Are We There Yet? (October 5, 2007)
Hi-res TIF image (359K)
Many people ask if we are at solar minimum yet and how do we know when we are. Solar minimum is the period when the Sun has reached its lowest point of solar activity in its 11-year cycle. One way to see if we are there yet is to observe the solar corona, easily seen in SOHO's C2 coronograph images. The structure we see in the coronagraph images is a marker for the global magnetic field extending into the corona and heliosphere. When the Sun is at its minimum and the corona is "relaxed", the elongated structures in the corona will extend out horizontally with both sides fairly balanced.
See the bottom coronagraph from 1996. At solar minimum, it's a simple "dipole" field, like a bar magnet's, and aligned with the solar equator. Compare that with the corona in an image from October 3, 2007 -- the structures are angled and unbalanced and they have looked like this for some time. In the absence of almost any sunspots over the past month or more, we still have this strong indicator that we are NOT there yet. Many predictors suggest that we will reach solar minimum sometime between January and March, 2008.
So, we'll just have to be patient.
SOHO began its Weekly Pick some time after sending a weekly image or video clip to the American Museum of Natural History (Rose Center) in New York City. There, the SOHO Weekly Pick is displayed with some annotations on a large plasma display.
If your institution would also like to receive the same Weekly Pick from us for display (usually in Photoshop or QuickTime format), please send your inquiry to firstname.lastname@example.org.