Venus Phase Naked Eye Experiment

Venus Phase Naked Eye Experiment

In the realm of naked eye astronomy it has always been considered one of the greatest challenges to view the crescent phase of Venus. It is said that those with the best vision can just barely accomplish this when Venus is at its thinnest crescent phase. At this point Venus has an angular diameter of very close to one arc minute. To have any chance of seeing the crescent phase, the observer must view during strong twilight so as to not have the tiny crescent shape be lost in the strong glare against the dark background. But do observers really see the crescent phase or is it tricks or aberrations that play with our minds and eyes?

I myself and others sometimes view Jupiter naked eye and get the sense that it appears “bigger” than the stars. Its disk is only on the order of about 35- 45 arc seconds depending on its position relative to Earth. This IS beyond any human vision and thus demonstrates that the illusion of seeing something of this nature that isn’t there can happen. So CAN people really see the crescent shape of Venus? We just had a rare chance in December as Venus was near the Earth but we will not have another chance until sometime after this year.

There is a way, however, to test our ability to resolve the phase of Venus naked eye by conducting a simple experiment. It so happens that a one-millimeter dot as seen from a distance of 11 feet 3 inches will subtend an angular diameter of exactly one arc minute. And using the laws of similar triangles a 2 millimeter dot would have to be seen at a distance of 22 feet 6 inches to be one arc minute and so on. Given this, it is possible to test our abilities to resolve Venus’ phase without optical aid. To accomplish this, simply sketch out your best thin crescent phase and make sure to make it as close to say 2 or 3 millimeters as possible. Make sure the sketch is dark and high contrast so as to give yourself the best chance possible to see tiny crescent. It is also a good idea to circle it so you know exactly where to focus your gaze.

Once you lock into seeing the tiny image from the appropriate distance and under good lighting, try to see if there is any distinguishable shape to what you’re able to see. So using a ruler, pencil, paper, and a measuring tape, it is possible to test YOUR ability to see the crescent phase of Venus.

Now for this article to have any meaning we need feedback from you. In the discussion of the article in the forums, let us know YOUR results and we can get a consensus as to whether or not it is possible to really make this amazing naked eye observation.