Schröter effect

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Schröter effect

A discrepancy between the predicted phase of Venus and the one that is actually observed. In particular, the effect relates to the fact that the calculated date of dichotomy does not coincide with the date on which Venus is seen to have a completely straight terminator. Morning dichotomy is usually earlier than predicted, evening dichotomy later. The reason for the effect is unknown; it may be due to observational error or atmospheric distortions. The effect takes its name from the German astronomer Johann Hieronymus Schröter (1748–1816), who noted it in the 1790s.

Schroter effect

[′shrōd·ər i‚fekt]
(astronomy)
The occurrence of the dichotomy of Venus earlier than theoretically predicted when it is waning, and later than theoretically predicted when waxing.
References in periodicals archive ?
During the event earlier this year, for example, I calculate that greatest separation occurred at 13h Universal Time on January 12th, whereas dichotomy occurred at 13h on January 14th--two full days later (not earlier, as the Schroter effect would predict).
Presumably, this accounts for some of the variation in the estimates of the Schroter effect. Likely more significant are seeing conditions, sky background (light vs.
Since then, every observer to make a serious study of the planet has confirmed the "Schroter effect."
(It was Moore, by the way, who coined the phrase "Schroter effect.") Back then Venus was a planet of mystery, and anything that could add to our knowledge of it was of value.
(Even yours truly, as an 11-year-old armed with a standard-issue, 60-mm refractor, made an estimate of the Schroter effect at Venus' eastern elongation in November 1965 and found that dichotomy occurred a week before the calculated time.)
The Schroter effect clearly had something to do with the Venusian atmosphere.
Although the Schroter effect was never more than a minor mystery and has now been fully explained, you can see this phenomenon firsthand in the days leading up to January's eastern elongation of Venus.
To record the Schroter effect, I tried to develop a more powerful method for measuring Venus at half phase.
The Schroter effect is directly revealed by the rightward bowing of the isophotes, indicating a concave terminator at a time when it was predicted to be convex.
While the Schroter effect is well known to Venus observers, it remains largely unexplained.