The understanding of the A and K indexes will become a very important issue when one begins serious HF operation. Next time you tune into WWV or WWVH at 18 minutes past the hour, you'll know what they are talking about. Sun spots are cool points on the sun's surface. Realize that these are the maximums and minimums. The A index is the level of geomagnetic activity.
Geomagnetic activity includes anything that upsets the magnetic field that surrounds the earth.
The A index can range from 0 up to 40. A lower number indicates that the geomagnetic field is less disturbed. Quite bands, therefore, correspond to low A indexes. Quiet bands allow weaker signals to come through more clearly, as there is less noise to interfere. Another interesting phenomenon to note is that the sun rotates once every 28 days or so.