The heliospheric current sheet (HCS) is the surface within the Solar System where the polarity of the Sun's magnetic field changes from north to south. This field extends throughout the Sun's equatorial plane in the heliosphere.The shape of the current sheet results from the influence of the Sun's rotating magnetic field on the plasma in the interplanetary medium (Solar Wind). A small electrical current flows within the sheet, about 10−10 A/m². The thickness of the current sheet is about 10,000 km.

The heliospheric current sheet, for the last three minima, has got down to 3°. The last reading was 8.7°. It has been declining at an average of 8.6° per annum. If it holds that rate, solar minimum will be in August 2009.

If it holds to the orange bounding line, solar minimum could be as late as April 2010.

The last reading on the classic series is 22.8° and this series got down to 10° on average in previous solar minima. At its decline rate, solar minimum will be in another 1.9 years