Shadows on the SunThe story of sunspots

Dr. Lyndsay Fletcher, University of Glasgow

Image: Bill Leslie, Forres

The first recorded observation

Photocredit: Michael Myers

364 BC – Chinese astronomer Gan-De records a darkening on the face of the Sun.

Sunspots recorded regularly by ~ 30 BC.

Observing through thin cloud or smoke?

Photocredit: Ed Sanders

A Perfect Body?300-250 BC - The Aristotelian view of the Universe

The Earth is at the centre of a set of revolving spheres,each carrying a perfect andimmutable celestial body

The Sun is one such perfect body and should therefore be free of flaws

But Theophrastus (374-287 B.C.) claims to observe flaws on the Sun

The first known drawing of sunspots?by John of Worcester, 8th December 1128

The first sunspot drawing

The Copernican Revolution

1543 - the Sun at the centre of the ‘Universe’Sunspot observations have a bearing on the 16th C. cosmology,

demonstrating that heavenly bodies are not perfect and unchanging.

The first telescopic observationsGalileo is usually credited with first turning a telescope to look at the Sun. This might not be correct!

Galileo Scheiner Fabricius Harriot

The four contenders are:

Galileo claimed tohave been observingsunspots since theAutumn of 1610.

However, his first public demonstration was in 1611.

The first known record of a telescopic sunspot observation

This was drawn by the English mathematicianThomas Harriot….

..on 8th December 1610

‘..the greatest mathematician thatOxford has produced.’

Thomas Harriot

1560 -1621

1613, Italy 2001, Hawai’i

Heinrich Schwabe

The 11-year cycle

Image: NASA/ISAS/LMSAL Yohkoh

1992

1996

2001

Movie: NASA Sun-Earth Connections

Close-up of an active region (TRACE satellite)

Iron filings around a bar magnet line up according to magnetic force field.

Coronal plasma is also tied to magnetic force field

Solar magnetic fieldWhite = ‘north’ Black = ‘south’

umbra

penumbra

A Simple Sunspot

Images: Swedish Solar Telescope

Why are sunspots dark?Because they are cooler than their surroundings, and so produce less radiation:

Why are sunspots cool?

Because they are so strongly magnetised

Magnetic field ‘resists’ convection, so heat from the rest of the photosphere can’t be fed into the sunspot

Image: NASA/ISAS/LMSAL Yohkoh

1992

1996

2001

A topical question – the effect of solar activity on climate

Clear historical association of periods of low sunspot number and the Earth’s climate. Is this still important?

http://solarb.msfc.nasa.gov/index.html

http://sdo.gsfc.nasa.gov/

http://trace.lmsal.com/

http://sohowww.nascom.nasa.gov/

More images and movies at: