Wednesday, 11 January 2017

Venus in colour

I've never taken a very good look at Venus. Yes, it's the brightest "star" in the sky and perhaps also the most beautiful one. But as soon as you point a telescope at it, you'll be bitterly disappointed. The reason for that is that Venus is covered with a thick layer of clouds, making it impossible to see any detail on its surface. So the only thing you'll see is a white little disk. Well, that's not entirely true because being closer to the Sun than Earth, Venus displays phases, just like our Moon. So if Venus doesn't appear as a disk, you'll see half a disk or a crescent. 

That's what I thought until now.

But my English astronomy friend Paul proved me wrong. Paul's one of the best planetary observers I know and he granted me the privilege to publish one of his sketches here on my blog. On the sketch you see four impressions of Venus. The left one's the normal telescope view and note that these observations were all made during daylight! Paul saw some clear structures in the supposedly monotonous cloud cover, especially that dark patch on the northern hemisphere. 

Next, Paul used three different colour filters. These block all the light apart from a specific colour and sometimes they make it easier to discern specific details on planets. The first is a yellow-green filter (W11) and apparently this made the south polar cap sligthly easier to see. Of course, being the hottest planet of our solar system there's absolutely no ice on Venus, but its polar atmosphere contains swirling vortices of clouds and that's precisely what Paul noted here. The deep red filter (W25A), on the other hand, seemed to kill most of the details on the planet. Finally the blue-violet filter (W47) brought out the dark markings a bit more.

So not only does this sketch demonstrate that Venus deserves a lot more attention from us astronomers, but it also gives you a very good idea of what you can expect when using colour filters.

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