Modification of solar lines propagating through the interplanetary medium

The optical depths of the solar H Lyman α and the He 584‐Å lines in interplanetary space are calculated. From these the solar line profiles at Saturn and Uranus are determined. It is found that the solar H Lyman α line can be diminished strongly within a spectral region of |Δλ| <0.2 Å from the line center. On the other hand, there is no significant absorption of the He 584‐Å line except in the downwind region where absorption occurs at Δλ ∼0.04 Å. The effects of solar line modification on planetary and interplanetary glow observations are discussed.