VENUS - Night Side

[videoguy]

Hi all

Some of you may find the attached image of interest being my latest attempt at imaging Venus in an unusual light. It's a stack of 500 (not sorted) images using a 1-micron filter and monochrome CCD camera. The phase (actually only 16-17% illuminated) is grossly exaggerated here due to the use of the cameras onboard frame integration function which effectively creates a longer duration exposure in order to reveal the faint thermal emissions from the planets surface radiating back through the clouds. Clearly the limb on the planets night side is visible. When I get some more time, I'll go through the sharpest frames recorded and process the final image to hopefully reveal more accurate structure to the amorphous dark patches that appear to be showing up against the thermal background radiation.

This is my 3rd run at imaging the thermal night side of Venus. It was just as fascinating tonight as it was last year although the seeing was far less forgiving compared to the morning imaging I undertook last year when ambient conditions are usually more favorable. As its illuminated side shrinks over the coming days I'll attempt to capture more of the night side hemisphere. For now though, this is all I have for show and tell.

[bird (Anthony Wesley)]

Nice image Steve.

Bird

[iceman (Mike)]

Nice one Steve, great job. I remember the article in AS&T last year when you got the night side details on Venus.

Excellent work and look forward to your coming results.

[Robert_T]

I really like this Steve as it's probing beyond nice snappies (nothing wrong with that) to see stuff few ever do. Excuse my ignorance, but what's a 1 micron filter?

Be really interested to see your re-process - reckon I can see two "patches" on the unlit side?

cheers,

[bird (Anthony Wesley)]

1 micron = 1000nm, i.e. long infrared. red light=650nm, green light=550nm, blue light=450nm.

Bird

[avandonk]

Thats very cunning Steve, to image the dark side of Venus in IR. I had a bit of a look to see what the atmospheres spectral transmission was and came up with this. I can now see why you chose one micron. Good sensitivity of detector and high transmission through the Earths atmosphere.

Bert

[h0ughy (David)]

I have learn't more in this thread in the past 5 minutes than the past 20 years. Thanks guys.

Could you do something similar afocal say with Mike's IR filter?

[videoguy]

Thanks guys.

Thanks Anthony for responding to Roberts question on filters and Bert for the cool graph.
I agree Robert, aiming for less commonly seen photo opportunities can be just as rewarding as an aesthetically pleasing one however if the clear skies hold out, I hope to obtain a good compromise between the two.

I can see those patches also and properly selecting the sharpest frames later should help emphasise them. I could in fact see them fading in and out on the monitor while capturing but they are not nearly as obvious as those I saw in July last year - see http://members.optusnet.com.au/ssmassey/venus.html

It was suggested in S&T last year that these dark patches are related to cooler topography (higher regions on the surface) but an AAO astronomer who reviewed my results felt that it was more likely (at 1-micron) to be denser regions of cloud seen in silhouetted against faint infrared thermal surface emissions.

Another good challenge for those interested is to image the crescent phase as thin as is possible. I've managed 1.25% and visually observed it at less than 1%.

It's all good fun!

[Robert_T]

Thanks Bird on the filter question. Steve, I can see from Bert's graph that atmospheric transmission is best at around these wavelengths. Do you think near infrared filters ( say ~750nm) would be useful for this or fall into one of those atmospheric opacity slots?


cheers,

[ving (David)]

that not something you see every day bird! good stuff

[videoguy]

Robert

A ~750nm filter will not see the faint thermal night side emission. When I was trying this back in May 2004, I did indeed try such a filter as an experiment but without success and the saturation of the crescent with the filter was far too intense anyhow. It requires a 1um filter and a detector with a some amount of spectral response at the 1-micron wavelength.