Lunt calcium-K star-diagonal module

By Steve Ringwood

Cak_B600_940x1343During Earth’s night, the freshest starlight that astronomers can receive is at best already over four years old. Wait until dawn though and the photons bursting from our nearest star are freshly minted barely eight minutes previously. As creatures forged in such stellar proximity, I often wonder whether we appreciate enough the advantage of having this sample so close to home!

Our Sun, of course, has long suffered our probing via the copious light it provides — telescopically for about 400 years, via the broad brush of its white light continuum. Yet only comparatively recently have we peeled away layers of detail from the Sun’s image by slicing out tiny wafers of that illumination. Having enjoyed the marvels that ionised hydrogen elicits, it has also become possible to make visible a layer underlying that betrayed by hydrogen-alpha, via a spectral line of calcium, at 393.4nm. At the edge of human vision, its violet profundity is barely caught by the eye, but it can be more easily imaged.

Incredibly, access to the calcium K-line is provided by this device alone, without requiring a dedicated instrument or supplementary filtration. Needing only a conventional refractor of 100mm aperture or less, this combined solar diagonal and blocking filter simply fits into a telescope’s two-inch focuser. Voila, an instant calcium k-line solar instrument.

Detail of super-granulation and other features (outside the reach of hydrogen-alpha telescopes) becomes available. The ‘user’ side of the module offers the choice of 1.25-inch eyepiece or t-thread fitting. Choose from one of the three available modules for a best configuration-fit for your instrument.

Price: With blocking filter B600: £799
B1200: £1,119
B1800: £1,299.

For more information: