The observing program in which our members were involved since the first year of activity was the one in white light; it consists in the survey and data collecting of sunspot groups visible on the photosphere. This program needs the easiest equipment: any kind of telescope equipped with a proper neutral density filter for solar observations. Daily data are collected on a standard form and sent to the coordinator which would calculate and edit monthly means. Downloadble form is available in here:
In PDF format
In EXCEL 97 format
In EXCEL 4.0 format
In EXCEL 3.0 format
For further information or joining this observing program please contact the coordinator.
The observation of the Sun in the H-alpha line (at 6562.8 Angstrom) needs an extremely narrow band interference filter, usually between 6.0 and 0.3 Angstrom, that permits detailed examinations of all solar limb events such as prominences (with 1.0 bandwidth or broader) and on the disk (with the narrower filters). It is possible to observe a lot of dinamic phenomenon such as prominences, both active (ARF) or quiescent (QRF), filaments, spicules, chromospheric facules and particularly energetic events such as flares. In conjunction with most international groups, in the 2006 GsRSI intends to start a regular chromospheric observing program in order to collect data and check long period variations of the magnetic activity, likewise just done with the white light observing program. Briefly this program consists in the counting of every active or quiescent structure visible on the solar limb which could give us an evaluation of the activity index (H and Rp), as closely described in the downloadble PDF document. A further development could consist in the survey of transient events such as flares, often correlated to coronal mass ejections (CME). It is possible to join the program both with visual and digital imaging techniques.
For further information and joining the program please contact the coordinator.
Also it is possible to observe the Sun in the VLF radio band (between 10 and 30 kHz) in order to reveal SIDs (suddenly ionospheric disturbances) which are sudden improvements of the signal, according to energetic chromospheric events such as flares. Every VLF signal spreads through the ionosphere by reflection, so it is possible to show a multiple reflection ground-ionosphere-ground of the radio signal. These “rebounds” permit to overcome the Earth curvature and cover very long distances. The ionosphere is divided in a multiple layers structure; one of these is called D-layer, to a height between 50 and 80 km. In case of a chromospheric flare we record a sudden improvement of the D-layer.
To record a VLF fluctuation caused by a solar flare we need to keep watch on the Sun from dawn to dusk.
In order to understand the proceeding of the radio signal, we’re trying to briefly explain the structure of the ionosphere (clearly shown in the following picture):
As we can see various regions (layers) characterise the ionosphere. During the day the low density ionization (about 1000 electrons/cm3) of the D-layer is not strong enough to reflect radio waves so that they pass-through it and reflect on the higher layers E and F. But the presence of D-layer partially brakes down the final signal. During the night the D-layer disappear and the waves are reflected with E and F layers.
When a solar flare happens during the daytime, the D-layer is highly ionized. Now the VLF radio waves, instead of passing through, are reflected. The radio signal increases because of two reasons:
In the following it is shown a plot obtained during a quiet-Sun day:
We can notice a sudden break down of the signal around 07.00 UT because of the origin of the D-layer correlated to the sunrise that causes an attenuation of the levels. This effect is called “sunrise-effect”. We can also observe a similar phenomenon at the sunset called “sunset-effect” for the same reasons. During the daytime the curve has a so called “mule-back” profile, with its maximum reflection at the midday, when the Sun shines high in the sky.
In case of a solar flare the plot would assume the following profile:
It shows an evident “jump” of the signal that represents the flare generated from the solar surphace, happened around 09.51 UT. The flare produces a strong increase of the ionization and reflectivity of the D-layer. The plot similarly shows what obtained by the satellite GOES8-10 (see in the following). The flare shown by the arrow was classified as C9.
Because of the Earth rotation and in order to continuosly study the Sun, the professional research centers need to extend the radio monitoring web. Thanks to these observations recently rare GRBs (gamma ray bursts) were observed during nightime.
For further information or to join this program please contact the coordinator or visit the IARA_Group website where more detailed documents could be found out also with regards to the instruments.