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The 15" refractor at Comanche Springs Astronomy Campus had its finder scope (a Stellarvue 80/9D achromat) equipped with a Baader Herschel Solar Wedge and a Solar Continuum Filter for today's transit of Venus. Credit: Jeff Barton from Richardson, TX, USA.{{free media}}

Lyc photon or Ly continuum photon or Lyman continuum photon are a kind of photon emitted from stars. Hydrogen is ionized by absorption of Lyc photons. Lyc photons are in the ultraviolet portion of the electromagnetic spectrum of the hydrogen atom and immediately next to the limit of the Lyman series of the spectrum with wavelengths that are shorter than 91.1267 nanometres and with energy above 13.6 eV.


The Hubble Space Telescope [Advanced Camera for Surveys] ACS image has H-alpha emission of the Red Rectangle shown in blue. Credit: ESA/Hubble and NASA.

"[T]he extended red emission (ERE) [is] observed in many dusty astronomical environments, in particular, the diffuse interstellar medium of the Galaxy. ... silicon nanoparticles provide the best match to the spectrum and the efficiency requirement of the ERE."[1]


  1. Adolf N. Witt, Karl D. Gordon and Douglas G. Furton (July 1, 1998). "Silicon Nanoparticles: Source of Extended Red Emission?". The Astrophysical Journal Letters 501 (1): L111-5. doi:10.1086/311453. http://iopscience.iop.org/1538-4357/501/1/L111. Retrieved 2013-07-30. 


A spectrum is taken of blue sky clearly showing solar Fraunhofer lines and atmospheric water absorption band. Credit: Remember the dot.

"[P]referential absorption of sunlight by ozone over long horizon paths gives the zenith sky its blueness when the sun is near the horizon".[1]

"For quenched galaxies, the Hα absorption trough is deep and can be traced through the nucleus and along the major axis. It extends to a radius at or beyond 2 Rd [where Rd is the galaxy disk scale length] in all but three cases. This makes it possible to determine a velocity width from the optical spectrum as is done for emission line flux, with appropriate corrections between stellar and gas velocities (see discussion in Paper I, also Neistein, Maoz, Rix, & Tonry, 1999). In the few cases where a velocity width can also be measured from the H I data, it is found to be in good agreement with that taken from the Hα absorption line flux."[2]


  1. Craig F. Bohren. Atmospheric Optics (PDF).
  2. Nicole P. Vogt and Martha P. Haynes, Riccardo Giovanelli, and Terry Herter (June 2004). "M/L, Hα Rotation Curves, and HI Gas Measurements for 329 Nearby Cluster and Field Spirals. III. Evolution in Fundamental Galaxy Parameters". The Astronomical Journal 127 (6): 3325-37. doi:10.1086/420703. http://iopscience.iop.org/1538-3881/127/6/3325. Retrieved 2013-12-20. 


This is Saturn imaged with the Stockholm Infrared Camera (SIRCA) in the H2O band. Credit: M. Gålfalk, G. Olofsson and H.-G. Florén, Nordic Optical Telescope.

At the right is Saturn imaged by the Stockholm Infrared Camera (SIRCA) in the H2O infrared band to show the presence of water vapor. The image is cut off near the top due to the presence of Saturn's rings.

The Sun's emission in the lowest UV bands, the UVA, UVB, and UVC bands, are of interest, as these are the UV bands commonly encountered from artificial sources on Earth. The shorter bands of UVC, as well as even more energetic radiation as produced by the Sun, generate the ozone in the ozone layer when single oxygen atoms produced by UV photolysis of dioxygen react with more dioxygen. The ozone layer is especially important in blocking UVB and part of UVC, since the shortest wavelengths of UVC (and those even shorter) are blocked by ordinary air.


This graph shows the power density spectrum of the extragalactic or cosmic gamma-ray background (CGB). Credit: pkisscs@konkoly.hu.

In the figure at right, CUVOB stands for the cosmic ultraviolet and optical background.

The diffuse extragalactic background light (EBL) is all the accumulated radiation in the Universe due to star formation processes, plus a contribution from active galactic nuclei (AGNs). This radiation covers the wavelength range between ~ 0.1-1000 microns (these are the ultraviolet, optical, and infrared regions of the electromagnetic spectrum). The EBL is part of the diffuse extragalactic background radiation (DEBRA), which by definition covers the overall electromagnetic spectrum. After the cosmic microwave background, the EBL produces the second-most energetic diffuse background, thus being essential for understanding the full energy balance of the universe.

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