Photographic observations

Dominik Gronkiewicz

Visual observations can provide nice views and lots of fun. However, photographic observations carry the most useful information for scientists nowadays.

Actually, „Solar photography” is a term that might be slightly misleading. Way more accurate is to call the F-Chroma observing action a „photographic monitoring of the Sun”. We would like to take advantage of hundreds amateur cameras looking everyday at the Sun to catch the energetic yet elusive events known as solar flares.

How does the „hunt for flares” look like? Well, technically, we ask you to set up your telescope and take a sequence of photographs of the Sun, one photo every 10 to 20 seconds. For how long? Well, as long as you're able to... As during every other hunt, you have to be patient and observe as much as possible. Some days you're going to end up with nothing, while other days you may register even a few events in the row. Click here to read more about observation cycle.

If you are interested in astrophotography, you might have noticed that most popular tutorials available on the Internet focus on obtaining beautiful, smooth images of celestial objects with lots of color and fine details. We, professional astronomers, put pressure on other aspects of processing than amateur astronomers. Scientific images look rather poor compared to many of these wonderful pictures. Their main purpose is to measure brightness, position or other feature of celestial bodies. Denoising algorithms and other digital enhancements would falsify the data and make any measurement impossible.

Regardless of you being totally new to astrophotography at all or a very advanced amateur astronomer with an impressive gallery, I would like to encourage you to read our tutorials of imaging for F-Chroma project. We describe differences between aesthetic and scientific photography in details in guidelines section.

Sun is a great object to be observed by amateurs and there are many organizations associating the visual observers that estimate Wolf number as well as other indicators of solar activity. During the last few years, decent telescopes and reliable detectors have become so cheap and common that we decided to push this organized activity one step further. Amateur hunt for solar flares, prominence eruptions and white light flares may provide priceless data for analysis of processes that occur in the chromosphere. Images may be used either for morphology analysis as well as photometry or comparison with data from professional observatories.

Already excited about catching solar explosions that could easily wash off our entire civilization?

Equipment

1. Telescope

To see the chromosphere (and be able to observe a typical solar flare), one must use a filter rejecting all the light except of very narrow spectral band emitted by chromospheric plasma, usually H-alpha line of neutral hydrogen or Ca-II K line of singly ionized calcium. So called “solar telescopes” come in various sizes and filter configurations. The resolution of even smallest models (of aperture 35mm – 40mm) is sufficient to register even low to mid-power flares.

Even the cheapest amateur equipment, despite being amateur, can provide scientific data if used mindfully. The smallest H-alpha telescopes available on the market (D=35mm) can provide valuable observations of even faint solar flares (see this low-C class flare in the picture below imaged with 40 mm H-alpha telescope). Very often, despite providing worse physical resolution, small equipment is easier to setup, maintain, less fragile to wind blows, bad atmospheric conditions and loss of collimation.

NOTE. Click HERE to read our introduction to solar filters.

Any telescope equipped with either a film or glass filter may be used for solar observations. These filters transmit a very broad part of spectrum, therefore emission of chromosphere is outshined by very luminous solar surface – photosphere. However, the strongest (at least X-class) flares can produce emission in white light, called white-light flares (or WL-flares). Such rare and short-lived (< 3 minutes) brightenings can be seen around active regions. Hunt for flares in white light may be very frustrating and fruitless for extended periods of time, but any results are of highest value.  For white-light flare hunt, I use a 10 cm achromatic refractor and a monochrome camera. 

2. Mount

Though any mount will do to perform solar observations, motorized mount that automatically tracks the Sun is an indisputable help during long observing sessions (over 2 hours). Equatorial mounts need a proper polar alignment, which may be tricky during daytime. On the other hand, azimuthal mounts cause image to be slightly rotated between frames. A well-configured mount will make your observations almost automatic.

3. Detector

Detectors in any form are suitable: a DSLR in RAW mode, a planetary camera, a deep-sky camera (if it is able to image the Sun without saturation). Digital cameras as well as deep-sky cameras usually provide 12-bit or 16-bit images, while most planetary cameras offer only 8 bits. On the other hand, by stacking a short high-cadence sequences of images taken with a planetary camera, one can boost signal dynamics as well as eliminate atmospheric seeing. Users of DSLRs should keep in mind that DSLR shutter has its limited lifetime and may stop functioning after reaching about 100000 hits (depending on camera model).

We provide tutorial for both data registration and further processing for users of DSLRs (click here) and planetary cameras (click here). A general guidelines for data processing can be found here.