Friday, September 20, 2013

September 22 - Autumn Equinox

Taken by June Gronseth via
There have already been some great aurora displays this year and with the Autumn equinox just around the corner and more sunspot activity coming to the Earth side of the sun, we should get a good show in the next couple of weeks.  Remember there are several of aurora resources on the September page for looking for aurora if you are not among the lucky people who live in the higher latitudes and get to see the aurora out of your kitchen window.








Visible light image from the Solar Dynamics Observatory 9/20/13


What do Sunspots have to do with Aurora?

Sunspots themselves are not that important for aurora, but solar activity is what causes aurora and sunspots are where solar activity usually comes from, hence more sunspots usually means more solar activity and more aurora.  The sun is currently in what is called solar maximum, which normally indicates increases solar activity, however there has not been a great deal of solar activity lately. Despite this lack of sunspot activity there has been enough solar activity to create some wonderful Aurora, and hopefully this new cluster of sunspots rotating into view will mean even more aurora in the coming weeks.









Why does the equinox have any impact on Aurora?

From David Hathaway- NASA Marshall
Late August or early September is often called aurora season by residents at higher latitudes. This is because the aurora can more easily be seen due to the end of the midnight sun and night. The vernal or Spring equinox should really be called aurora season, but aurora are seen at both equinoxes. Studies have shown that during both the fall and spring equinoxes geomagnetic disturbance and thus aurora are twice as likely as during summer and winter. This figure by solar physicist David Hathaway of NASA Marshall Space Flight Center uses 75 years of data to show the relationship between the number of geomagnetic disturbances and the time of the year. For a long time scientists did not know what made equinoxes special. Using data from space missions such as THEMIS, scientists now know that it is all about geometry. THEMIS showed us that there are special magnetic ropes connecting Earth's upper atmosphere directly to the sun. During the spring and fall equinox the geometry of the Earth with respect to the sun is such that its magnetic field is best oriented to connect with the sun. (From C. Alex Young at The Sun Today)