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Spiral sunspot on Feb 19, 1982

Sunspot recorded on May 21, 2016

by Salvato Giampaolo

Sun prominence recorded on July 18, 2012 by Jean-Pierre Brahic.


Today observatories like Sacramento, KPNO, Pic-du-Midi, Swedich Solar Telescope (SST), Dutch Open Telescope or satellites like SOHO, SDO, TRACE or Ulysses ensures a permanent monitoring of the Sun activity in all wavelengths of the spectrum. Others, experts in radioastronomy or elementary physics monitor its radioelectrical emissions.

Neutrino Hits Simulator


Far to have the mean to use similar instruments, what can do amateurs ?

Amateurs have much to do if they want their report be recognized as something else than a pleasant curiosity.

But what happened on February 19, 1982 suggests that amateurs can still produce scientific results. That day, for the first time in the history of telescope, we observed a spiral sunspots group that nobody could explain as you can see at left.

If by a strange coincidence, the sky should have been cloudy over the majority of professional observatories (what still occurs in one or another country from time to time) then the observation of an amateur should have been greatly appreciated by the solar astronomers. This was the conclusion of Patrick Siler McIntosh (1940-2016) from Sacramento Peak, the astronomer who developed the famous sunspot classification of the same name in early '80s to complete the classical Zurich classification of Brunner.

To complete these studies, the French association Les Observateurs-Associés du Pic-du-Midi (OA) are working hand in hand with solar astronomers to ensure a continous monitoring of the sun corona using the HACO coronograph installed at Pic-du-Midi in French Pyrénées. This is a real opportunity for an amateur to pratice both his/her hobby and do a true long run scientific study of our star.

Now, if you have the opportunity to use an interferential filter of a short half-bandwidth (0.4 - 0.7Å) filter and you have time left for monitoring the Sun activity in hydrogen-alpha light, then you can contribute to some scientific tasks.

For example you can warn dedicated dispatch centers when you see large prominences or chromospheric flares in order to forecast auroral activities and future electrical perturbations on Earth.

Another task consists to survey the Sun in H-alpha light and make correlations with magnetograms to forecast disturbances in the solar magnetic field and potential Coronal Mass Ejection (CME). At last you could discover a sismic event or sungrazers comets like has done SOHO.


Sunspot cycle








Dutch Open Telescope

CV-Helios Network


The Sun Today


Refraction and dispersion

of white light

Low resolution Solar spectrum


Among the numerous applications of spectroscopy, there is the study of the sun atmosphere, and specially its chromosphere.

We can observe the sun chromosphere through a spectrohelioscope and record bright emissions lines that appear, known under the name of "flash spectrum" (spectre-éclair in french). These events occur during a total eclipse of the sun, several seconds before and after the phase of totality while the sun light evolves through the relief of the moon surface.

At that time the continuum is no more visible and professional have identified in such spectra over 3500 lines. 

In this flash spectrum specific to the chromosphere, the helium lines are very bright although this element be ionized and hard to excite (and much faint in the photosphere, the Fraunhofer spectrum). You can also record calcium and hydrogen lines as other ionized metals that do not appear in the photosphere.

Those lines are the witnesses of a deep opacity of the chromosphere while we can see without using any specific method the continuum where the chromosphere is clear.

The chromosphere being opaque to those lines, that means all details we record belong to the chromosphere. This is this peculiar property that allows manufacturers like Daystar to design high selective interferential filters so we can explore the sun atmosphere just at the chromosphere level in the most used lines of H-alpha at 6562.3 Å and Ca-K at 3834 Å.



Sacramento Peak




A sunspot in H-alpha trichromy

pictured by Carey Fuller

As explained in the Digital Darkroom pages, beside the usual sun observation in H-alpha light with an interferential filter, you can also use it to create dynamic pictures.

Shifting the filter bandwidth towards the blue and red wings of the H-alpha line you can create tricolor H-alpha  composites. Knowing a 1 Å Doppler shift in the center of the line represents a moving of 45 km/s on the sun surface, such tricolor composites will reveal dynamic activity of the chromosphere much better than a ordinary B/W picture.

Another application is to map a portion of the spectral line to a region on the solar surface (professionals use this technique on stars). The blue wing of the H-alpha line exhibits the portion of the region coming toward us. A sunspot will therefore first appear as an irregularity in the extreme blue wing of the line as it come from the sun limb. As it rotates, the event progresses to the center then to the red wing of the H-alpha line. Using sophisticated modeling techniques, we can reconstruct the surface structure from a sequence of spectral observations.

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