BBSO is well known for its excellent observing conditions, namely, the constant excellent seeing and long periods of continuous
sunshine. Historical BBSO observations include full-disk synoptic data at BBSO (Singer-Link [SL]), Pasadena (CIT), and Israel (with about a quarter of disk field of view and covering a different time period from BBSO) stations, and high-resolution data obtained with its 10 and 26 inch telescopes. Most of the observations were carried out in the Hα wavelength, including both the line center and the red and blue wings. Video magnetograms obtained with the videomagnetograph (VMG) system using the 6103 A Ca I line with the 10 inch telescope were recorded on films from 1973 to 1994. He I D3 observations were another important and unique feature of BBSO for electron density diagnosis. The 10 and 26 inch telescopes each had three observing benches controlled by flip mirrors, and therefore, high-resolution images were normally obtained at six wavelengths. A typical setup was as follows: 10 inch: Hα blue wing, red wing, and VMG; 26 inch: Hα line center, D3, and white-light. The cadence of data ranges from about 10 s to 1 minute.

The BBSO films use Kodak products. The most recent data was recorded on 2415 Technical Pan (panchromatic), with red sensitivity for Hα observations. The telescope benches using films were 10 inch west, 10 inch east, and SL 8 inch full disk. Earlier film products were SO-115, SO-392 (extra red sensitivity). 26 inch west bench used Kodak SO-424 (ultrafine grain). The Israel films used SO-392 and SO-115. The CIT films used 2415 Technical Pan and SO-115 for earlier years of observations (Jeff Nenow, BBSO). Each film reel typically has a 9 inch diameter and contains about 15000-20000 images.

NSO/Sac Peak films mainly contain flare patrol (FLP) data covering 1963-1997. Most of the observations are full-disk Hα images in the line center and off-bands, with a nominal cadence of 1 minute. We also digitized earlier flare patrol data back to 1951. The NSO and BBSO data nicely complement each other. In addition, NSO observed solar prominences by taking over-exposed images every 3 minutes to monitor their eruptions on the limb. The NSO film data have been added to its Digital Library.

Table 1: Summary of Film Data and Current Progress (as of 2012 March)

In mid 2007, we did an initial inspection and a preliminary sorting of the BBSO films stored at Caltech. All the 35 mm BBSO films were transported to NJIT in late 2007 and then sorted out by students. NSO films were shipped to NJIT in several batches. The detailed lists of film reels are as follows:
BBSO: SL  CIT  Israel  10W  10E  26W  26E  Other
NSO: NSO1 NSO2  NSO3  NSO4  NSO5  NSO6  NSO7  NSO8

Digitizer arrived in 2009 Aug. > Larger image
Film digitization is carried out using the FilmStar 20K Pro film digitizer manufactured by Walde Inc., which has a digitization speed of about 9000 frames per hour. It converts film images to 12 bit digital data with a 2048 x 1600 pixels resolution. During the digitization process, frames of films are first detected by a line-scan camera and then imaged by a main DALSA camera. Each of the output image in RAW format has a size of 6.5 MB. Besides image array, the RAW header stores all the digitization-related information such as the exposure time and the 12-bit to 8-bit transformation table determined by the digitizer for the optimum display. Once the digitization of a film reel finishes, data are automatically transferred via a Gigabit network to our main server. When the server receives all the data, our programmed automatic IDL codes are triggered to extract information from the RAW files, convert them into compressed standard FITS files (4.5 MB each), make backup copies, and produce sample images and a 512 x 400 pixels quick-look movie containing all the frames in the reel. The final solar data product has a pixel scale of about 0.15 to 1 arcsec. The FITS header contains useful information such as the solar center and radius derived from limb fitting for full-disk images and the 12-to-8 bit conversion table as an extension.

Besides digitization, we also have devoted significant efforts to automatically decode the time stamps on films using artificial intelligence. This is a necessary step to provide an efficient archiving of the data. There are two types of time stamps, the digital clock and the analog clock. In collaboration with Yunnan Observatory and Chengdu University in China, we have achieved 95 % accuracy in handling the digital clock recognition. Decoding the analog clock (present in a small fraction of films) needs substantially more effort, and this task will be accomplished in a subsequent effort. At the current stage, the decoded time information has not been included in the name or header of the FITS product.

The digitized data from 1963 plus the recent digital data from Global Hα Network will be suitable for many different research projects. Some Important science questions to be addressed include long-term variation of the statistical properties of filaments (e.g., sigmoid and polar crown filament) carrying magnetic signature of solar cycle, statistical properties of filament eruptions, large-scale flows in the chromosphere (especially the differential rotation and meridional flow, the key players in the solar dynamo), and global activation of eruptions (such as Moreton waves and sequential chromospheric brightenings).


Image above: Some active regions during solar maximum 90.
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Image above: A glimpse of the past four solar cyles.
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Image above: A remarkable black-light flare in He I D3, in comparison with bright ribbon emissions in Hα.
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Image left: A huge Moreton wave originated from the site of an X9 flare, resulting in intriguing filament oscillations.
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More sample events can be found here.

One of the most outstanding achievements of this project is the education component. The movies of the digitized film observations have been used in the classroom teaching, for both astronomy and physics classes and in both graduate and undergraduate levels. Many students are attracted to the project and thus the solar physics. Over seven undergraduate students have joined and contributed to the project. Although digitization is part of their efforts, they have also used the film data for research. Some have obtained significant awards, such as the Goldwater scholarship, NOAA internship, and NJIT Provost Research award, as a recognition of their outstanding research. Two Ph.D. students have also used the film data in their theses. Notably, three post-docs supported by the project now become mature scientists with established reputation.