Summary: The visibility of Venus
Venus is the only planet or star that can be seen by the naked eye during the day. Following the
method of Westheimer (1985) for representing a point source as a single pixel on a screen with
a resolution of 120 pixels per degree, we can convert the magnitude of Venus and the sky
luminance into a luminance contrast signal with a contrast of 2.22. Detection models calibrated
to the Modelfest data predict that such a target is below threshold (Watson and Ahumada,
2005). Modifications are proposed to the models to keep Venus visible.
A Digital Venus
Following Westheimer's (1985) suggestion for representing a point source on a digital
display, we set the display resolution to 120 pixels per degree and solve for the contrast
needed to represent Venus. Using a sky luminance measurement of 4200 cd/m^2 (Minolta
CS100A) , the required single pixel contrast turns out to be 2.22.
The assuming an effective duration of 0.25 sec, the contrast energy relative to 10^-3
degree^2 seconds is 19.3 dBB.
Figure 1. The phases of Venus. At its
closest approach, Venus subtends 66
arc seconds. (credit: TBGS
Observatory, photo by Chris Proctor;