Astronomers can observe stars from the Earth or from space. On Earth, they have the major observatories like ESO (European Southern Observatory) (picture 1) at their disposal.

Every telescope is provided with high technology instruments. Thanks to these techniques, we can create ‘spectra’. The detectors mostly used, are CCD camera's CCD allowing to register at the same time images and spectra of stars or galaxies.
In space, instruments like the Hubble Space Telescope (picture 2) supply astronomers with highly detailed images. On the altitude where the Hubble is orbiting, we no longer find an atmosphere. That is why images are not disturbed and muddy, like pictures taken on Earth. Lots of other satellites are designed for specific research: Hipparcos, ISO, XMM,… Powerful computers permit to process and analyse the data delivered by the satellites.

To fulfil their studies, researchers of the observatory concerned with solar physics conduct missions in observatories dedicated to the study of the Sun (picture 3). They have specialised instruments at their disposal (e.g interferometers) to analyse the solar spectrum. These researchers also develop and use adapted instruments (e.g. glasses with a polarisator) for the study of the solar corona. Normally, this corona is only visible on Earth during a solar eclipse.

Besides that, the corona can also be observed by space telescopes completely dedicated to the study of the Sun, like SOHO (picture 4) and TRACE. Dispersion of sunlight by means of a prism or a similar dispersing instrument produces the “spectrum” of the Sun (picture 5). This spectrum is important because it provides insight into the physical conditions in the upper layers of our “daystar” (temperature, density, chemical composition…). It is measurement of lines, visible in the solar spectrum that enables the determination of the chemical composition of the Sun.

Starting from daily observations in about forty stations, an international sunspot number is calculated and distributed every month, as well as a separate index per solar hemisphere. These observations clearly show the cyclical character of the solar activity. The observatory moreover offers among other things predictions of the solar activity on a mid term range.

Researchers of the Royal Observatory of Belgium and the Belgian Institute for Space Aeronomy participate in different projects, aimed at observations, analysis, modelling and predictions of phenomena connected to the activity of the Sun, within the framework of a new discipline called Space Weather.

Researchers of the Belgian Institute for Space Aeronomy study the solar wind, which allows them to signal variations and draw conclusions about the stability of different structures present in the solar wind and the transport of energy. A good understanding of the phenomena also permits to explain what happens closer to the Earth, in the magnetosphere. This study is partly realized thanks to the scientists’ participation in different missions: space probe Ulysses (picture 6), of which the goal was to measure the characteristics of the solar wind around the Sun’s poles, the four Cluster-II satellites and the satellite SOHO.