Sunspots begin as small dark areas known as pores. These  pores  develop  into  full-fledged  spots  in  a  few days, with maximum development occurring in about 1 to 2 weeks. When sunspots decay the spot shrinks in size and its magnetic field also decreases in size. This life cycle may consist of a few days for small spots to near  100  days  for  larger  groups.  The  larger  spots normally  measure  about  94,500  miles  (120,000  kin) across.  Sunspots  appear  to  have  cyclic  variations  in intensity,  varying  through  a  period  of  about  8  to  17 years. Variation in number and size occurs throughout the sunspot cycle. As a cycle commences, a few spots are    observed    at    high    latitudes    of    both    solar hemispheres, and the spots increase in size and number. They    gradually    drift    equatorward    as    the    cycle progresses,   and   the   intensity   of   the   spots   reach   a maximum in about 4 years. After this period, decay sets in and near the end of the cycle only a few spots are left in the lower latitudes (5° to 10°). Plages Plages   are   large   irregular   bright   patches   that surround sunspot groups. (See fig. 1-2). They normally appear   in   conjunction   with   solar   prominences   or filaments and may be systematically arranged in radial or  spiral  patterns.  Plages  are  features  of  the  lower chromosphere    and    often    completely    or    partially obscure an underlying sunspot. Flares Solar flares are perhaps the most spectacular of the eruptive features associated with solar activity. (See fig. 1-2). They look like flecks of light that suddenly appear near  activity  centers  and  come  on  instantaneously  as though a switch were thrown. They rise sharply to peak brightness   in   a   few   minutes,   then   decline   more gradually.  The  number  of  flares  may  increase  rapidly over  an  area  of  activity.  Small  flare-like  brightenings are always in progress during the more active phase of activity centers. In some instances flares may take the form  of  prominences,  violently  ejecting  material  into the    solar    atmosphere    and    breaking    into    smaller high-speed blobs or clots. Flare activity appears to vary widely between solar activity centers. The greatest flare productivity  seems  to  be  during  the  week  or  10  days when sunspot activity is at its maximum. Flares are classified according to size and brightness.   In   general,   the   higher   the   importance classification,   the   stronger   the   geophysical   effects. Some  phenomena  associated  with  solar  flares  have immediate   effects;   others   have   delayed   effects   (15 minutes to 72 hours after flare). Solar flare activity produces significant disruptions and   phenomena   within   Earth’s   atmosphere.   During solar flare activity, solar particle streams (solar winds) are   emitted   and   often   intercept   Earth.   These   solar particles  are  composed  of  electromagnetic  radiation, which interacts with Earth’s ionosphere. This results in several reactions such as: increased ionization (electrically charging neutral particles), photo chemical changes (absorption of radiation), atmospheric heating, electrically charged particle motions, and an influx of radiation  in  a  variety  of  wavelengths  and  frequencies which include radio and radar frequencies. Some   of   the   resulting   phenomena   include   the disruption of radio communications and radar detection.  This  is  due  to  ionization,  incoming  radio waves,  and  the  motion  of  charged  particles.  Satellite orbits  can  be  affected  by  the  atmospheric  heating  and satellite  transmissions  may  be  affected  by  all  of  the reactions previously mentioned. Geomagnetic disturbances    like    the    aurora    borealis    and    aurora Australia result primarily from the motion of electrically charged particles within the ionosphere. EARTH Of the nine planets in our solar system, Earth is the third  nearest  to  (or  from)  the  Sun.  Earth  varies  in distance  from  the  Sun  during  the  year.  The  Sun  is  94 million  miles  (150,400,000  km)  in  summer  and  91 million miles (145,600,000 km) in winter. Motions Earth  is  subject  to  four  motions  in  its  movement through space: rotation about its axis, revolution around the Sun, processional motion (a slow conical movement or   wobble)   of   the   axis,   and   the   solar   motion   (the movement  of  the  whole  solar  system  with  space).  Of the  four  motions  affecting  Earth,  only  two  are  of  any importance to meteorology. 1-5