This area contains a series of occasional articles by IPS staff and their colleagues. Everything you always wanted to know about the Sun, space weather and much more.
For some general terms and definitions please refer to our glossary on Solar-Terrestrial terms
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New Solar Cycle Starts
The appearance of a reversed-polarity high latitude (30 degrees north) sunspot on 4 January, 2008 has been accepted by space scientists as the beginning of solar cycle 24. So we are officially into the solar cycle 24 now.
The Solar Cycle
The sun exhibits an extremely robust (reliable) periodic cycle of activity, going from very low activity at solar minimum to the highest activity at solar maximum then back to solar minimum again over an 11-year cycle. The sun has just gone past the solar minima towards the end of solar cycle 23 and we are now into the early stages of solar cycle 24. This can be seen by looking at the plot of sunspot number vs time sunspot number vs time which follows the tables of Monthly Sunspot Numbers in the Solar Section of the IPS website. The sunspot number is an index giving the number of sunspots on the solar disk, which is a way of gauging the level of solar activity. The smoothed sunspot number which defines the official solar minimum is the sunspot number averaged over 12 month periods centred on a given time. For example, the smoothed sunspot number for June 2006 is an un-weighted average of the monthly sunspot numbers from January to December 2006.
Sunspots and the Butterfly Diagram
At the beginning of a solar cycle sunspots form between 30 and 50 degrees north (or south) of the solar equator. As each solar cycle progresses from it's minimum to it's maximum and on to a second minimum, sunspots form at progressively lower latitudes until by the second solar minimum sunspots are forming very close to the equator. This is the situation at present, close to the end of Cycle 23. A butterfly diagram of the formation of sunspots throughout Solar Cycle 22 clearly shows this effect.
The Sun's Magnetic Field
When the transition from Cycle 23 to 24 occurs the magnetic field which surrounds the sun will change its polarity. This will be apparent in the magnetic structure of individual sunspot groups as seen in solar magnetograms such as those recorded at the IPS/USAF Learmonth Solar Observatory in Western Australia. With a change in the solar cycle, the polarity of the leader and trailer spots of a sunspot group are reversed. This observation, in conjunction with the latitude at which the new spot formed, will indicate that the change to the new solar cycle is underway.
Satellite eclipse season
For 21 days either side of the September 23 equinox, satellites in geo-stationary orbits will experience a total eclipse of the sun once every day. During the eclipse each day, satellites will be forced to shut down or to switch over to batteries. See an explanation of this bi-annual phenomenon. Around the same time, geo-stationary satellites pass very close to the sun as seen from the earth and suffer from interference. The IPS Sun-Satellite Interference Prediction Tool can be used to monitor interference affecting your favourite satellite. A list of names of key geo-stationary satellites can be found in the IPS Magnetopause Model.