The Sun at 19.5nm
SOHO observations of the Sun's outer atmosphere (FeXII at 19.5nm)
The level of solar activity goes through a cycle of maxima and minima with one cycle lasting roughly 11 years. In 1996 the Sun was around minimum, and in 2000 it reached maximum. In 2007 the Sun is again around minimum at the end of the cycle (no. 23).
The level of solar activity is matched by the number of sunspots on the Sun's surface. Sunspots are regions with an increased density of magnetic field lines that pass through the Sun's surface. Inside these regions, the surface is some 2000 degrees cooler than normal and therefore appears dark (in visible light), creating the distinctive appearance of sunspots.
Usually sunspots occur in pairs, with two sunspots of opposite sign as defined by the direction of the local magnetic field: N (outward magnetic field) and S (inward magnetic field). The relative position of the N (north) and S (south) sunspot is dependant on the pair's location on the Sun's surface and also changes with each solar cycle.
During cycle 23, on the Sun's northern hemisphere the orientation of all sunspot pairs is to have as leading and trailing spot the N and S spot, respectively, with respect to the Sun's rotation. On the southern hemisphere the orientation is reversed with the S spot leading and the N spot trailing.
With the next solar cycle this orientation is flipped in both hemispheres, as the Sun's global magnetic field reverses its orientation.
As a new cycle begins, the number of sunspots with the reverse orientation will increase and the ones with the orientation of the old cycle will decrease in number. In the transition period they can both occur on the Sun, as the two cycles have no sharp boundary and overlap.
SOHO constantly monitors the Sun and will continue to observe the evolution of the sunspots and the solar activity during the new solar cycle, which will culminate in the solar maximum in about 5.5 years time. Solar scientists predict that the upcoming solar maximum will be very active and could even be the most fierce in decades.
Length: 236
Rating: 4.80 (599 ratings)
Tags: SOHO Sun FeXII 19.5nm astronomy
|
Play |
