26 May 2017 - Mission Day: 7847 - DOY: 146

Then and Now: Ten Years After EIT's First Light

Click on any image for a larger version.

[EUV image of the Sun in 0.9 - 1.0 MK plasma, 1996/01/02]

[EUV image of the Sun in 0.9 -- 1.0 MK plasma, 2006/01/02]

[EUV image of the Sun in 60,000 K plasma, 1996/01/02]

[EUV image of the Sun in 60,000 K plasma, 2006/01/02]

Click on any image for a full-resolution (1024 x 1024) version.

SOHO's Extreme ultraviolet Imaging Telescope (EIT) obtained its first images 1996 January 2, one month after the launch of the spacecraft. Only two quadrants of the CCD detector were imaged in eight- and nine-times ionized iron (Fe IX and X) at 171 Å (upper left), at 19:12 and 19:24 UT; a full field of view image (2006 January 2, 19:00 UT) shows the Sun ten years later (upper right).

A full-field image in singly-ionized helium (He II) at 304 Å was obtained at 19:36 UT that same, first day of EIT imaging (lower left); ten years later (2006 January 2, 19:19 UT), another view in He II (lower right).

The 1996 images are offset vertically because they were obtained before SOHO's "boresight" was aligned closer to the center of the solar disk. EIT is bolted to the frame of the spacecraft and its view follows SOHO's. Both sets of images are taken at nearly the same phase of the roughly 11-year solar activity "cycle;" the 1996 January images were obtained less than a year before the end of cycle 22, and we expect the minimum of the current cycle 23 to occur sometime before the beginning of 2008.

[EUV image of the Sun in 1.5 MK plasma, 2001]

[EUV image of the Sun in 1.5 MK plasma, 2001]

Click either image for a QuickTime movie showing the variation in solar activity in 1.5 MK plasma (Fe XII 195 Å): small (256 x 256, 1 Mbyte) or large (1024 x 1024, 60 Mbyte)

SOHO's twelve instruments began obtaining data just a few days after launch, 1995 December 2. The Extreme ultraviolet Imaging Telescope (EIT) was kept at a higher temperature than the rest of the spacecraft for a month after launch, however, in an attempt to outgas any water vapor and other contaminants that might have adhered to the telescope interior or detector, so EIT's "first light" was obtained on 2006 January 2. We present those original images, as well as images from January 2 of this year for comparison.

EIT is the only orbiting telescope that provides continual imaging of the entire solar disk and low corona in plasma at temperatures of 60,000 to 2.5 million Kelvin --- and has been for the last ten years, except forSOHO's brief "vacations" in 1998 and 1999. In conjunction with SOHO's LASCO coronagraphs, EIT provides two to three days' advance warning of solar storms approaching the earth.

EIT will be joined later this year by the Extreme UltraViolet Imagers (EUVIs) in the SECCHI instruments on board the NASA STEREOspacecraft, and in late 2008 by the Atmospheric Imaging Assembly (AIA) on the Solar Dynamics Observatory (SDO) spacecraft. The TRACE Small Explorer images limited areas of the Sun at five times the spatial resolution of EIT; the EUVIs will have twice, and the AIA telescopes four times, the resolution of EIT.

EIT was built and is operated by a consortium of French, Belgian, and US institutions, under the leadership of Dr. Jean-Pierre Delaboudinière, who recently retired as Principal Investigator (PI). The new PI is Dr. Frédéric Auchere of the Institut d'Astrophysique Spatiale in Orsay, France.

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