase angle between Earth, Sun and Saturn), 2008 February 26 23:27, and 2008 March 04 23:56. All taken at Stag Lane observatory through the C-14 with Lumenera SkyNYX 2-0 camera.

See also my article on this subject in the 2008 April issue of the Journal of the British Astronomical Association.

First attempts at photographing stellar spectra

These are my first attempts at photographing stellar spectra, encouraged by a suggestion from Jack Martin, who showed me pictures he had taken using a similar grating and camera arrangement. The spectrum is allowed to drift across the camera chip more or less at right angles to its direction of dispersion, by turning the drive off during exposure, which makes the features in the spectrum apparent.

Vega is a typical star showing Fraunhofer absorption lines. Capella does not show much at the resolution of this system. This I believe is because it is binary, with spectra from the components Doppler-shifted differently, so they are separated and the lines partially covered up. Gamma Cassiopeia is a well-known “chemically peculiar” star (the prototype of the Be-type stars), which is spinning rapidly. This is thought to give it a hot “decretion disk” of  hydrogen around its equator, which is responsible for the emission lines in its spectrum.

The Star Analyser

I’m currently experimenting with the Star Analyser diffraction grating, inspired by Jack Marin, who showed me an amazing high-resolution view of the solar spectrum, with hundreds of absorption lines visible, through his LIRES III high-resolution spectroscope when he visited. Visually, at the eye-end of the C-14, the Star Analyser (which is about the cheapest astronomical-quality grating you can get, costing about £70) shows a perceptible difference between a “standard” star, like Vega, and a “strange” one, like Gamma Cassiopeia, with emission lines. However, you do have to know what you are looking for. I know because Jack showed me some photos of stellar spectra taken with a grating, C-11 and Canon EOS 350D camera.