The Sun

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In 1609, the Italian astronomer Galileo purchased in Venice an exemplar of a curious object, which was sold as a toy. It was a very primitive version of what later on would be called a telescope.

He used it to observe dark sunspots on the solar surface. These changed over time, with new ones emerging while old ones disappeared.

This was at odds with the conventional view of the heavens being perfect and unchanging.

Image: IYA2009 Secretariat.

Galileo's drawings of the sunspots (from the Istoria e Dimostrazioni, Florence 1613).

To see current sunspots imaged using modern telescopes and space probes, visit

Slide 7

Dissecting the Sun

In the 1670s the great English scientist Sir Isaac Newton turned his attentions to the Sun.

Using a prism, he separated light from the Sun into different colours, which he then recombined using a second prism.

The Sun was a complex object, but it was finally being studied in a scientific manner.

Image: Ricardo Cardoso Reis (CAUP).

A prism “splits” light.

To try Newton’s prism experiments for yourself, go to

Slide 8

The Sun and infrared radiation

In 1800, William Herschel was observing sunspots using experimental filters. He was surprised to find lots of heat produced when using a red filter.

This was present beyond the red part of the spectrum. It seemed to be coming from some kind of invisible light.

Herschel had discovered infrared radiation, and realised that the Sun was emitting a great deal of it.

Image: IYA2009 Secretariat.

Infrared radiation can be used to see people’s heat signature.

An introduction to the wider electromagnetic spectrum is here:

Herschel was a keen astronomer, and possessed his own observatory.

Slide 9

Helioseismology

Image: NOAO/AURA/NSF.

The waves of these "Sunquakes" penetrate the Sun to different depths, revealing the interior of the Sun.

For a more detailed description of Helioseismology, check the HELAS outreach webpage

Helioseismology is the study of the solar oscillations observed at the surface, to probe the structure and the dynamics of the Sun. This works in a similar way as Earth seismology with the study of earthquakes.

The technique is comparable to determining the shape of musical instruments from the sounds they make.

Image: B. Richardson (Cardiff University)

Slide 10

Source of the Sun’s power

The Sun’s energy was a puzzle that was only solved in the early 20th Century. It was proposed that temperatures in the core were so hot (about 15 million degrees) that nuclear fusion would take place.