1.3e describe the appearance and explain the nature of sunspot
1.3h interpret data (eg a Butterfly Diagram) in order to describe the longterm latitude drift of sunspots, determine the length of the solar cycle
and predict the year of the next solar maximum
Sunspots
Sunspots are produced on the Sun’s surface over an 11 year cycle
Sunspots appear dark against the bright photosphere
because they can be regions up to 2,000 K cooler
Sunspots are caused by a very high magnetic field
(Sunspots have a magnetic field of 0.2 Tesla the Sun’s surface has a magnetic field 2,000 times smaller)
Picture credit : University of Hawaii, Institute for Astronomy, Mees Solar Observatory,
Haleakala Observatories, Maui, Hawaii
Sunspots at an active phase of the solar cycle : 29th March 2001
The image below shows a detailed view of sunspots:-
PENUMBRA
seen as a grey area when
projected
(Temperature ~ 5,600 K)
THE FILAMENTARY STRUCTURE IS
CAUSED BY THE MAGNETIC FIELD
UMBRA
seen as a dark area when
projected
(Temperature ~ 4,000 K)
Picture credit : Institute for Solar Physics of the Royal Swedish Academy of Sciences, Sweden Observations: Göran Scharmer, ISP/Image processing: Mats Löfdahl, ISP
Sunspot groups can cover billions of square kilometres
Sunspots are short lived, usually lasting a maximum of 3 weeks
Sunspots often appear in pairs (one with a North Pole, the other a South Pole)
Sunspots drift across the face of the Sun due to the rotation of the Sun as it spins on its axis
Sunspots can vary in size, but can often be x3 the Earth’s diameter
1,400,000 km
(Each small square represents 20,000 km across)
Drawing of sunspots seen on 3rd March 1995
The largest sunspot is about 35,000 km across (almost x3 diameter of the Earth)
At the beginning of the 11 year cycle, sunspots will appear at high latitudes (i.e. far
away from the equator of the Sun, up to 35˚ to 40˚ north or south). The number of
sunspots will increase in the time moving towards a solar maximum, about 4 years in
to the cycle. Eventually, after the solar maximum, the number of sunspots drops again
and they will appear at lower latitudes (gradually moving towards the equator, within
5˚ to 10˚ north or south).
As one sunspot cycle ends and a new cycle begins, there may be an overlap where
sunspots are found at the two extremes at the same time – near to and far away from
the equator. The famous Maunder butterfly diagram below shows the changes:SOLAR
MINIMUM 1996
QUIET SUN
SOLAR
MAXIMUM 2000
ACTIVE SUN
30˚N
EQUATOR
30˚S
Picture credit : NASA/MSFC
The chart below shows the sequence of rise and fall of sunspots about every 11 years.
The variation in the number of sunspots from one solar cycle to the next can be seen :-
Picture credit : NOAA/NGDC
Predicting the start of the new solar cycle is based on the regular rise and fall in the
number of sunspots in each solar cycle. The graph below shows the sunspot activity
over recent years, together with the predictions for the future:-
Picture credit : NASA/MSFC/Hathaway
The start of the new solar cycle can be spotted when new sunspots start to appear well
away from the equatorial regions. A recent discovery is that when a new cycle begins,
the polarity of the leading sunspot of the pair changes. The sunspots of the next solar
cycle were detected on 4th January 2008, as seen in the images below:-
Picture credit : SOHO (ESA & NASA)
The image on the right shows the new pair of sunspots leading with a South Pole first,
followed by a North Pole – opposite to all the sunpots of the previous solar cycle. The
new solar cycle is the 24th since records began and is expected to peak in 2012. To
begin a new cycle with similar polarity would actually occur every 22 years.