Prominence Latitude

“I was interested in Brian Mitchell’s method of determining Prominence latitudes.  I would like to add an alternative which I have used for many years to advantage; the Protractor method, which I devised with the help of Alan Scott 15 years ago.

Like Brian’s way, a haircross is permanently attached to the bottom of my 40 mm eyepiece (I used a fine strand of nylon from a stocking).  The upper half of a commercial protractor is attached to the eyepiece and a separate pointer is clamped to the eyepiece holder, as illustrated.  At the onset of the observation, the haircross is achieved by bringing the E-W line of the cross to near N or S of the solar disc and by rotating the eyepiece and moving it in right ascension until it is aligned.  The disc is centralised and the pointer is moved at the 90º mark of the protractor.  When a prominence is seen, the eyepiece is rotated until the pointer coincides with the prominence.  The pointer thus shows the exact distance of the prominence from the N point and is marked on the drawing board.  This procedure is repeated for every prominence.  Obviously, an equatorial mounting is essential and a motor drive is of great advantage.”

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