En 1868, Lockyer et Janssen ont montré qu’il etait possible de faire un relevé journalier de la chromosphère et des protubérances au bord du Soleil en dehors des éclipses totales en utilisant un spectroscope. De 1892 á 1894, H. Deslandres, installé á l’Observatoire de Paris, montra “que la chromosphère entière est décelable dans la demi- sphère tournée vers la Terre” á l’aide d’un petit spectrohéliographe et d’un spectro-enregistreur de vitesses. Avec ces instruments de première génération il obtient des images de la chromosphère de calcium. “L’analyse spectrale et l’application du spectrohéliographe aux raies du spectre solaire ouvre un champ nouveau d’investigation extrêmement vasteȍ ècrit-il. Mai á l’aise á Paris pour développer ses recherches, il s’installe á Meudon. Lá, tout est á faire et il trouve peu de ressources. Il crée un sidérostat et un petit bâtiment pour recevoir les deux petits instruments de Paris, qu’il utilisera jusqu’en 1906. Mais en 1899 il a fait entrer á l’Observatoire de Meudon Lucien d’Azambuja, un jeune homme de 15 ans, soigneux et habile de ses mains pour l’aider dans ses installations et participer aux observations et aux recherches en cours.

We trace the history of observational solar prominence research from the early period when total solar eclipses provided the only means of observation, via the introduction of photography and spectroscopy in the 1860’s, to the present epoch when application of the Zeeman and the Hanle effects makes possible determination of the all-important magnetic fields in prominences.

Dividing prominence models into two classes, those that treat the support of the prominence against gravity and those concerned with the physical conditions in the prominence plasma itself, we describe the progress made in both classes of models since the 1950’s, when the first models were proposed. Finally, we comment on the necessity of combining aspects of the two classes of prominence models into a comprehensive picture that can account for the global nature of prominence support and stability, and where the adjacent coronal structures play an important role.

Past and recent observations of spatial and temporal variations in fine structure of solar prominences/filaments are reviewed. Magnetic fields permeate the prominence plasma and play a decisive role in shaping the fine structure and its dynamics. Consequently, the shape, orientation, and possibly the strength, of the magnetic field may be inferred from the observed sub-structures. The review discusses possible physical implications of small-scale structures in the low-β prominence plasma.

During the June 1996 campaign using the MSDP spectrograph at Pic du Midi and SUMER/CDS (JOP 12) on board SOHO, quiescent prominences were observed. We present observations and physical quantities of the June 5 prominence. Doppler shifts, temperatures and electron densities of fine structures were deduced from Hα data.

Emission-line coronal images in Fe XIV (530.3 nm) and FeX (637.5 nm) show faint enhancements at the location of quiescent prominences. Such enhancements can appear in the outer portions of a prominence, similar to the high-temperature sheath surrounding prominences as inferred from UV and EUV observations. The observational evidence supports the interpretation that this enhanced coronal emission is due to energy carried by the prominence threads and dissipated in the adjacent coronal region. Also, observed coronal loop interactions involving partial magnetic reconnection have associated Hα structures. These structures can have the appearance of an active prominence, similar to those typically observed in post flare loop systems. It appears that the association of such active prominences with the adjacent corona is fundamentally different from that of quiescent prominences. The observations indicate that these types of active prominences arise simply as a consequence of reconnection processes in the corona itself.

Since January 1996 (EIT first light) the Extreme Ultraviolet Telescope aboard SOHO has produced about 20,000 wide-field images of the corona and transition regions. Four different emission lines (He II, Fe IX/X, Fe XII, Fe XV) were selected to detail morphologies of magnetic structures in the corona. They show the different structures present in the corona with information about their topologies (Neupert et al. 1998). They provide the global temperature distribution in the quiet corona in the range 0.5 to 3 × 106 K.

The evolution of the corona during the first year of the SOHO mission revealed its nonuniform aspect and the nonregularity of the appearance of new active regions. Changes observed in active regions and coronal holes (e.g., August–September 1996) showed the complex role of magnetic fields including magnetic interactions and possible reconnections needed to explain some loop morphology evolution.

We describe the observational capabilities of the SOHO EIT and LASCO instruments for prominence research. A detailed comparison of EIT He II λ304 and BBSO Hα images of a quiescent prominence reveals differences in fine scale structure which are attributed to differences in radiation emission and transport mechanisms. Absorption features present in coronal EIT images are attributed to dense prominence features located between the source of the coronal emission and the observer. These features provide the locations of prominence material in coronal image sequences. Observations of a prominence eruption in both EIT He II and LASCO C1 Fe XIV images show the heating of chromospheric material to coronal temperatures during the prominence eruption. In the last phase of the prominence eruption, a coronal mass ejection (CME) is initiated as a dark cavity forms over the prominence material and a bright loop-like structure forms over the dark cavity.

