May 26, 2017

Event of the Week: 29.06.09: The Deepening Solar Minimum.


Two tiny active regions (light spots) just starting to make themselves known…(credit: ESA/SOHO).

Something mildly bizarre is happening on our nearest star, the Sun. Or should we say, a lack there of… This weeks astro-event is a sort of non-event, but one of the big mysteries of 2009; where exactly are the sunspots? Turning that newly constructed white-light filter we built last week on our mild-mannered star shows a definite lack of activity in the solar photosphere. This isn’t entirely abnormal, as the Sun is just coming off of a solar minimum that occurs every 11 years. What is unusual is the length of this minimum; we’ve had over 600+ spotless days since 2004, a quarter of which have been in 2009 alone. A typical minimum consists of an average of 485 days. You have to go way back to 1913 to find such comparable a lull! Two tiny sunspots appeared last week, which prompted the discussion as to whether the latent solar cycle #24 is finally amping up or not. Both spots belong to the new cycle, their reversed polarity giving them away. Using the technique of helioseismology, Frank Hill and Rachel Howe at Tucson’s National Solar Observatory have discovered that the Sun’s internal dynamo isn’t dead, just sleeping. They predict that the subsurface tachocline should begin intersecting the surface at the junction of 22 degrees latitude by the end of 2009, and activity should resume. It’ll be a wait and see mystery that will only deepen if the spots don’t return to roost; and does this portend a stronger than usual maximum around the solar bend? Stay tuned!

This week’s astro-term of the week is Sporer’s Law. First worked out by astronomer Gustav Sporer, this law simply states that sunspots form at higher latitudes at the beginning of a solar cycle, and then gradually progress downward to lower latitudes in both hemispheres as the cycle progresses. We never see spots above 45 degrees of latitude, and astronomers aren’t quite sure why. The link between the solar cycle and the climate isn’t yet fully understood. Could a spotless Sun mimic or mask the effects of global warming? Both Earth and space bound telescopes are keeping a constant watch on our Sun. Cries of another Maunder minimum, a time from 1645 to 1715 that was marked by harsh winters and almost no sunspots were seen, may be a bit premature… cycle #24 were art thou?