Introduction to observing and imaging Venus

My interest in Venus dates from the ’90s when I joined the Planetary Section of the UAI (Unione Astrofili Italiani) and at present I am co-ordinating the observations of this planet coming from Italian amateurs that I share with the A.L.P.O. and B.A.A. Venus sections. Although neglected if compared to Jupiter or Saturn, Venus is a fascinating subject that reveals many interesting details both to the visual observer and to the imagers, particularly in violet and UV light. Moreover it can be observed in full daylight as well as in twilight and can be followed along most of its orbit and sometimes even during the conjuctions with the Sun, provided conditions are favourable.

For more than twenty years I reported my Venus observations in the form of drawings, sketches, phase and intensity estimates. On 2015 I started to complement my visual work by imaging Venus with a 130 mm newtonian and a 210 mm Dall-Kirkham. I found the seeing here in Milan to be good enough to allow taking fine images with plenty of details. I made use of a Meade W47 and Astrodon UV Venus filter plus a IR-cut. The Meade filter is of a very good quality and allows to capture the same details of the Astrodon filter with only slightly less contrast. However it withstand better the average daytime seeing while the Astrodon, being more selective toward the UV needs both a clear sky and a very steady air. 

A further useful filter is the Baader Ca-K 395nm developed for imaging the Sun at short wavelengths. In terms of contrast and details it lies somewhere between Astrodon and Meade W47 but it seems less satisfactory.

As focal multiplier for the DK I used a UV-grade DCV lens of -50 mm f.l. purchased through Edmund Optics. Based on several comparisons I found it to be far superior to any commercial Barlow for this purpose. In fact many Chinese-made extenders, particularly of the so-called “apochromatic” type made of three to five lenses, are very poor performers in the violet and UV range. For the newtonian I adopted the somehow obsolete technique of the eyepiece projection through a 8 mm TeleVue Plossl, however I have been very satisfied of the results.

Every image is the result of the selecting and stacking with AS2! of at least 6000 to 8000 frames. Raw images have been processed with IRIS, sometimes with Registax.



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