Images of the Sun in Hydrogen Alpha by Michael Caligiuri

Series: 2021

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Solar Photosphere and Chromosphere

Photosphere: The 100km thick inner layer of the solar surface where light escaping from the Sun's shell radiates. Images of the photosphere reveal features such as sun spots, spicules, filaments, ribbons, and grannules. Filaments can form as ribbons across the solar disk and rise up through the chromosphere from the photosphere. To learn more about the solar photosphere, click here.

Chromosphere: The second of three main layers of the Sun's atmosphere, roughly 2,000 kilometers deep. The chromosphere sits just above the photosphere where coronal ejections, prominences and solar flares can be observed.  Prominences are filamentary clouds and arches of hydrogen plasma suspended above the photosphere by strong variable magnetic fields.  Many prominences remain captured by the magnetic fields for days.  A coronal mass ejection (CME) is an unusually large release of plasma and magnetic fields from the chromosphere. CMEs follow solar flares and and are normally present during a prominence eruption. For more Information on the solar chromosphere, click here.


About the Images

Equipment: Images of the sun's photosphere and chromosphere were captured using a Lunt 100mm solar telescope. These scopes are equipped with a hydrogen-alpha filter passing light with a wavelength centered on 656.28 nm with a 0.7A bandwidth. The telescope is equipped with a DSII double-stack etalon module, narrowing the bandwidth from 0.7A to 0.5A increasing details of the surface (photospheric) features. Harmful emissions are further blocked by an 18mm blocking filter. A high resolution video camera is used to record dynamic changes in the layers of the sun's photosphere. The current configuration uses a Point Grey Grashopper (USB3) instrumented with a 0.83" CMOS chip. Attaching a Televue Powermate 2.5x barlow between the blocking filter and camera increases resolution even further with an effective focal length of 1785 mm.

Solar H-alpha telescopes are equipped with etalons for tuning the centroid of the narrow band of light allowed in. Tuning the etalon (e.g. by pressure tuning or tilting) compensates for the high velocities (i.e. Doppler effect) that characterize fast moving prominences and ejections. Current configuration has two etalon tuners.

Data Acquisition: Video images are acquired using frame rates ranging from 42/sec (full frame) to over 150 f/s (for selected regions of interest). Generally, I'll collect 1000 frames per file. A 42 f/s 3000 frame exposure takes 68 seconds. Typical imaging sessions involve collecting 10-15 video files from different regions of the sun over a 1 hr period of time. Conditions and even features can change noticeably over an hour or two, so multiple files are created to capture these changes. Each file is approx 6.5GB in size. Needless to say, file management and image back-up can be a challenge. Currently using FireCapture v2.4 for data acquisition.

Processing Workflow: Video files are automatically analyzed to select the sharpest subset (usually 10-15%) of frames. These frames are then registered using several alignment points and stacked to create a single 16-bit image file. Combining many single frames improves S/N.  Stacking is done using AutoStakkert 2.0. The image then undergoes sharpening and further processing such as inverting, colorizing, more sharpening, and noise reduction in Photoshop.















Collection of Solar (and lunar) Transits


Solar Imaging Telescope: Lunt LS100THa/PT DSII

Lunt 100 mm Solar Scope

1785 mm effective focal length; f/18 dedicated H-alpha telescope; 0.5A bandwidth centered on Ha at 656.28 nm wavelength;

PointGrey Grasshopper model 23S6M 2.3MP CMOS camera; 2 inch Feathertouch Focuser and 18mm blocking filter.


Solar Image Archives

2020 2019 2018 2017 2016


A few links to Solar Images from NASA and on-line Media:

Click here for the Wiki site on sunspots and the 11-year Solar Cycles

Click here for a drawing of the outer layers of the Sun (credit:

Click Here for the closest images ever taken of the Sun

Click here for a NASA image from the SDO taken on Sept. 30, 2014 in extreme UV light. The Earth is shown to scale.

Click Here for current (up to the minute) Ha images of the sun from 7 NSO solar observatories