20
Manual: Cool-Ceramic Safety Herschel Prism Mark II
Observing Techniques
It is particularly appealing to observe a complete solar cycle over its course of about
11 years. The last minimum with a virtually spotless sun was in 2019/2020, since when
the number of spots has been increasing again, probably ending at a spotless Sun
again in 2031.
Hints and tips
Especially for solar observations, seeing (air flicker/air turbulence) plays a major role
because the atmosphere heats up strongly during the day, especially in summer.
Depending on the observation site, there is a specific daily curve of seeing conditions
(good and bad). Experience shows that there are two times of day when the seeing
conditions are mostly passable; namely in the morning (before the atmosphere has
heated up) and late in the afternoon (before sunset) when the atmosphere cools down
slowly and continuously.
Furthermore, the line of sight towards the sun is important. If you look at the sun over
an evenly vegetated area (park, meadow, water surface), the seeing conditions will be
better than if you observe over "chaotically" built-up areas (houses, etc.).
As mentioned above, for regular solar observations it is important to determine the
best seeing conditons for your own observing site.
Two further points to improve the seeing conditions – and thus the image quality:
• Use the Solar Continuum Filter as described above.
• During observation breaks, the telescope should not be pointed directly at the sun,
so that the objective, the air column in the tube and also the Herschel prism can
cool down.
Visual observation
Rim darkening
Rim darkening of the sun is a constant solar
phenomenon and is immediately noticeable
when the entire disk of the sun is observed in
the telescope in an overview. Rim darkening
occurs because the sun consists of hot gas
whose temperature decreases towards the
surface. In the centre of the observed solar
disk, deeper, hotter regions can be seen,
which radiate more strongly. Towards the
edge, on the other hand, we are looking at
less hot and therefore also less bright layers. If
the sun were a solid body, no darkening of the
edges would be observed.
