Topic 1.3- The Sun


This resource covers everything from Topic 1.3 on the GCSE 2009 astronomy specification. However, I have not covered h- interpret data (for example a Butterfly Diagram) in order to describe the long-term lattitude drift of sunspots, determine the lenght of the solar cylce and predict the next years maximum.

How can the Sun be observed safely by amateur astronomers?

The safest way and the most reccomended way for amateur astronomers to observe the Sun is to use an inderect projection method. In other words a pair of binoculars or a telescope will focus and enlarged image of the Sun onto a screen, reducing the brightness to a safe level.

What is the Sun's diameter?

1.4 million km.

What is the Sun's mean distance from the Earth?

150 million km.

What is the temperature of the Sun's photosphere?

5800 K.

What is the chromosphere?

The chromosphere (sphere of colour) is a relitavely thin part of the Sun's atmosphere (2000km). It is not usually visible as the light from the photosphere is far too dominant. However it can be obrserved as a reddish/pink ring just before totality has occured during a solar eclipse.

What is the corona?

It is a glowing region of ionised gas and has a temperature of 2million K (hot enough to emit X-rays). It can be observed during a total solar eclipse.

What are sunspots?

Sunspots are a temporary spots or patches on the photosphere, and are dark in contrast to their surroundings. They are cooler areas that correspond to strong localised magnetic fields. The magnetic fields inhibit the upward motion of convecting solar material, preventing it from reaching the top of the photosphere, resulting in lower temperatures. Sunspots usually occur in pars or groups of opposite magnetic polarity.

What do the typical structure of indivdual sunspots consist of?

  • And umbra, which is the central region that appears to be darker. It is around 2000K cooler than the photosphere.
  • A penumbra, the slightly lighter surrounding region. It is about 200K cooler than the photosphere.

What is the photosphere?

The photosphere is the part of the Sun that we see.

What is the average temperature of the photosphere?

The average temperature of the photosphere is 5800K.

What is the Sun's rotational period?

The Sun's rotational peroid varies from 25 days at the equator and 36 days at it's poles.

Why is there variation


Samantha Sonuga


Please feel free to notify me of any mistakes or anything I should add :)



hi I was wondering how you get the specification for the astronomy gcse? thank you