Shadows on the Sun The story of sunspots

Shadows on the Sun The story of sunspots Dr. Lyndsay Fletcher, University of Glasgow

Image: Bill Leslie, Forres

The first recorded observation 364 BC – Chinese astronomer Gan-De records a darkening on the face of the Sunspots recorded regularly by ~ 30 BC. Observing through thin cloud or smoke? Photocredit: Michael Myers 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 and immutable 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 sunspot drawing The first known drawing of sunspots? by John of Worcester, 8 th December 1128

The Copernican Revolution 1543 - the Sun at the centre of the ‘Universe’ Sunspot observations have a bearing on the 16 th C. cosmology, demonstrating that heavenly bodies are not perfect and unchanging.

The first telescopic observations Galileo is usually credited with first turning a telescope to look at the Sun. This might not be correct! The four contenders are: Galileo Scheiner Fabricius Harriot

Galileo claimed to have been observing sunspots since the Autumn 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 mathematician Thomas Harriot…. . . on 8 th December 1610

Thomas Harriot 1560 -1621 ‘. . the greatest mathematician that Oxford has produced. ’

1613, Italy 2001, Hawai’i

The 11 -year cycle Heinrich Schwabe

1996 1992 2001 Image: NASA/ISAS/LMSAL Yohkoh

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 field White = ‘north’ Black = ‘south’

A Simple Sunspot umbra penumbra

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

1996 1992 2001 Image: NASA/ISAS/LMSAL Yohkoh

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?

More images and movies at: http: //sohowww. nascom. nasa. gov/ http: //solarb. msfc. nasa. gov/index. html http: //sdo. gsfc. nasa. gov/ http: //trace. lmsal. com/