The most striking features of the Sun this week are the dark areas at the northern and southern polar regions (seen here on 16 June 2006) when viewed in ultraviolet light. Since coronal holes are 'open' magnetically, strong solar wind gusts can escape from them and carry gas from the solar atmosphere out into space. These magnetic fields in polar coronal holes must extend from one pole to the other, but they extend so far out into space that we have not been able to track them with certainty.

Polar holes are most easily visible when the Sun is near its period of least activity (solar minimum) in the 11-year solar cycle. At this point, the Sun's magnetic field is simplifying into a "dipole," like the magnetic field around a bar magnet, but it won't stay that way for long. Before very long, the cycle of increasing activity will begin again as the magnetic poles begin to reverse places again over the next 11 years.

Coronal holes appear darker because there is simply less ionized gas emitting the spectral line being observed, from eleven-times ionized iron in this case.

Previous Picks of the Week

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 steele.hill@gsfc.nasa.gov.