Is Venus Brighter Than Normal?

It seems to be a widely held belief on GLP that Venus is noticeably brighter now than in years and decades past. In a small poll I put out there asking if Venus was brighter than normal, 113 posters voted yes, 38 no, and only 13 voted "not sure."

Human estimates of an object's magnitude are lower in accuracy than they are in precision; the human eye can fairly accurately detect changes in brightness while monitoring an object like a variable star, but observer to observer variations can be quite high. On page 4 of the book "Astronomical Photometry: Past, Present, and Future" within the article titled "Photometric Precision and Accuracy" by Christiaan Sterken, E.F. Milone, and Andrew T. Young, it states

Figure 1 of this article shows the precision of naked eye measurements to be no better than .1 magnitude, so to be generous, that is the minimum accuracy of this experiment in order to answer the question, "is Venus noticeably brighter than before?"

How can we objectively and quantitatively answer this question? With CCD photometry. In astronomy, photometry is used to measure the brightness of celestial objects on what is known as the magnitude scale. If you know the brightness of one object, the brightness of a second object can be computed with the following formula:
Magnitude (of unknown) = -2.5*log10(intensity of unknown/intensity of known) + magnitude (of known)

Just before dawn, Venus currently has about the same altitude above the horizon as the brightest star in the night sky, Sirius as seen from the T-11 telescope I used (discussed below). Because Venus is so bright (brighter than any star in the sky except for the sun), it needs a bright star to compare it to so that they can both be imaged with the same exposure setting without over-exposing either and going beyond the dynamic range of the camera, and because Sirius and Venus were both at about the same altitude over the horizon they experienced equivalent amounts of atmospheric extinction.

This morning I imaged both Venus and Sirius back to back using a Planewave 20" Corrected Dall-Kirkham Astrograph with a FLI ProLine PL11002M CCD camera using its photometric V filter, the T-11 telescope on the itelescope.net network. Here are the resulting images, loaded into the astronomy version of ImageJ for analysis (both measurements of the intensity have already been made and are visible in the measurements window):
[link to i319.photobucket.com]
[link to i319.photobucket.com]

The inner ring around each is where the program is integrating the light to calculate the intensity. The outer concentric ring is a donut-shaped area around the object of interest that the program uses to subtract out any background noise and light in the image so that only the light from the object of interest is being measured (not the skyglow around it). Venus had a measured intensity of 118458.254726 and Sirius was 10586.866282. These are arbitrary units, so we need to plug them into the above formula to calculate the magnitude of Venus. Given that Sirius has a photometric V magnitude of -1.47 ( [link to simbad.u-strasbg.fr] ), Venus had a V magnitude of about -4.09 this morning.

Now how do we know if that's normal or not? Well obviously it would defeat the point of the thread to ask NASA, so let's use something older than NASA. In 1949, Andre-Louis Danjon published a formula for calculating the variation of Venus' visual magnitude (V) based on the solar phase angle using data he had collected over the previous 10 years.
[link to i319.photobucket.com]
This formula agrees with later determinations of Venus' magnitude (Knuckles, CF., Sinton, MK., and Sinton, WM 1961, "UBV Photometry Venus," Lowell Obs. Bull., 5, 153-156) to within about .1 magnitudes, the accuracy we're aiming for. Plugging this into the general formula for predicting the magnitude of a planet seen here:
[link to i319.photobucket.com]
We find that at the time the image of Venus was taken this morning (05:38:53 UT), it should have had a visual magnitude of about -4.03, well within the accuracy expected for the Danjon formula, and far beyond the accuracy and precision attainable by naked eye visual measurements. In short, there's nothing wrong with the brightness of Venus.