2007 SOHO EIT IMAGE
1997 SOHO EIT IMAGE
SOHO moves around the Sun in step with the Earth, by slowly orbiting around the First Lagrangian Point (L1), where the combined gravity of the Earth and Sun keep SOHO in an orbit locked to the Earth-Sun line. The L1 point is approximately 1.5 million kilometers away from Earth (about four times the distance of the Moon), in the direction of the Sun. From that vantage point, SOHO’s Extreme ultraviolet Imaging Telescope (EIT) has enjoyed an uninterrupted view of our daylight star for the last eleven-plus years. All previous solar observatories have orbited the Earth, from where their observations were periodically interrupted as our planet `eclipsed’ the Sun.
SOHO’s Pick of the Week featured this remarkable milestone:
Pick of the Week — Then and Now — February 9, 2007
On 2007 February 8, the SOHO Extreme ultraviolet Imaging Telescope (EIT) became the first spaceborne solar imager to observe a complete solar cycle. EIT has now been observing for the mean length of a solar cycle, 11.1 years, since its first image was obtained on 1996 January 2. SOHO is the first solar observatory in space to observe a complete solar cycle. It has the unique opportunity of offering a retrospective reaching back over an entire solar cycle. So we can select and compare images and movies of the Sun almost exactly 10 years apart. We took a snapshot of the several weeks (January 15 – February 5, 2007) and pulled together frames from ten years ago (January 15 – February. 13, 1997).
The Sun is fairly close to solar minimum (its lowest level of solar activity) for both of these periods, so one would expect both sequences to show a similar level of activity. In fact, it does. We see very few active regions and no major solar storms. It would appear that the 1997 frames are a little crisper with a bit more sharpness. Well, 11 years of staring at the Sun has probably taken a toll on the CCD imager. Still, what is most remarkable is that a single spacecraft has held up so well and produced such a long and valuable observation record, a record that scientists around the world are studying and analyzing every day.
Images and story courtesy of NASA/ESA.