Venus (18 March 2007)

Date: 18 March 2007 U.T.
Time: 1:17 - 2:00 U.T.
Telescope: 13cm refractor
Magnification: 218x
Seeing: from Fair to Poor to Bad
NELM: bright twilight
Filters: Moon-SkyGlow, #47, #80A, #23A, #21, #58, #56, #11, #15

This observation began shortly after sunset using only the Moon-SkyGlow filter under Poor seeing conditions. The planet's gibbous phase and slightly shaded terminator were easy to discern. For the remainder of the observations the MSG filter was used in addition to the various colored filters.

At 1:25 I tried a #47 Violet filter, but found the resulting image to be too dark.

At 1:30 a #80A Blue filter was used. The seeing improved to Fair. The limb of the planet (away from the terminator) seemed to be brighter than the rest of the planet. The planet's disk and phase were fairly sharply defined. Hints of subtle shadings were suspected on the planet's disk.

At 1:37 a #23A Red filter was used. The visible details were similar to those seen with the #80A filter.

At 1:39 a #21 Orange filter was used. The planetary limb remained bright. Disk detail became less distinct.

At 1:42 a #58 Green filter was used. At this point in time the subtle, disk details became more distinct than with any of the previous filters. The subtle shadings were sketched.

At 1:46 a #56 Green filter was used. Seeing became suddenly worse, ranging from Poor to Bad.

At 1:50 a #11 Yellow-Green filter was used. Seeing remained Poor to Bad. Nevertheless, the terminator shading was suspected to be enhanced. The disk details may have also been enhanced; but the Poor to Bad seeing made it difficult to be certain.

1:53 a #15 Yellow filter was used. The seeing turned Bad.

1:55 the #58 Green filter was tried again. The seeing appeared to improve. Another sketch was made of suspected disk details. This time a small bright patch was suspected along the north-preceding limb. The other disk details were in good agreement with the earlier (1:42 U.T.) sketch.

Conclusions: The #58 Green filter seemed to bring out the most detail. It's unknown if the addition of the Moon-SkyGlow filter helped or not when used with the various color filters. The 2-inch MSG filter was screwed into the 2-inch star diagonal while the various 1.25-inch color filters were, one at a time, screwed into the eyepiece. It's unknown if any of the filters were responsible for improved or worsened apparent seeing conditions.

The so called subtle disk details may or may not have been actual albedo variations in the atmosphere of Venus. It's easy for the eye to be tricked into seeing such things. Further observations will be necessary in order to draw any meaningful conclusions.