A comparison between the SXT and EIT

Science Nugget: Oct 31, 1997

This week's entry is actually from Oct. 16. The Extreme-ultraviolet  Imaging Telescope (EIT) calibration rocket flew successfully (see the EIT rocket Web page) and obtained splendid images, for which we believe we have overlapping data from SXT (at the time of writing we did not have an exact time for the EIT image).
This comparison shows an EIT 171A image on the left, and an SXT AlMg image on the right (Oct. 16, 18:26:54 UT; negative color table to show the faint features better). Apologies to the EIT team for not using their standard blue color table for this wavelength! Also their image, a 1024x1024, has been reduced here to 512x512, the resolution of the SXT data. As noted on the EIT Web pages, this comparison is a lot cleaner than the one with the routine SOHO data, and it seems likely that some quantitative data analysis would be interesting.

As has often been noted (see e.g. Golub, Solar Phys. 174, 99, 1997), the structures seen in both images are in roughly the same place. However the details differ almost completely! We are clearly seeing two extremely different slices of the corona, in spite of SXT's broad-band response. Note for example the trans-equatorial loops on the W limb that EIT sees but SXT does not; and the X-ray bright points in quiet regions that SXT sees but EIT does not.

H. Hudson 31-Oct-97 (email hudson@isass0.solar.isas.ac.jp)