Diffuse far-ultraviolet ( FUV : 1370–1670 Å ) flux from the Taurus molecular cloud region has been observed with the SPEAR/FIMS imaging spectrograph .
An FUV continuum map of the Taurus region , similar to the visual extinction maps , shows a distinct cloud core and halo region .
The dense cloud core , where the visual extinction is A _ { v } > 1.5 , obscures the background diffuse FUV radiation , while a scattered FUV radiation is seen in and beyond the halo region where A _ { v } < 1.5 .
The total intensity of H _ { 2 } fluorescence in the cloud halo is I _ { \hbox { H$ { } _ { 2 } $ } } = 6.5 \times 10 ^ { 4 } photons cm ^ { -2 } s ^ { -1 } sr ^ { -1 } in the 1370–1670 Å wavelength band .
A synthetic model of the H _ { 2 } fluorescent emission fits the present observation best with a hydrogen density n _ { H } = 50 cm ^ { -3 } , H _ { 2 } column density N ( H _ { 2 } ) = 0.8 \times 10 ^ { 20 } cm ^ { -2 } , and an incident FUV intensity I _ { UV } = 0.2 .
H _ { 2 } fluorescence is not seen in the core presumably because the required radiation flux to induce fluorescence is unable to penetrate the core region .