Call for Solar Observers (Sept. 19–27)

Does your version of stargazing involve pointing your telescope at the Sun? With the right equipment, you can aid a project that aims to catch a solar flare in the act of erupting. The observing campaign is coming up soon: September 19–27, 2015.

By Dominik Gronkiewicz

UPDATE (September 16, 2015): The F-Hunters website is back up! You can visit the website to join the mailing list and find out more about the project. You can also still follow the F-CHROMA Facebook and Twitter pages to keep up with developments.

Solar flares are the strongest explosions in the solar system — even the faintest flares are thousands times stronger than a nuclear bomb. They release enormous amounts of energy stored in the Sun’s magnetic field. Yet they can hardly be seen against the backdrop of the Sun’s brilliant visible surface.

But that doesn't mean that they play no role in our lives. A flare can eject tons of plasma toward Earth, often producing Northern Lights (the beautiful part) but also potentially disrupting communications, generating electric blackouts, or causing costly satellites failures. So there’s plenty of motivation for scientists to work out the physical mechanisms behind solar flares.

F-CHROMA, short for "Flare Chromospheres: Observations, Models, and Archives," is a European project that analyzes multi-wavelength observations and compares them to physical models for a deeper understanding of how flares affect the solar atmosphere. In particular, scientists are interested in the chromosphere, a middle layer of the Sun’s atmosphere where the temperature rises from 6000K to 25,000K (10,000°F to 45,000°F). The chromosphere’s plasma radiates only at specific wavelengths, producing spectra lines such as H-alpha and Ca-K, which amateur astronomers can pick up using narrowband filters on a solar telescope. (The only time we can see the chromosphere without narrowband filters is during a total solar eclipse — then any filaments of gas can be seen as red streamers against the white corona.)

Solar Flare

The 53-cm H-alpha spectrograph in Bialkow Observatory, Poland, observed a strong, X17-class solar flare on October 2, 2003.

The chromosphere plays an important role in the complicated mechanism of solar flares: it’s the region where magnetic fields somehow dump a big part of the energy that goes into flares. By observing plasma in this layer through many instruments working in different spectral ranges, we find out the physical conditions in the solar atmosphere.

Between September 19th and 27th, astronomers will perform simultaneous observations from several ground-based solar observatories: the 1-meter Swedish Solar Telescope on the Spanish island of La Palma; Richard B. Dunn Solar Telescope at the National Solar Observatory, Sacramento Peak, New Mexico; and the hydrogen-alpha spectrographs in Bialkow, Poland, and Ondrejov, Czech Republic. Two space observatories, IRIS and SDO, will collect ultraviolet observations that are not possible from the ground due to the absorption from Earth's atmosphere.

To make these observations even more complete, F-CHROMA is inviting amateur astronomers to join the campaign and photograph the Sun with their telescopes. H-alpha, Ca-K, and white-light (neutral-density) solar filters are suitable. Amateurs can produce images using CCDs or DSLRs in Raw mode, data that will provide useful context for observations from larger telescopes. In addition to filling data gaps, this occasion presents a unique opportunity to compare amateur and professional data.

Even a 35- to 40-mm solar telescope with an H-alpha filter can capture a low-power (C-class) flare. But persistence is required for the payoff — solar flares are highly unpredictable and can require hours of observation to capture a single event. Amateurs will have to take images every few seconds so that, in the event a flare does occur, we can analyze its evolution. As the amateur arm of F-CHROMA, we call ourselves the F-Hunters, as we turn regular solar observations turn into a hunt for solar flares.

C-class solar flare

Left: A class C2.2 solar flare observed on August 22, 2014, with 40-mm H-alpha solar telescope and monochrome CCD camera (D. Gronkiewicz). Right: The corresponding ultraviolet image (30.4-nanometer ionized-helium line) taken with the Solar Dynamic Observatory (SDO / AIA).

To join our team of flare hunters, go to the F-CHROMA website and subscribe to the newsletter, which we’ll use to send out daily targets picked by our science team (usually the active region number) during the campaign. Before September 19th, when the campaign starts, we suggest participants take a look at the Observer's Guide. It contains safety information, imaging tutorials and restrictions, and important tips on observing solar flares. Observers willing to contribute to the F-CHROMA database can send their processed images (saved in lossless format) using the site’s online form.

The F-CHROMA team hopes that the F-Hunters campaign will be a first step toward future tighter collaboration between amateur astronomers and solar physicists.

Dominik Gronkiewicz is the F-Hunters campaign coordinator.