Download Osterbrock Sky Spectra

Astronomical nightglow (sky) spectra from the HIRES echelle spectrograph on the Keck I telescope are now available on line as ASCII files. The Keck I telescope is located on Mauna Kea, Hawaii (155 28'20" W, 19 49'34" N, 4207 m above mean sea level). The spectra cover the 400-900 nm range and are co-added from 168 roughly one-hour observations taken over the solar-minimum 1993-97 time period. The wavelength calibration is believed to be accurate to 0.0005 nm, and the resolution is about 37,000, or about 0.02 nm at 750 nm. For convenience in downloading, the spectrum is broken up into ten files covering 50-nm intervals.

This spectrum is the best available nightglow spectrum in terms of wavelength coverage, spectral resolution, and the simultaneity during each one-hour observation. The original spectra were collected on clear nights with an average elevation angle of about 60 degrees, with few measurements below 40 degrees. Comparison of these spectra with others obtained near solar max show that in the latter case there are strong additional features that appear, from ionospheric processes.

The strongest features are the usual nightglow observables - OH, Na, the 0-1 O2(b-X) band, and the red and green lines of O. Amplification reveals many weaker features, including a great number of bands in the O2 Atmospheric Band system, many OH lines not previously seen in the nightglow, and atomic lines of H, O, N, and K.

Subsequent versions of these files will include intensity calibration, after renormalization using the astronomers' spectra of standard stars. The "continuum" baseline signal comes mostly from unresolved starlight and sunlight scattered by interplanetary dust and the moon into the field of view of the telescope, but has been normalized to unity in the co-addition. There may also be an atmospheric component. The solar component can be verified by identifying the "down" peaks as Fraunhofer absorption lines. The background continuum is also demonstrated by atmospheric absorption in the Fraunhofer A-band region.

Each line of the ASCII data files has two comma-separated columns

wavelength, intensity,

with wavelengths in Angstroms. Some isolated "noise" channels (zero intensity or single point maxima or minima) have not yet been removed.

Preparation of this Web page and the Osterbrock Sky Spectrum files was supported by grant number ATM-9714636 from the National Science Foundation CEDAR program.

Download Osterbrock's "norder" Sky Spectrum

FTP transfer - may not work with some browsers
- 400-450 nm (16,881 points)
- 450-500 nm (15,101 points)
- 500-550 nm (14,222 points)
- 550-600 nm (12,488 points)
- 600-650 nm (11,383 points)
- 650-700 nm (10,651 points)
- 700-750 nm (9,929 points)
- 750-800 nm (9,293 points)
- 800-850 nm (8,696 points)
- 850-900 nm (8,219 points)
Gopher transfer - may not work with some browsers and may add "." at end
- 400-450 nm (16,881 points)
- 450-500 nm (15,101 points)
- 500-550 nm (14,222 points)
- 550-600 nm (12,488 points)
- 600-650 nm (11,383 points)
- 650-700 nm (10,651 points)
- 700-750 nm (9,929 points)
- 750-800 nm (9,293 points)
- 800-850 nm (8,696 points)
- 850-900 nm (8,219 points)
http transfer - may insert HTML commands in saved file (use copy and paste)
- 400-450 nm (16,881 points)
- 450-500 nm (15,101 points)
- 500-550 nm (14,222 points)
- 550-600 nm (12,488 points)
- 600-650 nm (11,383 points)
- 650-700 nm (10,651 points)
- 700-750 nm (9,929 points)
- 750-800 nm (9,293 points)
- 800-850 nm (8,696 points)
- 850-900 nm (8,219 points)

Related Web Pages

Send comments and suggestions to david.huestis@sri.com

URL: http://www.nvao.org/NVAO/download/Osterbrock.html