Weekly Science Notes from the Yohkoh Soft X-Ray Telescope

These weekly science notes are intended to give an unspecialised but scientifically fluent view of ongoing X-ray observations of the Sun from the Soft X-Ray Telescope (SXT) aboard the orbiting Yohkoh satellite. A nugget is a lump, esp. of native gold or other precious metal.   These weekly science notes are nuggets, in the sense that they may have a rough exterior, but they have a precious substance beneath the surface.

Sometimes the authors of these nuggets -- the scientists who operate SXT -- get carried away with technical jargon.   When that happens, use the glossary and/or the list of acronyms.  

To find all nuggets on a given subject, see the topic index or use the search window at the bottom of this page.

Weekly Nuggets came into being in 1997, when it became obvious that a huge wealth of information was contained in the Yohkoh data base, and a continuing record of the highlights was needed. During this year it became clear that we had passed the minimum of the 11-year sunspot cycle sometime in 1996.  The rise to solar maximum was underway!
The Nuggets in this year cover a diverse range of topics -- including flares and solar active regions (whose understanding is an important goal of Yohkoh), but also other phenomena related to the solar cycle, the effect of the Sun on Earth, and the "two steps forward, one step back" beginnings of the lurching return to a higher level of solar activity.
In this year, close collaboration with the ESA/NASA Solar and Heliospheric Observatory (SOHO) focussed attention on so-called halo coronal mass ejections (CMEs) as solar eruptions headed toward Earth. The solar activity level lagged behind expectations -- would it catch up? Would the peak really come in Y2K, as expected?
Almost five years ago scientists predicted that the the maximum of solar cycle 23 would probably occur this year. As the year unfolded we saw many flares and coronal mass ejections, and by the end of the year it became clear that their prediction was very close to what really happened. A big event this year was to have been the launch of NASA's HESSI solar flare mission, but a shakeup and a launch vehicle problem delayed it until 2002.
By any definition, it's the beginning of the millennium. Have we hit solar max yet? It's impossible to tell, until we're many months past it. Even the official prediction as of the end of 2000 from the Space Environment Center at NOAA shows that we can't yet really be sure whether it's already happened or will happen during this year. We could only repeat our previous bit of advice -- stay tuned.
Research is an uncertain business. Although it seems likely that old Sol hit the maximum of the sunspot cycle in the year 2000, the statisticians tell us that because the Sunspot Number started to go up again during the year 2001 we can't be entirely sure. Yohkoh enters this year with an uncerain future, as well, as the result of the troubles described in an earlier nugget.

A Glossary of useful terms
MSU Solar Homepage

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