Simultaneous XUV and microwave (μ – ѡ) observations of a solar filament, performed by several instruments onboard SOHO and by the Very Large Array (VLA), are analyzed. The filament appears as a dark structure, very similar in shape to the optical Hα filament, in all images taken in the transition region (TR) lines observed by CDS, in the Ne VIII lines observed by SUMER at λ = 770Å and 780Å and at all radio wavelengths with 1.7 cm ≤ λ ≤ 6 cm. Contrary to that, in six TR lines observed by SUMER at λ > 1300Å no trace of the filament, either in absorption or in emission, is visible. Finally, at λ = 21 cm, as well as in all images taken in coronal lines by CDS and EIT, a dark feature is present at the filament position, although with less defined contours than in the first-mentioned TR images. The constraints imposed by all these observations are discussed and interpreted.

A statistical approach is proposed for the study of the prominence fine structure. Intensity variations in several EUV lines are measured in different regions of prominences. The expected number of fine structural elements is derived.

Preliminary results of the morphology of prominence fine structure are presented. Long time series of three post–flare loops, a spray and an eruptive prominence were digitalized and analyzed. The length-to-width ratio of the blobs was determined and, in some threads, a continuous movement of separate blobs of matter was detected.

A polarization analysis of E–limb prominences on November 3, 1994 is presented. Photometry and data reduction of 24 prominence pictures based on IDL software and Stokes–vector presentation and applied to Hα emission resulted in an accuracy of 1–1.5% in determination of the polarization degree and of 1.5–2.0° in the polarization direction. Distributions of polarization degree (polarization images) for prominences and the “white light” corona are presented. A polarization degree of 2–5% for prominences and 10–25% for the nearby white light corona are found. The polarization direction is found to be tangential to the solar limb. It is noted that eclipse observations can provide a powerful method for deriving the magnetic field at high altitudes in the coronal volume.

Heinzel et al. (1995) have proposed that diffusive penetration of the incident chromospheric Hα radiation could explain the bright rims of filaments. We examine this suggestion with the help of new 2D radiative models of filaments and show that our computations do not support this explanation.

The behaviour of extended filaments in the vicinity of a new emerging magnetic flux site has been investigated during the 2N/M5.8 flare on September 1 and several flares on September 2, 1989.

Filaments are present in highly non-potential magnetic configurations. On one hand, the complexity of modeling such 3-D configurations makes a useful comparison between observations and models difficult. On the other hand such highly sheared regions are more interesting and challenging for understanding eruptive phenomena like flares and coronal mass ejections. Fortunately, the presence of cold plasma allows us to measure the magnetic field inside prominences. Together with photospheric field measurements and other morphological observations, these provide a large set of puzzling constraints for plausible models of the magnetic configurations. Models are reviewed in the framework of present observational constraints with the aim to clarify a piece of the mystery which surrounds the magnetic configuration of filaments.

It is now commonly accepted that prominence plasma is supported in magnetic dips, in particular in twisted flux tubes. But present two-dimensional models are unable to explain the observed presence and structure of prominence feet. This requires three-dimensional models. We modelled the field using linear force-free field equations. Combining a small number of harmonics, and using observational constraints, we have found the area in the parameter space where prominences are likely to be present. Then, adding 3-D harmonics, we show that feet appear periodically underneath the prominence body. For great helicity, the parameter space is mostly fulfilled by configurations which have feet alternating between both sides of the prominence axis, as observed. The lateral feet are formed by dips in the vicinity of small magnetic polarities, that are located in a low field corridor where the prominence stands. The modelled configurations show in a natural fashion many observational aspects of prominences, such as the vector magnetic field measurements in prominences and the chirality patterns.

A critical review is made of the results of magnetic field measurements in prominences obtained by the Zeeman and Hanle methods. By considering the example of three prominences, some discrepancies between the methods are shown. The authors consider that the magnetic field measurements by the Hanle method inadequately represent the actual magnetic field pattern. To overcome these discrepancies a comparative analysis of magnetic field measurements in prominences by both methods is required.

Some aspects of inverse polarity of transverse magnetic fields in filaments are presented following from their fine structure and structure of the chromosphere underneath.