Observations with the NRL spectroheliograph $082A on board Skylab (Tousey et al., 1973) showed the presence of a large number of protrusions above the solar limb (the largest ones sometimes called 'superspicules'). These spicule-like features are especially well visible in the Le line of He + at 304 A. A preliminary discussion of them is given by Bohlin et al. (1974). This research note compares the spicule-like structures in the 304 A. line with the He spicules.
On 1974 January 29 and 31, we obtained simultaneous (At <30 s) observations in the 304 A line on Skylab and in the He line with the vacuum telescope/universal filter combination at the Sacramento Peak Observatory. The H~. observations consist of filtergrams taken in rapid succession at the He line center and at He_+ 0.5 A. Figure 1 shows a sample of the January 31 data. The observations were made near the north pole, since the 304 A spicules appear to be best visible in the polar regions. Precise registration between the images was obtained by comparing the location of prominences at an adjacent part of the solar limb. This, however, was not as easy as first anticipated since prominences are quite different in appearance in the two lines. There definitely is not a one to one relationship between He and He H (304) brightness in prominences. Some of the brightest He + prominences are weak or absent in the He observations. Also inside each prominence the structures seem to be quite different. This limited the accuracy of alignment between the images to + 15". Two methods were used in comparing the images in the two lines' (i) we made a direct visual comparison between the images allowing for a maximum _+15" shift, and (ii) we measured the location and orientation of spicules in both images and defined a correlation criterion. In both methods also different portions of the limbs were compared in order to establish a significance level.
Direct visual comparison failed to show a significant correspondence between the spicules in the He n (304) and H:: images. Some of the spicular features in the one line